GEOLOGY AND SLOPE FAILURE IN THE MAYBESO VALLEY, . .
PRENCE 0F WALES ISLAM, ALASKA ‘

Thesis for the Degree of Ph. .D.
' MICHIGAN STATE UNIVERSITY
DOUGLAS Na, SWANSTGN

, 1957

 

   
 

  

LIBRARY

Michigan State
University

L1 {Ii iflllliliflflflfi

 

IMHLHLLL

 

 

 
    

This is to certify that the

thesis entitled 'n " A .. ,
(re?) [mi -_ we I- g 1 1r i’f‘n‘f ’Ii

51 Faetaors Af'feeefng SW
W3 on Prince of Wales Island
,Wm ofmememm-ka

presented by
Douglas Neil Swanston
has been accepted towards fulfillment

of the requirements for

Ph.D. degree in _._§e<>.12gx

WJVAMM 7,” 275/1?

/ Major professor ( fl

Date Ma 31 1967

 

0—169

 

SUPPL EMENTARY
MATERIAL

A" BAAI

INBACK ur qu
W74 w

Tweak

“@6413 g” 2‘60:

 

 

 

 

ABSTRACT

GEOLOGY AND SLOPE FAILURE IN THE MAYBESO VALLEY,
PRINCE OF WALES ISLAND, ALASKA'

by Douglas N. Swanston

Maybeso Creek valley lies on the western shore of
Twelvemile Arm, a fiord-like extension of Kassan Bay On'
the east coast of Prince of Wales Island, southeast Alaska.
It lies within the South Tongass National Forest and is
one of the first areas in southeast Alaska to be logged
on a large scale by the "clearcut" method.

Underlying bedrock is a moderate to highly deformed
and moderately metamorphosed sequence of greywackes, shales,
conglomerates, and black argillites with minor-amounts of
limestone and flows of andesite lava. Three large intru—
sions of probable Cretaceous age are exposed in the valley.
These are the Karta Valley pluton, of quartz-diorite and.
granite, a stock—like diorite body underlying Harris Peak,
and a diorite body underlying the north side of the pass
at the head of the valley. At least two periods of fault-
ing in the late Mesozoic and early Cenozoic are thought to
have occurred. The earliest tectonic disturbance is repre-
sented by two northward trending faults crosscutting the
valley, while the younger displacements parallel the valley

strike and offset the other two.

Douglas N. Swanston

The valley has been glaciated extensively with de-
posits of at least two separate glaciations of mid- to
late-Wisconsinan age represented. Evidence of a proba—
ble upper—middle Wisconsinan advance is represented on
slopes above 1,500 feet by isolated patches of a thoroughly
oxidized and leached till, as well as by a single deposit
of the same till underlying a more recent till deposit in
the valley bottom.

A late Wisconsinan advance is represented in the
valley by extensive deposits of a compacted blue-grey till
cemented with CaC03. A 0-14 date from mollusks in a
raised marine beach directly overlying the blue-grey till
indicates deposition of this till prior to 9,510 i 280
y.b-p. Four identifiable recessional moraines in the
valley bottom, each also containing blue-grey till, mark
successivezmmreatal phases of the late Wisconsinan ice,the
youngest being formed prior to the advent of the Thermal
Maximum, approximately 6,000 y.b.p.

Blue-grey till, veneering side slopes of the valley
up to an elevation of 1,500 feet, has a three-foot surface
zone of weathering. Within this zone, numerous debris
avalanches and flows have occurred. Field evidence indi: \

cates that rising pore—water pressures in the weathered 5
till, frequently in excess of l2A#/ft.3, is the most im- :
portant factor in debris avalanche development. Fre— j
quently this factor reduces shear strength of the weatheredk
till as much as 65 percent. Maximum pore—water pressure }

I

 

Douglas N. Swanston

occurs at total saturation of the soil, which in turn is
closely related to periods of extremely high rainfall.
In~Maybeso valley, a rainfall in excess of 6 inches per

day is believed enough to cause total saturation of a

3-foot soil, which is the average thickness of the weathered
till. A study of maximum precipitation and rainfall data
for Alaska suggests that rainfall of this intensity occurs
every two to three years, which provides a tentative ex-
planation of the two observed periods of maximum debris
avalanche activity, in the fall of 1958 and 1961. Although
similar debris avalanches and flows occurred prior to log—
ging, there has been a significant increase in their develop—
ment following completion of logging operations. This is
attributed largely to destruction of the anchoring in—
fluence of tree roots passing through the porous weathered
surface till and into the structurally more competent un—

weathered till at depth.

GEOLOGY AND SLOPE FAILURE IN THE MAYBESO VALLEY,

PRINCE OF WALES ISLAND, ALASKA

By

.“

3.," l I
Douglas Nf'Swanston

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

Doctor of Philosophy
Department of Geology

1967

PREFACE

Large scale commercial logging using the "clearcut"
method was begun in southeast Alaska early in the last.
decade. This method, based on sound economic and silvi-
cultural principles, requires total logging and removal
of all timber from a logging site regardless of individual
economic value. The result-is a denuded slope which, while
increasing the speed of reseeding and ultimate reforestation,
temporarily exposes these s10pes to accelerated erosion.

In 1964, as part of investigations into the.effects
of logging on slope erosion, the author was hired by the
United States Forest Service Institute of Northern Forestry
to report on the bedrock and surficial geology and related
mass wastage phenomena occurring in Maybeso Creek valley
near Hollis, Prince-of Wales Island, Alaska. Maybeso Creek
valley was one of the first areas in southeast Alaska to
be logged on a large scale by the "clearcut" method. The
significant relationship here is that there was an alarming‘
increase in mass wastage following the completion of logging.
This, of course, has prompted considerable concern for.the
long term implications of widespread logging of this kind.

The following study attempts to analyze this-problem.

The data collected, and the analyses and interpretations

ii

made, essentially concern the geology and mass wastage
effects in this prototype locale. In this program, in-
valuable.financial assistance and equipment and advice
have been provided by the Institute of Northern Forestry
and its staff, both at Hollis and in Juneau, and also by
Dr. M. M. Miller and other members of the technical staff.
of the Glaciological and Arctic Sciences Institute of
Michigan State University both at Juneau and in East
Lansing, Michigan.

Thanks go to Dr. T. M. Wu of the Civil Engineering
Department at Ohio State University, formerly of Michigan
State University, for aid and suggestions with respect to
the soil mechanics aspects of this research. Appreciation
is also extended to A. E. Helmers of the United States
Forest Service and to members of the writers thesis com-
mittee for helpful criticism and suggestions with respect
to this manuscript. These include in addition to Dr.
Miller and-Dr. Wu, also, Dr. J. E. Smith, Dr. A. T. Cross,

Mr. H. Dillon and Dr. C. E. Prouty.

iii

TABLE OF CONTENTS

PREFACE

LIST OF TABLES.

LIST OF FIGURES

LIST OF APPENDICES . . . . . . . . .

LIST OF MAPS

INTRODUCTION

GEOGRAPHICAL SETTING.

Location. . . . . . . . . . . .
Climate . . . . . . . . . . . .
Vegetation . . . . . . . . .
Drainage.

Soils.

GEOLOGICAL AND GEOMORPHOLOGICAL INVESTIGATIONS

Previous Geological Work
Geomorphology

Structural and Lithological Control of
Drainage. . .

Quantitative Watershed Analysis

Mass Wastage Phenomena .

Bedrock Geology
Faulting. .
Glacial Geology

Older Till

Younger Till

End Moraines

Effect of Moraines on the Maybeso Drainage
Elevated Marine Deposits .

iv

Page.
ii
vi

viii

xiii

xiv

I._J

OKD \O GDNIU'IU'IUT U'l

'_l

12
17

24-
A3
A5

A9
51
57
6A

70

Page

Ground Moraine . . . . . . . . . 7A
Cirque Distribution . . . . 78
Glacier Correlation and Possible Chrono—
logies. . . . . . . . . . . . 83
SOIL MASS MOVEMENT ASSOCIATED WITH RECENT LOGGING
IN MAYBESO VALLEY . . . . . . . . . . 104
Characteristics of Slide-Prone Soils. . . . 118
Piezometric Head Investigations . . . . . 123
Development of Piezometric Head . . . . 123
Pore- Pressure Measurements . . . . . . 130
Field Methods . . . . 132
Results of Piezometric Investigations . . 136
Analysis of Results . . . .~ . . . . 141
Stability Analysis of Selected Debris
Avalanches in the Maybeso Valley . . . . 151
Conclusions . . . . . . . . . 166
BIBLIOGRAPHY. . . . . . . . . . . . . 170
APPENDICES . . . . . . . . . . . . . 181

LIST OF TABLES

Table Page

I. Quantitative Watershed Measurements of
Maybeso Valley . . . . . . . . . 1A

II. Mineral Content of Selected Rock Samples
From Maybeso Valley . . . . . . . 33

III. A Typical Karta Soil Profile in the Study
Area . . . . . . . . . 55

IV. Depth, Thickness, and Description of
Varved Lacustrine Deposits from Behind
Crackerjack Moraine . . . . . . . 67

V. Orientation and Elevation Distribution of
Abandoned Cirques on Prince of Wales
Island. . . . . . . . . . . . 80

VI. Comparison of Average Floor Elevations and
Characteristic Morphology of Individual
Cirque Systems on Prince of Wales Is—
land and in the AlaskauCanada Boundary
Range . . . . . . . . . . . . 87

VII. Cross Correlation of Regional Cirque
Systems with Morphogenetic Phases of
Glaciation in the Alaska- Canada Bound-
ary Ranges {after M. M Miller, 1956
and 196A). . . . . . . . 88

VIII. Order of Sequence of Glaciations in the
Taku District and Their Probable Re—
lation to the Maybeso Valley Deposits . 92

IX. Provisional Correlation of North American
Pleistocene Chronologies with Respect
to the Sequence Described in Maybeso
Valley. . . . . . . . . . . . 103

vi

Table Page

X. Regression Equations and Related Corre—
lation Coefficients for Curves A
and B Relating Piezometric Head and
Total Rainfall . . . . . . . . . 139

XI. Maximum Values of Pore-Water Pressure and
Piezometric Rise Obtained During the
1965 Fall Rainy Season (Late September
to Mid-November) . . . 1A1

vii

LIST OF FIGURES

Figure

1. Aerial View Southeast of Maybeso Valley
Showing Extensive Clearcutting . . .

2. Map of Southeast Alaska Showing the Location
of Study Area and Other Areas Where an
Apparent Increase in Mass Wastage Has
Occurred . . . . . . . . .

3. Map of Central Prince of Wales Island Re-
lating Maybeso Valley to Principal Topo—
graphic Features. . . .

A. View of "Mile-Square" Clearcut from Bank of
Maybeso Creek. . . . . . .

5. Debris Avalanche Paths in Steep V—Channels

6. Debris Jam in Steep V— Channel in the Study
Area. . . . . .

7. Small "Slip— Outs" Occurring in Residual
Soils on the Upper Slopes of Maybeso
Valley . . . . . . .

8. Debris Lodged at Lower Edge of Avalanche
Scar. . . . . . . .

9. Boulders Imbedded in Log and Stump by Force
of Debris Avalanche. . . . . .

10. Channel Excavation by Debris Flow on Lower
Part of Slope Well Below Zone of Initial
Failure. . . . . . . . .

11. Cross Profiles of Maybeso Valley Showing

'~ U-Shaped Cross Section and Probable
Distribution of Bedrock Units and
Glacial Till . . . .

l2. Intense Folding in Black Argillite.

viii

Page

18

21

22

23

25

26

27

29
30

Figure Page

13. Brecciated Greywacke Recemented with-
CaCO3 in Outcrop Along.Fault Trace . . 32

1A. Conglomerate Facies in Greywacke Showing
Outline of Pebbles and Cobbles as They
Appear After Surface Weathering . . . 3A

15. Conformable Contact Between Greywacke and
Argillite. Argillite Above; Greywacke
Below. . . . . . . . . . . . 36

16. Two Views of Fine-Grained Leucophyre Dike
Cross-Cutting Black Argillite. . . . 37

17. Bedrock Dip Readings from Various Lo—
cations in Maybeso Creek Valley . . . A0

18. Sketch Map of the Major Structural Fea-
tures and Most Prominant Secondary
Folds as Previously Mapped in the
Craig Quadrangle (after Payne, 1955
and Condon, 1961) . . . . . . Al

19. Fault Notch Near Water Reservoir for
Hollis Camp. . . . . . . . . . A6

20. Older Till (Dark) Underlying Younger Till
(Light). The Lower Limit of Weathering
in the Younger Till is Marked by
Dotted Line. . . . . . . . 51

21. Till Fabric Analyses of Three Selected
Sites in the Older and Younger Till. . 52

22. Bar Graphs of the Weathered and Unweather-
ed Younger Till Showing Marked Similar—
ity in Mechanical Composition of all
Samples with Respect to Several of the
Main Slide Locations Shown on Map 3. . 56

23. View of Maybeso Moraine Crossing the
Mouth of the Valley . . . . . . . 59

2A. Diagram of Probable Former Ice Movement
Down Maybeso Valley into Twelve—Mile
Arm . . . . . . . . . . . 61

25. View of Crackerjack Moraine Crossing the
Middle of Maybeso Valley. View Across
Valley Toward Southeast. . . . . . 62

ix

 

Figure Page

26.--View of Haystack Butte Moraine in the Upper
Middle Part of the Maybeso Valley. View
Across Valley to Southeast . . . . . 63

27. Pro—Glacial Lake Deposit Behind Crackerjack
Moraine. Person in the Picture Has His
Right Foot at Base of the Clay Layer and.
His Hand at the Beginning of the Rhythm-
ites . . . . . . . . . . . . 66

28. Jointed Bedrock Core of Maybeso Moraine. . 71

29. Cross-Sectional Sketch of the Marine De-
posit at the Mouths of Harris River and
Indian Creek. Shell Samples for Radio-
carbon Dating Were Taken-from the Ex-
posed Silt Layer . . . . . . . . 73-

30. Sketch of Marine Deposit in Front of
Maybeso Moraine. . . . . . . . . 75

31. View Toward Northwest Showing Valley Side
and Micro—Drainage Channels in Ground
Moraine . . . . . . . . . . . 77

32. Histogram Relating Numbers of Well-Defined
Abandoned Cirques to Their Common Ele-
vations on Prince of Wales Island. . . 81

33. Projected Ice Distribution of Older Glaci-
ation (Intermediate Mountain Ice Sheet)
in Maybeso Valley Area . . . . . . 90

3A. Cook Inlet Pleistocene Chronologies in
Southern Alaska (After Karlstrom). . . 9A

35. Postulated Appearance of the Younger Glaci—
ation (Lesser Mountain Ice Sheet) in

the Maybeso Valley. . . . . . . . 95
36. C. J. Heusser's Correlations of a Hollis

Muskeg with the Muskeg on Lower Montana

Creek near Juneau, Alaska . . . . . 99

37. View of the "Mile—Square Clearcut" in
Maybeso Valley Showing Location of
Principal Debris Avalanches and Flows . 105

Figure Page

38. Longitudinal Profile of Slide 1 from Point-
of Origin to Spur Road 122 . . . . . 107

39. View of Slide 1 Showing Debris Flow at
Base of Slope . . . . . . . 108

A0. Cross Profile of Slide 1 from Zone of
Initiation to Base of Slope at Spur Road
122.. . . . . . . . . 109

A1. Sketch of Typical Till Section Near Slide
Origin. Note Principal Zone of Water
Movement Near the Contact Between
Weathered and Unweathered Till. . . . 111

A2. Cross Profile in the Zone of Initial Fail-
ure, Slide 2. . . . . . . . . . 112

A3. Longitudinal Profile of Slide 2 from Zone
of Initiation to Base of Slope at Spur
Road 122 . . . . . . . . . . 113

AA. View of Slide 2 from Valley Bottom Showing
Accumulated Debris at Base of Slide
Scar . . . . . . . . . . . . 11A

A5. Longitudinal Profile of Slide 3 from Zone
of Initiation to Base of Slope at Spur
Road 122 . . . . . . . . . . 116

A6. Cross Profiles of Slide 3 from Zone of
Initiation to Base of Slope at Spur Road
122.. . . . . . . . . . . 117

A7. Classification of the Weathered and Un-
weathered Younger Till in Maybeso Valley
According to Particle Size Distribution. 120

A8. Cumulative Curves for Weathered Till Show-
ing Particle Size Fractions in Percent
by Weight. . . . . . . . . . . 121

A9. Cumulative Curves for Unweathered Till
Showing Particle Size Fractions in

Percent by Weight . . . . . . . . 122
50. Diagram of Shear Stresses Acting on a Unit
Block of Soil . . . . . . . . . 127
xi

Figure

51. Piezometer Being Lowered Into Auger Hole
Near Slide 3

52. Volt-Ohm Milliammeter Used for Taking
Water Level Readings in Piezometers

53. Diagram of Typical Piezometer Placement
in the "Younger" Till. Note Cork-
Filled Inner Tube . . . .

5A. Graph of Rainfall vs. Piezometric Rise
During the 196A Autumn Field Season

55. Graph of Rainfall vs. Piezometric Rise
During 1965 Autumn Field Season.

56. Graph of Piezometric Rise vs. Total Rain-
fall Per Day for Two Locations Within
Pro-Existing Drainage Depressions

57. Schematic Diagram of Drainage Depressions
Showing Probable Increase in Cross—
Sectional Area (A) and a Resulting
Rise in Piezometric Surface with In—
creased Flow Volume Downslope

58. Schematic Diagram of a Slide-Prone
Slope Showing the Migration Upslope
of a Constant Gradient Piezometric
Surface With Increasing Rainfall

59. Theoretical Graph Showing Relationship
Between Rainfall, Flow Rate, and
Piezometric Head.

60. Diagram Illustrating Possible Development
of Progressive Slope Failures Upslope
Within Areas of Concentrated Sub-
surface Water Flow

61. Diagrammetic Representation of a 8011
Mass Ar alyzed by the Method of Slices
(After T. H. Wu, 1966)..

62. Diagram of Principal Forces Acting on a

Soil Particle on a Slope (After
Strahler, 1956) . .

xii

Page

131

133

135

137

138

1A0

1AA

1A5

1A6

150

155

163

 

LIST OF APPENDICES

Appendix

A. Sample Calculation of Factor of Safety

Using a Unit Block on a Plane Surface.

B. Diagrams, Data and Calculations for
Mechanical Analysis of Slide Areas
1, 2, and 3 . . . . . .
C. Development and Uses of An Isosinal

Contour Map

D. Brief Glossary of Terms Used.

xiii

 

Page

182

185

192

196

Map

 

LIST OF MAPS

Page
Geologic Map of Maybeso Creek Valley and In
Part of Harris River Valley . . . . . Pocket
Glacial Geology of Maybeso Creek Valley and In
Part of Harris River Valley . . . . . Pocket
Planimetric Map of Maybeso Creek Valley
Showing Location of Principal Slide Areas
Studied and Sample and Instrument
Locations . . . . . . . . . . . 206
Isosinal Contour Map of Maybeso Valley . . In
Pocket

xiv

_—-_—_.__

INTRODUCTION

Landslides are common throughout southeastern Alaska
where topography is oversteepened by recent valley glaci-
ation, and where high rainfall is an effective triggering
force to the process of slope failure. The potential for
developing critical and abnormal conditions.for increased
mass wastage following logging was recognized A0 years ago
by Munger (1927), and also by Taylor (1932) but the direct
relationship between slides and logging has been of limited
practical interest until the early 1960's. In 1961 interest
in the causes and effects of soil mass movements in the
Alaska Panhandle was eSpecially aroused by the marked in-
crease in slope failures in areas recently logged by clear-
cutting.

Thus, a reconnaissance study of recent sliding was
undertaken jointly by personnel from the Institute of
Northern Forestry and United States Forest Service Region
10. The purpose was mainly to outline possible causes and.
effects of such sliding and to recommend future lines of
research and study into the problem (Bishop and Stevens,
1965).

Maybeso Creek valley on Prince of Wales Island was

chosen as a starting point of this study (Figure 1). This

 

was the first and oldest clearcut area to show the marked
increase in slope failures. From Maybeso valley a recon-
naissance was extended to other clearcut areas having
accelerated mass movements. The most significant of these
other localities were in Neets Bay and Gedney Pass on Behm
Canal, north and east of Ketchikan (Figure 2).

As a result of this reconnaissance-a more detailed
study of the geologic and geomorphic relationships and the
mechanics of slope failure was begun in April 196A. Each
of the three areas included in the initial reconnaissance
were considered for this more detailed study with a final
decision to concentrate studies in the Maybeso valley.

The Maybeso valley was chosen as a prototype area for
several reasons. As mentioned previously, this was the
first and oldest clearcut area to show marked increase in
slope failure following logging. The landslides develOped
in glacial till soils which generally support the best
timber stands. Till slopes are therefore of greatest con-
cern to the land manager in Alaska in his quest to under-
stand this situation better and to prevent or control the
development of slope instability. Of additional advantage
has been the existence of partial weather records and land-
slide observations maintained in Maybeso valley over the
years 19A8-l965.

The results of the study as reported in this paper are
part of United States Forest Service Research Project 1601

concerning soil stability in coastal Alaska.

 

Figure 1.-—Aerial view southeast of Maybeso valley
showing extensive clearcutting.

 

 

 

 

 

 

bl
0/0
AnChorage <1" er
5%
‘ I
. {3:33 4" /
0 ~. /
\
\
KI
(UMCU

sun! ,
a 1
f \

9
y \ tchikan

t
. A

Q
L ‘ ID
'Otorsburg \1 .
‘%\f§1_$cal:e:

30milos
s grunge”
0. STUDY AREAS
\_\ ‘ a
\AVN
\
I
Seattle
NH ,’2
' Noon Icy E.“
5
w
s
t :3“) / ‘
t
ALAOKL --
cAIAlA

 

 

 

 

Figure 2.-—Map of southeastern Alaska showing the location of study

area and other areas where an apparent increase in mass—wastage
has occurred.

GEOGRAPHICAL SETTING

Location
Maybeso valley is on the east coast of Prince of
Wales Island at the southern end of the Alexander Archi-
pelago. The location lies about A5 miles west of
Ketchikan, Alaska, on the west shore of Twelvemile Arm,
a deep and narrow fiord extending southwest from the head

of Kasaan Bay (Figures 2 and 3).

Climate

The climate of this region is cool, moist, and tem-
perate, characterized by mild and wet winters, and cool
and wet summers. The approximate annual rainfall in Hollis
under present conditions, averages 108 inches; with a mean
annual temperature of AA0 F. The heaviest rainfall periods
are during the months of April and May and during October.
and November. The lowest precipitation takes place in July

and August.

Vegetation

 

Prior to logging the Maybeso valley was covered be—
low timberline by a dense rain forest of western hemlock

(Tsuga heterophylla (Raf.) Sarg.) and Sitka spruce (Picea

 

sitchensis (Bong.) Carr.) with scattered occurrences of

 

 

VA /

R& «v
b
3 \

\‘3/

A

  

N
KOWL

A
W
W

x
x
\ I
_\ I.
f
1,
4.x\
V”
A

  
 
 
 

.
/
wgf
W
WéT/v
\\.

f

 
  

A

 

 
 

Wales Island relating Maybeso Creek

\
W
\‘W
.\‘
\ \x

\

 

    

 

Figure 3.-—P1animetr1c map of central Prince of

 
  

salt woo-r

 

 

"'trm't'stt...

 

S. G. S. Craig

Noteworthy debris avalanches are indi—

cated by dashes, areas above timberline are shaded (based on U.

valley to principal topographic features.
Quadrangle Map).

 

 

western red cedar and Alaska yellow cedar. Much of the

understory vegetation consists of huckleberry,bunchberry,
dwarf dogwood, rushy menziesia and red-berried elder with
devil's club and skunk cabbage growing in wet areas.
Sedges and grasses are common on the forest floor but be—
come much denser in cutover areas and natural openings

where light is abundant.

Drainage

Principal drainage in the valley is by surface.flow;
however, subsurface flow in the soil mantle is also signifi-
cant, especially on the upper valley slopes.

Subsurface flow over bedrock is the principal drain-
age mechanism in areas not characterized by glacial till.
Here the soils are mostly coarse and permeable, and com-
prised of colluvium with a thin organic surface mat of
forest litter and moss.

In glacial till zones subsurface water moves princi—
pally on the interface between weathered surface material
and unweathered underlying till° This movement is con-
centrated in linear subsurface zones lying beneath shallow
surface gulleys and collecting depressions oriented up
and down slope. Surface flow generally does not occur in
these depressions except on the lower slopes where seepage
volume is large ehough to saturate completely the weathered
glacial soils. The-subsurface flow zones are probably the

result of differential weathering of incipient surface flow

channels which developed in the unweathered till following

the retreat of glacial ice.

éai—La

Five soil series are recognized in the Maybeso valley
(Stevens, 1964). Their characteristics are differentiated
primarily on geographical association and on similarities
of parent material. Of—these, the Karta soils and the
Tolstoi soils, as delineated by Stevens, cover more than
90 percent of the valley. These are.the principal soils
dealt with in the present study.

The Tolstoi soil is represented by shallow, well—
drained soils developed on steep slopes, covered by col-
luvium and underlain by fractured bedrock. These soils
cover most of the valley lepes above.l,500 feet elevation.

The Karta soil is a podzol develOped on the glacial
till which covers much of the valley below 1,500 feet. These
soils are found on both steep and shallow slopes and are

underlain by a more-or—less impermeable, unweathered till.

 

fig-

GEOLOGICAL AND GEOMORPHOLOGICAL

INVESTIGATIONS

Previous Geological Work

 

Geological investigations in the Hollis area were
reported early in this century by Brooks (1902) in a preli-
minary study of the Ketchikan mining district. C. W. and
F. E. Wright (1908) also included a brief description of
the area in their report on the Ketchikan and Wrangell min-
ing districts. Other early work concerned general obser-
vations of portions of the geology of the Alaska panhandle
by members of the United States Geological Survey in con-
nection with regional studies of southeastern Alaska
(Buddington and Chapin, 1929; Chapin, 1916, 1918, 1919;
Wright, 1909; and others).

In 1961, W. J. Conden of the United States Geological
Survey summarized the geological work in the Craig Quad-
rangle (scale, l:63,360), which includes the Maybeso valley.
This study was abetted by geological interpretations from
vertical serial photographs. This paper serves as a useful
reference concerning the main lithologies and the general
distribution of bedrock. C. L. Sainsbury (1961), also of
the United States Geological Survey, expanded this study
in part of the Craig Quadrangle NE of the Maybeso valley.

The bedrock and structural relationships described in

9

lO

Sainsbury’s paper are more detailed and have particularly
aided the writer in his interpretations of the geology of
the Maybeso valley. In 1964, Herbert and Race also pub-
lished a report on geochemical investigations in selected.
areas of southeast Alaska, including the Maybeso and Harris
River valleys.

Several unpublished file reports on the Maybeso area
are also available at the Alaska State Division of Mines
and Minerals and the United States Forest Service in Juneau

(Roem, 1938; Banta, 1937; Jones, 1962).

Geomorphology

 

Structural and Lithological
Control of Drainagg

 

Maybeso Creek flows eastward from a relatively low
ridge at the head of the valley to Twelvemile Arm, a deep
and narrow fiord extending SW from Kasaan Bay (Figure 3).
The area is typical of the glacially modified valleys
throughout southeastern Alaska. It has a broad.U—shaped.
cross-profile with steep side walls and rounded ridge
tops (Figure l).

The valley is floored with glacial till extending
on either flank to elevations.of 1,200 to 1,500 feet. Post-
glacial fluvial deposits fill the valley bottom near May-
beso Creek and form alluvial fans at the mouths of small
yet deep and narrow canyons dissecting the side slopes.

The valley floor is further broken by a sequence of

ll

moraines-and by occasional till-covered bedrock knobs or
drumlin-like features smoothed and streamlined by the
former-passage of ice (Map 2).

The orientations of the Maybeso valley and Harris
valley, to the south and west, are controlled primarily by
lithology.and faulting of the bedrock. Substantial control
is.also exerted by Jointing. Figure 3 shows a planimetric
view of the principal drainage systems which-illustrates~
this bedrock control. As a case in point, Harris River
flows south from its head water sector in the central high—
lands of the island, and then abruptly turns east to its'
outlet in Twelvemile Arm. Maybeso Creek bends in a narrow
U-shared pass through the ridge separating the upper Harris
valley from Maybeso valley, and from here it too flows in
an easterly direction. In the figure it is seen that the
tributaries of both streams intersect the main channels at
right angles, thus revealing the north-south and east—west
trends of structural weakness representing a regional joint
system.

The long axis of Maybeso valley parallels the general
strike of the bedrock through most of its length. Near the
valley head, however- strike of the bedrock is offset
abruptly and bedrock crosses the valley forming a series
of benches. This structural truncation suggests faulting
which probably prodeced the initial zone of weakness along

which Maybeso valley was formed. Similarly, the upper.

l2

portion of Harris River flows in a valley generally parallel
to the strike of the beds in that sector but the river's
rightangle bend toward the east causes it to cross this
lithologic trend (Map 1). This structural truncation by
lower Harris River valley is also indicative of faulting.
It is clear from the above relationships between
topography and structure that faulting and variations in
lithology, and to a lesser extent, jointing developed in
association with the faulting are the prime factors in the
topographic development of the Maybeso valley and the sur-
rounding area. Similiar bedrock controls on topography
have been described in other parts of the Alexander Archi-

pelago by Brew and Loney (1963) and Brew (1966).

Quantitative Watershed
Analysis

Quantitative drainage pattern measurements in the May-

 

beso valley were made following the methods suggested by
Strahler (1956), and adjusted according to available data.
Measurements were made on United States GeologiCal Survey
contour maps having a scale of 1: 31,680 and lOO—foot con-
tour intervals. The drainage network in the Maybeso drain—
age basin was traced out to the smallest tributary observa-
ble and an order was then assigned to each succeedingly
larger segment of the channel network. The lowest order
was assigned to the tertiary channels observed on the

slopes, and the highest order assigned to the principal

13

channel, in this case, Maybeso Creek. By this analysis
Maybeso channel is a fifth order stream, a value indicat-
ing a recently formed drainage basin (Table 1). The number
of streams in each order was then counted and ratios be-
tween progressively higher orders calculated. Bifurcation
ratios reveal that there are 3.9 times as many first-
order as second—order streams, A times as many second-order
streams as third, A times as many third-order streams as
fourth, and 2 times as many fourth—order streams as fifth.
This pattern generally follows the law of stream numbers
which states "the number of stream segments of successively
lower orders in a given basin tend to form a geometric
series, beginning with a single segment of the highest
order and increasing according to the bifurcation ratio"
(K. G. Smith, 1958). The ratio prevalent in the Maybeso
basin is approximately 4. All orders correspond to this
ratio except the fourth and fifth which have a ratio of
two. This low value may be due to the lack of detail on
the topographic map from which the stream orders were de—
Ifiived, but in the writer's Opinion, more likely it is the
PEBsult of the following. The fact is that this ratio lies
within bifurcation limits characteristic of natural drain-
éuges in areas of uniform climate and early stage of develop-
meth. For this reason it would appear that lithologic con—
tITDls are not reflected as much as might be expected here,

becéause of youthfulness of the tributary sections and the

 

 

1H

omhmoo mho> n osszoe

 

 

. m.flE w.>a mono % c m
m m u .HE w.sw n memoppw och mo newcoa Hmuoe n urmcoa o oceans

so.m om.m .HE\oo mmfl m.HE oom.sa .HE ms.m .fls s.m H m
w.m o.m -

sm.m om.m .flE\pm mm: m.HE omm.m .flE mo.a .flE H.m m :
m.H 0.:

sw.za om.m .flE\uo mam m.flE 02w. .HE ow. .flE N.m m m
m.H 0.:

&©.mm os.:fi .fiE\um mama m.HE 0mm. .HE em. .HE m.wa mm m
m.H s.m

ea.mm om.:m .HE\oo szzm m.HE mmo. .HE m. .HE @.mm mHH a

macaw oaoam pcoflpmpo won< oapmm spwcmq gpwcoq owpmm honasz hoopo

R owmmo>< o ommpo>< owmpo>< owmno>< Lumcoq owwpo>< Hmpoe coapmopsmflm Emoppm

 

.onHm> owonzmz who no mucoEoLSmon ponmhopmz o>fipmpflpcm3@||.H mqm<e

15

fact that much of the basin is still mantled with glacial
till.

The ratio of average lengths between the fourth—
order (principal tributaries) and fifth-order (main streams)
channels is large indicating an increase in length of the
main stream of five times the length of its largest tri-
butaries. This again is an expression of the recency of
the drainage basin, i.e., on having only a single channel
with a very limited number of tributary drainages. Further-
more it underscores the role of structural control exerted
probably by faulting and less resistant strata. This may
also explain the low bifurcation ratio mentioned earlier
between the fourth- and fifth—order streams.

The average areas and gradients of slopes are gener-
ally commensurate with the same mathematical laws governing
bifurcation and length ratios in classical fluvial circum-
stances. Such a correspondence might appear incongruous in
oversteepened glacial valleys; however, this is interpreted
as bearing out once again the recency of the present drain-
age.pattern which, in the majority of sectors, still lies
on till.

Drainage density is also low, about four channels
for every square mile of land surface. This further cor—
roborates the youthful character of the valley. By field
inspection the two most important factors in the develop-

ment of drainage density in the Maybeso valley have been

16

revealed: The first of these is resistance of the bedrock
and of overlying surface materials through which channels
are cut. Resistant and impermeable materials of course,
develop fewer channels.

The bedrock in the Maybeso valley is composed of a
variety of lithologies: greywacke, shale, conglormerates
and minor limestone and black argillite. These have all
undergone varying degrees of folding and faulting. Thus,
over short distances the bedrock may vary from soft shale
to hard slate. Maybeso Creek and its principal tributaries
were formed by differential erosion along zones of weak-
ness due to the folding, faulting and lithologic variation
noted above. Much of the bedrock, however, is overlain by
dense, indurated glacial till of late Pleistocene age.

Till is a weak material when exposed over an extended time,
however, in View of the youthfulness of these deposits and
the till hardness found, it is considered that the physical
nature of the glacial deposits has had relatively greater
effect on the total number of the tributary streams than has
the bedrock. The shallow channels and rivulets that drain
into the principal tributaries are a direct consequence of
the youthfulness and compact nature of the till and the
steepness of the slopes on which it was deposited. May-
beso Creek and its principal tributaries are subsequent
streams, the shallow channels and rivulets are consequent.

The important implication here, is that the main stream and

l7

principal tributaries are pre-Glacial in origin while the
other lesser tributaries are post—Glacial.

The second of these factors is the permeable nature
of the weathered zone in the late Pleistocene till. The
till through much of the Maybeso drainage basin is compact
and impermeable. Its upper surface is, however, weathered
to a depth of two to three feet. Permeability of this zone
is high, as illustrated by the fact that even during periods
of maximum rainfall (in excess of 6 inches per day) no
appreciable surface runoff has been observed on the till
covered slopes. Thus, through this weathered zone, there
is considerable subsurface water percolation which accounts
for much of the low drainage density revealed in the stream

analysis.

Mass Wastage Phenomena

 

Soil mass movements are of frequent occurrence on the
glacially oversteepened flanking slopes of the Maybeso drain—
age basin. The most recent sliding is clearly identified
by bare, linear strips on the side slopes where organic soil
and vegetation have been removed (Figure 4). Older slide
areas are revealed by strips of alder and low shrub repre-
senting various stages of successional growth. Evidence
of past sliding is also found in the form of buried soil
profiles and strips of even-age timber.

Soil mass movements in the Maybeso valley have de—

veloped under three sets of conditions to be discussed

18

 

Figure A.——View of "Mile Square Clearcut" from the
banks of Maybeso Creek. Note the three large
slide channels in the logged area.

19

below. These are the factors of gradient, material, and
water. The slide phenomena in each set are similar.
Bishop and Stevens (1964) have classified all of these
slides as debris avalanches and debris flows using the
systems of Sharpe (1960) and the Highway Research Board
(Eckle, 1958).

In each case the landslides begin as more or less
intact masses that suddenly break away and move outward.
These revert to debris avalanches as stresses within the
soil mass cause breakdown of soil structure. Downslope
they become debris flows because of substantial increases
in water content.

One of the combinations of gradient, material, and.
water conditions concerns debris avalanches and debris flows
on the extremely steep (45—500) slopes of deeply incised,
steep gradient stream channels. In this circumstance
avalanches start in loose unconsolidated lithosols and
weathered glacial till. They are considered as initiated
by the weight of added water in unstable soil profiles dur-
ing periods of high rainfall with the tripping mechanism
often related to stream undercutting. Many times these
slides have short runs beginning at the top of a gulley
slope and ending at the streambed (Figure 5). If enough
material is involved, upon reaching the stream it may be—
come a debris flow in consequence of the marked increase

in water. More frequently, the material is simply carried

 

20

away through increased sediment load in the stream. Rapp
(1960) and Bishop and Stevens (1964) describe a phenomenon
associated with this kind of flow resulting from debris
accumulations in the bottom of steep—sided channels. Often
forest debris forms a dam across the stream at the base of
a slide. Thus, subsequent material added by avalanching
accumulates behind this barricade (Figure 6). When the dam
gives way a large-volume debris flow takes place. Logging
aggravates slides of this type because of the excessive
accumulation of slash.

A second set of conditions develops in residual soils
on steep, open slopes where incipient debris avalanches or
smaller "slip-outs" occur. These lesser slides develop in
an active creep zone above the limit of glacial till. Bed-
rock generally serves as the sliding surface (Figure 7).
These small slides often develop at the heads of consequent
tributaries and are common high on slopes. The mechanics in
this case are similar to those involved in the steep-sided
gulleys previously described.

A third set of conditions is associated with mass move-
ments particularly damaging to forest soils, and hence of
prime concern in forest management. These mass movements
are also debris avalanches which revert to debris flows,
but they occur on valley slopes of lesser gradient, i.e.,
35 to 400, and within shallow drainage depressions (Figure

A). They develop over broad areas in weathered blue-grey

 

 

 

 

wall channels.

22

 

Figure 6.-—Debris dam in steep V—channel in study
area.

 

 

Figure Z.——Small "slip—outs” occurring in residual
soils on the upper slopes of Maybeso Creek
valley.

2A

glacial till covering much of Maybeso valley below the
1,500-foot elevation. In this case the sliding material
is essentially the Karta soil.

These slides, as in the first condition, frequently
begin as relatively short debris avalanches, transforming
to debris flows when over abundant water is present. When
they revert to debris flows, remnants of the debris
avalanche deposits are often found intact at the transition
point (Figure 8). These debris flows, comprised as they
are of heterogeneous material with a high water content
often completely fill their gulley paths and even spread
out and overwhelm low vegetation and rock protuberances
outside the gulleys. The deposits at the base of such
slopes frequently have a lobed pattern characteristic of
bisco-plastic flow. The movements are massive, rapid, and
exert much power. Pebbles and boulders are often found.
deeply inbedded in stumps (Figure 9), and the flows even

erode the hard, blue till right down to bedrock (Figure 10)°

Bedrock Geology

 

The main bedrock types in the Maybeso valley are meta-
sediments, altered locally to varying degrees by regional
folding and subsequent intrusions.

Four distinct beds of black argillite, separated by
thick sequences of grey-green greywacke, slate and conglo-
merate are exposed in Maybeso valley (Map 1). Three

cross-profiles showing lithologic structure of the valley

25

 

Figure 8.--Debris lodged at lower edge of avalanche
scar. Detail shown within rectangle.

 

r .V
5”.” 'mV‘I'VVL‘

 

0
Figure 9.—-Bou1ders‘imbedded in log and stump by
force of debris avalanche.

 

 

Figure lO.-—Channel excavation by debris flow on
lower part of slope well below zone of initial
failure.

 

 

 

28

are given in Figure 11. Locations of each profile are

also shown in Map 1. Thin, discontinuous limestone units
occur at scattered locations and are associated with the
argillite and greywacke. Also, isolated units of locally
thick andesite are found interbedded with the greywackes
and slates. The argillites vary from slightly metamor-
phosed shaley members to highly-metamorphosed slates.

Where strongly folded they are in many places intruded by
quartz stringers running both parallel to and cross—cutting
bedding planes (Figure 12). The lightly metamorphosed mem-
bers are more or less evenly bedded with little folding in
evidence, but are well silicified locally. Near the upper
and lower argillite—greywacke contacts, interbedding of
these two units is common.

Petrographic analysis of selected bedrock samples re-
veals that graphite is a predominant constituent of the
black argillite with lesser amounts of cryptocrystalline
quartz and unidentified clay minerals (Table II). Budding-
ton and Chapin (1929, p. 77) describe graptolites collected
from sililar argillites on the west side of Thorne Bay
(Figure 2) as Ordovican. Sainsbury (1961, p. 310) places
the age of rocks on the south side of Kasaan Bay from
Kasaan Island to Twelve-Mile Arm as early Silurian, the
evidence being fossils collected from back argillites in
Tolstoi and Thorne Bays (Figure 3). No fossils have been

found in Maybeso valley but the proximity of the Maybeso

b-

2°00

,

l [125 A
7/ ’ /J
/I jig/1J1?)
3 2%”
I

     
  

 

XI

    

 

I!

Horizonvcl Scalti

n/amso g'cywutlt. nholo and
conglomnula

Von-cal Sun. I/npoo
block any”...

anlvcolExaglvullon 2.64
duo'i'0.quurll
0 l 2 dioll'.
mm.

glacial IIII

loulv lvoco

Figure ll .--Cross profiles of Maybeso Creek valley showing the U—shaped cross profile and
probable distribution of bedrock units and glacial till.
map 1.

 

Position of each profile is shown on

 

 

 

 

30

 

Figure l2.--Intense folding in black argillite
showing intruded quartz stringers.

31

valley deposits to Sainsburyls.Silurian units and their
apparent structural continuity indicate a similar age for
the Maybeso deposits.

The second principal bedrock type in the valley is
a green-grey fine-to-coarse—grained rock (Sainsbury, 1961;
Condon, 1961), which varies from shale to volcanic grey—
wacke to a greywacke conglomerate. Shale or slate is also
commonly found near the top of the sequence, underlying
the black argillite. These units increase in coarseness
downward. Near the argillite contact, the shale or slate
is commonly altered to chlorite schist. In several places
in the vicinity of fault or shear zones the greenegrey units
have been brecciated and recemented with CaCO3 (Figure 13).
Isolated units of argillite are frequently found in many
places interbedded in the shale and slates.

The predominant constituents of the greywacke and
associated rock types are acid plagioclases and pyroxene
mixed with chlorite (Table II). Mineral clasts of a vol-
canic nature are sometimes present. Occasionally, fragments
of dark volcanic rock also can be observed. The conglomer-
ates present in the bedded sequences are made up of pebbles
of petrographically similar material which frequently cannot
be distinguished until surface weathering brings out the
pebble outlines (Figure 1A).

The argillite and greywackes, and the slates and
shales, weather rapidly and appear white on exposed sur-

faces. The tendency of both of these rock types to produce

32

 

Figure l3.-—Brecciated greywacke recemented with
CaCO3, in outcrop along probable fault trace
on north side of valley.

33

TABLE II.——Mineral content of selected rock samples from
Maybeso valley (reported by W. L. Gnagy, U. S. Bureau of
Mines).

 

Sample
number

Spectroscopic

Minerals

Rock type

 

no report

albite oligioclase
>lO<SOZ

chlorite >lO<SOZ
epidote >10<SOZ

altered andesite or
greywacke

 

Al, Fe, K, Na
detected

hydromuscovite--
serecite >502
goethite >0.5<2.0Z
chlorite >lO<SOZ

greywacke

 

10

Al, Fe, Mg detected
Cu, Ti, V, Zn <0.lZ

cryptocrystalline
quartz and clay )50Z

carbonaceous material=

probably graphite
>10<SOZ
pyrite *0.1<0.5%

carbonaceous
slate

 

lOa

no report

albite—oligioclase
>50Z

chlorite >10<50%
epidote >O.5<2.0Z
goethite >0.l<0.5%

altered
andesite

 

65

no report

albite-oligioclase
>502

augite >lO<SOZ
chlorite >10<SOZ
calcite >O.5<2.0%

altered
andesite

 

67

no report

 

chlorite >50Z

albite-oligioclase
>10<SOZ

greywacke

 

 

 

 

 

(a) Radioactivity and fluorescence not detected.

(b) Samples 10a and 65 were taken from dikes cross—cutting the country
rock and are considered leuc ophyres by the writer. Samples 6, 9,
and 67 were taken in country rock at the mouth and near the head of
the valley. Sample 10 is from an outcrop of black argillite.

Remarks:

3U

 

Figure lA.——Conglomeratic facies in greywacke show—
ing outline of pebbles and cobbles as they
appear after surface weathering.

35

similar appearing weathered surfaces has caused some con-
fusion and some error in interpretation during earlier
reconnaissance surveys in the valley. Of the two,
argillite is the more resistant to weathering.

As a rule, black argillites underlie the major breaks
and irregularities in the upper slopes, while the greywacke
and related rocks underlie the low areas and eroded sections
of the valley flanks. The drumlinoid features of the lower
valley mentioned earlier (page 11), however, were formed on
bedrock knobs of greywacke. These knobs, where exposed at
the surface, exhibit the same degree of weathering as
similar bedrock on the higher flanks of the valley.

As mentioned earlier, a predominant joint pattern is
also shown in the valley area. The main strike directions
measured are at N6°E and N78°W. Dips are respectively,
52°NW and 89°NE. Ice plucking at these joints followed by
scouring and streamlining by the over-riding glacier pro-
duced the till-covered drumlinoid forms found in the valley.

The two principal bedrock units are conformablylinter-
bedded (Figure 15) and appear to be closely related in age.
Intense folding appears to be limited to the black slate.

Numerous leucophyre dikes of fine-grained grey-green
igneous rock closely approaching diorite in composition
(Table 11) cut across the meta—sedimentary beds. These
intrusions strike in a NNW direction and dip at steep

angles to the SW (Figure 16). Their fine texture and, in

 

36

 

Figure 15.——Conformable contact between greywacke
and argillite. Argillite above—-greywacke
below.

 

 

‘2 7%.

Figure 16.-—Two Views of fine—grained leucophyre
dikes crosscutting black argillite.

38

some cases, development of amygdaloids indicates a near-
surface intrusion where rapid cooling and release of
volatiles took place.

A granodriorite pluton, probably associated with the
Coast Range Batholith of Cretaceous Age, intruded into the
area north of Maybeso valley (Sainsbury, 1961, p. 337).
This intrusion may have preceded the leucophyric dikes that
cut the Maybeso valley sediments as has been found else-
where in southeast Alaska (Map 1) (Smith, 1939) although
direct evidence of this was not found in Maybeso valley.
The contact of the pluton is near the ridge crest separat—
ing the Maybeso from the Karta valley to the north (Map l).
Faulting related to the force of intrusion of this pluton
has been reported in the greywacke-argillite beds in the
upper part of Half-Mile Creek (Sainsbury, 1961). Another
pluton of quartz diorite composition, thought to be of the
same age, underlies the Harris Peaks. A third pluton of
similar composition to the other two underlies the ridge be-
tween Maybeso and Karta valleys on the north side of the
pass between the Maybeso and Harris River valleys (Map 1).
This pluton is separated from the Karta valley pluton by
a thick sequence of meta-sediments.

The Maybeso valley and vicinity has undergone moderate
to intense regional metamorphism. The area shows intense
folding in some places while in others evidence of much

deformation is scarcely discernable. In areas of intense

39

folding, strikes and dips are extremely variable in short
distances but the overall regional strike direction is
northwest with a dominant dip to the southwest (Figure 17
and Figure 11). These beds are in the NE limb of the
Prince of Wales geanticline (Payne, 1955) as noted in
Figure 18 and which has a NW axial trend across Prince of
Wales Island. This geanticline is part of the NE limb of
the central province of the southern synclinorium accord-
ing to Payne and has recently been identified as the
"Prince of Wales high" by Brew, Loney and Muffler (1966).

The positioning of the Maybeso valley in terms of
regional structure plus the thick sequences of greywacke,
black argillite, and layered andesites corroborates a
eugeosynclinal origin (Kay, 1942; Krumbein and Sloss, 1956).
These greywackes are commonly greenish-grey due largely to
abundant minerals of metamorphic rocks, including slate,
schist, and quartzite. Unweathered ferromagnesium minerals
are common, with graded bedding a typical structure. Grey-
wacke conglomerates are frequently found interbedded with
shales, which are usually the fine-grained equivalent of
the greywackes. There is little limestone present but
other lithologies occur such as black argillite.

The black color in these argillites is probably due
to organic material accumulated under reducing conditions.-
Again, such conditions are indicative of rapid burial

during eugeosynclinal sedimentation. The beds are

40

 

 

 

Figure l7.--Bedrock strike and dip readings from
various locations in Maybeso valley. Note
variable dip, with predominant strike to the
N. W.

 

Al

 

so Wfl:" \ ‘ b
27 Q‘ 2\§\- "1“ {bi/J A

3‘\ :‘\/;éi;s ' \\\

 

Q
. /\X )5
\fi \ \\
/ ISLAND 4.
\ Hollis
\ ‘~
’
\ A I v ,
0 ’ ‘:‘\:s <
\‘ \‘\
l “\ \
55 .“ L. .

 

 

 

 

Figure 18.--Sketch map of major structural features
and most prominent secondary folds as previously
mapped in the Craig Quadrangle (after Condon,
1961).

A. Prince of Wales geanticline (Payne, 1955).
Prince of Wales—Kuiu anticlinorium of
Buddington and Chapin (1929); includes
Kashevarof anticlinorium:

Kuiu anticlinorium
Kosciusko-Tuxekan-Heceta synclines.
Central anticlinorial province (in-
cludes San Fernando anticlinorium).
Southern synclinorium: a. central
synclinorial province; b. Dolomi-
Sulzer anticlinorium; c. southern
synclinorial province.

5. Southern anticlinorium (northern part
only)

.1: WNH

B. Seymour geosyncline (Payne, 1955). Keku—
Gravina synclinorium of Buddington and
Chapin (1929).

.. l . {dim . .
.-,.........“Muddi

 

 

 

42

commonly without fossils but sometimes show planktonic
organisms such as graptolites irregularly distributed
through the beds (Sainsbury, 1961).
While the folding of some of the individual beds is
intense, the major units are parallel in strike and dip.
It is reiterated that the strike is to the northwest but
at a slight angle to the valley bottom, and the dip is
steeply to the southwest. As a result, much of the lower
valley lies in the less resistant greywacke which has lent
itself to fluvial erosion and modification by ice.
l Also in consequence of the regional structural trend,
l the south-facing slope of the Maybeso valley is relatively
smooth and lacks angular breaks in slope. In contrast
structural terraces, strongly characterize the north-facing
slope. This is well shown in the cross sections in Figure
11. Because of such distinct structural benches resulting
from differential erosion on lithologies of differing re-
sistance, few landslides have developed on the north-facing
valley flank.

Because bedrock dips on the south—facing valley flank
average 45° to the southwest, fairly smooth and unbroken
slopes occur there, offering few obstructions or natural
supports for the soil cover and natural vegetation. Also
as a result there is less resistance here to down—slope
soil movement and hence, most of the well—developed slides

in the valley are found on these south-facing slopes.

113

At least two separate periods of faulting are sug—
gested. The earliest was probably late Cretaceous or early
Tertiary, post—dating the intrusion of the Karta valley
pluton, as will be shown. This faulting is represented by
two north—trending fault zones found crossing the middle
and the mouth of Maybeso valley. The first passes up
Half—Mile Creek and across the Karta valley ridge, appar—
ently cross-cutting the Karta valley pluton. It is con—
spicuous on the topographic maps and aerial photos (Pill—
more, 1956; Pillmore and McQueen, 1956). Movement along
this fault is not clearly apparent but there is indication
of dip—slip displacement with the east wall up and a dip
to the west. Principal evidence is that the southwest-
dipping black argillite beds found along this fault zone
are offset to the southwest along the east side of the
fault.

The second fault crosses the valley in a north-south
direction three miles from tidewater. This fault has a
narrow zone of shearing and mineralization along which
most of the producing mines were located during early
mining activities. This fault zone passes over the ridge
between Harris and Maybeso valleys and is in the black
argillite where it is marked by a shear zone mineralized
by veins of gold—quartz. Across the Maybeso valley it

creates an apparent offset in black slate as it passes

mu

up the ridge between Maybeso and Karta valleys. The trace
of this fault to the north is marked by a zone of concen-
trated sulfide mineralization. Where the fault corsses
the Karta valley pluton, a possibly related re-entrant
occurs (Map l). The apparent movement of this fault is
dip-slip with the east wall up.

A subsequent fault is indicated with a northwest trend
cross-cutting the other two. This is suggested by geo—
morphological evidence near the head of the valley, in-
cluding the presence of a narrow, U-shaped pass penetrat-
ing the ridge between Harris and Maybeso valleys. This
pass is considerably higher than the valleys on either side,
and without evidence of extensive fluvial erosion. It is
probable that this pass represents the locus of a rather
large fault crossing the ridge and paralleling the strike
of the valley. Additional evidence suggesting the existence
of such a fault is furnished by the apparent offset to the
east of the black argillite zone which crosses the valley
(Map l), as previously described. Movement appears to
have been predominantly a dip-slip with the south side dis-
placed upward.

There is also evidence of possibly related faulting
even farther east, particularly on the north side of the
valley near its mouth. Here the previously cited breccias

of greywacke occur, cemented by CaCO These braccias

3.
drop out along the main road west of Half-Mile Creek

 

45

(Map 1), (Figure 13). They are interpreted as fault
breccias, with counterparts found on the valley walls

east of Half—Mile Creek near the water reservoir for Hollis
Camp. In this sector too, a narrow defile occurs high on
the side slope, which, in the writer's opinion, is fault
related (Figure 19). Associated with these breccias is
another offset of the black argillite to the east (Map 1).
This too suggests a continuation of the fault zone along

the north side of the valley near its mouth.

Glacial Geology
Two distinct and clearly differentiated glacial tills

occur in the Maybeso valley. The most recent till is a
bluish-grey, compact and relatively unweathered material
extending, as has been previously noted, to a maximum ele-
vation of about 1,561 feet above sea level. The actual
upper limit varies considerably depending upon slope
gradient, surface erosion, and weathering (Map 2). This
till is considered a correlate of the younger till described
by Sainsbury (1961) from north and east of Maybeso valley
and was deposited by the last major ice advance on Prince
of Wales Island. The older till, deposited by an earlier
ice advance, is light brown in color, and a much more
thoroughly weathered material. It has been found beneath
the younger till only in one locality near the bottom of

the valley, but is well represented by erratics and patches

   

 

146

 

 

Figure l9.-—Fault notch near Hollis Camp reservoir.

d7

of what are believed to be older till on the ridges border—
ing the valley.

The ridge tops bordering the Maybeso valley and
vicinity are rounded and show evidences of extensive glacial
scour (polished pavements, grooving, striations,crescentric
plucking structures, etc.). During the glaciation that
modified these ridges only the very highest summits pro-
truded above the ice. In the vicinity of Maybeso valley
only the Harris Peaks and possibly Granite Peak stood
substantially above this most extensive ice sheet. Evi-
dence for this is the serrated and irregular ruggedness of
these higher summits and the general absence of glacier
scour.

Thus, the earliest recognized major ice advance at-
tained a thickness sufficient to cover most of the ridge tops.
The older till may be a correlate of this early ice advance.
The latest major ice advance reached to lower elevations and
was limited to the lower flanks of the valleys, resulting
in restricted deposits of the younger blue-grey till. Of
course other ice advances, and certainly many lesser
fluctuations than those indicated, probably occurred, but
evidence of such has been removed or otherwise modified
by the intensity of these main glaciations.

Sainsbury (1961) suggests two possible causes of
the great ice thicknesses attributed to the earlier major

ice expansion which inundated all but the highest peaks

 

A8

of Prince of Wales Island. His first suggestion was that
continental glaciers have pushed westward from the Coast
Range with sufficient thicknesses to override the higher
ridges of the Alexander Archipelago, including, of course,
Prince of Wales Island. He points out, however, that the
general southeastward trend of ridges, valleys, roches
moutonnees, and lake basins on Prince of Wales Island sug-
gests that ice sculpture was accomplished by ice moving in
an east to southeastward direction. This suggests further
that there is a more local expansion of ice from the high—
lands to the west, that is, from the center of the island,
rather than by continental ice from the east or northeast.
The southeastward trend of valleys, ridges and roches
moutonnees on its own, does not appear to be a reliable
criterion for a highland ice center, in that others have
shown that main valley orientations in the Alexander Archi-
pelago and the Boundary Ranges to the east are essentially
controlled by structural and lithological factors and not
by glacial movements alone (M. Miller, 1963 and 196A; Brew,
1965). The writer's observations in the Maybeso valley,
however, tend to confirm the second hypothesis. For
example, mineralogical and lithological content of the
older and younger tills is of local origin and quite simi-
lar except for a predominance of black argillite clasts in
the older till. This suggests a similarity of source area

and tends to corroborate the concept of a westward highland

 

49

source. Such a concept is further indicated by the pre-
sence on the valley walls of unweathered bedrock striations
and grooves, plunging from 5° to 30° to the east. They
indicate, of course, down-valley flow in that direction.
The fabric of both tills is also oriented to the east,
plunging down valley. This would be expected where the
deposition by ice is confined, at least partially, within
the valley and flowing to the east. Finally, there is

some evidence that there may have been a plant refugium on
Prince of Wales Island during the late Wisconsinan which
would have depended upon some land area to remain above the
ice (Harris, 1965; Taylor, 1936). Further consideration of

this problem will be given later.

Older Till

The older till is exposed in a small patch at about
600 feet elevation in a quarry on the north side of and near
the center of the Maybeso valley (Figure 20). Also note
starred site on Map 2. This deposit is about 6 feet thick,
is brownish grey in color, and relatively coarse in tex—
ture. It contains semi-rounded boulders of diorite, ande-
site, and greywacke, with large amounts of semi-rounded to
angular fragments of black argillite. Faceting and stri-
ations characterize some of these contained boulders,
cobbles and pebbles. Although the deposit in Maybeso valley
has been thoroughly oxidized and leached, there is no

weathering rind developed on constituent particles as is

 

50

commonly found in early Wisconsinan deposits underlying late
Wisconsinan till described from other areas in the Pacific
Northwest (Crandell, 196“) and Alaska (Karlstrom, 1964).
Thus, the older till is not necessarily of great age.

There also is a detectable fabric in the till, its
orientation being at a slight angle to the valley and
plunging toward the valley center. Till fabric analyses
were made using the Brunton technique at three selected
sites. The results are shown in Figure 21. Lying directly
above this remnant of the older till deposit is the younger
till. It is believed by the writer to be a correlate of
older till described by Sainsbury (1961) which he relates
to the period of high level glaciation preceding the wide—

spread valley glaciation which deposited the younger till.

Younger Till

The younger till overlying most of the bedrock is
bluish grey in color and extremely hard and impermeable.
It contains a large amount of rounded boulders, cobbles,
and pebbles of greywacke and diorite; with lesser amounts
of semiurounded to angular fragments of black argillite.
All of these are imbedded in a matrix of highly calcareous
silty sand. Till fabric measurements show fabric is
oriented at a slight angle to the valley and plunging into
it (Figure 21). It is clear that fabric strike in the older

till is southeasterly, whereas the younger till fabric is

 

51

 

Figure 20.——Older till (dark) underlying younger
till (light). The lower limit of weathering
in the younger till is marked by dotted line.

 

— —
~ - '5“th

52

    

 

       
     
           
   
       

  
     

     

       

 

O :... ‘
l o «w «ml-uni». o t t \
-'.'.'."I.":..‘.“\\\‘
h ~§§ Q “I: 0 eioo‘ I ‘
llllll.5"-.-':::$S.~ts‘§\uir:$!¢,'¢.’e‘g€t‘.‘nl"‘IIIIIII“
w—""'""::iii:ss‘ssss‘sieeresaiiai::“"""' .
II IllllIm-u-“ragweedsissfisflg-nmfl'mflll
Illfi‘ua‘utiwi’iirlgr.7s3§isii-::u.'.'.',"'ll
oo t . 'Jnn
““‘\‘u"u':"'
‘ “ ”regains:assess ”I
so ‘ ' 3““. "I

Older till

weathered—-—— O
Younger iilll:

un-weathered

 

Figure 21.—~Till fabric analyses of three selected
sites in the older and younger till.

53

related to more southerly flow. This, of course, corrobor—
ates what has been revealed by differences in erosional
forms related to the main directions of flow in the main
earlier and younger glaciations.

The younger till is weathered to a maximum depth of
5 feet. High on the slope, the weathering zone is quite
shallow, but with a decrease in slope the depth of weather-
ing is greater.

The weathered zone is everywhere weakly podzolized.
The A horizon is from 6 inches to 18 inches thick on steep
slopes and as much as 42 inches thick on more gentle slopes,
where thick organic mats develop. The B horizon continues
down to the unweathered bluish-grey till. It varies from
about 18 inches thick in steep areas to as much as 36 inches
thick on less steep slopes. It has been both oxidized and
leached, is yellowish brown in color and somewhat friable,
although its mechanical analysis and fabric are similar to
the unweathered portion of the till.

At the contact separating the weathered and unweathered
till, the lower limit of the B horizon, a narrow zone from
one to six inches thick occurs. This zone is distinguished
by a mottled yellowish grey collor, and some iron staining.
In it there is also considerable root penetration and it has
been partially oxidized and leached. This is the most re-
cent increment in the development of the weathered profile

and is further noted in Table III, which shows a typical

5A

Karta Soil profile. This profile was taken in the vicinity
of recent sliding in Maybeso valley (Charles Gass, personal
communication).

The reason for the compactness of the younger till is
not entirely clear. It is presumed to be largely due to
weight of the former overriding ice, as evidenced by develop-
ment of the orientation fabric in and below the B soil hori-
zon. Carbonate cementation has played an additional role in
the duration. Till on the end moraines is characterized by
a similar hard and resistant quality, but without fabric.
Acid tests reveal a high proportion of carbonate in the till
matrix at both type localities. Of interest is the lack of
clear evidence of ablation moraine at the sites studied,
although the presence of such may be masked by development
of the soil profile.

The till is essentially a silty sand with a low clay
size particle content. The sand, silt, and clay size
fractions in selected samples excavated from both the
weathered and unweathered till segments at slide locations
1, 2, and 3 are shown in Figure 22. Here the marked simi-
larity of all samples is striking. The weathered till of
Karta soil, when moist, is somewhat sticky and cohesive
but, upon air drying, it becomes hard and resistant.
Shrinkage cracks develop with further drying. The till
material loses most cohesiveness when completely dried

under which circumstances it often crumbles at the touch.

 

55

TABLE III.--A typical Karta soil profile in the study area.1

 

 

Depth Representative Profile of Karta
Horizon (inches) Soil in Study Area
01 5—4 Living mosses and undecomposed leaves
and twigs.
02 4-0 Reddish black (10 R 2/1) peat; wet, non-

sticky, non—plastic; many fine medium
and few coarse roots; pH 3.5; abrupt
wavy boundary.

A2 0-1 Pale brown (10 YR 6/3) gravelly silt loam;
weak fine subangular blocky structure; wet,
slightly sticky, slightly plastic; coarse
fragments 40 percent by volume; many fine,
medium, and few coarse roots, common fine
and medium pores; pH 4.0; abrupt wavy
boundary.

B2hir 1-14 Yellowish red (5 YR 5/6) gravelly silt
loam with dark brown (7.5 YR 3/2) varie-
gations; gravelly silt loam; weak fine
and medium subangular blocky structure;
wet, slightly sticky, slightly plastic;
coarse fragments 40 percent by volume;
common fine, few medium, and coarse roots,
common fine and medium pores; pH 4.5;
clear wavy boundary.

Cl 14—17 Olive (5 Y 5/3) gravelly silt loam; mas—
sive; weakly cemented; 75 percent coarse
fragments, few fine roots, pH 5.0; clear
wavy boundary.

C2 l7-21+ Olive (5 Y 5/3) gravelly silt loam; mas—
sive; strongly cemented by CaCO3, with
pockets of non-cemented, very porous
glacial till; pH 5.5, 75 percent coarse
fragment by volume. In transition zone
to underlying unweathered till.

 

lFrom Charles Gass, soil scientist, South Tongass
National Forest, Alaska.

 

i. “a?
>%.wri _.

56

DISlUfbed Samples—Unweathered Ti ll

 
   
 

 
 
 
 

 
  
 

         
         

    

 

   
 

  

   
   

  
 

     

 
     
             

 

 

   
   
 

   
 

 

 

  

 

   

 

 

 

 
 
 
 

 
  
 

   
  

 

 

  

    

 

 

 

 

lop'slide sllde3 slide3 gop
% 3 ' slide 2 slidel
‘37 so slide 2
w,_ 1250!: 77on sand iooon noon
0
noie‘sond,sulv and clay poriiclesore sepercted otdiameters of 2.4, .07 00d .003 mm. '83PeCliVely
Dustulbed Samples—Weathered Till
0/0 -
by so '°P*"de ma. 3 shde3 slude3 9'ide3 5"“ 3 “”193
3
silt
O
% .. lOp'slide lop.s|nde slide 1
by 50— 2 I
q sand ft
1 .. 1080f: sand 1150“ 1000
: suit
0 coy
Undusfurbed l2A—mch Pedlstol Samples Weathered Till
top top edge bottom 0' to ed e
0/0 .4 edge of boiéom f ofslip—out slip—out ofglipaoui
4 ' -— 9 .
by 50.. 3"p out slip—goeu? slide 3 slide3 slide2
Wt. qsand tludel slide] sand
: sill l silt
0

Figure 22.—-Bar graphs of the weathered and un—
weathered younger till showing marked similarity
in mechanical composition of all samples with
respect to several of the main slide locations
shown on Map 3.

57

The upper limit of the younger till is marked by a
discontinuous break in slope, or berm, corresponding to the
elevation of the surface of the glacier which deposited the
till. This berm, which lies between 1,200 and 1,500 feet,
can be traced intermittently along the flanks of the May-
beso and Harris River valleys. It is also seen along the

flanks of Twelvemile Arm.

End Moraines

 

The younger till deposited on the sides of Maybeso
valley is thin near its upper limit, but it thickens con-
siderably toward the valley floor. Locally, till thick—
nesses at these lower elevations exceeds 20 feet.

In the lower reaches of the valley floor the till
covering is also pierced by several bedrock knobs over parts
of which till was deposited in drumlinoid forms. Four
distinct end moraines are identified (Map 2). The till in
all of these features is of the same composition and tex—
ture as the younger tills on the higher and steeper slopes.
It is commonly weathered to a greater depth in the valley
bottom (e.g., 5 feet maximum here as compared to 3 feet
maximum on the slopes) but the depth is quite variable.
This variation in depth of weathering reflects not only
the effect of slope but connotes the importance of local
fluctuations in water table. These factors are well known
as significant in determining the depth of leaching and

soil formation (Jenney, 1941; Ellis, 1938).

 

58

The mouth of Maybeso valley is crossed by a well-
developed terminal moraine, hereafter referred to as the
Maybeso Moraine. This moraine possesses a bedrock core
and, in effect, is a bedrock ridge modified by glacial
scour and covered by a mantle of variable thickness till
(Figure 23). The moraine is approximately one mile long
and 1/4 mile across at its widest part. According to Davis
and Mathews (1944) such bedrock-cored moraines are common
in the valleys of the British Columbia Coast Range. They
postulate that such bedrock cores are caused by a marked
decrease in glacial erosion near the mouth of valleys
where valley glaciers enter a larger ice stream. These,
of course, are nothing more than bedrock thresholds. The
conditions at the Maybeso valley mouth are assumed to have
been comparable to those postulated by Davis and Mathews
during Wisconsinan time.

The glacier in the Maybeso valley was relatively short,
in effect being a typical cirque-headed valley glacier. It
was nourished by small amounts of ice from two cirques on
Harris ridge, and by overflow from the central highlands
through the U—shaped pass at the head of the valley. Where
the Maybeso glacier joined a larger glacier moving down
Twelvemile Arm (Figure 24), a change in erosive power is
inferred which resulted in formation of the bedrock thres-
hold underlying the Maybeso moraine. There is, in the

writer's opinion, a strong possibility that this threshold

59

 

Figure 23.—-View of the Maybeso moraine crossing
the mouth of the valley. View is southeast
toward Twelvemile Arm.

60

at the valley mouth represents a select basal stub of a
much older lowland cirque threshold. This kind of feature
has been observed by the writer in other deglaciated
valleys in southeast Alaska and has been described by
Miller (1961) in the Taku-District, near Juneau.

A second terminal moraine, referred to hereafter as
the Crackerjack moraine (after the abandoned Crackerjack
gold mine on the slopes above it), is found in the center
of the valley. This moraine is about 1 mile long and 200-
300 feet across. It is also composed of indurated younger
till (Figure 25). Where it crosses the valley, there is a
sharp change in direction of Maybeso Creek, and evidence
that a meltwater lake was impounded behind it.

Up-valley from the Crackerjack moraine occurs the
Haystack Butte moraine (Figure 26) named for its proximity
to a bedrock butte resembling a haystack. It is also com-
posed of the same material as the earlier moraines de-
scribed. Maybeso Creek is also deflected by this cross—
valley terminal moraine (Map 2).

A fourth moraine or moraine complex, referred to here-
after as the Snowdrift moraine (after the abandoned Snow-
drift gold mine nearby), consists of a series of low,
hummocky ridges approximately six miles up-valley from
tidewater. This complex is composed of younger till and
represents the last recessional moraine system identified
in the Maybeso valley prior to final disappearance and with—

drawal of ice derived from the upper Harris valley.

llr.

 

___ ,

' .1- .v‘i. 0

 

61

.83 wishiofiosm. E .6530 mg mcflofl t 9655

$820 >o2m> Omon>m§ .5 Egon oZmOuo E cofiosoou >01 pmomoco Eocmocfi no Econ 302 .EE.

oZEnoZoBH 3E >o2m> Omon>m§ Esoo EoEo>oE one 555% oEmnocd we Sonatas: . am 8:03

 

 

 

 

\‘lVV \\\\\\\
\\\\\\\M\\\\\\\\.

\\\\\\ \\\\.

M\\\\\\\\\\..\... . \fw \\\\\
\\\\\\ .\. /. \\\\\
\\ .. l. \\\..

 

 

Ec< o__Eo>_o>>w so:o> omoo>o<<

 

 

62

 

Figure 25.-—View of Crackerjack moraine crossing
the middle of the Maybeso valley. View across
valley toward the south.

 

63

 

Figure 26.—-View of Haystack Butte moraine in the
upper middle part of the Maybeso valley. View
across valley to the southeast.

 

64

Each of the above noted moraines possess a weathered
zone of approximately the same depth, suggesting little
soil development between times of deposition. It is pre-
sumed that this retardation of true soil development was
a result of a period of colder periglacial conditions
associated with the ice retreat. It should also be noted
that each of these moraines is relatively broad and sub-
dued, thus having the character of still-stand or slow
recessional development rather than the constructional
topography normally associated with vigorous readvances

and sudden retreats.

Effect of Moraines on the
Maybeso Drainage

The Snowdrift moraine complex has exerted a slight
control on the Maybeso Creek drainage in causing several
short bends in the channel as the stream cut across these
moraine ridges (Map 2). The Haystack Butte moraine has
caused a sharp bend in the stream channel on the north
side of the valley where it truncates the moraine. No lake
sediments have been found to indicate that the Haystack
Butte moraine dammed Maybeso Creek for any length of time.
Thus, it is quite likely that the narrow cut in the mor—
aine through which the Maybeso Creek flows was originally
produced by a meltwater stream flowing off the ice.

Maybeso Creek also cuts across the Crackerjack

moraine through a narrow channel. Exposed in a bluff on

65

the west side of this moraine is a thick sequence of

varved clays deposited in a former glacial lake dammed
behind the moraine (Figure 27). Varved deposits have

also been found on the west side of the moraine near its

top and on the north side of the valley behind the Crack—
erjack moraine. These deposits indicate that the lake
formed behind the Crackerjack moraine and remained there

for some time. The nature and extent of these lacustrine
deposits are discussed later. Eventually, the lake over-
flow cut deeply through this moraine, establishing the
present creek channel and completely draining the impounded
water. The lake was dammed on its eastern margin by the
Crackerjack moraine but the exact position of its western
margin has not been defined. No lake deposits have been
observed up-valley from this section. Drainage, however, is
very poor with muskegs covering most of the valley floor be-
tween Crackerjack and Haystack Butte moraines, indicating
very poor draining conditions. The lake's western margin
may, therefore, have rested against the ice front which
deposited the Haystack Butte moraine.

Map 2 shows the probable position of the lake at an
estimated mean elevation of 250 feet above present sea level.
At least 23 varves of alternating fine sand and clay have
been counted. These accumulated to a thickness of 5 1/2
feet above about 2 feet of very fine, sticky clay. A thin,

compact layer of coarse sand occurs below this clay (Table IV).

66

 

Figure 27.—~Pro—glacial lake deposit behind Cracker-
jack moraine. Person in the picture has his
right foot at base of the clay layer and his
hand at the beginning of the rhythmites.

67

 

.22 2.2.

 

0:00 0:22 m2 om.N
00>02 002009000 :2 0:00 000000 m . 0 on . s >020 022 >220 0020:2502 >20:2m m . 0N. . N
>20 520220 0:22. >00> m . NN om . s 0:00 0:22 N .2 on . N
0:00 000000 0 .m ow. 0 >20 0022 >220 0020:2802 >20:22 0. mm. N
>020 >220 o.m 02 .m 0:00 0:22 N. 2 ooN
0:00 00.2000 0 . mm . 24 >020 022 >220 0020:2802 30:22 0 . om . N
>20 >20 0 .2 om . 2V 0:00 0:22 0 . 020 . N
0:00 00,000 m. 00.0 >020 022 >220 0020:2802 30:22 0 . 3. N
>020 022 >220 0020:2802 >20:2.2 m . om . 0 0:00 0:22 o . mm . N
0:00 0&0 0. 00.1. .0020 8.02 3:0 08002802 >280 EN 8.”...
>20 022 >220 0020:2802 30:22 0 . 2 om . 2V 0:00 0:22 0 . O2 . N
050 men 0. 0:. >020 8:2 3:0 0982802 >280 0. 80
>020 022 >220 0020:2502 30:22 0. om .0 0:00 0:22 m2 oo.N
050 0:0 0. 34. >020 8:2 3:... 0805s.: .2050 0. mm. 2
>020 802 .220 080552 3000 0. 8.2. 0:00 052 0. 2 8.2
0:00 0:22 0 . m2 . 2. >20 00.2 >220 0020:2802 30:20 N .2 mm . 2
>20 0022 >220 0020:2802 30:22 20 . N 02 . 2. 0:00 0:22 0 . mm . 2
0:00 0:22 o . m cm . m >20 0x2 >220 0020:2802 30:22 0 . om . 2
>20 0022 >220 0000:2602 30:20 20 . N ow . m 0:00 0:22 m . NN . 2
0:00 0:22 0 . ON . m >020 022 >220 0020:2802 30:22 0 . 00. 2
>020 8:02 >220 0882602 2000 N2 02 .m 0000 0:20 0. E2
0:00 0:22 m .2 mo . m >20 0022 >220 0020:2802 >20:22 N . s om . 2

>020 022 >220 0000:2802 >20:22 N ..2 co. m 200000 .2000 + 00>2 02:00.5 200 on.
:0222 2:00 0D town“. 50 0Q :0222 2:00 00 IMMWHH :22 0Q

 

 

 

 

 

.0:2020E.200020200po

0:0 0:2:00 Eonm 00200000 0:20005002 00>L0> 00 :0200220000 0:0 .000:20H:0 .cpdoail.>H m2m<e

68

This might be but a partial sequence. Its existence, how-
ever, is important as support for the conclusion that these
are recessional moraines, deposited under decaying ice
conditions.

Flint (1957) states that the majority of "known bodies
of mechanical rhythmites are the product of glacial melt—
water deposits and hence record the near presence of glacier
ice where and when they are laid." Such an association of
rhythmites with glacial deposits is obvious in Maybeso
valley. Because of the valley morphology and presence of
at least 2 feet of very fine, sticky, non-varved clay, shown
in the table to lie near the base of the section, this is
interpreted as the deepest part of the lake, with the waters
shallowing considerably up-valley. The nearly 5 inches of
basal sand noted in the profile was presumably deposited
during the initial stages of lake formation; i.e., as the
ice retreated up-valley to the position of the Haystack
Butte moraine. In this lake, it is also assumed that coarser
lacustrine materials were deposited farther up-valley.

The 2-foot clay section may represent a period of
colder temperature when the ice front was stable and the
lake surface was possibly frozen much of the year, thus
allowing finer particles to settle. To be gleaned from
such evidence is at least some of the glacial and peri-
glacial conditions typifying a few years in the late

glacial history of this valley.

 

69

The rhythmites (varves) above the basal clay may
indicate annual variations in glacial sediment in the stream
as glacier equilibrium conditions ended and the ice resumed
a slow retreat. No identifiable organic material has been
found in these layers. The short sequence of rhythmites
may be explained by relatively rapid lowering of the lake
level as the outlet was cut through the Crackerjack moraine.

There are four distinct notches or breaks in the May-
beso moraine where it arches across the mouth of the valley.
One of these is the present outlet of Maybeso Creek, lying
about 50 feet above sea level. The other three transect the
moraine at levels higher than the present valley floor. The
lowest elevated notch, on the south side of the valley,
developed at an elevation of approximately 100 feet. The
other two, on the north side of the valley, occur at ele-
vations of 150 and 180 feet.

The Maybeso Creek notch is bedrock floored and lies at
the center of the moraine (Map 2 and Figure 28). There is
no bedrock exposed in the bottom of the more elevated
notches, although bedrock does rise on either side to form
glacier scoured knobs veneered with a thin till. The till
cored nature of these notches and lack of any obvious
fluvial erosion or deposition features in the higher three
notches suggests that they did not serve as drainage
channels, at least during or following deposition of the

Maybeso moraine. Also, the absence of lake deposits in

 

70

the lower Maybeso valley behind the moraine suggests that

these notches did not serve as lake outlets following ice

withdrawal. More likely, they represent low areas in the

bedrock core of the moraine which perhaps served as drain-
age outlets during earlier periods of ice advance and re-

treat.

In the lower portion of the valley behind the Maybeso
Moraine, there is much evidence of recent changes in posi-
tion of the stream bed. Old channel positions are repre-
sented by low muskeg strips on either side of the present
stream. This reflects the change in local base level by
Maybeso Creek as it incised its outlet through the valley

mouth moraine.

Elevated Marine Deposits

 

Sainsbury (1961) reports shell fragments from the
younger till near the mouth of Maybeso valley. The writer
has not been able to locate any such site. The writer,
however, has identified marine deposits in a raised beach
and terrace in Indian Creek and the Harris River valleys,
and at the mouth of Maybeso Creek at an elevation of about
30 feet above sea level (Map 2). This marine terrace di-
rectly overlies the younger till and was developed after
the retreat of the last ice advance in the Harris River
and Maybeso Creek valleys.

The best exposure of this deposit occurs in a stream

cut in Indian Creek (Map 2). This section consists of 8

 

71

l:aru0fi——5;:2L‘

. as:

 

Figure 28.--Jointed bedrock core of Maybeso moraine
causing falls in Maybeso Creek.

72

feet of interbedded marine sands and silts containing
numerous shells of recent pelcypods identified by Dr. K. J.

Boss of the Agassiz Museum of Harvard University as

 

Clinocardium nuttalli, Saxidomus giganteus Deshayes, Macoma

incongrua von Martens, Macoma nasuta conrad and Macoma

 

 

lrgta Dall. These genera are all common to the coastal
waters of southeast Alaska today. This marine deposit is
overlain by 10 feet of coarse, cross-bedded stream gravel
topped by soil (see Figure 29). The soil zone consists of
2 feet of forest litter above a 6-inch—thick dark brown
oxidized zone. Below this lies a light brown zone with an
undulating layer of iron oxide observed at the base. The
iron oxide zone delineates the present oxidation front.

The above noted marine deposit is also found at the
mouth of Harris River valley and continues to exhibit the
same characteristics as the Indian Creek segment. It is
mapped as a continuous terrace unit looping across Harris
River valley (Map 2). Structurally, the terrace disappears
near the mouth of Maybeso Creek valley. Additional evidence
has been found, however, that the beach deposit does con-
tinue across the mouth of Maybeso Creek in front of the
Maybeso moraine. Auger holes drilled along the outer mar-
gin of the moraine in connection with a road relocation
survey [Alaska Department of Highways, Project S-O92M(l)]
have exposed a silty sand layer approximately 10 feet thick

and 30 feet above sea level at two separate locations.

 

73

 

 

0 0000000 floooooggoooood
00000 0 0 “00000 00600000000000

€\\

 

\‘fi ‘

 

p
a,\ 9 _ as
2"“ a a sum. FRAGMENTS fl7___@

6’49 0CD 6’4767c7 G’O<9<?C)C?GD 67'

 

 

 

 

 

 

organic layer

stream gravel

 

marine sin

younger 'ill

 

 

 

oxidation
from

 

Figure 29.-—Cross-sectional sketch of marine deposit
found at the mouths of Harris River and Indian
Creek. Shell samples for radiocarbon dating
were taken from exposed silt layer.

7H

These are respectively: a flat bench near the mouth of
Maybeso Creek and at the mouth of a small stream outlet at
the southern end of the moraine. The deposit near May—
beso Creek is covered by a thin organic soil. The deposit
at the stream outlet is covered by about 8 feet of sandy,
silty gravel. Marine shell fragments were found in the
auger samples from the Maybeso Creek deposit. Figure 30
is a cross-sectional sketch showing the position of-the
beach deposit in front of the Maybeso moraine.

Sainsbury (1961, p. 330) reports a marine beach approxi—
mately 50 feet above sea level at Coal Bay, north and east of
Hollis which probably correlates with the Indian Creek—Harris
River-Maybeso Creek deposit. A radiocarbon date was obtained
from the well-preserved recent marine shells in the Indian
Creek deposit. Details of this analysis will be discussed

later.

Ground Moraine

 

As has been shown, basal ground moraines control the
occurrence and distribution of many of the debris avalanches
and flows which have developed in this valley. The follow—
ing facts are reiterated to stress the important relation—
ship of glacial geology to the engineering objectives of
this study. It has been noted that till is found up to
elevations of 1,200 to 1,500 feet. Also, as mentioned
previously, it usually occurs on the north-facing slope

in isolated pockets or as discontinuous sheets separated

 

- .rsd- .. _.

 

 

 

75

 

 

 

 

.00....
0.

F9

 

soi|

till

beach deposfl
bedrock

AAC)RAIFJE

MAYBESO

 

 

 

.'.'0A A - -

&?z

HCDLLIS
ANCHORAGE

-‘, ? -. ,' .. :Q'
".0 - - . ‘
25;:- ([320.

O
0.
£9»

.‘9
Q*fi$:Z§ri

.3. ‘ I

O -
. ' .’.‘
. . _ _
. .
.. .

     
  

I 0-. .-
'ODOCCOOOOIOOOIOOOIIOC

f!! f _
a?‘oo

$90

 
   

  
   

.inc
-I§L.V'\\\\\\\
iAwQaa‘\\\\\\\\
“(b-93’. \\\\\\\\\
J09"- \\\\\\\\V
36Q§5 \\\\\\\\\\
0gbfl'\\\\\\\\\\\
1.0; \\\\\\\\\\\~
.jw§;\xx\\\\\\\\\\
5055‘ \\\\\\\\\\\\~

xv \\\\\\\\\\\\\i
so.) \\\\\\\\\\\\\\‘
1' \\\\\\\\\\\\\\\
sf», \\\\\\\\\\\\\\\\
,aaU \Ax\\\\\\\\\\\\\\
sfi;5'\\\\\\\\\\\\\\\\\\
:50; \\\\\\\\\\\\\\\\\\\
54¢“ \\\\\\\\\\\\\\\\\\\\
;;sx \\\\\\\\\\\\\\\\\\\\\
5G9? \\\\\\\\\\\\\\\\\\\\\\
;9 \\\\\\\\\\\\\\\\\\\\\\\

:ék- \\\\\\\\\\\\\\\\\\\\\\\\
3%“ \\\\\\\\\\\\\\\\\\\\\\\\~

.. \\\\\\\\\\\\\\\\\\\\\\\\\\‘
- \\\\\\\\\\\\\\\\\\\\\\\\\\\‘
\\\\\\\\\\\\\\\\\\\\\\\\\\\\
. \\\\\\\\\\\\\\\\\\\\\\\\\\\\\
. \\\\\\\\\\\\\\\\\\\\\\\\\\\\\
; \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
\\\\\\\\\\\§§>§§§§\§\\\§\\\\\\\\

xxxxxxx

\

,4“
\M
/‘%W

 

 

 

Figure 30.——Sketch of marine deposit in front of Maybeso moraine.

 

 

76

by bedrock ridges and outcrops. On the south-facing slopes,
a much more continuous veneer of ground moraine covers the
surface producing a relatively smooth, even slope to the
valley floor.

This till surface supports a weathering zone extend—
ing to an average depth of 3 feet on the higher slopes. It
is in this zone that debris avalanches and flows occur.
Initiating zones of these landslides are located near the
upper limit of glacial till; i.e., near the high stand of
late Wisconsinan glaciation. The unweathered till surface
serves as the lower limit of the failure zone.

All the slides observed in these glacial tills have
occurred in shallow drainageways developed by intermittent
surface flow and by previous sliding (Figure 31). Near the
upper till limit the channels are broad and rounded, probably
outlining micro-drainage basins. It is in this part of the
regional ground moraine that the initial zone of slope fail-
ure generally occurs. In each case, at some distance down—
slope, the broad depressions become a single twisting chan—
nel. Debris flows are commonly restricted by such channels.
Erosion often occurs all the way to bedrock.

These drainage channels are most common on the south—
facing valley slopes. Slides already have occurred in some
of them. Sliding is imminent in others. In nearly every
case where slides have not yet developed, water flows on
the surface only after saturation from intense, prolonged

rains. This indicates that a substantial subsurface flow

 

77

 

Figure 3l.—-View toward northwest showing valley side
and micro—drainage channels in ground moraine.
View shows south-facing slopes three to five
miles from mouth of valley. The valley mouth
lies to right, Maybeso Creek may be seen in
lower left. A drumlinoid feature is indicated
by small arrow.

78

occurs in the mantling till. In_a number of these shallow
channels, older slides have taken place at lower elevations,
that is, between 700 and 900 feet.

In the valley bottom, the older till is found as
previously described. This, too, is assumed to be a rem-

nant of ground moraine.

Cirque Distribution

 

Ljunger (1948) has used the distribution of cirques as
indicators of former glacier limits in Scandinavia. R. F.
Flint (l9U7) has also considered old cirque levels as being
excavated during former ice advances in the western states.
More recently Miller (1961) has demonstrated that the distri-
bution of abandoned cirques can be used as indicators of the
former mean position of permanent regional névé lines during
major phases of glaciation and has also clarified the chrono-
logical significance of these erosion basins in terms of
Pleistocene ice fluctuations in the Alaska-Canada boundary
range.

A map survey of the areal and vertical distribution of
abandoned cirques in the total area of Prince of Wales Island
(Table V) shows five significant changes in cirque floor
level corresponding to significant shifts in the former
position of the regional snow (névé) line. Figure 32 re-
lates the total number of well—defined cirque basins to the
elevations at which they occur. Note in this figure that the

five distinct cirque systems are suggested by differences in

 

79

total number of cirques occurring within individual ele—
vation ranges of 200-300 feet. The differences in numbers
designating each system are a function of the relative age
of each system and the duration of time at which the snow
line remained within the elevation range of that system.
Thus, the system with the largest numbers and sharpest
cirque configuration is related to the most recent major
ice advance. In older systems the cirques would tend to be
more subdued and their numbers less because of subsequent
glacial modificiation.

Three rather dominant cirque systems within the total
sequence are recognized (systems II, III, and IV). Those
believed related to the last major valley ice advance on
Prince of Wales Island are represented by system III. These
occur at elevations of between 1,100 and 1,300 feet and ap-
pear to be composite in nature indicating that the regional
snowline remained at or near these levels for a consider—
able time. The cirques are strikingly well—developed and
frequently occur in tandem with older and younger cirques.
The cirques of system II occur at elevations of between 700
and 900 feet. These abandoned cirques are fairly well de-
fined, but more subdued than those in system III, and fre-
quently are manifest by tarn lakes or small tributary valleys
hanging above the principal valley floors. These cirques

are related to an earlier ice advance.

 

80

 

 

0003 00m 0003 00>
0003 00m 0003 000
0003 coma .2 0003 ooaa
0003 coma .0 mm mm :m cm
0003 com II II II || ||
0003 ooaa 0003 ooaa I a I I a 0003 comm
0003 coca .2 0003 coma I I a I a 0003 comm
0003 coma a a a a a 0003 ccam
0003 00m 0003 00am .0 0 m N m N2 0003 0002
0000 0022 m 2 0 0 m2 0003 0002
0000 0002 .0 0000 00m 0 0 m 0 m2 0000 0002
0003 oo>
0003 000 0003 000 0 0 m N mm 0003 00ma
0003 ooaa 0003 ooaa 0 ca m ma mm 0003 ooaa
0003 coma .3 0003 coma .Q
a m m 0 ca 0003 com
0003 com 0003 com a m m m :a 0003 oo>
0000 00m2 0000 002 m m 2 2 02 0000 000
0003 coma .0 0003 coma .0 I c m a m 0003 com
3m mm 32 32 309822 23O200>0am

0:0202 00203 3o 00:200
:o 0:080o20>0c 000020 800:05

0:0202 00203 3o 00:200 :o

0000020 00:o0:0o< 3o :02000200020 0:0 :O2000:020o

 

.UCMHWH WGHGZ .HO @2332“ch CO mmfivhfio .HO COHUSQHcaPmHU COHPM>®H® 62.23 COHPMPC®H¢HOII.> Mdm¢9

 

81

35
l Ill

number

 

" soo woo 1500 2000 2500
o l ovcflon .
n.

Figure 32.--Histogram relating numbers of well-defined abandoned
cirques to their common elevations. Prince of Wales Island.

 

82

The cirques of system IV, found at elevations between
1,500 and 1,900 feet, are very sharply developed, and of
much more recent age. In one instance, a cirque at 1,700
feet in the central highlands still supports a small snow
field. Most of them are seen as relatively small cirque
basins.

Remnants of the lowest and oldest cirque system,
system I, occur at elevations of 100 to 500 feet. These
are indistinct due to extensive modification by later
valley glaciation. The best developed of the criques-are
quite often elongated and contain lakes. The bedrock core
of the moraine crossing the mouth of Maybeso valley may,
as previously noted, be a remnant threshold of one such a
low-level cirque.

The cirques in system V are few in number and of most
recent age. These range in elevation from 2,100 to 2,600
feet, with one at 2,600 feet supporting a perennial snow
field or possibly a glacieret.

The most common axial orientations of these cirques
and their associated U—shaped valleys is northeast and
southeast, indicating a general ice flowage paralleling
the regional structural trends (Condon, 1961, p. 29).

The indicated predominance of eastward flow, as previously
discussed, is contrary to the accepted concept of ice flow
westward from the Coast Range. Again, this reflects Sain—

bury's View of the probable existence of an ice field to

 

 

 

83

the west in the Prince of Wales Highlands during the major
Wisconsinan ice expansions.

In the principal study area three separate cirque
levels are found. These represent systems II, III, and IV,
and will be referred to later when the entire cirque se-
quence is used as a guideline to a possible Wisconsinan
chronology for this sector of the Alexander Archipelago.

Glacier Correlations and
Possible Chronologies

 

 

Two major ice advances of late Pleistocene Age have
been indicated in the Maybeso valley. The youngest is
represented by well-developed topographic forms and ex-
tensive deposits of compacted till weathered to shallow
depths. The older is represented by a single isolated
deposit in the lower valley and by intermittent remnants
on the ridges surrounding the study area. These are too
small and sporadic to map, though they may presumably be
correlated with erratics and extensively weathered older
till deposits found below the glacially rounded summits
and ridges at high elevations north and east of Maybeso
valley (Sainsbury, 1961, p. 329).

A similarly prominent two-fold till pattern of the
late Pleistocene has been observed in other glaciated areas
studied in Alaska, the most recent of these deposits having
been reported as late Wisconsinan age, with the earlier
deposits as upper mid—Wisconsinan to pre-Wisconsinan in
age (M. M. Miller, 1956; Péwé, 1953; R. D. Miller and

E. Dobrovolny, 1959; and Karlstrom, 1957, 1961, 196“).

 

8h

The possibility for long-range connection of the Prince of
Wales pattern to those elsewhere in Alaska and the Pacific
Northwest will be considered.

It has been shown that lithology of both tills in the
Maybeso valley is similar, consisting of rounded to semi-
rounded cobbles and pebbles of greywacke, black argillite,
and diorite in a silty rock flour matrix which, under
microscopic study, appears to have been derived from the
same material.

It has also been shown that the fabric of both tills
and striations on the underlying bedrock plunge in a down—
valley direction suggesting that both ice advances origi-
nated in the highlands at the center of the island. Sains—
bury (1961) has recognized a similar origin for glacial
deposits to the north and east of Maybeso valley. M. M.
Miller (1964) provides clear evidence in support of a theory
for local ice centers from the Juneau Ice Field in the
Alaska-Canada Boundary Ranges near Juneau, Alaska. Here geo—
morphic evidence strongly indicates that nunataks extended
above the ice at elevations of 6,000 feet in peripheral
areas and 8,000 feet in the crestal zone during the maxi-
mum Wisconsinan. During this time the outlet glaciers
formed extensive valley ice tongues extending into the low-
lands on both sides of the range. This left large ice-free
areas between the Coast Ranges and the Rocky Mountains, and

probably also similar ice-free areas to the west of the

 

85

boundary range, such as in the Alexander Archipelago. In
these areas flow presumably came from local mountain centers.

Dahl (l9U6), working in Scandinavia, shows similar
relationships on the Norwegian Peninsula. He points out
that a continental ice sheet, moving into deep water, can-
not extend far since, upon floating, it is quickly broken
up and carried away by the sea. He also points out that
the ice surface of a glacier will maintain a rising slope
back from a relatively low terminus so that relatively high
land near the sea could well protrude above the ice. Addi—
tional field evidence indicates that such conditions per-
tained on Prince of Wales Island during Wisconsinan time.
Such evidence is as follows: (a) the apparent absence of
any indications of over-riding ice on Granite and Harris Peaks
and the highland peaks in the center of the island, couples
with the extensive glacial rounding of surrounding ridge
tops in convex forms, a regional morphology very character—
istic of all ridges up to 3,000 feet on the island; (b) the
similarity of till lithologies to local bedrock types; and
(c) the presence of large numbers of angular to semi-rounded
pebbles, cobbles, and boulders of soft metasediments from
local bedrock in the till indicating short transportation
distances from their source.

Further support comes from the discovery of subalpine
fir (Abies lasiocarpa) reported by Harris (1965) on the

ridge separating the Maybeso valley and Harris River valley

 

 

86

at an approximate elevation of 3,000 feet. This is the
first occurrence of the species reported on an island in
southeast Alaska and is approximately 80 miles northwest
of the nearest previously reported occurrence at Very
Inlet and Boca de Quadra (Taylor, 1929) which lie on the
mainland near Salmon Arm on the British Columbia border
(Figure 2). The relative isolation of the Prince of Wales
occurrence and its limited development at high elevation
suggests that the stand descended from a loca1.refuge which,
at least during the latest major glaciations, existed on
nunataks rising well above the ice in the center of the
island.

A five-fold sequence of tandem cirques, markedly
similar in form and development to that found on Prince of
Wales Island, has also been described by Miller (1956 and
1961) for the Alaska-Canada Boundary Range (Table VI).
This sequence is believed by Miller to represent former
mean positions of the regional snowline which have raised
and lowered cyclically during the past glacial ages. Ac-
cordingly, he has made some tentative correlations of the
individual cirque systems in the sequence with certain
morphogenetic phases of the late Pleistocene glaciations
he has recognized in the Alaska—Canada Boundary Range
(1956; 196H; personal communication).

Similarity of the individual cirque systems of the

Prince of Wales Island sequence morphogenetically to those

87

 

.002023002 05200250 30 mw>w5
5023 0303020500 005200500 .002223I0o2 320003
00 500000 005020 2000m5oa0 50030 .3022050

.502002002&

0002 30 000050 0>20000wo0000 30 502005

I003 000002052 000000050 0000052200 0200050
.0522 000520 0>000 2203 0000002 322000500
.05050020>00 30 002003 0000050 M52000ww30
052000 00050 .0000052200 3230050 .005003 2203

.0522 000529
0>000 0000002 322000500 .05050020>00 30
002003 0000050 0520000030 .00050 “005003 2203

.5020000 2020020 00030005 050000
5023 05050020>00 30 002003 0502 0 0520000030
.000005020 0005 0020 22:0 5050 0052300 000000

00200000 052005 00 202>3220 .2225 .0000 52000
0>000 002000 500002030 .00020 0020 0505500

0 052050000000 3200530000 5000000 30 5020000
I003 30220>I53o0 0 00 0502 5000 0 30 00500003
2003020 0020 0>0o5oo 050 5003 00002050I250m

0003 commlccam
mlo

0003 ccmmlocaw
:I0

0003 cowalccca
mIo

0003 comalccm
mln

0003 ccmlcmm
2I0

.0030020 0000052200 00 0000200000

3200002 002 .52000 30 50305 00 505500 00003
1500 03200Io03 .002223 3050 050 002 320000
.00000 2000>00 52 .050 3022050 “052000 030020
003020>00 32050003 .500030 030020 0005023

.52000 52 05002>0 20200005

03200Io03 050 03200 503: .2220 052500 005500
0502 22050 3220300 .52000 525023 005200

I500 000520 02 .0522 000520 0>000 0o 00 0520
I03ooo 52000 030020 00050 .003020>00 3230050

.5020020020 30 00050 0>20000wo00 052

I030 05050020>00 535250: .00020020 30220>
000005 030020 ..0.2II52000 5003 30220> 5300
2203 000500x0 32005003 002 .052500 0302

5000 22050 5023 50305 002 00 2220 5000000

00 0520005 005 3205030003 52000 .5020020020
30220> 00002 30 502000232005 052000ww30 50200
Iw5oa0 0500 5023 52000 030020 005003I2203

.5020020020

30220> 000005 030020 00205 30 000300
.00020020 30220> 00002 30 0000003 00000000
5020000030 50305 52000 0005 05003 32505500
2220 0030530 .0302 5000 05200500 3205030003
52000 .2220 2020020 30 00050> 5250 0 5023
0000>oo 050 000005020 .2 5050 0052300 000000

.50305 52000 050 00 0500000
3205030003 02220 002030 .532>3220 050 2220
2020020 5023 002220 52000 0000030 .000000020

0003 commlccam
>

0003 comalccma
>2

0003 comalccaa
222

0003 ccmlccm
22

0003 ccmlccm
H

 

002002000000050 52000

00500
50200>020 050
50200502000
20>00 030020

002002000000050 52000

00500
50200>02m 050
50200502000
a0>00 030020

 

22002 .002222 0000<0
00500 30005300 000500I00002<

050202 00203 30 005203

 

.00500 30005300 000500I00002< 050 52 050 050202
00203 30 005200 50 0500030 030020 20302>2052 30 3002055005 02002000000050 050 050200>020 00023 00000>0 3o 5002003500II.2> mqm<e

 

 

 

 

88

050 502m00 0>20000000 5000 52 000500 002 00 05200000 502020500 02023002 0259

.0502w00 5000 052000330 000500 02w520 0 00 005

 

 

 

 

 

 

 

2
505 050002 0 00
2 .3 2 m :00053 00050
50520500023 002 52005502 0003 0003
020025 00300 0000000: oomlomm 2:0 oomnoom 2
:00050 00050
0MMMMN5MMMWW 002 5200530: 0003 0003
. 000200500052: oom2|oom mlo oomloow 22
0003 0003
:00050 oow2loom2 mro oom2uoo22 222
00050 002
52005303
50520500023 000000: 0003 0003
0000 oommnoo2m 0:0 oom2loom2 >2
2:00050 02023 0003 0003
002 00050000: commuoo2m mlo oommloo2m >
0002050050 50200>02m x0052 50200>02m x0052
50520500023 200200020 00050
5023 50200200000 020050wo500oz 0m50m 00005500 050202

2050202>o00 00000mm5m

000500|05002<

00203 30 005200

 

.250m2 050 mmm2 .002222 .2 .2 00030V 0w50m 000053om 0005001000020 050 52 5020020020
30 000050 0200500050005 5023 0500000 033020 20502000 30 50200200000100000I|.22> 00009

 

 

89

of the Boundary Range sequence and the similar dominance
of three cirque basin systems of equivalent form and
development suggests a probable close correlation of the
Prince of Wales Island sequence with that in the Alaska—
Canada Boundary Range. Table VII shows the probable re-
lationship of the Boundary Range and Prince of Wales Is-
land cirque sequences with the morphogenetic phases of
glaciation recognized by Miller. Note the three dominant
cirque systems in each sequence correspond respectively to
the Intermediate and Lesser phases of the Mountain Ice
Sheet Glaciation, a glaciation of regional proportion
which is believed by Miller to represent Wisconsinan maxima;
and to the Extended Ice Field Glaciation, a stage of dis—
tinct proportions corresponding to pulsation limits of the
latest Wisconsinan.

Early Ice Advance.——An early ice advance is repre—

 

sented in the Maybeso valley by the older till. This ad-
vance is believed related to the highest elevation to which
glacially smoothed bedrock extends, that is, about 3,000
feet. This means that most of Prince of Wales Island was
covered by ice during this extensive phase of Wisconsinan
glaciation, with only the higher peaks standing as nunataks
(Figure 33). This high—level glaciation is believed re—
lated to the first truly well delineated cirque system
(system II) recognized on Prince of Wales Island and, as
such, may be considered a correlate of the Intermediate

phase of the Mountain Ice Sheet Glaciation reported by

 

9O

.>0000> 00023002 050 50 30050 000 52005502 00000050000 n 5000000000 50000 30 5035500000 000 0000000001...mm 0.5000

IL

 

05:00.0:

||Oll|u

000000

003520

3
I 3.0.053: \

0:05.305 \
00.. .0 50:03.0
.OQCEE \
I \

 

OmWDxOZ \’

 

 

 

O ,/ .<< 0. . 50.0
..H :w

 

 

 

 

 

91

Miller (196“) in the Alaska-Canada Boundary Range. Its
correlate in southern British Columbia may well be the
Phase III glaciation described by Davis and Mathews (l9uu).

As stated earlier the older till is also similar in
physical characteristics and stratigraphic relationship to
the "older till" described by Sainsbury (1961) in the
northeast portion of Craig Quadrangle and which is be-
lieved to be a direct correlate. In the Juneau area an
older till deposit, the "basal drift," is also located
beneath a cemented blue-grey younger till as reported by
Miller (1963, 1964); who has tentatively correlated it with
the Greater to Intermediate phases of the Mountain Ice Sheet
Glaciation. As indicated earlier, and based on relative
weathering characteristics and probable relationship to
cirque system II, the older till is presumably not much
older than upper mid-Wisconsinan. As such, it would be a
correlate of Miller's "Intermediate phase of the Mountain
Ice Sheet Glaciation." Further work may reveal the Prince
of Wales Island ”older till" to be older, which would
probably make is a correlate of the Greater Mountain Ice
Sheet phase, but this is not born out by present evidence
(Table VIII).

Regardless of the open question of chronology, this
early ice advance, as represented by the older till, was
considerably more rigorous and extensive than the later

ice advance reported in Maybeso valley. As such, it is

 

92

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

00520002 22295
50250025 5052050002 00050 00050 52205
. . ..I I: .I 1 02000 002 52350: 0000000 [200.520.8000 1.. |.. I. .l
o 0 5022005000 00 02002 05020 05000
1! 05200022. 2229 . 5052050002 00050 00050 002 00520002
00 020% 222522
.0580 30 .8 m 5355: 3020050302 522552
0520002 - 50200020003 00520002
m55m0 T. In I. .l L .
o 05 0m 5050000039 00050 00050 505200 0525
50000050000 5052050002 002 52005502 000002 .I10M0202m2l
50000000 2229 0000 505000259 222200
Tlllllllnll2 0005500 ill II..II nll.lm0mmm Illlammm20mm2-
002003050 5000020> 02020002 00050050 0050500020
20>00052
5552552 2050059 205005020000 5552502 2050059 5552502 2050059
0200 000 00 00 0 002 :00050 0200 000
0 2 z < 0 0 .0 00000002 000000005: 2 0 2
00520002 00000 05020>25v0 5020020020 00 000050 00520002 00000
50520500023 02505000 0200500050002 0.002222
00220> 0005002 52 00 005020>25c0 00200025 5509
00000000 05020020020 050 52 05020020020

 

 

.00200000 00220> 0005002 050 00 50200200 02505000 02050
050 00200025 5509 050 52 05020020020 30 00505000 30 0000oln.222> 000<9

 

 

93

assumed to represent the maximum phase of the middle to
late Wisconsinan Glaciation on Prince of Wales Island.

Age wise, it may be tentatively correlated with the Moose-
horn Substage of the Naptowne Glaciation (lu,OOO-l7,000
years age), which corresponds to the Maximum Wisconsinan
in the Cook Inlet area (Karlstrom, 1961, 1964; also

Figure 34). This would also place it within the time
range of the early Fraser Glaciation in the Puget Sound
lowland (Crandell, 1964) (Table IX).

Late Ice Advance.——The more recent ice advance is
represented by extensive deposits of "younger till" which
has been noted to occur up to elevations of about 1,500
feet. As explained below, this glaciation is tentatively
considered to correspond to the lesser Mountain Ice Sheet
Glaciation in the Boundary Range (Miller, 196“) and, as
previously indicated, it is closely related to the second
dominant cirque system (system III). This would in part
relate it to a minimal Phase III glaciation as depicted by
Davis and Mathews (194M). The postulated appearance of
this younger glaciation during its maximum extension is
shown in Figure 35. The younger till, characterized by a
blue-grey color and light brown surface weathering zone,
corresponds to the "younger till" of Sainsbury (1961) and
the "upper drift" from the Juneau—Taku River areas (Miller,
1963). This is the youngest till of regional extent in an

area just recently deglaciated. A radio—carbon date from

 

94

I005oo 00000550 200505205001025 050 “050025 000252 5000
120020 5050025 050 05300002 050 00 0>050 2020020 00022000500

.20002 ammm2 .500002005v 050200200000 2020000 050 00000550
200505205001025 050.0050025 .00252 5000 .05020020020 5050025 050
05300502 050 00 0000

.0000» ooo.mm 0002 050 00 0>05o 2020020

..0022 .2222 .Eo5pm25m0v mco0pm2

n050200

.Aomm2 .mmm2 .500002005V 050200200500 200505205ool025
050 050022

.502000 00252 5000 050 00 0>05o 2020020 00022000500

.<

.505002005 00000 .05002< 50050500 52 002002050050 05000002020I|.:m 005020

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

59.002 000.5000 0.9.2.02 COU 2030009 50:02 0.005500
.055... 000E239 05009 0.0.3.0 00:5. 50100002 0 A o
P
_ .
.\ 1 /..L , /(x u _ a _ u u d2
_ E
/\/.\‘/\J./ — . rNL 1 [C
Ill .\1 _ 1f L \_l x1/.\P A\ /
II I\/'\) \ .l (\ l!\ 1‘ v
Ian D
_ _ . _ 2 _ _A-
5c .24 ¢J< NZ _ < . < 5 mu m 74 2’ .9 0 < 2L <
o n . o— n. N am
.230 000:. D<IUP
m :5! 0505533 0500.. 50.30 50:5. 5...! I 0 k 0 H n _ v m N _ _
OI I v
m /)K/\ % _ y \\2/t\A/(. r/ nHu
1’
a. /. . / I\ l I\ \ /.\ _
m , . «5 _ 2
Av. Z<¥m(5< ZC...<.U<5O m23090<z
0
o 0. on on v L
.300; COO—x. O (lUm
.00003— 0.05002; H 5030. TOE—00:00 _ 50.00.... — 3.00.925. .020” 5305:; ~ 500:3. — cU.cO.£(— 09.09502
W 00.50.00.0232002 00.360.05.05 50:23.0 05.0.0.0 co..0_uo.O 0...... 005.5U cot—0.00.0 05:30 .0005
W/\‘ / \\/ \\\ / \ / \L/ \‘f _
HP // \\ / \\ // \\ //‘ M \\\ _ / \ //
\ o
m n .u 4Lthw. / \ _
w AIITII
mm on Wk 00— nmp on. mm. CON nNN OWN
.05 2005 0000 £05.:

 

 

 

 

 

 

 

 

 

95

 

   

. 00.50 >029, 0002302 050 50 30050 000 52005502 500030 5000000020 00550..» 050 00 0050500000 0000550000....0m 00502.0

 

              

05:000..

0030.. .0
2.0.0.5:
.50E0>0E

00. .0 50:09.0 \
3905.5 \

., .,00..§il,w_.,..oi1llc..1xlrlo..fln 4X0

«I‘ll-l°‘lJ-Ii|.

  

 

 

 

 
 

96

the marine beach on Indian Creek near the Maybeso valley
places the latest valley bottom deposition of the younger
till as pre-9,SlO: 280 y.b.p. Thus, it is presumed to
represent the last major main valley ice advance in south—
east Alaska before the close of the classical Wisconsinan
Age (approximately 10,000 y.b.p.).

The relationships discussed in the previous section
provide a basis for a possible correlation of the latest
ice advance in Maybeso valley with the Killey substage of
the Naptowne Glaciation occurring between 10,500 and 14,500
years ago, although subsequent more detailed investigation
may reveal it to represent a post Killev condition peculiar
to the Alaska panhandle. These dates were extrapolated from
a plot of radiocarbon dates obtained by Karlstrom from the
more recent glacial advances in the Cook Inlet area near
Anchorage, Alaska (Figure 3A).

Also, Crandell (196“) has recorded a younger Wisconsinan
Drift from the S. W. Olympic Peninsula whose degree of
weathering and induration are similar to those of the
younger till from the Maybeso valley. The general simi-
larity of present climate in these two regions reinforces
the possibility that these tills are correlates. The
”younger Wisconsin draft” in the Olympics is oxidized to
a depth of about 2 feet and lacks even a thin weathering
rind on the stones in the soil profile, a condition which

also characterizes the younger till from the Maybeso valley.

 

97

Moraines and other constructional topography in both cases
are sharply defined and possess poorly integrated drain—
ages. Crandell has correlated parts of this drift with the
Vashon Drift in Puget Sound, deposited during the Fraser
glaciation which was the last ice advance in the Puget
Sound lowland. This drift is also oxidized to a depth of
about 2 feet with stones in the weathered profile lacking
weathering rinds. Radiocarbon dates from above and below
the Vashon Drift indicate that the drift was deposited be-
tween 13,000 and 20,000 y.b.p. The ice advance which de-
posited the younger till on Price of Wales Island may thus
be broadly correlated with the latest phase of the Fraser
Glaciation in the Puget Sound lowlands (Crandell, 1964).
Again, however, orographical circumstances peculiar to this
cordilleran region may later vitiate such attempts at
teleconnection.

Maybeso Valley Moraines.--As has been shown, the re-

 

treat of the latest ice advance is, marked in the Maybeso
valley by a series of four recessional moraines in the valley
bottom and a discontinuous lateral moraine system occurring
between 300 and 400 feet above sea level along the lower
valley walls. It is stressed that these valley bottom de-
posits represent the dying pulsations of the youngest glac-
iation, whereas the higher slope deposits represent the
maximum phases of the younger glaciation. These final

glacial pulsations are believed correlates of the glaciation

 

 

 

 

 

   

 

98

which affected the third dominant cirque system (system IV)
on Price of Wales Island. In turn they would be probable
correlates of the latest Lesser Mountain Ice Sheet Glaciation
and the Extended Icefield Glaciation in the Alaska—Canada
Boundary Range (Miller, 1964; Table VII). The youngest
date which can be applied to these recessional moraines is
9,510i 280 years b.p. This is based on the previously de—
scribed radiocarbon dated shell samples obtained from the
raised beach which passes in front of the Maybeso moraine.
This beach on—laps the moraine and extends clear across
the valley. It is therefore a distinct feature which post—
dates the moraine formation (Figure 30).

The Crackerjack moraine was probably deposited some-
time before 7,800: 300 y.b.p. This date is inferred from a
comparison of the pollen stratigraphy and location of lig—
neous peat horizons in a peat bog core taken from a muskeg
directly in front of the Crackerjack moraine with a dated
core from Upper Mountana Creek near Juneau (Heusser, 1960).
The date was taken at the base of the core Just above the
till. Figure 36 compares Heusser's profiles for the two
muskegs. Note the marked similarity of dominant species
in each profile and the occurrence of ligneous horizons
at approximately the same time intervals.

The pollen stratigraphy and location of ligneous peat
horizons in these two cores are markedly similar to peat
bog cores taken from muskeg sites elsewhere in the Alexander

Archipelago and British Columbia (Heusser, 1960, Chapter VIII).

 

99

 

I 6 o Iouuaqg
Iogaol ,s d 9:01 —!‘d‘H

 

wnufiong

aoaaogpodxiod
I 1
LLI

“4| solo)”;

2: wnuqanl1 1. \ I‘m.j

2| aoaamadxg '- Q- ‘ A u- A -j

3” snulv

ouogsuauaw ofinsl

oHAquJanq ofinsl

Mn"
mm”, 0,,” Mi

— -
JO uo n —_ te‘ O..-
o; a 3 s ugd

_ 0
E1553 51‘ £ “1741*

 

E

7300 i .—>
Figure 36.-—Comparison of C. J. Heusser's palynological profiles of a Hollis muskeg with the muskeg

300 ybp

louuaq;
— gdeH

aoaaogpodxlod ‘-‘ .‘j
,,,.,,,,3 A j

-‘
0' wnuqawfi 4*.

II

I gogaolsuod ago]

 

wnufioqu

LLS

aoaamadkg -‘ “AAL A

snu'v - .- u-fl

ougusua‘Jaw 060310-“.0‘

HWOHJHS 093w

lat—HM I—A

D'l‘q-dOJa‘aq Dfinslm
M. .

ouoguoa snugd

 

- m n V '0 ~O

 

 

The lower ligneous horizon in the Montana Creek

section has been Carbon—1U dated at 7800 + 300 y.b.p.

on lower Montana Creek near Juneau, Alaska.

100
sec le 0/0

H—A—H

0

 

 

 

 

 

 

lOO

Heusser believes these profiles to represent the sequence
of climatic events which occurred during the major post—
Glacial warming trend (Hypsithermal). He has accordingly
used the similarities discussed above, coupled with radio—
carbon dates from selected cores to determine what he con—
siders a reliable set of time brackets for the Hypsithermal
in this area, beginning approximately 8,000 y.b.p. and
ending approximately 3,500 y.b.p. Thus, the Crackerjack
moraine, which was deposited before the formation of the
Hollis muskeg, may mark the last pause of the receding ice
in the valley before the beginning of Hypsithermal time.

The two remaining moraines, the Haystack Butte and
the Snowdrift, are post 7,800: 300 years b.p. The Snow-
drift, a low hummocky moraine marks the final dying puls-
ations of glacial ice before total withdrawal from the valley,
presumably in consequence of the culmination of the Hypsi—
thermal warming interval, referred to also as the Thermal
Maximum, beginning 6,000—7,000 y.b.p.

These age relationships, plus the indicated similarity
of the Maybeso valley glacial sequence to that described from
the Alaska-Canada Boundary Range, permit a tentative corre-
lation of the moraine system in Maybeso valley with the
moraine system described by Miller in the Taku District
(1956) of the Boundary Range 170 miles to the north. On
this basis the Maybeso moraine is suggested as a correlate

of the King Salmon moraines in the Taku River valley while

 

 

 

101

the Crackerjack and Haystack Butte moraines are provis-
sionally related to the Tulsequah moraine system of the

Taku District. The Snowdrift moraine, marking the last
pulsation of ice in the Maybeso valley, is probably a
correlate of the Sittakanay system which Miller believes
terminated with the advent of Thermal Maximum Time. In
Table IX a provisional correlation is given of the various
late Pleistocene Chronologies discussed in comparison with
the standard Pleistocent Chronologies from the mid-continent
and Rocky Mountain regions.

With deposition of the Snowdrift moraine and final
withdrawal of ice from the valley, active glaciation was
essentially brought to a close. Later glacial fluctuations
during the Neoglacial (Early and Late Little Ice Age) be—
ginning approximately 2,500 years b.p. (Miller, Anderson
and Egan, 1967) are recorded by small moraines at high
elevations reported by Sainsbury (1961) and protalus ram—
parts in high—level criques. Some of these still contain
perennial snow fields in the central highlands to the west.

It is probable that in the future older till deposits
will be unearthed relating to early Wisconsinan and pre-
Wisconsinan glaciations. Deposits of this age have al—
ready been reported from the Kenai lowland and the Cook
Inlet Region by Karlstrom (1961, 196M), and in the Taku
District of the Alaska-Canada Boundary Range by Miller

(1956, 1963, 196M). For this reason those sections of

 

 

 

102

Tables VIII and IX relating to deposits of this age have

been annotated by question marks.

103

393 I3... .i la

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

o m.
aowumwumnu xczum
mwm awaoca
:owumwumau 95:15 I wwvfim mwamwmomw um . A:
fimwumawuwucH mamamzam w
. I HmwomfiwumucH
m. e .I I I I a w mam
e vaum zaumm w Mum coEm w
Hui—wusw an
Hangmaw u s m
couumuumau xucx u~30 m.w. T. oo.mm
IIIII III. [I II II I.I m.m n. voo.om
I I I II I I I u mtmuCM
I I I I 1180.8 H w n s a
093m awau< 1303.. m m I I1 m
Iaoz m. 03 £03m w 93:33, we
M. Eagle I on .I I L 33 W U
3:96 Howumam aaw U. A
wgouamz N umwgor m I M
" low a l | [I ooo.om I.
wwmum oxoam m N towuwfiumawumucw mwmfixao HmwomawumucH I I m ”30.ri
m I I . I :mHHmUEumw m
I u meuwaw>J wpmuw ream 000 mm m s “.0 . N
I I wmem cflaxcH a lumluluI Iml . P w... o N
I II D ,
:Hu uovao I wcmum W. m. H ovmuwumucH mm. M cmwpuofiuooz u
chocwmoo: o wvmum e e e u II 1 S
I I..I. II.I II I..I 1 III .I_I H cozmm> m.” w W m
I I cmuwmuwfiwulmumfil l mvmum N w 1 wpmum 3va W m m. cm
0 H3”. humanor mwmum Haanom A933“ m I I I II o. 1-0 mumuwua mr amxwwuuozH 3 wom.ma
“ o o mcoaul . . Waum mefixW mpmum 9255 u v H u a wooJH
oo 4 H . .
_ Imsuoza amaumawlumom II mpmum mxma cmuwpfl;
M ax lTII Q~AI I mvmuw GEHQ uHu OOm.o
Hmecuwm 2 HmEmsuHm z Hméuwzuwma»: :H L . j»: .
,I III I II I I I i 334 man—um; uamumm
mcwaaumsm. a 9 x. V w . _
23232 1.3382 n E m. 832:: 8; ._ $8835 n mm m
u 352. mm... lgjmjw o
_. NHMQMQ muncdu 119.0me umaaflz pmuwmv coma douumapwvm uuuwmu Amooa Hawvcmuu pwuwpv Amoma ncoasuwm Hmuwmv Aoom: GNEHHHZ w kw": j:
__ mxmm~< .pcmqu mxmmjx mxmmjx COuxcfimez pumvcmum cowwwm ucwcHuCOUIpHE 95 mo mummy.
moan: Mo mecca wwcmm .Cmpczom :uuoz Axiom—icon fiasco: 5.7395 5 mung; c2355: zxoom Emvamum mcwooumfimam
_. xmaamg» omonzmz uUHuumfiQ 3x3. uchH xooo osmoOumwme mum; .

 

 

pooammp Sufi:

.mmHHm> Omonzmz cfl pmpflpommo mocosvom opp oo

mmflwoaocopco ocmoOPmflon cmoHLmE< Lppoz mo COHpmHoLLOo HMCOHmH>omeI.xH mqm<B

 

 

SOIL MASS MOVEMENT ASSOCIATED WITH RECENT

LOGGING IN MAYBESO VALLEY

0f the numerous landslides occurring in Maybeso
valley, those on glacial till are by far the most impor-
tant from the standpoint of apparent increased activity
due to logging. Three of these slides were selected for
detailed study. Each of these developed during a heavy
rainfall in October 1961 and each lies on the south—facing
side of the valley in a "mile-square clearcutting." Each
were also underlain by a continuous sheet of till on the
upper slopes and developed within the shallow depressions
marking principal subsurface drainageways. The timber in
this area was cut during the summer seasons of 1965, 1966,
1967 and 1968 by the high—lead method (Figure 37).

Slide 1, located just west of 120 Creek, occurred on
a slope of about A00. The slide began in the weathered
till at about 1,250 feet elevation (Figure 37). The slip
surface was hard, blue, unweathered till. The unweathered
till was covered by 3 feet of weathered till overlain with
l/2 foot of organic material. Bedrock, exposed by sliding
and water erosion, outcrops in several places in the

bottom of the slide scar indicating the shallowness of the

104

 

 

 

105

 

Figure 37.--View of the "Mile Square Clearcut" in
Maybeso valley showing location of principal
debris avalanches and flows. Slide locations
are shown by number.

 

 

 

106

till in this locality. Several tree stumps are still rooted
in the center of the slide scar just below the zone of
initial failure.

The failure area is about 100 feet wide. Sixty feet
below the upper edge of this slide scar there is a break
in slope marking the toe of the initial zone of failure.

For purposes of analysis the failure surface along which

the slide developed may be considered rotational. It
approximates the arc of a circle with a l55-foot radius
(Figure 38 and Appendix B). Below this the weathered till
and surface materials were removed by slide erosion in a
lOO—foot wide, l60-foot long area. Slide debris accumulated
at the base of the failure zone although most was channeled
into the notch depression in which it was carried downslope
to the valley floor (Figure 39). Cross-sections of the
slide source area, and at five additional positions down-
lepe, are shown in Figure 40. These illustrate the relation—
ship of sliding to the weathered and unweathered till zones,
to the surface drainageways and to the incising of the mass—
wastage notch or downcutting which took place as displaced
material moved to the valley floor.

During wet weather seepage was observed along the
exposed surface of the C horizon (unweathered till) at the
upper edge of this slide scar and a similar seepage was
observed in till sections downslope. Partings lined with

organic material, along which the later seeped, were found

107

Good comm Dena ooog 90nd oo§~ 00n~ 0&WH omua Good 000 com Can 300 com ooq 00m oo~ owH o

 

        
 

 

 
    
        
  

 

     

_ _ _ _ r _ _ I— _ F _ a p can
vacuumuu anaconauo:
:Hfiuu nox:50>: A/ 1.00q
ho admomuv xuusu // // /
Ouzu choc gnu as: ouudc 9.9:: / ~//
. //
sauna ouzmmuwon0u w>_w:ouxo HU/nH/x
MUHH/n/zx
////n////nn
// //// ////
.838 .3284 do 2.... finfxnmuumfi loam
.IN/xxxw/xnmnu Lflau umwcso>
////
////
x
// ////
59: r
\\ IHU/// Hz 000
/ ,
smog: recuvua wwuaa Ho ”swam zun nua,
w \\ ///,Hm~/ ,,/ .udmom cu Ginsu
mama / ,, x, . .
wAAMH :u N\\\\ /~h ,m,w/me/.. Sofia .mooam pmaba co dawn Mo Mupoamu
ozo~ Hausa secuvoa c“ xaoun o>wmcwux / ,./.~Hu,/ nii., xciuczm .uwa omom uaam cu cawwuo No ucaoa
Joann xuohvon w>umc3gx; :LSE ”M ,,w,,/. aOuw a wqum Mo wafiwoun Hacavsuwwcoqll.wm muJMam
noun vm—_0uu:091uc_:n ~_1EW\ /. .Ison
Leon vo-0pucoUu_c_c~ ~_mEx xx
noun v-~0uuczo9uc_o~ __dEW\\ u;
noun vo~_oh_c:uluc_o_ Lfiaem ,. ,
xutuvws 3‘ 93¢ xnwun aanEm
nequQMIvu 10055» filoow
“.4“ ;Luu:wn mad: Jacuflt;
Taco
/.r .
. : , .,,// ”
Jurcavn buy: ; azulr can: . ,/.
mayday Amandzu vwanjuu fiuummflu mnrhfl .m -
\ 782
assuage Juanfivo Saba. N
“Has an guano Mfiaam
ach51r cu saw inopn HdwEm
avccwso wc_oquuuoug Josue:
ca mqonmv avian _9 azueucimcoi Lo mcmccwmwatnflmauwumu uufifim um Tcfiucoa on wan xmwun wmhmH
nafiaum kuoou on asp xmwun ~HmEA
a maiow
up.” «cwwzflm unquacL Lo «mew uwaofi mcncflwov smear :. xmoun J \A
V\ _
wduhao magma» .ua mma _

 

 

 

 

 

 

108

 

Figure 39.--View of slide 1 showing mass wastage
notch and debris flow at base of slope.

 

 

109

SLIDE 1

TOP OF SLOPE

 

    

\ ELEV. m 1240 ft.

’— —-_

~_———

 

 

fl \ ELEV. m 920 ft. .—
\ / /‘
\ \ /
,\\‘ \ / / /
\ \ t/jl / /
\\\ \\m _____. ,/ /”
\ “—— _——'-‘/

      
 
     

ELEV. W 625 ft.

ELEV. N 580

\

BASE OF SLOPE scale

Figure UO.——Cross profiles of slide 1 from zone of initiation to base of slope at

Spur Road 122. Dashed lines denote former position of A and B horizons in
soil mantle.

 

 

110

to be scattered through the B horizon (weathered till) with
particular concentration at the B-C interface. Frequently,
partially decayed rootlets were observed in these partings

(Figure Al).

Slide 2 is west of slide 1 (Figure 37) across an
intervening stream divide. Its upper edge lies at 1,200
feet elevation with the gradient of the sliding surface
380. This slide also occurred in weathered till at the
head of a very slight drainage depression. The slide sur-
face coincides with the upper surface of hard, blue till
(Figure A2). Here the weathered till is 2 1/2 feet thick,
covered by 6 inches of organic material. The initial slide
scar is 86 feet wide with a break in slope about 90 feet
below the upper edge. This break is not bedrock-supported
and is the toe of the initial zone of failure. The initial
surface of sliding can again be considered rotational, approxi-
mating the arc of a circle with a radius of 280 feet (Figure
A3 and Appendix B). Below is a wide area from which weathered
till and organic materials were removed by slide erosion.
One hundred feet below the toe the end of the open slide
scar is marked by an extensive accumulation of slide debris
(Figure AA).

Water seepage along partings lined with fine organic
material was again observed in and at the base of the B
horizon (Figure Al). This slide does not seem to have had

the erosive power of the others, perhaps because of lesser

 

111

. 3230.8 02590

mcE firs pee: .mofitwa mo meow m >9 @9788 mg “09:00 35. .23
poumfimozc: pew poemsumog on”. comzfion “03:00 9: some Ewe
um>oE .853 m0 meow 33053 9: 302 .5020 opzm or: some

coflomm :3 pmuonumoBCSIpmumfimoB 303.3 6 mo sopoxm Ilsa: oesoE

 

       

     

     

 

N \\\\.\
\ \
v\\\\\\\\& o 0 q 0 o
\\\\\\\\\
\\\\\\\\\. Q 4 Q
‘\\\\ \\ Q
a \ I \C q 0
XXI“? o
\\\ \\\\ g Q
\\ \\\
\\ \ \
x“ O z: 385.835 O \\
\
\ Q
\ O acute... \\ Q
\
as 4 a.
o o 0..
O Q :3 Q 0\ MNYIWK

 

vusoswouz,

at w.

 

 

 

 

 

 

 

.cowwhoe HHom cohonpmoz ths

moCHH pocmma .wCHUHHm Hmfiuflcfi mo meow SH oaamogg mmoaOIl.m: mpswfim

 

mmOAm mo ROB H< N mqum

 

 

113

wonmumuv Haucouwuo:

 

 

   

  

          

coma OONH coda coca com com ooh ooc 00m ooe com ooN owH o
_ _ _ _ _ _ .e _ _ p _ _ con
66¢
E... a
.//// :3 page» .. ~ 68
/////// alilrll
. //////////////x
.4/////////////////
/////.///////////
x. .. xxnfiunnnnunuuuuxi
«NH .vx Hana dilf/x/HNHH/N////H//Hmnh .wawom cu :awuv qum .xoouvoa mo
”WMWhvv/H/HHHH/HH////H/, wuswomxu uaonuwa ma noun ovwdm ouoz .NNfi
2.8 o>oau\o\ .Amw/uuuuwuuuuuuflunn/ 28m ham um 23?. we 33 3 833:5 mo o8
noun Signage”. I. xxxnunnuunnuan/x. 25s sob N 2:? no 238.. guangée 93»:
31$ v//////////////.
. J/HNNHHHNHHHHH/
noun newuaaaasuuu nfiunvv awe: ////////////
a... Axxnxx/
snows uwsamuwoaOu yvvs./////////L/ 5
Ha ///////////. ޢc
..w/////////////.
L. /////////////.
:.L /////////////
. . .flxxxxx/
J )flH////////// N mnHAm
R? ////////////,
)fiv7////////////
2. /////////////
.//////////// LXI
\ :‘v /////////// ,
.on///////////
acquwaaasuum ouunuv cu 05v macaw aw mxmuun .fl?///HHHHHHH/
§.uV.///////
I . .92”?
:Av.
394%”?
..C///////
as mean u 030 a u fidMWHnflflflx/x
aqueouma madam uooa we uauuxu umonuuwu one nxu a n .4..¢fl7//H//L//HnnhnA/// yaca
moaaun finanon nfiuaov ovum» we nowuua=l=uuu an vuuavOua =mn0un= no anode ca mxmuun ...//.HHHHH/////////A/,
Es. ///////////////
auto //////////////.
\(\ .. .u u. #VVW///////////////,
\ .. 0...... .ar////////////////
vouooaaou neon man cannot uvwam mo unseen «mama a muons oaoam ca sauna ; .xrnuWV//////////////
laced
@332. «3% .3 333 was 88 30:55 x/HHHMHflmmuunnn/x/
waaunwxo hangouboua and .ovuau an u:=om an nu>aumausu cum wadsoau ma nous: seas: aw waosauno «shy .wwunov no / vfl//////////A/,
usuao>0i Houuadu tendon «bad 51. noun: vac uawaoau haucomoum ma nous: gown: cw voeuwmno mud maonadnu uoawumwv
N .masu lemon I uuoaa undxdu aouoouo oauuaa auo> Aug: wouwmonuv ma auwuuuma ovwflm sows: roams macaw nu snows
anon etude Hawuwafi mo ouvo none; I Auuu unanuuwo umfiSmmdv ocean ovHHw mo soauuuswfiwaoo cu 09v cuedm aw anon; ..~H
mswvuu one .uu can

 

 

M-JthdI-‘HOI

114

I”:
‘ x:

”904??

1 I

 

Figure AH.—-View of slide 2 from valley bottom (on
left) showing accumulated debris at base of
slide scar. (Notching of slide 1 is visible
behind tall snag on right).

115

volume of debris and the shallow nature of subsurface
drainage produced by more limited water supply during the
period of sliding. Another factor which may have caused
resistance to sliding was the presence of rooted stumps
behind which debris accumulated without further downslope
movement. No conspicuous channel erosion took place below
the slide scar. The slide debris spread out and spilled
over a wide downslope area despite the presence of small
surface drainage channels on the slope (FigureAA).

Slide 3 is west of slide 2 near a leave strip in the
valley center (Figure 37). This slide also was initiated
at 1,200 feet elevation near the head of a well—developed
topographic depression. The toe of the failure zone de-
veloped some 70 feet downslope at an elevation of 1,150
feet. The failure surface is once again considered ro-
tational, approximating the arc of a circle of 285-foot
radius (Figure 45 and Appendix B). In this case the scar.
is 60 feet wide at its toe with the base of the sliding
surface sloping 36°. Below the break in slope is a large
area exposed by slide erosion some 130 feet long and below
which the slide materials were channeled by an existing
drainageway in which considerable erosion also took place
(Figure 46).

Two small, incipient slides also deve10ped in weathered
till on the east side of slide 3 at an elevation of about

980 feet (Figure 37). Here too, seepage, and in some cases

awo-

 

116

wuuwumuu «mun—Duals:

 

 
                  
   

coca ooaa cowa 0 AH o H o o o cow oo o n o N 0H
_ _ _ .1 .1. s. .1... I. I _ _. m. 4 .. g.
;//// /
wuuuum ”if
[000
Human: Quid mo :3 human—or a
coaum~saluuw cu can maven
euao~u>uv naauu xn... I n
.34.! manna-5 Juan—won On 051 1!qu nun: / t/fl/hfl 8
«Fun Juan—gon—
Junuan 69C waltz .
usuallxuouvoa vauafiofi hHQmOAu we wnou m uu>o cu zany uo . m ~3MHMUM
3.32. :2: «0 widen: 3 03. 2.3m 3 Ana:— v 2 Nu." v 3. m u
macaw we own; 0.. Icaumwuwuu we uaou
Eek A m o w a a a mac IL m l
nauuuao accuses as was osoam.=« mumps u n uu.a u H.uou H nauauu a m: an: a. can
loco
.Haau
vokon—uflul uflquHnu-h Gnu.— 05 «in H1: vmuusumaafl: vwwonxu «o ougumamOH
unduuiuun.‘ 05 ha vow—id mafia-wane”. uuaaumav m a.“ wuunu .uvaam 0.3 «a
"one:
IOGOH

.39.»; 0.3 .53. nuns—anon; vuuuuumun a.“ Hugs—U ”Ban 9: we mvum nozuaw a?

onu nous: nu Aoununu usuaan any annuab u=uuo unasum vuuooz "uuoa
Mundane hunk-a ou ouuu undue Home souu omddnu waaxnaa anon aw Jack»

M mnHAm

  

vumo~o>uv wua «evade

”Hag a“ uoaoau>ov

Aonuaoa xuouvmn o: .Hawu aw vonoao>uv I

    

aged» ad Alana

made-H uul .uu nau

   

I 8AA

oeNH

 

 

 

fl-JflD‘O-IHOI

 

117

SLIDE 3

_‘ TOP OF SLOPE

 

        
    
     

   

ELEV. w 1075 ft.

ELEV. m 1050 ft.

   

ELEV. N 900 ft.

/

/

BASE 0F SLOPE Scale

 

Figure N6.——Croes profiles of slide 3 from zone of initiation to base of slope It
Spur Road 122. Dashed lines denote former position of A end B horizon: in
soil nubile.

 

118

free water flow, occurred in the B horizon of the weathered

till in areas marked by partings lined by organic material.

Characteristics of Slide
Prone Soils

 

 

As has been shown, the material underlying the slide
prone soils is unweathered till. It is compact and practi-
cally impermeable to water flow from above. On the other
hand, the slide prone soil or weathered till, while retain—
ing some of the characteristics of the parent material, is
more friable and permeable.

Mechanical analyses of the weathered and unweathered
segments were made using dry sieving and Bouyoucos hydro—
meter methods. These show that each segment has approxi—
mately the same composition, differing mainly in degree of
oxidation and leaching (Figure 47). Cursory microscopic
examination of the sand and silt fractions also indicates
the majority of particles to be angular to subangular in
shape and composed of fragments of greywacke and argillite
mixed with individual grains of quartz, feldspar and ferro-
magnesian minerals. In both weathered and unweathered till,
the clay and silt—sized particles account for less than 20
percent of the total.

In the weathered till unit weight values based on
analysis of 19 random samples taken in the area of sliding
vary within the range of 71 to 1M1 lbs/ft3. The low values

are probably due to high organic content as the result of

119

buried A horizons and roots passing through the soil pro-
file. An average value for the wet unit weight of the
weathered till in the zone of sliding is 111 lbs/ft3. Dry
unit weights (field dry) are somewhat lower, averaging 103
lbs/ft3. These values, while a little high, lie within
the range of expected unit weight values for the Karta
soil (Freeman Stevens, Soil Scientist, personal communi-
cation) and can thus be used as an index of the unit weight
of the slide prone soils. Unweathered till unit weights
are somewhat higher, being in the range of 123 to 1A5 1bs/ft3.

Cumulative size distribution curves for the weathered
and unweathered segments of the younger till are shown in
Figures 48 and 49. These are based on the unified classifi-
cation (Casagrande), and are characteristic of moderately
well-graded materials with appreciable amounts of coarse
material being present. The average uniformity coefficient
(Cu) for weathered till is 26 with an effective diameter
(D10) of .037 mm. Unweathered till has a uniformity co-
efficient of 23 and an effective diameter of .033 mm.
Atterberg Limits determined for five representative samples
were so low as to be of little value for interpretative
purposes and, hence, are not reported here.

It is of interest to note that these two sets of
curves are significantly similar, but do reveal the in-
creased percentage of fines in the weathered samples, as

is to be expected. The effect, of course, is to increase

120

 

 

’ MM
{RRMVMA/VW

 

 

 

   
 

V

Tfihrflwwrwmmww.

 

 

VV

 

 

g QAxquA.AA
.gfwggggégmnfi

Figure U7.--Classification of the weathered and unweathered tills in
Maybeso valley according to particle size. Using U. S. Engineers
Department classification.

 

 

121

.pzmfioz mm ”2.80an CH

mCoapompm oNHm oaoaphwa measonm Haws. oohonpmmé .Ho mo>L50 o>HpmH5E50II.m: 9.3me

$23.0 _ 02$

:5 _ >30

rte—o.

 

a
IAIII

 

 

 

  

.Ho_. 0 euuee>1

NMO

one use 3223 I

_
_ L
_

 

ON

On

0*

oo

oo—

Cumull'l v. x

 

 

122

.pcwfiws an pcoohmm CH
mCOHpomhm oNHm maceppmg wcfizocm HHHp monogamosc: no mo>p50 o>fipMHSESQII.mz wpswfim

$220 _ oz<m . _ :5 _

 

 

Cumulo'lvox

 

r‘c

 

w

123

moisture retention and capillary force in the weathered
segment. Generally, however, both the weathered and un-
weathered tills lie in the category of silty sand ac-
cording to the Unified Classification* and can be con—
sidered jointly as "mixed soils" in engineering usage.
Such soils have varying amounts of cohesion resulting from
external factors such as capillary tension and anchoring
effect of roots. An additional fact of importance is that
there is considerable free water movement above the un—
weathered till surface once the weathered till has become
saturated by infiltrating rainfall. Details of this are

elucidated by the investigations described below.

Piezometric Head Investigations

 

Development of Piezo-
metric Head

 

Pore-water pressure in the weathered till is thought
to be a primary factor in debris avalanche and flow develop-
ment.

During the dry months water movement is limited to
a zone 2 to 6 inches thick, and lying directly above the
unweathered till surface. Seepage is along interconnected
soil voids and partings in the till, the latter partly the
result of down—slope growth of rootlets along the surface

of the compact unweathered till (see Figure Al).

 

*

Soil classification developed by A. Casagrande and
now used by many U. S. Government agencies and State
Highway departments.

124

During the wet months, an increasing volume of water,
moving laterally through the soil as saturated flow during
heavy rainfalls, causes a rise in the piezometric surface,
with two important consequences: (1) decreased shearing
resistance along the potential sliding surfaces because of
progressive structural changes in soil materials, and (2)
increased pore water pressure with a consequent decrease in
shearing resistance of the soils.

The first of the foregoing effects results from chemi-
cal and physical changes through increased water content,
in return producing loss of cohesion between soil particles
by destruction of capillary forces. Because this satur—
ation requires time, a slope is more susceptible to sliding
after an extended rainy period than it is at the onset of
rain. By similar reasoning, the slopes are more prone to
mass wastage at the end of the snow melt season than at
the beginning. The total effect of this process is not
fully known, but in Maybeso valley the studies here dis-
cussed demonstrate this process to be significant in condi-
tioning slopes for slide release when the critical moisture
content is exceeded.

Historically, increased pore-water pressure has been
shown as a primary factor in the sliding mechanism of
aggregate slopes. During periods of heavy rain the
piezometric level of water in the soil naturally rises.

The net effect is an increase in water pressure in the

125

soil voids. This is designated as HyW, with (H) equal

to the height of rise and (vw) being the density of water.
Karl Terzaghi (1950) likened the effect of this increased
pressure to a hydraulic Jack. In other words, the hydro-
static pressure of the water may carry part or all of the
weight of the overlying soil, in effect causing it to be
jacked up or "float" and hence greatly to reduce its
"shearing resistance." The effect of increased pore pres—
sure is also well illustrated by a consideration of the
Mohr—Coulomb theory of failure.

To start with, a classical and well known engineer-
ing concept pertains, first proposed nearly a centery ago
by Mohr (1871). The principal delineates failure in a
material occurring if the shear stress on any planeequals
the shear strength of the material, and states that shear
strength is a function of the normal stress (0) on that
plane. In simple equation form,

S = f(c), where (S) is shear strength and (o) is

normal stress.

Even before this statement, Coulomb (1776) defined
the function (f) as a linear function of the normal stress
(0). Thus, the equation S = f(o), for the stress acting
at an angle (a) to the shear stress, is written as
S = C + 0 tan ¢. In this equation, called "Coulomb's
equation," (S) is the shear strength of a given soil and

(C) is a constant of cohesion, the latter being a measure

 

 

 

126

of the capacity of the soil to resist shearing stress.
Cohesion (C) is largely related to the shearing strength
of adsorbed layers (water, clay) and cementing materials
that separate individual grains at their points of con-
tact. The symbol (0) is the total normal stress or unit
weight of the soil mass and (¢) is the angle of internal
friction, this in other words being the angle of shearing
resistance of the soil.

The angle of internal friction (¢) is defined (Glos—
sary, Appendix D) as the angle at which the driving forces
in a soil mass are equal and opposite to the resisting
forces due to friction and is a measure of the strength of
a soil due to the interlocking of the individual soil grains.
This strength is attributed in part to density of the soil
mass (amount of compaction) and in part to its degree of
grading, particle size and shape (Hough, 1957, p. 1A9).
Figure 50 shows the geometrical relationships between
(¢), (0), and shear stress(s) in the soil. Experimentation
and field experience have indicated (Terzaghi and Peck,
1960, p. 66) that for clean sands, silts, and silty sands
the relationships between normal pressure and shearing
resistance are similar and hence the angles of internal
friction for these materials are similar.

For loose sands, silts, and silty sands, which in-
clude the slide prone soils in Maybeso valley, the angle

of internal friction varies around the angle of repose for

127

 

 

 

 

 

¢= L of internal friction
a: saturated unit wt. of soil
52 shear stress on block

Figure 50.—-Diagram of shear stresses acting on a unit block
of soil.

128

clean sand. From an engineering point of View, this angle
of repose is defined (Terzaghi and Peck, p. 81) as the
angle between the horizontal and the slope of a heap of
sand produced by pouring dust dry sand from a small ele—
vation. This angle, approximately set at 34° is a refer—
ence angle marking the maximum slope at which loose co-
hesionless materials will stand when unaffected by forces
other than gravity and friction. As thus defined the
engineer‘s angle of repose is constant while the angle of
internal friction varies with changes in certain soil
properties. In general, it may be said that increasing
density of the soil mass increases the angle of internal
friction, while increasing moisture content tends to de—
crease it slightly.

It is of interest to note that the geomorphologist's

"natural angle of repose" as defined by Van Burkalow (1945)

 

for materials of the size and angularity considered here,

is similar to the engineer's angle of repose with respect

to average value (approximately 34°) and basic definition
(Glossary, Appendix D). Van Burkalow's natural angle of
repose, however, also recognizes changes in the angle of
repose of a given material with changing density and soil
moisture conditions. These changes are similar to those
defined previously for the angle of internal friction. A
sharp distinction between the angle of internal friction,
and Van Burkalow's natural angle of repose thus becomes dif—

ficult. For convenience, in the succeeding sections the

129

angle of repose will be considered from an engineering
point of View.

Coulomb's equation S = C + 0 tan ¢, with (¢) thus
defined, therefore represents soil strength as a factor
of total normal stress applied to the soil mass at fail-
ure, where total normal stress includes both an effective~
stress, transmitted through points-of contact of indi-,
vidual soil grains, and a neutral stress represented by
pore-water pressure between the grains. Because in this
study we are primarily interested in the effect of pore-
water pressure, Coulomb's equation will be expressed in
terms of effective stress, where effective stress (3)4
equals total normal stress (a) minus pore-water pressure
(u). Thus Coulomb's failure criterion is expressed as

follows:
S = O + (o — u) tan ¢ (1)

In the foregoing equation, 0 = o - n, O = effective
cohesion and 3 = effective angle of internal friction.
Equation (1) shows how variations in pore-pressure and
true (5) affect the strength of soils. For a given total
stress (0), an increase in pore—water pressure decreases
the effective normal stress, thus decreasing the shear
strength of the soil. The reverse is true for a decrease
in pore—water pressure assuming, in both cases, that (O)

and (E) remain constant.

130

Pore—Pressure Measurements

 

To determine the extent of this piezometric rise so
that its relative effect on the slide-prone soils in May—
beso valley could be evaluated, especially adapted piezo-
metric tubes were placed at selected sites within the slide
areas. These devices measure piezometric head, which is
the height above a reference surface that free water rises.

The basic piezometer device, based on an original
design by A. Casagrande (1949), consists of a porous tube
24 inches long and 1 1/2 inches in outside diameter (Norton
Tube) connected to l/2-inch outside diameter polyethylene
tubing (Figure 51).

The original specifications of the device were altered
because of the shallow nature of the measurements required.
The porous tube was shortened to 12 inches and, in at least
two instances, it was shortened to 6 inches with a corres—
ponding decrease in length of the polyethylene tube. The
method of packing and sealing remained the same in both
cases. Rockiness of the soil, combined with steepness and
difficulty of access of the well sites, prevented the use
of a drive pipe, the water Jetting method, orla tool and
cable or rotary drilling techniques. A blade auger was
used to drill the holes for piezometer emplacement. Three-
inch holes were drilled to a point Just below the upper
surface of the unweathered till, intersecting the lower
zone of water movement. If water flowed into the hole

freely, the piezometer was considered to be in place.

131

    
   

   

wt? -'
‘k l" .

 

 

Figure 51.——Piezometer being lowered into auger hole

near slide 3.

132

Before final placement of the tube, the hole was
washed and filled with clean water, and one foot of clean,
saturated sand poured in. The porous tube was then in-
serted to the bottom of the hole with an excess head main—
tained in the tube at all times. Elevation of the tube
top was noted and saturated sand poured in to fill the
open space around it. A one-half-foot layer of sand was
poured in above the top of the porous tube and the hole
sealed with five layers of bentonite, each one-inch thick.
Piezometric rise was recorded by inserting two bared wires
into the polyethylene tube. When the wire tip touched the
water surface a circuit was completed and the needle on an

ohmmeter deflected (Figure 52).

Field Methods

 

Ten piezometers, numbered 1 to 10, were installed
during the latter part of August in the 1964 and 1965 summer
field seasons. They were thus in place for measurements
during the autumn rainy season. The sites were on open
slopes above or within linear depressions where subsurface
drainage was indicated. Several auger holes were drilled
at each site to determine thickness of the weathered till.

A piezometer was then installed in the most promising one.
The slope angle at each was between 35 and 40 degrees
(W 70-85 percent grade). Piezometer locations are shown

on Map 3.

 

Figure 52.——VOM meter used for taking water level
readings in piezometers.

134

In the fall of 1964, from September 28 to November
10, readings were made at 3—day intervals in slide sus-
ceptible areas 1, 2, and 3 (Map 3). In the fall of 1965
more concentrated readings were begun in an expanded well
network. These readings were limited to a large area (area
1) of about 1/2 square mile where the largest number of
wells were located; and also to a second area (area 2) of
about 1/8 square mile on the south side of Maybeso valley
(map 3). These readings were made on wells in each of the
two areas on alternate days from September 22 to November
17. The results obtained in the latter sector were incon-
clusive because most of the units were dug up and destroyed
by bears. One remained intact, however, and the results,
as will be shown, are comparable with those discussed for
the larger area.

In 1965 a more reliable method was devised for record-
ing absolute maximum piezometric rise during the season.
A polyethylene tube, about l/8-inch i.d., with powdered
cork in the bottom end, was inserted into each operating
piezometer (Figure 53). As the piezometric surface rose,
powdered crok was carried upward on the free water sur-
face. When water levels fell, cork adhered to the tube
walls at the point of maximum rise.

Throughout the 1964 autumn season, rainfall was
measured at a weather station at Hollis, near the mouth of
Maybeso Creek where a recording rain gage and standard

weather shelter are located (Map 3). In the autumn of

135

polyethylene

tube

qfiinch

d
e
H
k
r
o
c
h
c
n
L?

e
b
u
I
O
n
M
Y
h
'
e
v.
o
P

Q

bentonite

weathered

ther send

fill

cyHnder

I
U
0
r
o
P

a

d
e
r
e

d
w
o
P

cork

fllter

gauze

 

/////////////////////
////////////////////
////////////////////
////////////////////

/////////////////////

////////////////////z

//////////x

/////, ////
//////, ////
////. ///,
////.H///,
//// fl ///.
//// ///,
//// ///.
//// d ///
//// u///
////o ///
////h ///
////u ///
////e.///
////w,///
/////n.///
/////u,///
///// ,///
. //////////
//////////
//////////

ypical piezometer placement in the

Note cork—filled inner tube.

Figure 53.—-Diagram of t
"younger" till.

 

136

1965, rainfall was also measured with a recording gage

placed in (area 1) at an elevation of about 1,000 feet.

Results of Piezometric
Investigations

 

 

Figures 54 and 55 show the relationship between
piezometric head and rainfall during the 1964 and 1965
fall rainy seasons. The graphs reveal how the wells
showed rapid fluctuations with rainfall variations. A
short lag (of 2 or 3 days) in piezometric rise occurred
at the beginning of the rainy season for most wells. This
lag reflected the time necessary for the soils to reach
saturation.

The 1964 piezometer head values gradually leveled
off late in the season despite undiminished rainfall. This
coincides with the appearance of a winter snow cover-start—
ing late in October on the ridge above the well sites. A
short rainy season and no significant chilling of snow
cover effect developed during the recording period of 1965.

A curvilinear relationship exists between rainfall
and piezometric rise as determined from regression analyses
of the 1965 field data (Figure 56). The basic units are
average piezometric head and the accumulated rainfall per
day. The mathematical relationship is the second-degree

polynomial:

Y

a + — + OX (2)

 

137

[seqaug]

hzxanaatzeeh‘ee

3Iuewozegd
1 e- e rs u H e n d

p°°q

~

t

I!

«N s‘ \x
.—

 

.c0mmom 30G c5350 33 or: maize mm? OCEEoNoE .m> 28:2: mo LawnOIIém 839m
Hie—or.— 95...
>02 to . Rom .
we.

      

vs 3 e. 1 \5 P u. I E es
.

     
 

 

 

 

- I o
.
N
a
e
h
n .m
rl.
m
n
axov.1e~ocm_m0t .m
:0 _o>o_ {DE 301 . v R
10m... u_:eEon_ <e
:EEO.
izou
I k.

#00—

138

hbkvh\nfls¢

poeq aIJIawozogd
2

i X

as

“"21. .

[s
2':

anhanhsainaz

.c0w00w 30$ cassava mama 05 0550 am? 35050on

 

ess 5d.

a .

4/

     

 

 
 

 

 

 

 

most peacmfiot
:0 _o>o_ {DE 20

v00... at «OEON3 <

 

2050..
:cv

moo—

09:

     

e

s,
\

e.

    

 

 

 

flax—up”— oE_ .—

.00

we >15. 01 ex 2 3 3 e‘ e.

a

 

 
  

.Qew

          

.m> 20.0.58 mo Lamcwi. mm 0.303

Rainfall [inches]

4""

139

Curve A represents the average results from the group of
all piezometers on the upper s10pe, at the top or outside
of the drainage depressions. Curve B represents piezo-
meters positioned lower on the slope and well within
drainage depressions. The correlation coefficients (r)
for the points surrounding each curve are seen to be high.
Table X shows regression equation (2) and corresponding
correlation coefficient for each curve:

TABLE X.-—Regression equations and related correlation
coefficients for curves A and B.

 

 

 

Curve Equation r
A i = 5.17 - '2i2 + 1.85x .81
B i = 7.66 _ iiil + 6.51X .86

 

Maximum piezometric heads obtained during the autumn
of 1965, and the resultant pore—water pressures, are shown
in Table XI. Maximum values for piezometers l, 3, 5, and
10 (the single surviving piezometer on the north-facing
slope), are conspicuously high. All of these piezometers
are located well within drainage depressions. The remain-
ing piezometers listed in this table lie above the de-

pressions on the open slope.

PIEZOMETRIC HEAD (inches)

Figure 56.—-Graph of average piezometric head vs. total

    

 

 

 

luo
w._ -a”

35i— ‘ '2

0' .
np— gf _‘“°::
0‘... \.
O... “
CURVE . 3’ J 3
a _ on" ‘30 v
e". m
e" g
k . a
m__ -n‘=:
n A.
..... 1 a
‘5 ...... . ...... _ 7. E
CURVE‘ A ............. <
........... mm. E
............ —‘ 52 g
t 2
_'5
‘ ““lnlnnlinunl l I l n
0 3 ‘ 5 |

RAINFALL (inchevday)

 

rainfall per day for two locations within pre-

existing drainage depressions.

 

 

 

lUl

 

o.m:a

m.mm

OH

m.Hm

o.m

m.am

m.wm

ma.mm

0.0H

0.:OH

0.0m

:.m:

0.5

m.mm m.:m :.©©H AmpM\mnHv
whammmya nova:

Immoo Eseflxmz

m.mH m.oa o.mm Ammnocfiv
commmm Gama“

mmmfi msfipse name

onpoSommfio Esafixmz

m m H amnesz ummeoNon

.Aaonsm>021UHE op pmnsopmom opmav commom zcfimp flame mama map wcfipso Umcfimpno
omfih cappoEomoHQ UopmHog Ucm madmmmpo hopmzlmaoo go mmsHm> Ezefixmznnon mqm<e

 

 

 

142

Analysis of Results

 

Figure 56 shows good correlation between piezometric
head, rainfall, and areal position with respect to drain-
age depressions. Since pore-water pressure is directly
related to piezometric rise, the same correlations hold
true for pore—water pressure. Both curves begin at the
same x axis value, approximately .05 inches of rain.
Beyond this point there is a rapid increase in piezo-
metric head with continued increase in rainfall increase.
After approximately .05 to .10 additional inches of rain
has accumulated, piezometric head increases more slowly
and the ratio of rainfall to piezometric head becomes
fairly constant. Curve B shows greater piezometric head
increase than Curve A, indicating higher piezometric head
due to increased volume of flow downslope.

The relationships shown in Figure 56 can also be
interpreted using Darcy's flow equation through porous media,

in which

Q = kill (3)
where Q = flow rate of water through soil
k = permeability coefficient of soil
1 = hydraulic gradient

A = gross cross—sectional area of flow
channel.

In the study area (k) is assumed constant though in fact
it should have a slight decrease downslope due to partial

filling of soil pores by sediment transported from above.

1M3

This factor represents the till soil's ability to transmit
water. The value (i) is the hydraulic gradient, comparable
to the gradient of the piezometric surface in the soil and
is an assumed constant over the length of slope. The
factor (A) is controlled by subsurface drainage channel
configurations where flow takes place.

At the beginning of a rainy period, no piezometric
head develops because soil permeability is great enough to
remove the water infiltrating into the soil from the sur--
face. At this time, water moves along discontinuities or
percolates through intragranular pores directly as the re-
sult of gravity flow through larger spaces and by changes
in moisture tension in the smaller pores (Baver, 1940,
Chapter VI). Piezometric head.develops only when the
amount of water entering the soil is greater than the soil
permeability at which times a condition of saturation
exists. As rainfall increases, piezometric head begins to
rise and Darcy's equation applies. As a result of rising
piezometric surface, the cross-sectional area (A) of the
flow channel correspondingly increases at an exponential
rate. The relationship is illustrated schematically in
Figure 57. As a consequence of the increase in piezometric
level downslope, the piezometric surface thus defined
maintains a gradient [the hydraulic gradient (1) in
equation (3)] beginning at zero piezometric level at some
point upslope and terminating at a downslope point of

total saturation and surface flow. Figure 58 illustrates

.—

 

 

11M

 

 

 

   

A: :ross-seciional area "2

0: flow rate ft/sec

Q

Figure 57.——Schematic diagram of drainage depression to
illustrate probable increase in cross sectional
area and a resulting use in piezometric surface
with increased flow downslope.

 

IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIlIlIIIE:::“““—————————————1

1A5

this relationship schematically. Field observations and
measurements of changing piezometric level with elevation
in the areas of established well networks (Map 3) indi-
cates that this gradient (i) is developed over slope dis-
tances of approximately 300 feet. These observations and
measurements also indicate that with increasing rainfall,
piezometric surface migrates upslope while maintaining

essentially the same gradient.

 

Figure 58.——Schematic diagram of a slide prone
slope showing the migration upslope from
l to 3, of a constant gradient piezometric
surface with increasing rainfall.
Because in equation (3), (Q) is directly proportional
to (A), (Q) also increases at an exponential rate when the

piezometric level rises. Figure 59 further diagrams the

probable relationship between increments of rainfall (AP),

1&6

flow rate (AQ) and changes in piezometric head (Ahp). At
the point of initial saturation (S), flow rate (Q) is O
and piezometric head is 0. Following saturation of the
soil, as more water is added, hp increases very rapidly
at first because of the relatively small initial values

of (Q) and the large volume of water moving downslope.

Ahp
A0

 

 

 

 

Figure 59.--Theoretical graph showing relationships
between rainfall (AP), flow rate (AQ) and
piezometric head (Ahp).

As the piezometric level continues to rise, however, (Q)
also becomes larger and is able to remove increasingly
larger amounts of the water being added to the soil from
the surface and from upslope. Thereafter the piezometric
head increases more slowly. These curves approach each

other as rainfall increases, meeting at a point within or

at the surface of the soil. If the curves intersect within

 

 

147

the soil, an equilibrium condition between flow rate and
the water supply is indicated. Such would result when

the addition of water to the soil is at a constant rate.
When the curves intersect at the surface, of course there
is complete saturation of the soil and surface runoff.
takes place. This point, representing both maximum piezo-
metric head and maximum soil flow rate, is shown as (th)
in Figure 59.

At-the study site the generally constant piezometric
head observed after mid-October, 196A (FigureSA) may be
attributed to the development of the semi-permanent autumn
snow cover on the area upslope from the well sites. This,
of course, also presumes the arrival of generally sub-
freezing winter temperatures on the higher ridges. The
presence of winter snow—cover and the development of lowered
temperatures thereafter served as.a damper on large piezo-
metric fluctuations by maintaining a steadier supply of
water also at reduced volumes. Thus a fairly constant flow
rate (Q) and a similarily constant piezometric head (hp)
was maintained, in effect resulting in a stabilizied piezo—
metric level below the surface. The flow rate under these
circumstances balanced the addition of water to the soil.
As a result, pore-water pressures were maintained at-a much
lower level then those common during earlier parts of the
rainy season. In this way the sliding was terminated in
the autumn and or at least its manifestations minimized in

Maybeso valley.

 

1A8

It is of interest that in subsequent research in
which the writer has been involved on the year—around
glacio—hydrological regime of the Ptarmigan Glacier near
Juneau, a similar leveling of flow has been observed in
the outlet stream of the glacier after the onset of mid—
October snowfall (A. E. Helmers, C. Zenone and D. N.
Swanston, 1967).

As stated previously, within drainage depressions
the piezometric head is highest. It also increases down—
slope. This is because of localized concentration of
flow into such depressions, with resultant increases in
volume of subsurface flow (Figure 57). Where the soils
become completely saturated, their shear strength is re-
duced to a minimum and they become most susceptible to
sliding conditions. Soil saturation within the depressions
develops first, of course, downslope and, as flow-volume
increases the zone of saturation moves progressively upslope.
Where the slopes approach or exceed the angle of internal
friction sliding becomes imminent and small slip—outs may
develop. Evidence of recent small slip-outs which pre-
sumably have formed in this way have been observed by the
writer at lower elevations in many of the drainage depres—
sions in the study area with indications of even earlier
sliding, in the form of overturned soil profiles and buried
organic horizons, above and below.

The implication is that some drainage depressions

may evolve and enlarge by small-scale slides occurring

 

1A9

progressively upslope. In these cases, a slip-out in a
subsurface drainage channel first occurs where pore-water
pressures are greatest. Above this slip—out later slip-
outs may also take place due to high pore-water pressures
and reduced shearing strength in.the soil as a result of
undercutting. A hypothetical sequence of slip-outs of
this kind is schematically illustrated in Figure 60.

The regression equations for Curves A and B in
Figure 56 may be used to forecast piezometric head for
given rainfall amounts and s10pe location. Solutions for
rainfalls in excess of 2.5 inches per day are, of course,
extrapolations, and in fact in this region rainfall in.
excess of this amount is unusual. By using these equations,
however, approximation of prevailing piezometric levels at
times of known slope failure can be obtained.

The most recent occurrence of observed accelerated
mass momvements was on October lA-l5, 1961. With respect to
this two-day period Bishop and Stevens (1964) have reported
a 6.41-inch rain accumulation, five inches of it in one day.
Since the slides occurred within the drainage depressions,

a calculation using Curve B suggests that the corresponding
piezometric head (at a rainfall rate of 5 inches a day) was
in excess of 40 inches. Because soils in the area of
initial slope failure do not exceed 36 inches in thickness,
it is presumed that these soils were completely saturated

when the sliding took place. Rainfall accumulations of

150

 

Figure 60.--Diagram illustrating the suggested

development of progressive soil failure

upslope within areas of concentrated sub-

etc.

Slip 1 precedes 2,

surface water flow.

151

this magnitude are, of course, quite unusual, even in this
region of high precipitation. Rainfall frequency data for
Alaska (J. Miller, 1963) indicate that a rainfall of this
magnitude occurs at 2— to 5-year intervals. In the Maybeso
valley this interval agrees in frequency with at least~
one other extensive mass movement episode which took place
in December 1959 (Bishop and Stevens, 1964). Longer range
correlations were not possible because of the lack of-ade—
quate data. Solar radiation correlations by M. M. Miller
(1963, 1967), however, suggest there may be some interest
in looking at approximately 11 and 22 year cyclic develop-
ments of unusual precipitation for possible correlation
with unusual episodes of land sliding in coastal Alaska.

Stability Analyses of Selected Debris
Avalanches in the Maybeso Valley

 

 

Stability analyses are based on theoretical soil
mechanics in homogeneous materials, with results modified
by engineering experience and practice. Direct application
of theoretical soil mechanics to the slide prone glacial
soils in Maybeso valley is quite difficult because of the
heterogeneous nature of such slope materials, the extreme
variability of soil water conditions involved, and the
related variations in stress-strain with time.

Conditions during periods of field investigation are
rarely the same as pertained when sliding actually took

place. One, therefore, has the difficult problem of

152

extrapolating soil and slope conditions at the time of
sliding in order to determine a useful index of stability
by which potential slope failures can be assessed. This
index, called the factor of safety, is defined as the
ratio between the potential resisting forces and the
forces tending to cause downslope movement. The value of
such an analysis in the Maybeso valley is twofold. It,
provides a chance to estimate the forces known or believed
to be acting on the slope where sliding has occurred, and
it provides a means of characterizing slopes according to
their slide susceptibility.

The performance of a.stability analysis requires,
firstly, that the shear characteristics of the soils in—
volved in sliding be obtained [(5), effective cohesion;

(3), effective angle of internal friction; and (y) unit
weight of the soil]. Secondly, it requires that the approxi-
mate surface of failure be determined.

Shear characteristics were obtained from five undis—
turbed slide-prone soil samples taken in the vicinity of
the three slides set aside for detailed study in Maybeso
valley. They were analyzed by means of triaxial shear tests
at the Civil Engineering Laboratory, Michigan State Univer-
sity. These samples were taken from the weathered till near
the slide origins and indicate that the weathered tills have
an effective cohesion (5) of O, and an effective angle of
internal friction (E) of 37° (T. H. Wu, personal communi-

cation). Soil water measurements in the weathered "younger"

153

till have also indicated that the soils at failure are
completely saturated, and thus maintain their maximum unit
weight at approximately 111 lbs/ft3. Surface loading of
the slide-prone soils due to weight of stumps is considered
negligible. Field observations and excavation of stumps

in the slide areas indicate that most of the weight of
individual stumps is carried by roots that penetrate the
soil profile and anchor in the compact, unweathered till
beneath (Patric and Swanston, 1967).

The sliding surface was determined in the field by
locating the base plane of the slide, which, as has been
shown, is the upper surface of the unweathered till; also
by determining the general thickness of material above the
slide plane, and by measuring the slope of the sliding sur—
face.

In the case of the slide-prone soils in Maybeso valley,
pore pressures developed during periods of intense rain have
also been shown to have considerable effect in reducing
shearing strength. For example, in the areas of sliding,
soil thickness rarely exceeds 36 inches. Because at fail-
ure, the soils are completely saturated, active pore-water
pressures in the slide-prone areas are in excess of 187
lbs/ft2 which reduces effective stress on the soil by at
least that amount. There are also indications that the
anchoring effects of roots in the unweathered till are an

external factor affecting soil strength. This is reflected

‘V'

 

154

by an "apparent cohesion" of the soil. Thus, deStruction
of roots by clearcutting or other means may be an impor-
tant factor in reducing resistance to sliding. These
factors will also be taken into account in the analysis.
For convenience, the sliding surface was approxi-
mated by a "critical circle," tangent to the base plane
and marked at its upper and lower limits by the upper
slide scar edge and the first break in slope not caused by
bedrock. The critical circle has to satisfy the require—
ment that the ratio between the moment of forces tending
to resist sliding (shear strength) and the moment of forces
tending to cause sliding (shear stress) are at a minimum.
This ratio is the factor of safety (F). At failure, the

Factor of Safety has, therefore, a theoretical value of l.

 

Final analysis was made using "The Method of Slices,"
as described.by Wu (1966) and Hough (1957). This method
allows shear strength-stress relationships and the Factor
of Safety to be calculated with reasonable accuracy. It
is especially useful when pore pressure effects are being
considered. Comparison calculations of the Factor of Safety,
based on a unit section of an infinitely long slope with the
same characteristics, are shown in Appendix A. In the
circular arc method, a mass of soil (a-b-c in Figure 61)
is divided into a number of segments. The forces acting on
each segment are evaluated from consideration of the mean-

ing of equilibrium conditions. An equilibrium conditiOn

 

155

.pcoewow Hm3pfi>flpcfi cm co weapon mooaom .o

.mpcoEmom Hw3©H>HUCH 0pc“

popfl>flp95m one can amazonflo m an popfleflaop mmmE aflom Hapoa .w

.Aooma .53 .m .B popemv moofifim go cospoE one
he pomzamcm mme HHom a mo coapmpcomoagon oaumEEmnmeQll.Hw opswfim

T

\/ :
/LAA\\. Ho
NV .

a ;a

 

 

 

 

156

in a mass of soil occurs when a balance between opposing
forces is achieved. This is determined by the summation
of the relevant forces on all segments.

The forces on an individual slice consist of the
weight of the slice (AWn), the surface load acting on
the slice (Qn), the normal and shear forces (Tn) and (Pn)
acting on the failure surface e—f and the normal and
shear forces (En), (Fn), (En + l), and (Fn + l) acting on
vertical faces c-e and d—f (Figure 61-b). The angle (a)
is the slope angle and (o) the angle of internal friction.
With so many forces acting, the system is rather indetermi-
nate. In order to obtain a solution, therefore, certain
assumptions must be made. These concern the magnitude and
point of application of the forces (En) and (Fn). An
approximate solution is obtained by assuming the resultants
of (En) and (Fn) as equal to those of (En + l) and (Fn + l),
and that their lines of action coincide. This leaves only
the forces (Wn), (Qn), (Pm), and (Tn) to be dealt with.
Assuming conditions of plastic equilibrium in each segment
(that is the soil is assumed to be perfectly plastic) the

following relationships may be cited:

"U
ll

(Awn + Qn) cos a

a
ll

(AWn + Qn) sin a

157

The unit pressure on f—e for each segment in the arc

a—b is equal to:

o = 1/AL [(AWn + Qn) cos d]

Shear stress on each segment is equal to:

T = 1/AL [(AWn + Qn) sin a]

In the presence of pore—water pressures (U), unit

pressure on each segment is reduced to an effective pressure:

3 = l/AL [(AWn + Qn — uAL) cos d]

Shear stress (T) remains unchanged.

At failure, the shear stress on the surface is equal‘
to the shear strength. If the shear stress is not sufficient.
to produce failure, then the ratio of shear strength to

shear stress is the previously defined Factor of Safety,

 

(F). The total shear stress over the entire arc is the
summation of shear stresses on the segments. This sum
may be expressed as E (AWn + Qn) sin a. From the previous
discussion we may substitute (3) into the equation for
shear strength (equation 1). The selected shear strength

(S AL) on each segment of the arc thus becomes:

3 AL = (E + 6‘ tanFML = EAL

+ (AWn + Qn — uAL) coso tan¢

 

 

158

The total shearing resistance over the entire arc is ex-

 

pressed as the sum

ZECAL + (AWn + Qn - uAL) cosa tang]

The Factor of Safety is then given by the equation:

 

Z[5AL + (AWn + Qn — uAL) cosa tang]
F:
2(AWn + Qn) sino

 

(4)

It has been previously stated that surface loading of the
slide-prone soils in Maybeso Creek valley is negligible,
thus, the term (Qn) can be removed from equation (A) and

the Factor of Safety becomes:

 

Z[6AL + (AWn — uAL) COSd tanEJ

F 2W sind (5)

 

Calculation of the F factor for the slide areas in
Maybeso Creek valley, using the previously determined shear
characteristics of X = 370 and 5 = 0, results in values for
the F factor which are less than one (see equations a1, a2,

a Appendix B).

3,
At failure, the F factor is assumed to be 1. The
discrepancy that exists here can be removed by assuming the
existence of an "apparent cohesion" in the soil that does

not show up in laboratory tests. Such an "apparent co-

hesion" (symbolized as 5a) was observed in the field and

may be due to several different factors. Capillary tension

 

 

159

would cause a limited amount of "apparent cohesion," prior
to complete saturation of the soil profile. A much larger
"apparent cohesion" is probably due to the roots pene-
trating into the unweathered till surface, producing the
anchoring effect previously discussed.

By setting the value of (F) at 1 when failure occurs
an approximate value of (5;) can be determined for each
slide mass at failure and under the influence of poreawater

pressure. Thus,

ZEEa AL + (AW — uAL) cosa tang]

 

 

F = 1 = 2(AW) sina
and,
C = (1) [ZAW sina] - [2(AW) - HAL) 005“ tan?) (6)
a EAL

Soil stability calculations following this procedure
were made on the three slides studied. The greatest pore
pressure at failure in each was taken as the pore-water
pressure developed when the soil profile is completely
saturated. Scaled cross-sections of the slide roots and
the assumed soil mass delineated by a circular arc are
shown in Appendix B. The soil mass was divided into seg-
ments and the forces acting on each segment were analyzed
separately according to the method described in previous
pages. The weight of each segment was divided by counting

the unit squares enclosed by the scale diagram and

160

multiplying by the soil unit weight. The angle (a) was
also measured directly from the diagram. The final calcu—
lations and results of the stability analysis are shown in
Appendix B.

The value (Ca) was obtained, then used to calculate-
an F factor at maximum soil strength for each of the three
slides analyzed (Appendix B). For each slope a calculated
F factor was derived for each with slide materials at their
wet and dry unit weights and in the absence of pore-water
pressures (equations 10, 1d, 20, 2d, 3c, 3d, Appendix B).
Actual F values under dry unit weight conditions are probably
somewhat higher than the calculated value because of an in—
creased (Ca) value due to capillary tension.

The calculated Factor of Safety (F) of each of the

 

slide-prone slopes at the point of slide origin lies be—
tween lLEQ and lLQQ in the absence of pore-water pressures.
The difference in F factors for a soil at wet and dry unit
weights in the absence of pore—water pressure is small.
These values indicate a more than adequate stability under
natural soil and lepe conditions and in the absence of
pore—water pressure, since values as low as 1.1 are fre-
quently considered adequate for highway and railroad

slopes (Hough, 1957). At complete saturation, and thus

 

maximum pore—water pressures, these values are reduced to

 

a Factor of Safety of l and sliding becomes imminent.

 

 

161

It is clear, from the above discussion, that pore-
water pressure is an effective triggering force of debris
avalanches in Maybeso valley and is most effective at
complete saturation of the soil profile. Such a.com-
pletely saturated condition is believed to occur during
a rainfall in excess of 5 inches per day, a situation
which has been previously suggested to arise at 2— to 5-
year and possibly greater intervals under natural condi-
tions. It is of interest that such a period roughly corre-
sponds with the observed periods of maximum slide activity
in the valley to date, although it must be noted that the
time of observations in this valley covers only about a
decade. In the absence of pore-water pressures the Factor
of Safety for the slide-prone slopes is well within the
range of normal slope stability.

It is also clear that an-apparent cohesion for the
slide—prone soils does exist and is due to external factors
not reflected directly in the physical properties of the
soil. In the areas studied this value varies from 69 to
89 lbs/ft2 and, in the writer's opinion, could only have.
resulted from the anchoring effect of large roots growing
through the slide—prone weathered till and into the under-
lying compacted and unweathered till. Bishop and Stevens
(1964) suggested this possibility in their preliminary
report. They also noted an apparent 3-year lag in acceler-

ated sliding following logging and suggested that this may

 

162

be the time necessary for root deterioration to reduce
soil shear strength to a low enough value for sliding to
be initiated.

Effective sliding occurs on slopes above 30°. With
decreasing slope, shear strength and the Factor of Safety
increases. This can be seen by once again considering
equation (5) for calculating the Safety Factor. In this
case we will deal with a unit volume of soil not influ—
enced by pore-water pressure. Thus, with (uAL) equal to

O and summation signs removed, equation (5) reduces to:

F:

 

CAL + W 008d tan¢ (7)

W sina
In equation (7) (a), of course, equals the angle of slope,
(3) is the effective angle of internal friction, and (5)
is effective cohesion. Under these conditions, (5) is
constant and (AL) a thickness of the soil mass, is unity.
(W) is also unity and (E) is constant. With decreasing
slope the sine of (a) decreases faster than cosine of
(a). The difference increases and therefore the F factor
correspondingly increases as the slope gets smaller. This

points up the strong relationship between slope angle and

 

slide susceptibility.

 

A. N. Strahler (1956) has developed a method of
slope analysis that expresses this relationship particu-
larly well. By determining the sines of the slope angles

for a large number of points in the area studied, an

163

isosinal map can be produced by contouring the values
(Appendix C). For cohesionless soils, the sine of the
slope angle represents "that part of the total gravi-
tational force acting on the slope that tends to produce
downhill sliding or flowage of rock particles or fluids
on the surface." A soil particle located at point "p"
on the slope is affected by forces Fg = mg, where (m)

is mass in lbs., and (g) is the acceleration of gravity
in lbs/ft2. FS is the shear stress (1) in lbs/ft2. (Fn)
or o is the force normal to the surface, also expressed
in lbs/ft2. (F8) and (Fn) are components of (F8)' The
elementary trigonometric relationship of the principal
forces acting on a soil particle on a slope.(Strah1er,

1956), is depicted in Figure 62.

 

 

Figure 62.—-Diagram of principal forces acting on a
soil particle on a slope (after A. N. Strahler,
1956).

 

 

16A

sino = gi fiL , by geometry, a = o
g g

When considering a unit mass of soil surrounding
point "p" on the slope, the downlepe force [shear
stress (T)] operating on that mass is given as T = Fg sin a,
which is the well established equation for the shear stress
in a cohesionless soil. Note that (Fg), in this case repre—
sents the column or weight of material.

Thus, the isosinal contour map tells the general
location and distribution of shearing stresses produced by
gravity on a cohesionless soil slope. Also, for a perfectly
cohesionless soil the Factor of Safety is defined as:

_ tan¢
F — tand (8)

 

(Terzaghi and Peck, 19A8). As the slope angle approaches
the internal friction angle, (F) approaches 1, and again
failure is imminent. The isosinal contour corresponding
to the sine of the internal friction angle can then be
used as the critical isosine around which sliding is most
likely to occur.

Field and laboratory investigations indicate that,
while the slide—prone soils in the Maybeso valley are not
entirely cohesionless, they do have a semi-cohesionless

character. A non—rigorous solution of the isosinal slope

-.
4- .

 

 

165

analysis can, therefore, supply useful results as to slope
stability, and the possibility of slide occurrence.

Field studies in Maybeso valley indicate that the
majority of debris avalanches and flows develop on slopes
greater than 300 and are especially frequent around a
critical angle of 37°. On the isosinal contour map of
Maybeso valley (Map A), this angle is represented by the
critical contour 0.6 which is the sine of 37°. Above this
critical contour, sliding is imminent with the destruction
or disruption of any of the forces acting to hold the soil
in place. Below the critical contour is a zone of decreas-
ing instability arbitrarily marked at its lower limit by
a slope value of 30°. This slope value corresponds-to a
Factor of Safety of F = 1.5. This is an approximate value
for the slide areas analyzed at their maximum stability
(eq. 8). Below this contour, slope soils may be considered
stable under natural conditions. The zone of instability
between these two limits is located principally in the
deeper stream notches and in a narrow band near the 1,200
foot contour. The narrow band in the vicinity of maximum
slide activity corresponds to the till shoulder marking
the upper limit of younger till.

By such mapping of slope angles, specific areas of
slide development can be located and from this knowledge
any necessary steps may be taken to prevent or control the

occurrence of new slope failures.

 

 

166

Conclusions

 

Investigation of mass wastage processes and their

relationship to geologic, geomorphic, and engineering

factors in an area of recent large-scale sliding has led

to the following conclusions:

1.

Bedrock composition has exerted little direct
control on the development and distribution.

It has, however, supplied the material from which
a late Wisconsinan till (the younger till) was
formed, which overlies the bedrock in much of
the valley. This late Wisconsinan till is a
prime vehicle for mass movements and, in fact,
large numbers of debris avalanches and debris
flows have occurred within its borders.

Bedrock structure and faulting have provided
considerable control on development and distri-
bution of mass movements in the valley, parti-
cularly on the south slope, where bedrock.dips
into the slope creating numerous benches and
terraces serving as barriers to slide develop—
ment. Few mass movements have taken place on
this slope and those that have occurred on small
patches of late Wisconsinan till lodged behind‘
the terraces and benches. Small-scale mass
movements, in the form of debris avalanches,

are common on the north slope of the valley in-

 

 

167

alluvium and till-covered bedrock surfaces which
dip steeply into the valley. They are also
common in walled fault line canyons cutting the
flanking slopes of the main valley.

Large—scale mass movements in the form of debris
avalanches and debris flows occur on Open slopes
in Maybeso Creek valley in the weathered zone of
an initially compact late-Wisconsinan glacial‘
till. The weathered segment of this till is
disaggregated and highly permeable; the under—
lying unweathered till is compact, strongly
cemented with calcium carbonate, and highly
impermeable.

The majority of mass movements develOp within
pre—existing surface drainage depressions in which
subsurface water becomes concentrated.

The majority of mass movements are initiated on.
slopes greater than 30°, a value significantly
close to the angle of repose of these materials,
established roughly at 34°. These develop most
frequently on slopes near the angle of internal
friction of the weathered till soil which, under
natural conditions in this area, averages out at
about 37°. A contour map of the sine of the
slope angle or, more simply, the angle of slope,

provides a convenient method for determining the

168

areas which are most susceptible to slides. The
critical contour, defined as that contour above
which sliding is imminent, is determined by the
angle of internal friction.

6. Pore—water pressures developed in the slide—prone
soils as a result of high rainfall play an im-
portant part in increasing the susceptibility of
the soil to sliding. This is probably the princi-
pal triggering force that initiates sliding.
Information obtained from piezometers on the
s10pes indicate that at the time of failure, the
soil in the vicinity of slide initiation was
completely saturated.

7. Analysis of three of the most recent and destruc-
tive debris avalanches and flows using methods of
soil mechanics, indicates the presence of an
"apparent cohesion" which cannot be accounted for
in the physical properties of the soil. This
cohesion is attributed to the anchoring effect
of tree roots extending through the weathered till
and into the unweathered till. Gradual deterio-
ration of these roots following clearcutting-re-
duces the "apparent cohesion" and significantly
increases susceptibility of the slope to failure.

It is clear from the data and information provided that

the fundamental understanding of slope failures under the

described conditions demands a clear and broad understanding

169

of the nature and distribution of glacial till deposits,
their hydrologic characteristics, the magnitude of the
slopes on which they are deposited, and the effects of
covering vegetation as a stabilizing influence. To this
end, the present study provides basic measurements and
techniques, plus a background of field information and
interpretation, so that tentative predictions of slide
susceptibility elsewhere in southeastern Alaska can be
made. This should be especially helpful in areas where
conditions similar to those described in the prototype

locality are found.

 

 

BIBLIOGRAPHY

170

In . ‘

I

wiv'un .

4211‘; w"
I.‘ ‘ .

 

BIBLIOGRAPHY

Armstrong, J. E., and Tipper, H. W., 1948, Glaciation in 4
North Central British Columbia: Amer. J. Sci., v.
246, pp. 301—310.

, 1956, Mankato drift in the lower Fraser Valley
of British Columbia, Canada: G. S. A. Bu11., v.
67, No. 12, pt. 2, pp. 1666-1667.

 

Baker, R. F., 1956, Landslides and the engineer: in_
North Carolina State College, Symposium on geology
as applied to highway engineering, 7th Annu. Proc.
1956, pp. 3-13.

Banta, H. E., Unpublished report dated July 26, 1957, on
mining possibilities in Harris and Maybeso valleys:
on file at No. Forest Exp. Sta., Juneau, Alaska.

Baver, L. D., 1940, Soil physics: John Wiley and Sons,
N. Y.

Beaty, C. B., 1956, Landslides and slope exposure: J. Geol.,
v. 64, No. 1, pp. 70—74.

Bernardini, F., 1957, Contribution to the control of land—
slides in the Emilian Apennines 1.: Munti Boschi,
v. 8, No. 7, pp. 311-321 (Ta1.—Eng.).

Bishop, D., and Stevens, M. E., 1964, Landslides on logged
areas in southeast Alaska: U. S. Forest Serv. Res.
Paper NOR—1, 18 pp.

Bowden, K. L., and Wallis, J. R., 1964, Effect of stream
ordering technique on Norten's laws of drainage
composition: G. S. A. Bu11., v. 75, pp. 767-774.

Brew, D. A., Loney, R. A., et a1., 1963, Structural in—
fluence on development of linear topographic features,
southern Baranof Island, southeastern Alaska: U. S.
Geol. Surv. Prof. Paper 475-B, article 28.

Brew, D. A., Loney, R. A., and Muffler, L. J. P., 1966,

Tectonic history of southeastern Alaska: C. I. M.
Special Volume No. 8, pp. 149-170.

171

172

Brooks, A. H., 1920, Preliminary report on the Ketchikan
mining district, Alaska: U. S. G. S. Prof. Paper 1,

120 pp.

Broscoe, A. J., 1959, Quantitative analysis of longitudinal
stream profiles of small watersheds: Columbia Univ.

Dep. Geol. Tech. Rep. No. 18, 73 pp.

Buddington, A. F., 1927, Coast Range intrusives of S. E.
Alaska: Geol., v. 55, No. 3, pp. 224-246.-

, 1927, Abandoned marine beaches in S. E. Alaska:
Amer. J. Sci., 5th ser., v. 13, pp. 47—52.

 

, and Chapin, T., 1929, Geology and mineral deposits
of southeastern Alaska: U. S. G. S. Bull. 800, 398 pp.

 

Capps, S. R., 1932, Glaciation in Alaska: U. S. G. S. Prof.
Paper 170, 8 pp.

Casagrande, A. J., 1936, Characteristics of cohesionless
soils affecting the stability of slopes and earth fills:
J. Boston Soc. Civil Eng., v. 23, pp. 13-32.

, 1949, A non-metallic piezometer for measuring pore
pressures in clay: Appendix of Soil Mechanics in Design
& Construction of the Logan Airport, J. Boston Soc.

Civil Eng., v. 36, No. 2.

 

Chapin, T., 1916, Mining developments in southeastern Alaska:
U. S. G. S. Bull. 642.

, 1918, Mining developments in Ketchikan and Wrangell
mining districts, Alaska: U. S. G. S. Bull. 662—B,

pp. 63-75.

, 1919, Mining developments in Ketchikan district,
Alaska: U. S. G. S. Bull. 692-B, pp. 85-89.

 

 

Condon, W. H., 1961, Geology of the Craig Quadrangle,
Alaska: U. S. G. 8. Bull. 1108—B, 43 pp.

Coulomb, C. A., 1776, Essai sur une Application des Rigles
des Maximis et Minimus a quelques Problimes de Statique

Relatifs a l'Architecture: Mem. Acad. Roy. Pres. Duris
Savants, v. 7, Paris, France.

Crandell, D. R., 1964, Pleistocene glaciations of the south—
western Olympic Peninsula, Wash.: U. S. G. S. Prof.

Paper 501-B, pp. 135-139.

173

Crandell, D. R., 1965, The glacial history of western
Washington and Oregonz‘;n The Quaternary of the
United States, ed. H. E. Wright and D. G. Frey,
Princeton Univ. Press.

Crandell, D. R., Mullineaux, D. R., and Waldon, H. H.,
1958, Pleistocene sequence in southeastern part
of the Puget Sound Lowland, Washington: Amer. J.
Sci., v. 256, pp. 384-397.

Croft, A. R., and Adams, J. A., 1950, Landslides and sedi—
mentation in the north fork of the Ogden River, May
1949: Intermountain Forest and Range Exp. Sta. Res.
Paper 21.

Dahl, Eilif, 1946, On different types of unglaciated areas
during the ice ages and their significance to phyto—
geography: New Phytologist, v. 45, pp. 225-242.-

Davis, N. F. G., and Mathews, W. H., 1944, Four phases of
glaciation with illustrations from S. W. British
Columbia: J. Geol., v. 52, pp. 403-413.

Eckle, E. B., 1958, Landslides and engineering practice:
Nat. Res. Council, Highway Res. Board Spec. Rep. 29,
No. 21, 232 pp.

Ellis, J. H., 1938, The soils of Manitoba: Manitoba Econ.
Surv. Board, Winnipeg, Manitoba.

Flaccus, E., 1959, Landslides and their revegetation in the
White Mountains of New Hampshire: Duke Univ. Ph.D.
Botany, Univ. Micro., Inc., Ann Arbor, Mich.

Flint, R. F., 1957, Glacial and Plesitocene Geology: John
Wiley and Sons, Inc.

Forbes, H., 1946, Landslide investigation and correlation:
Amer. Soc. Civil Eng. Proc., v. 72, pp. 169—198.

Fredricksen, R. L., 1963, A case history of a.mud and rock
slide on an experimental watershed: Pacific N. W.
Forest and Range Exp. Sta., Res. Note No. 1, Jan.
1963.

Frye, J. C., and Willman, H. B., 1960, Classification of
Wisconsin Stage in the Lake Michigan glacial lake:
Illinois State Geol. Surv. Circ. 285, pp. 1-15.

Garber, Lowell, 1965, Relationship of soils to earthflows
in the Palouse: J. Soil and Water Conserv., Jan.-
Feb., pp. 21—23.

 

 

174

Goldthwait, R. P., 1959, Post Wisconsin glacial changes
in S. E. Alaska: G. S. A. Bu11., v. 70, No. 12, pp.

1794-1795.

Grim, R. E., 1953, Clay Mineralogy: McGraw-Hill Book Co.,
Inc., N. Y., 384 pp.

Harris, A. S., 1965, Subalpine fir on Harris Ridge near
Hollis, Pr. of Wales Island: Northwest Sci., v. 39,
No. 4, pp. 123—128.

Hann, J., 1903, ln_Ward R. and de 0., eds. Handbook of
Climatol.

Helmers, A. E., Zonone, C., and Swanston, D. N., 1967,
Progress report on 1966—67 winter observations of
runoff from Ptarmigan Glacier, Alaska: section in
Federal Office of Water Resources Research project
report, via Glaciological and Arctic Sci. Inst. of
Mich. State Univ.

Hennes, R. G., 1936, Analysis and control of landslides:
Wash. Univ. Eng. Exp. Sta. Bull. 91.

Herbert, C. F., and Race, W. H., 1964, Geochemical in-
vestigations of selected areas in southeastern Alaska,
1964: State of Alaska, Div. of Mines and Minerals-—
Geochem. Rep. No. 1.

Heusser, C. J., 1952, Pollen profiles from southeastern
Alaska: Ecol. Monogr., v. 22, pp. 331—352.

, 1953, Radio carbon dating of the thermal maximum
in southeastern Alaska: Ecology, v. 34, pp. 637—640.

 

, 1954, Additional pollen profiles from southeastern
Alaska: Amer. J. Sci., v. 252, pp. 106-119.

 

, 1960, Late Pleistocene environments of N. Pacific
North America: Amer. Geogr. Sox., Spec. Publication 35.

 

Horton, R. E., 1945, Erosional development of streams and
their drainage basins; hydrophysical approach to
quantitative geomorphology: G. S. A. Bu11., v. 56,
pp. 275-370-

Jenney, Hans, 1941, Factors of soil formation: McGraw-Hill
Book Co., Inc., 281 pp.

Jones, H. W., Unpublished report dated October 3, 1962 on
bedrock structure in the Hollis area: on file at No.
Forest Exp. Sta., Juneau.

175

Kardos, L. T., Vlasoff, P. 1., and Twiss, S. N., 1943,
Factors contributing to landslides in the Palouse
region: Soil Sci. Soc. Amer. Proc., v. 8, pp. 437—440.

Karlstrom, T. N. V., 1955, Late Pleistocene and recent
glacial chronology of southcentral Alaska [abs.]:
G. S. A. Bull., v. 66, No. 12, pt. 2, pp. 1581-1582.

, 1957, Tentative correlation of Alaskan glacial
sequences, 1956, Science, v. 125, No. 3237, pp. 73-74.

 

, 1957, Alaskan evidence in support of-a post-
Illinoian, pre-Wisconsin glaciation [abs.]: G. S. A.
Bull., v. 68, No. 12, pt. 2, 11. 1906—1907.

 

, 1961, The glacial history of Alaska; its bearing
on paleoclimatic theory: Annals New York Acad Sci.,
v. 95, article 1, pp. 290-340.

 

, 1964, Quaternary geology of the Kenai lowland
and glacial history of the Cook Inlet region, Alaska:
U. S. G. S. Prof. Paper 443.

 

Kay, Marshall, 1958, North American Geosynclines: Geol.
Soc. of Amer. Memoir 48.

Kerr, F. A., 1936, Quaternary glaciation in the coast range,
northern B. C. and Alaska: J. Geol., v. 44, pp. 681-
700.

Kesseli, J. E., 1943, Disintegrating soil slips of the
coast ranges of central California: J. Geol., V.

51, pp. 342—352.

King, C. C., 1958, The uniformatarian nature of hillslopes:
Trans. Edinburgh Geol. 800., v. 17, pt. 1, 11:81—122.

Kirk, E., 1919, Paleozoic glaciation in S. E. Alaska:
Wash. Acad. Sci. J., v. 9, No. 4, pp. 102e108.

Kranskopf, K., Bates, F. S., and Griggs, A. B., 1939,
Structural features of a landslide near Gilroy,
California; J. Geol., v. 47, pp. 600-648.

Krinsley, D. B., 1965, Pleistocene geology of the southwest
Yukon Territory, Canada: J. Galciol. v. 5, No. 40,

pp. 385-397.

Krumbein, W. C., and Pettijohn, F. J., 1938, Manual of
sedimentary petrography: Appleton-Century—Crofts,
Inc., N. Y. 549 pp.

176

Krumbein, W. C., and Sloss, C. C., 1956, Stratigraphy and
sedimentation: W. H. Freeman and Co., San Francisco,

497 pp-

Lawrence, D. B., 1950, Glacier fluctuation for six cen-
turies in southeastern Alaska and its-relation to
solar activity: Geogr. Rev., v. 40, pp. 191-223.

Ljungner, E., 1948, East-west balance of the quaternary
ice caps in Patagonia and Scandinavia: Bull. Geol.
Inst. Upsala, v. XXXIII, pp. 12596.

Maxwell, J. C., 1960, Quantitative geomorphology of the
San Dimas Experimental Forest, California: Columbia
Univ. Dep. Geol. Tech. Rep. 19, 95 pp.

Means, R. E., and Parcher, J. V., 1963, Physical properties
of soils: C. E. Merrill Books, Inc., Columbus, Ohio,
464 pp.

Melton, M. A., 1957, An analysis of the relations among
elements of climate, surface properties, and geo—
morphology: Columbia Univ. Dept. Geol. Tech. Rep.
11, 102 pp.

Miller, John, 1963, Probable maximum precipitation and
rainfall frequency data for Alaska: Dept. of Commerce,
Weather Bur., Tech. Paper 47.

Miller, M. M., 1956, Glaciology of the Juneau Ice Field,
Southeast Alaska: ONR Final Rep., Task No. 83001,
2 vols., 800 pp.

, 1961, A distribution study of abandoned cirques
in the Alaska—Canada Boundary Range: Geology of the
Arctic, Univ. Toronto Press, pp. 833-847.

 

, 1963, Taku Glacier evaluation study: State of
Alaska, Dep. of Highways.

 

, 1964, Morphogenetic classification of Pleistocene
glaciations in the Alaska-Canada Boundary Range:
Amer. Philosophical Soc. Proc., v. 108, No. 3.

 

, 1967, Alaska's mighty rivers of ice: Nat. Geogr.
Mag., vol. 313, No. 2, p. 208.

 

, Anderson, J. H., and Egan, C. P., 1967, Neo-
glacial chronology in southeastern Alaska from recent
radiocarbon dates: [abs.] Michigan Acad. Sci., Arts
and Letters, Ann Arbor, Mich.

 

177

Miller, R. D., and Dobrovolny, E., 1957, Pleistocene
history of the Anchorage area, Alaska: Science in
Alaska. Eighth Alaska Sci. Conf. Proc.

Mohr, 0., 1871, Beitrage zur Theorie des Eddruckes: Z.
arch. U. Ing. Ver. Hannover, v. 17, 1. 344 and v.
18. pp. 67, 245.

Moorhouse, W. W., 1959, The study of rocks in thin section:
Harper & Brothers, N. Y., 514 pp.

Munger, T. T., 1927, A research reconnaissance of south-
eastern Alaska: Unpublished report, Pacific N. W.
Forest & Range Exp. Sta., U. S. Forest Serv., Port-
land, Ore., on file at No. Forest Exp. Sta., Juneau.

Munns, E. N., 1950, Forestry terminology; a glossary of
technical terms used in forestry: 2nd edition, Soc.
Amer. Foresters, Wash., D. C.

Patric, J. H., and Swanston, D. N., 1967, Hydrology of a
Karta soil: accepted for publication by J. Forest.

Payne, T. G., 1955, Mesozoic and Cenozoic tectonic elements
of Alaska: U. S. Geol. Surv., Misc. Geol. Invest.,
Map 1-84.

Pewe, Troy L., 1956, Brief review of Plesitocent events:
and climatic changes in Alaska: [abs.] Alaskan Sci.
Conf., Proc., 4th, Juneau, September 28-October 3,
1953, pp. 186—189.

, 1960, Multiple glaciation in the Yukon-Tanana
upland, Alaska, a photogeologic interpretation:
Science in Alaska, Proc., Eleventh Alaska Sci. Conf.

 

Pillmore, C. L., 1956, Map of Salt Chuck area, Prince of
Wales Island, Alaska, showing linear features as seen
on aerial photos: U. S. G. S. Misc. Geol. Invest.

Map 1—230.

, and Kathleen, McQueen, 1956, Map of Hollis area:
U. S. G. S. Misc. Geol. Invest. Map I-231, I-232.

 

Pollack, V., 1917, Concerning slides in soils of glacial
origin: Geol. Reichasnstadt, Wein, v. 67, heft 3 and 4.

Price, P. H., 1954, The landslide problem in the con—
struction and maintenance of highways in W. Virginia:
ln_Morris Harvey 0011., Highway Engineering, 4th Annu.
Symposium, pp. 54-65.

178

Putnam, W. C., and Sharp, R. P., 1940, Landslides and
earthflows near Ventura, California: Geogr. Rev.,
v. 30, pp. 591—600.

Rapp, Anders, 1961, Recent development of mountain slopes
in Karkevagg andsurroundings, northern Scandinavia:
Geografisca Annaler, V. 42,.pt. 2—3, pp. 73-200,
Stockholm. '

Richmond, G. M., 1965, Glaciation of the Rocky Mountains:
in The Quaternary of the United States, ed. H. E.
Wright and D. C. Frey, Princeton Univ. Press.

Roem, J. C., Alaska Territorial Mining Engineer, unpub-
lished report dated June 2, 1938 concerning the
Harris River and Maybeso Creek areas: on file at
Alaska Div. of Mines and Mineral Resources, Juneau.

Rossman, D. C., 1956, Recon. total intensity aeromag. map
of southern part of Pr. of Wales Island, Alaska:
U. S. G. S. Geophys. Invest. Map. GP 135.

Sainsbury, C. L., 1961, Geology of part of Prince of Wales
Island, Alaska: U. S. G. S. Bull. 1058-H, pp. 299—
362.

Scheidegger, A. E., 1960, The physics of flow through porous
media: MacMillan Co., N. Y., 313 pp.

Sharpe, C. F. S., 1960, Landslides and related phenomena:
Pageant Books, Inc., N. J., 137 pp.

Smith, G. K., 1953, Erosional.processes and landforms in
Badlands National Monument, So. Dakota: ONR Project
NR 389—042: Tech. Rep. 4, 128 pp.

Smith, Phillip, 1939, Areal Geology of Alaska: U. S.
Geol. Surv. Prof. Paper 192.

SOWers, G. B., and Sowers, G. F., 1951, Introductory soil
mechanics and foundations, McMillan Co., N. Y.

State of Alaska, Dep. of Highways, Proj. S—0294(1)
completed 1967.

Stearns, H. T., 1941, Shore benches on North Pacific is-
lands: G. S. A. Bu11., v. 51, pp. 773—780.

Stevens, M. E., 1964, Unpublished report on the Hollis
soil survey area: U. S. Forest Serv., on file at
No. Forest Exp. Sta., Juneau.

179

Strahler, A. N., 1952, Hypsometric (area-altitude) analysis
of erosional tOpography: G. S. A. Bull., v. 63,
pp. 1117-1142.

, 1954, Statistical analysis in geomorphic re-
search: J. Geo1., v. 12, No. 1, 11. 1-25.

 

, 1954, Reliability of simplified slope sampling
methods: [abs.] G. S. A. Bull., v. 65, No. 12, pt.
2, 1. 1310.

 

, 1956, Quantitative slope analysis: G. S. A.
Bull., v. 67, No. 5, pp. 571—596.

 

, 1957, Quantitative analysis of watershed geo-
morphology: Amer. Geophys. Union Trans., v. 38,

pp. 913—920.

Tan, E. K., 1947, Stability of soil slopes: Amer. Soc.
Civil Eng. Proc., v. 73, pp. 19-38.

 

Taylor, R. F., 1929, Pocket guide to Alaska trees:
U. S. D. A. Misc. Publication 55, 16 pp.

, 1932, The successional trend and its relation to
second-growth forests in southeastern Alaska:
Ecology, v. 13, 11. 381-391.

 

Terzaghi, Karl, 1943, Theoretical soil mechanics: John
Wiley and Sons, Inc., N. Y., 510 pp.

, 1950, Mechanism of.landslides: in application

of geology to engineering practice: G. S. A.,
Berkeley Vol., pp. 83—123.

 

, and Peck, R. B., 1960, Soil mechanics in engineer—
ing practice: John Wiley and Sons, Inc., N. Y., 566 pp.

 

Thomas, E. S., 1939, Landslide forms in the middle coast
ranges: Berkeley Univ. of Calif. Library, unpublished
M. S. thesis.

Tomkin, J. M., and Britt, S. H., 1951, Landslides, a
selected annotated bibliography: Highway Res. Board
Bibliogr. 10, Wash., D. C.

Trask, P. D., 1955, Some applications of geology in soil
mechanics and foundation engineering: Amer. Soc.
Civil Eng. Proc., v. 80, separate 477, 21 pp.

180

Trask, P. D., 1958, Effect of clay contention strength
of soils: Ch. 50 of Johnson, J. W., ed., "Coastal
Engineering," 6th Conf. Proc., Dec. 1957, pp. 827-843.

Twenhofel, W. S., 1952, Recent shoreline changes along the
Pacific Coast of Alaska: Amer. J. Sci., v. 250, pp.
523—548.

, and Sainsbury, C. C., 1958, Fault patterns in
southeastern Alaska: G. S. A. Bull., v. 69, No. 11,
pp. 1431-1442.

 

Van Burkalow, 1945, Angle of repose and angle of sliding
friction, an experimental study: G. S. A. Bull., v.

56. pp. 669—705.

Wagner, N. R. T., 1944, A slide area in the Little Salmon-
River canyon, Idaho: Econ. Geol., v. 39, pp. 349-358.

Wahlstrom, E. E., 1955, Petrographic mineralogy: John Wiley
and Sons, Inc., N. Y., 408 pp.

Waldon, H. H., Mullineaux, D. R., and Crandell, D. R., 1957,
Age of Vashon glaciation in the southern and central
parts of Puget Sound Basin, Washington: G. S. A. Bull.,
v. 68, pp. 1849—1850.

Ward, W. H., 1945, Stability of natural slopes, Geogr. J.,
v. 105, pp. 170—197.

Weller, J. M., 1960, Glossary of geology and related sci—
ences: 2nd edition, Amer. Geol. Inst., Wash., D. C.

Williams, Howell, 1958, Landscapes of Alaska, their geo—
logic evolution; Berkeley Univ. Calif. Press, 148 pp.

Wright, C. W., 1909, Mining in southeastern Alaska:
U. S. G. S. Bull. 379, pp. 67—86.

Wright, F. E., and Wright, C. W., 1908, The Ketchikan and
Wrangell mining districts, Alaska: U. S. G. S.
Bull. 347, 210 pp.

Wu, T. H., 1966, Soil mechanics: Allyn and Bacon, Boston.

 

APPENDICES

181

 

APPENDIX A

SAMPLE CALCULATION OF FACTOR OF SAFETY

USING A UNIT BLOCK ON A PLANE SURFACE

182

A simple check can be made on the results of the

method of slices by analyzing the forces acting on a block

having the soil and slope characteristics of unit thickness

The results are certainly

on a slope of infinite length.

less exact but provide an index of the correct magnitude

of forces involved.

h

'''''' \\\\\\\\\.

 

 

\\\\
. \ \
\AWWWW\\\\WNW\\\\\\\\

= 3
ysat. 111 lbs/ft

7= 37°

3 ft

a = 37°

183

184

Thus, in Maybeso valley,

I = ’ ‘ = h ' = h
AW Slna Ysat. Slnd AW Ysat.
:: = h

0 AW cosa Ysat. COSd

_ = _ s

O (Ysat h ywh) co c

S = 7 * 3 tan?

 

at failure F = l

1 = C + (Ysa h — ywh) cosc tan¢

 

thus, YZat. h sinc
C = Ysat. h sino — (Ysat. h — ywh) ooso tan¢
= (111) (3) (.602) — [(111)(3) - (62.4)(3)1[.7991[.7541
= (200.46) — (333.00 - 187.2) (.799) (.544)
— (145.8) (.602)
Ca = 112.631 lbs/ft2

using this value of CA, F, in the absence of pore-water

. . fl _ 112,00 + 200.46 _
pressures - 200.00 _ 1.56.

 

APPENDIX'B

DIAGRAMS, DATA, AND CALCULATIONS FOR MECHANICAL

ANALYSIS OF SLIDE AREAS l, 2, AND 3 (MAP 3)

185

 

186

 

mo.oomw
mm H u -.aena + ma.mmem u possessoo =sse: as Haom new: a

. . He.aamm I
as H - me.emaa + Aaowama.amv .

Amusmmoum noum3lonoa on .cowumusumm umv m .Amuv mDHm> mfinu wean:

 

II
N
U

.um.nwfl\§ma.mm

Ho I do H MD
NN.mmem . .ou.sea\emfi.ammm u .um.sea\eae.amam I

.wcfiumnmao ousmmoua noumslmuoa Susanna spas .ouaawwu u<

mu coamonoo ucouwamm no 6H as comma

on ooze mocmuomwflp mnu .mSSu .Acowuwcwmop hnv H n m .mufiawmm u<

 

 

 

 

ousmmoum .um.cwa\§ac.nmmm

poumalouoa SDwamE um o w0 w m waHESmmm mom. u .uu.aHH\*mH.mmmm+c n m
mn.qmo~ N~.aqmn Hq.nmmw mo.oomm aa.mmmm . oo.Ho
nm.¢¢a Nm.¢ma oo.HHH oo.mOH mm.wq mmo. com. com. HH.¢~ oo.-~ oo.oom mm.~ea o~.Hm mm.q, cm.o 0.0m oo.~ ma
oa.¢mm mo.on ~q.qm~ mm.-~ HH.me one. man. 0mm. om.ow~ om.mmm oo.mam oa.wo~ mn.o~ om.m m~.H o.~m oo.m «a
no.0mq mn.mmq N~.mmm ww.qom mm.mmm mmo. mmw. new. cm.aom om.HNm om.moo qo.amm he.ooa om.m Ho.H o.mm om.o ma
«H.Nwm wa.oqm um.~qm cm.~om mm.qmm mac. mam. «mm. oo.mno om.mqm om.mmw om.moe H¢.Nma om.m mH.~ o.mm ow.w NH
o¢.Hoo mo.mnm o¢.Hoo mo.mmm mq.oN~ moo. mas. Noe. cm.mq¢ oo.oom oo.mmm cm.mqm «c.0qa m~.m mm.~ 0.5m oo.m HH
mm.m~n oo.mho «H.Nmm mm.~mo Hw.mmm «mm. wwm. oao. on.moo oo.H~NH oo.mmHH o~.mHo Ha.qoa mm.m mo.m o.wn oo.HH OH
mo.wq~ NH.qme Nm.~ow mo.mqn HH.mmm 0mm. 5mm. mmo. mm.moo ow.o-~ om.owHH ~¢.m~o Hm.mma mm.m ww.~ o.mm om.HH m
mo.nno na.mam mo.omm mn.qm~ Hm.omm mam. com. moo. om.mwm oo.NmmH oo.omNH om.men om.swa oo.q oo.m o.oe oo.~H m
ma.nmo na.man we.omw mn.qmn Hm.omm sum. con. new. o~.mmm oo.NmmH oo.omma ow.wqm o~.mma oo.¢ oo.m o.oo oo.NH n
Hm.mmn mN.moN on.mmm ~w.oaw cw.amm mom. mmm. owe. om.mwm oo.NmmH oo.omNH ow.qu om.mwa oo.q oo.m o.H¢ oo.~H o
o~.mwc w¢.cmo mw.oaw wa.mmm mm.oam com. me“. ace. No.oam oo.HNNH oo.MMHH mm.H0m em.m~H oo.¢ Hw.~ o.Nq oo.HH m
om.Hmo ma.owm No.oam so.Hmm mo.omm New. mam. moo. wq.mmq om.moHH om.HmOH No.mmo ow.~oa mN.e Ho.m o.qq om.oa q
on.~mm mu.~am ma.mmn em.m0m 05.0mm own. map. mam. mm.mmq 0m.smoH om.msm mm.mnm mm.mma om.q mo.~ o.oe om.a m
mn.HmN oo.mm~ mH.Hnm mm.qem qa.ma com. ace. men. oo.om 0m.ome om.moq oo.eqq oo.mm m~.e on.a o.wq ow.q N
50.noH Hm.mm ow.mma an.~ma Nw.m I mwe. moo. cos. oo.NH I oo.-m oo.ooN oo.emm om.oe oo.m m~.o 0.0m oo.~ H
\wmdu mama scam 3c dcfim 3< acmu dmoo was» omoo dmoo dawn um.:fia\* .uw.caa\* .uw.sfla\§ .um.cwa\* N.uM\§ A.qu A.uwv d Am.uwv dOHuomm
dmoo 3< dmoo 3< nos App A4<1|3<v qunzq no: 3n map 34 Ad: 1 A< a: mwu¢

uoz zap um; um: mwmpm><

 

m.oa\eaaa u hos» um.uu\amoH u see» meme. u same no u o mosm u e

 

187

 

‘1 ‘4 ‘

 

  
        

.. ..x. manna»... . .H. ... . ///////// //////////////////////////////
000.0...mm1u .... .0.-. /////// ///// // ////// // //// ///////////////

.. ......m...”Q.....0.....t..-0......A.V...nV 0.. ////////////////////// //// ///////////l/

a sOflWow . .0“. n... // // //////// // / /// //// /// ////// ///////
6 / ... o00.0.0.o . ///// /////////////////////////////I///
/.W.... ...fiO....0..ow0.o.. / // // //////////////// ////////////// //

. . ... . ....HJ ”m5. 0.. /// // // ///////// /// //// ///./ /////l //
A , -mrou. . ..rpWO..o. $0. .. //// // //////// //// ////////// // // ///
l .o .6... . -

. .... WUoOOOQ ././////////////////////////

.2 tixn .. //////////////[l /////L//
0. .

’ o
o O
.0...“ .vfl.....0.....o...o..o
...... ”.320... we}. ...0 //////////// //// // // //
’0. 0:... .0de . ... . // //// //// //// // // I/ /
0.. .u .. .....0 .
.. .0....

I o
o o .. o . .
.DUo. ...0 . ”0.. ////////////////////////////
I... W..............0....a..O.......Q...O..o.. . ////// /// //// // //// //.//// //
. 9 . . .

    

..oo... .. / //////////// // // ////
.. ..0. .. /// //////// ////////
JO... 01120.0 .// // ////////////// /
.ooo . tom! //////// // // //////
..MO..0..o....0........u.//////////// ////
, ...4. 0 . ”n.0,”! //// ///// /// ///
2.0....0001. .00. I /// // ////// //
....tmumonu... .. .....O ... // // //// // //
........0... 01......0 ..O. //// //// ///

0 info)?! ..pi/ ////// ////
#0.. ......o..0&... fl/x/ H/ fl/ ///
. 23.0.. / / ///
.0: n .ooltau 0.. ..
.1... o. ...:01 10.0.1 l///////
.00. 00 "as! .0 $5.:

l.o.%..o.......- f???
«a.» nap ".....il.
:33 0.0.: .0 v..-

. ...O. No.00... .... . ///////
Nauru... ....:..
_ no . .. a

00'” 2 at... .0 0.0:.

  
    
 

1w. WW... /////

 

meuuwmoum HHom HmUHmhsa Ou pwumHmu

uos omsmo Hmcumuxw am oh xHHmQHoaHua one mo aOHmonoo ucmummmm

am mm sow pouaaooom on ado 05Hm> :uwcouum Macaw GH moaoHUmep use

en.qm¢HH

N©.H u u m

mH.anHH + em.mm¢m Hmsvo one mmwuum ummnm paw nuwamuum nmonm mumsS

 

 

 

 

ee.emeHH . . - e.me u m
u as oe\ee mm 1 . - . o
ma.seoaa + Ho.emVHa.mwv a oosom = s: as Hush sun: N as same am NNMNH .
an.-m~H am.-m~H am.NNmNH u H u s

 

He.ewme + He.wmvmm

mm cOHmmsoo ucoummmm do aH a: amxwu
on ones ooewuwmep can mscu .HaOHuHcHwop znv H u m ousHHMw u<

.em.H u H~.HmaHH + em.mmem u H~.HmmHH + Ho.wonm.mmo u a

musmmmum poum3louom 0>Huom on us: GOHumusumm u<

.mHHom msu GH wGHuoaonm uoou mo uHsmou

 

 

188

 

ecu on Ou po>oHHmn mH was N.uw\*qw mHoumaHxOHQQM mHssvm mm we o=Ha> mHAH whammmua nonmanonoa asamea um o u w m waflasmmm com. u ¢qummmw u m
HN.HmoHH mH.moOHH mm.NNmNH qu.meHH Hq.oqu oo.ww
mm.me mw.mmH mm.mHH mm.on mm.~n mwo. ooa. mmq. oa.mOH om.mmm om.mmm oo.HmH o~.Hm om.m on. o.mN om.~ mN
mo.mm~ H<.mmm m~.q@H m~.owH mm.mHH mmo. com. com. mq.¢NH om.mwm om.oom mo.qHN mH.Ho om.m mm. 0.0m om.m NN
mo.¢mm oo.m~m mH.¢o~ ma.-~ oo.NoH one. mew. 0mm. Ho.mmm oo.mmm oo.mHm om.Hom HH.ow om.m mm.H o.Nm oo.m HN
Hn.omq mm.m~q NN.mmm ww.<om Hm.qH~ mmo. mmw. new. Hc.¢mm om.HN~ om.moo mm.me wo.oOH oo.m om.H o.mm om.o 0N
Hm.omm Hw.qu mm.mo¢ mw.Hm¢ mq.n- mNo. me. mmm. mm.mom om.mmm om.Nnm No.wo¢_ no.0NH omen mo.m o.¢m om.m mH
Hm.Nmm qm.oqm em.n¢m mq.wom mN.moN 0H0. me. cum. Hw.qm¢ oo.qmm ow.mww @N.mHm om.NoH On.m m~.N o.mm oo.w wH
¢m.¢oo me.mom H¢.mmm wo.mqm am.mmm OHo. mow. wmm. wo.mH¢ oo.m¢m oo.HNm um.owm mm.cmH mn.m mq.N 0.0m oo.m NH
om.mco Mn.mHo mo.¢mo mm.mmm ow.mw~ 0H0. mow. wwm. em.moc om.mmOH oq.mOOH om.owo om.moH mm.m mo.~ 0.0m ow.m 0H
mo.H0m oo.Hmo mo.Hom oo.Hmo qm.qu Noe. mas. Noe. 0H.NNm om.moHH om.Hw0H <m.mqo oo.HmH mn.m mn.N 0.5m om.OH mH
so.mmn mo.~wo qo.mmH no.Nwo nq.mmm Noe. mam. Noe. qm.mmm oo.H~NH oo.mMHH oo.wco qw.mmH mn.m mw.N 0.5m -oo.HH «H
nN.mNm oo.mNc qH.Nmm mm.m¢o w~.w0m «mm. wwm. oHo. oo.aHm oo.H~NH oo.MMHH oo.~o~ om.an mn.m oo.m o.wm oo.HH MH
nm.mm~ oo.mmo «H.Nmm mm.m¢c m~.wom cam. was. oHc. oo.aHm oo.HNNH oo.mmHH oo.Nom o~.~wH m~.m oo.m o.wm oo.HH NH
mo.NHn 55.000 o¢.wmm «N.mwo OH.mmN can. wwm. 0H0. ow.oo¢+ ow.meH c<.NHHH oo.~o~ o~.~wH mm.m oo.m o.wm ow.0H HH
wo.~wo o~.mmo oH.mmm o~.owo om.m- own. mum. owe. om.mmq+ 0m.moHH om.HwOH qH.omc wo.cwH mm.m mm.~ o.mm om.0H OH
sm.aoo me.HNe eH.eHA Hm.soo wo.m- own. ass. aNo. e~.oae+ om.meHH om.oooH eo.soe om.sHH me.m mw.~ o.mm om.OH a
wN.mno om.ooo oo.wNn sm.mmo OH.ooN mum. can. moo. mm.omq+ 0N.NMHH oo.OmOH Hq.Hwo NH.qu om.m om.~ o.os o~.0H w
5c.ooo Hm.qam mn.an mN.Noo om.qm~ mum. con. mew. no.qu+ oo.OHHH 00.0m0H mm.woo om.noH oo.¢ we.~ o.oq oo.OH m
m¢.wom on.m~m qm.mmo HH.woo mm.MHN aom. mmn. owe. oo.mmm+ oo.moa oo.mmm oo.qNo oo.omH oo.¢ om.~ o.H¢ oo.m o
om.mNm w~.owq o~.Hmo Hm.mwm mo.mm~ oom. men. moo. Hm.mmm+ ow.mqo om.mmw mH.qqm mw.~mH oo.q wH.N o.~q om.w m
w~.moe w~.ao< ON.non mo.ohq mN.HqH Hmm. Hm“. Nwo. om.omm+ oh.qu oH.omo om.qu oo.oHH o~.q om.H o.mq 05.0 q
«w.~Hm aN.om~ mH.Hoq q~.~mm om.ow New. mHn. mac. mm.moH+ o~.mmm oo.mmm NN.HHq Nu.oo mm.q mm.H o.qq o~.m m
mq.an Om.q0H m¢.mmm eq.wHN om.- mmm. men. New. wo.me + oo.mmm oo.mom mo.mw~ No.mo om.q Ho.H o.m¢ oo.m N
0H.wn ma.mm Hw.on mo.cm oo.mm I own. mac. mHm. mo.mc I oo.HHH oo.m0H ao.omH ao.wm om.q No. o.o< oo.H H
xmwamu wcmu och 3d ach 3d .Wswu omoo menu omou dmou caHm .uw.nHH\a .um.:HH\§ .um.cHH\* .uw.:HH\§ N.uM\§.IN.umV.IIN.wwv o AN.umv GOHuowm
ewoo 3a smoo :4 oos sue Haasuzav q<suaa hos 34 ans 3a an; s as e mou<

um: App up: uoi wwmuo><

 

 

m.ou\eHHH u nos» mm.oe\emoH u see» Home. u echo no u u loam u m

N uvHHm

189

 

 

90 feet
slope: 38°

radius: 2.0 {eet
depth to slide surface: 3 feet

or: of circle with

cord of are:
angle ef

2

U
D
-
d
“

 

5

 

 

1.9(3

 

 

 

 

HwMSmmmum Mmumslouoa o: .:0Humu=umm umv m .00 waHm> mH:u wdeD
. I 0H.H5 n a

N “0:30 - 3.38 - $430 0

no uOHmonou udwpmunm an nH a: nuxmu

wn umsfi muuwumwva mnu wanu|.AGOHqume0 000 H u m UHDHHmw ad

 

 

 

 

 

whammwum nwumalwuoa asaHnms am 0 n w m mnHfismmm 000. u MM.MMMW u 0
05.0000 00.0000 00.0000 00.H000 H0.0000 0H.H5
m0.H0 0H.50 -.~m 05.00 0H.~0 000. H00. H00. 05.00 00.00 00.00 00.00 . mN.HH 00.0 0H. 0.00 00. 0H
00.00H 50.05H N0.00H 00.5HH 00.50 000. 000. 000. 05.50H 00.55N 00.500 05.00H 00.00 00.0 05. 0.00 00.N 0H
00.000 00.000 00.000 00.HON 05.55H ~50. H00. 000. 00.00N 00.000 00.000 00.000 05.05 00.0 0~.H 0.50 00.0 5H
00.H00 50.000 ~5.0Hm 0H.000 00.000 000. 050. 000. 00.000 00.000 00.000 05.000 00.50 00.0 00.H 0.00 00.0 0H
00.000 00.000 00.000 0~.0H0 5H.50~ 000. 000. 000. 00.000 00.000 00.055 50.000 N0.0NH 00.0 H0.~ 0.00 00.5 0H
00.000 «0.000 00.000 0H.000 00.55N 000. 500. 0H0. 00.000 00.000 0N.000 00.000 «0.00H 00.0 00.0 0.Hm 100.0 0H
00.000 0H.NHO 00.500 ~H.500 05.000 000. 000. 000. 00.000 00.000H 00.500 00.000 50.50H 00.0 00.0 0.00 00.0 0H
00.050 H0.0N0 00.000 05.000 05.050 000. 000. 000. HH.0m0 00.000H 00.000 00.Hm0 00.00H 05.0 05.0 0.00 00.0 NH
00.0N5 00.050 00.000 H0.H00 00.000 000. 000. 000. 00.0H0 00.00HH 00.HO0H 00.000 N5.05H 05.0 00.0 0.00 00.0H HH
00.005 0H.005 00.000 00.005 50.000 0H0. 0H0. 050. 00.000 00.H~NH 00.00HH 0H.000 00.00H 05.0 00.0 0.00 00.HH 0H
H0.005 mH.H00 00.000 00.5H5 00.0Hm 0H0. 000. 000. 00.0H0 00.HNNH 00.00HH 00.005 00.50H 05.0 00.0 0.00 00.HH 0
H0.005 0H.H00 00.000 00.5H5 ~H.0Hm 0H0. 000. 000. 00.HNO 00.H-H 00.00HH 00.000 00.00H 00.0 00.0 0.00 00.HH 0
m0.H05 00.H00 00.H00 m0.H05 00.050 ~00. 005. 000. 0H.000 00.00HH 00.HO0H 0m.HH5 00.55H 00.0 00.0 0.50 00.0H 5
00.5H0 00.050 00.0H0 00.000 00.000 000. 555. 000. 00.000 00.000H 00.050 00.050 00.00H 00.0 05.0 0.00 00.0 0
00.050 00.000 00.000 00.000 00.0HN 550. 005. 000. 00.050 00.000 00.500 H0.0H0 05.00H 00.0 00.0 0.00 00.0 0
00.000 0H.500 00.500 00.500 0H.00H 000. 005. 000. 0H.000 00.000 00.000 00.H00 H0.NmH 00.0 0H.~ 0.H0 00.5 0
00.000 «0.050 00.500 00.000 H0.00H 000. 005. 000. 50.50~+ 00.HN5 00.000 00.000 00.00H 00.0 05.H 0.00 00.0 m
H0.N0~ 00.0HN 00.000 50.50N 00.00 H00. H05. ~00. 00.00 + 00.HNO o0.Hmm 00.Hmm 00.05 00.0 0~.H 0.00 00.0 N
HN.05 50.05 00.00 00.00H HH.~ ~00. 0H5. 000. 00.0 + 00.00H 00.00H 00.00H 0~.Hm 00.0 00. 0.00 om.H H

\kMdMQ w:Mu cch 3Q ccHw 3< many umOU WGMu amoo awou anm .uw.=HH\0 .u0.:HH\0 .uw.:HH\0 .uw.:HH\0 u.u0\0 n.qu A.uwv U Am.uwv aowuuwm
.88 30 $8 30 3: Eu 30.723 03-34 33 30 .Cn 34 .2: n 04 an $2
003 xuv go: uwB wmmnw><
mdtij u $3» ”MJMESH u 0:: m005. u 0:3 me u p “.50 u 0

m mUHHm

 

nuns -
w

 

191

 

 

  

 

.
-
fl
0
U
3 u
a. 0 t
*3 " a 0
’2 5 g
.. ‘ on
3" .c ;: 2.
9
~‘.' 3 - °
.0: C O C
”on 0 0- a
t -
0‘ .1: O
B ‘0 o- a
V“ n. I. o
B u ‘ fl

 

APPENDIX C

DEVELOPMENT AND USES OF AN ISOSINAL CONTOUR MAP

(After Arthur N. Strahler)

192

Procedure:

1.

3.

On a map of relatively large scale (in case of

the Maybeso valley, approximately l/3l,680 is

the only map available) locate all of the major

slides.

On an acetate overlay locate a large number of

points for which the amount of lepe can be

adequately determined.

8..

Slope determination is made with dividers
set at a specified interval corresponding
to a predetermined ground distance. At

any point "p" where slope is desired, the
divider is set down on a line normal to

the contours and equi-distant on either
side of ”p". The drop in elevation is then
determined by counting contours and parts

thereof intersected by the line.

After the slope is determined for each point,

calculate the sine of the angle of slope:

 

 

MPH
c B( b
° = a_C_
SinB ab

193

 

19“

These values are then recorded on the overlay and

contoured as an isosinal map.

Theory:

The sine of the angle of slope represents that part
of the total gravitational force which tends to produce
downhill sliding or flowage of rock particles or fluids
on the surface.

Consider a soil particle at "p" affected by forces
Fg = mg, FS or y (shear stress) and Fn or o, a force normal

to the slope surface. FS and Fn are the components of F

by geometry, 8 = ¢

F
sin¢ = FE fiL
8 g

 

 

or y = ngin¢ F sinB = mgsinB

8

When considering a unit mass, the.downslope force
is equal to gsinB. The sin contour map tells the distri-
bution of that part of the gravitational acceleration g.
contributing to the downlepe force at any given point on

the surface.

 

'II- -I

195

Practical Application:

Where viscous fluids or plastic solids flow down-
slope, the isosinal map may supply the relative value of
the shearing force to which the rate of shear is directly
proportional. In the case of plastic solids following

Bingham's Law:

%% is the rate of’Shear (u is velocity, y is depth).
F
This is equal to —§—§—£, where FS or y is the shear—

ing force exerted by the action of mg = Fg; (i.e.,

that force represented by the ososinal lines); f

is the yield stress of the soil or the shearing

strength and is dependent to a certain extent on

water content of the soil; and v is consistancy or

unconfined compressive strength of the clays.
Assuming that Fg remains constant for a given location on.
the slope, the value of f will vary according to moisture
content of the soil and will range from greater than to
less than y. If greater than y no sliding occurs. If less
than y sliding is eminent. The critical isosinal line then
will be the line representing that value of y for which f
is equal. This value of f will have to be arrived at by
taking measurements of shearing strength of the soils at
different water contents.

NOTE: The critical value of y will be altered drasti-
cally from the ideal considered if the pore—water pressure
in the subsurface is found to be appreciable. It will reduce
Fg by its counteracting upward action and thus reduce y and

subsequently reduce the critical value of f and the isosine.

APPENDIX D

BRIEF GLOSSARY OF TERMS

196

BRIEF GLOSSARY OF TERMS

(With some references compatible with Glossary of
geology and related sciences, 1960, E. N. Munns,
ed.; and the Forestry terminology, 1960, J. M.
Weller, ed.)

ablation moraine.--drift believed to have been deposited
from a superglacial position through the melting of
underlying stagnant ice.

 

age.--formal geologic time-stratigraphic unit correspond—
ing to a stage.

angle of internal friction.-—the angle at which the driving
forces in a soil mass due to gravity are equal and
opposite to the resisting forces due.to friction.
It is a measure of the strength of‘a soil due to the
interlocking of the individual soil grains.

 

angle of repose.-—(l) the maximum angle at which a material
such as soil or loose rock remains stable [A.G.I.],
(2) the angle at which loose material will stand when
piled (Van Burkalow), (3) slope angle below which
mass wastage by creep occurs.

 

andesite.-—a volcanic rock (extrusive igneous rock) composed
essentially of andesine and one or more mafic.minerals.

 

andesine.——a variety of plagioclase feldspar high in sodium.

 

anticline.——an upfold or arch of rock strata dipping in
opposite directions from an axis.

 

anticlinorium.——a series of anticlines and synclines so
arranged structurally that together they form a general
arch or anticline. Often with superimposed minor folds.

 

Atterberg limits.-—to aid in eliminating the personal factor
in describing soil consistency, A. Atterberg arbitrarily
established three stages of consistency for fine-«
grained soils. These are liquid, plastic, and solid
states. These states are defined by limits of water
content and deformation characteristics. Thus, liquid
limit is defined as the water content at which a soil
has such small shearing strength that it flows to close

 

197

198

a groove of standard width after jarring in a
specified manner. The plastic limit is the water
content at which the water content at which the soil
begins to crumble when rolled into threads of speci—
fied size. The shrinkage limit is the water content
that is just sufficient to fill the pores when the
soil is reduced to its minimum volume by drying.

argillite.——a dark, sometimes organic rock derived either
from a siltstone, claystone, or shale that has
undergone a somewhat higher degree of induration
than is present in those rocks.

 

avalanche scar.--as used in this paper, avalanche scar
refers to the zone of initial failure of the slope,
however, in.some cases the term could also include
the channel produced by the avalanche.

 

bedding plane.-—in sedimentary or stratified rocks, the
divisions which separate the individual layers, beds,
or strata.

 

bench.-—a small terrace or comparatively level platform
breaking the continuity of a declivity or slope.

' berm.——a side—valley shoulder in till or bedrock.

bifurcation ratio.-—the ratio of.number of stream segments
of one order to the number of segments of the next
highest order. This is a dimensionless number for
expressing the form of a drainage system. Most use—
ful where powerful geologic or structural controls
dominate.

 

breccia.--a fragmental rock whose components are sharply
angular and not water deposited, as distinguished
from fanglomerates and conglomerates whose components
are slightly to greatly waterworn.

butte,--a detached hill or ridge that rises abruptly; a
"knob."

Cenozoic Era.--the latest of six main eras into which geo-
logic time is sometimes divided. It extends from the
close of the Mesozoic Era to and including the pre—
sent, and includes Tertiary and Quaternary Periods.
Began approximately 70 million y.b.p.

 

clearcutting.—-(l) an area on which the entire timber
stand has been cut; (2) removal of the entire stand
in one cut.

 

 

 

199

cirque.——a deep, steep-walled amphitheater or-bowlsshaped
recess in a mountain, caused by glacial erosion.

cirque threshold.--a bedrock sill or threshold at the
mouth of a cirque resulting from reduction in glacial
erosion near a cirque glacier's terminus.

 

cohesion.--the capacity of stocking or adhering together.
In effect, the cohesion of soil or rock is that part
of its shear strength which does not depend on inter—
particle friction.

 

colluvium.——a general term applied to loose, incoherent
deposits on a slope brought there chiefly by gravity.

 

conformable contact.——the place or surface where two differ-
ent kinds of rocks come together with no evidence of
disturbance or erosion taking place between their
times of deposition.

 

conglomerate.—-round, waterworn fragments of rock.or pebbles
generally comented together by another mineral substance.

 

consequent stream.-—one which follows a course that is a
direct consequence of the original slope of surface
on which it developed.

 

craton.--a large relatively immobile part of the earth which
has maintained its position and elevation throughout
most geologic time.

debris avalanche.——the sudden movement downslope of the soil.
mantle on steep slopes caused by its complete saturation,
through protracted heavy rains.> Usually results in a
gully-like erosion scar.

 

debris flow.——(l) a mass of water—lubricated debris moving
much like wet concrete; (2) a general designation~
for all types of rapid flow involving debris of
various kinds and conditions.

 

diorite.——a plutonic rock composed essentially of soda.
plagioclase (usually andesine) and hornblende, biotite,
or pyroxene.

dip.——the angle at which a stratum or any planar feature
is inclined from the horizontal. The dip is at right
angles to the strike.

dip—slip fault.--a fault in which the net movement is
practically in the line of the fault.

 

200

drift.-—any rock material such as boulders, till, gravel,
sand, or clay transported and deposited by a glacier,
or associated glacio—fluvial or glacio-lacustrine"
processes.

drumlinoid form.—-features having the form of a drumlin.
A streamlined elongated form produced either by
erosion or deposition by overriding ice.

 

effective stress.--stress which tends to cause compression
or deformation of the solid phase of the soil.

 

 

end moraine.—-a ridge—like accumulation of drift built along
the margin of a valley glacier or ice sheet.

 

epoch.——a subdivision of a period of geologic time corres-
ponding to a stratigraphic series.

 

era.——in general, the largest division of geologic time
usually representing hundreds of millions of years;
specifically, a division of geologic time of the.
highest order comprising one or more periods.

eugeosyncline.—-an orthogeosyncline in which volcanic rocks
are abundant, and characterized by island arcs.

 

facies.—-the continuity represented by a descrete geological
unit of sedimentation characterized by a similar
mineral composition, type of bedding, fossil content,
etc.

factor of safety.——the index of stability with respect to
a sudden failure. It is the ratio of potential re-
sisting forces to the forces tending to cause movement.

 

Fanglomerate.-—angular, water deposited aggregate of mixed
material similar to conglomerate except that fragments
are still angular to subangular, conoting a nearby
source or provinence. Similar in appearance to
glacial till.

 

fault.—-a fracture or fracture zone in earth materials along
which there has been displacement of one side relative‘
to another on a surface parallel to the fracture. Dis-
placement may be in inches or miles.

geanticline.—~a broad uplift, generally referring to the
land mass from which sediments in a geosyncline are
derived.

 

geosyncline.--large, generally linear trough that subsided
deeply during a long period of geologic time in which
a thick succession of stratified sediments and possibly
extrusive volcanic rocks commonly accumulated.

 

201

glacieret.--(l) a small simple alpine glacier; (2) a very
small glacier on a mountain slope or in a cirque.

 

greywacke.--a rock composed of angular to sub-rounded
grains of quartz, and small fragments of siliceous
slates, phyllites, and other rocks with contained
grains of feldspar and ferromagnesian minerals
(mica, amphiboles, pyroxenes) usually bonded to-
gether in a matrix of clay and silica.

 

ground moraine.--(l) sedimentalogically this is the material
carried forward in and beneath the ice and finally
deposited from its undersurface. Lodgment till is
a compact and highly stressed version of ground mor-
aine; (2) a moraine of low relief devoid of trans-
verse linear elements. Till plain is an equivalent
term, though till plains may-also be covered with
ablation moraine.

 

Joint.-—a fracture or parting surface which interrupts
abruptly the physical continuity of a rock mass.
Joints which approximate a common strike and dip or
represent a common surface, even though warped, are
considered in a set.

Joint system.——two or more Joint sets or any group of Joints
with a characteristic pattern.

 

Karta soil.—-a relatively well-drained podzol soil in S.E.
Alaska derived from glacial till. The soil typically
has a light grey leached layer about one or two inches
thick lying beneath the surface organic zone or forest
litter. Beneath it is usually found a splotchy, red-
dish brown, iron—stained horizon. Underlying the
iron-stained horizon is unweathered till.

 

leave—strip.——a strip of timber left standing in a clear-
cutting to provide seed for future forest regeneration
by natural reproduction.

 

 

leucophyre.—-light-colored intrusive igneous rocks. In
this paper, applied to intrusive dikes of andesite
texture.

lithosol.——one of a group of azonal soils having no clearly
expressed soil morphology and consisting of a freshly
and impecfectly weathered mass of rock fragments.

 

Mesozoic Era.—-one of the grand divisions or eras of geo—
logic time, following the Paleozoic Era and suc-
ceeding the Cenozoic Era. Began approximately 300
million years b.p. and ended approximately 70 million
years b.p.

 

202

mollusk.-—an invertebrate belonging to the phylum Molluska,
and including clams, snails, and chambered nautiluses.

neutral stress.—-pressures in the bulk pore-water are
called neutral stresses in contrast to normal or
effective stress which acts independently in the
solid phase.

 

névé.—-area of retained snow that accumulates on high
mountains or in the nourishment zone of a glacier
and does not completely melt during the summer.
Note areal connotation of this term. The material
itself is called old snow (if density is 0.3 to 0.5
gms/u) and firm (if density 0.5 to 0.75gms/u).

Ordovician Period.-—the second of the periods comprising
the Paleozoic era. Began approximately 500 million
y.b.p.; ended approximately HMO million y.b.p.

 

orthogeosyncline.—-a long, narrow geosyncline, forming belts
adjoining the-stable craton.

 

Paleozoic Era.—-one of the major divisions of geologic time
following the pre-Cambian era and coming before the
Mesozoic era. Beginning approximately 600 million
y.b.p. and ending approximately 2-0 million y.b.p.

 

partings.——small joints and irregular planes at or near the
interfact between the B and C horizons of the Karta
soil.

 

pelecypod.--an invertebrate characterized by its bivalvular
exoskeleton. A class of the phylum Molluska°

 

period.-—the fundamental large unit of standard geologic
time usually represented in tens of millions of years,
and composed of a number of subperiods or epochs.
For example, the Ordovician period.

piezometer.--a device for measuring the height of-a piezo—
metric or static saturation zone surface.

 

piezometric head.——the head of water or water pressure at
a specific level of a piezometric surface.

 

piezometric surface.-—an imaginary surface that everywhere
coincides with the static level of water in an aquifer.

 

plastic equilibrium.--a body of material is in a state of
"plastic equilibrium" if every part of it is on the
verge of failure.

 

203

Pleistocene Epoch.-—the earlier of the two epochs com-
prising the Quarternary period. Also called the
Glacial epoch. Began 1 1/2 to 2 y.b.p. and ended
approximately 10,000 years ago. Many scientists
believe we may still be in the Pleistocene, in which
case the Pleistocene and Quaternary are synonymous.

 

pluton.--a body of igneous rock that has formed beneath
the surface of the earth by consolidation of magma.

podzol.——a highly bleached-often leached soil low in iron
and lime. It is formed under moist, cool climate.
conditions with considerable percolation of-ground—
water resulting in the removal of surface carbonates
and oxides.

pore—water pressure.-—pressure produced by the load of
water in the soil and transmitted to the base of the
soil stratum through the pore water. Also called
neutral pressure.

 

pro~glacial lake.—-a lake of glacial origin formed beyond
the frontal ice limits of a glacier. Sometimes called
a fosse marginal lake.

 

protalus rampart.--a ridge of detritus that accumulates by
sliding or rolling down over semi-permanent snowbanks.
They occur most commonly in cirques and are similar
in appearance to moraines.

 

radiocarbonA——an isotope of carbon, commonly designated,
as 01 .

 

radiocarbon date.-—the age of a material before preSent,
determined by measuring the proportion of the isotope
01“ in the carbon it contains.

 

rhythmite.--rhythmic laminations of a sedimentary deposit
not necessarily annual.

 

shale.——a laminated sediment in which the constituent
particles are predominantly of the clay fraction.

slash.——branches, brak, tops, chunks, cull logs, up-rooted
stumps, and broken or up-rooted trees left on the
ground after logging.

slate.--a fine-grained metamorphic rock possessing well-
developed cleavage. The metamorphosed equivalent
of a shale.

slip-out.——a small scale downhill movement of a mass of
soil under wet or saturated conditions.

 

 

204

Silurian Period.—-the third period of the Paleozoic era.
Beginning approximately 440 million y.b.p. and ending
approximately A00 million y.b.p.

 

stade.——time unit usually used when representing glacial'
deposits of lesser magnitude then a stage. It has
a somewhat variable time value from place to place.

stream order.--first order streams are the smallest un—-
branched tributaries; second order streams are
initiated by the confluence of two first order
streams, etc.

 

itrike.--the direction or hearing of a horizontal line in
the plane of an inclined stratum.

subsequent stream.--a stream course controlled mainly by
rock resistance--i.e., one which has grown.headward~
by retrogressive erosion along belts of weak structure,
this also represents streams which, having developed
in one cycle, persist in the same courses in a
following cycle.

 

syncline.--a fold in rocks in which the strata dip inward
from both sides toward the axis. The opposite of
anticline.

 

synclinorium.—-a compound syncline; a broad regional syncline'
on which are superimposed minor folds.

 

talus.--a collection of-fallen disintegrated material that
has formed a slope at the foot of a steeper declivity.

tarn.——a small mountain lake or pool, especially one that
occupies an ice—gouged basin on the floor.of a cirque.

terrace.-—a relatively flat, horizontal, or gently inclined
surface, sometimes narrow and long, which is bounded
on one side by a steeper ascending slope, and on the
other by a steeper descending s10pe. If in till or
bedrock, may be called a berm.

till.——nonsorted, nonstratified aggregate of sediment
carried or deposited by a glacier. If highly in-
durated, call a tillite.

 

till fabric.--a distinct and measurable orientation of the
particle elements of which till is composed.

 

 

 

205

Tolstoi soil.—-relatively shallow soils derived from

 

total

colluvium from bedrock on very steep (60-100%)
slopes. Soils are one to three feet deep; have a
grey, leached horizon beneath the organic matter
layer. Beneath this is splotchy, reddish brown
iron-stained horizon overlying fractured bedrock.

stress.——the total stress applied to a soil mass,

 

including both effective normal stress transmitted
through the solid phase of the soil and neutral.
stress transmitted through the bulk pore water.

unit weight.—-weight per unit volume of soil.-

 

unit dry weight.——weight of solids per unit of soil volume_

 

in its natural dry state.

 

unit wet weight.—-the total weight per unit volume of a

 

moist or wet soil.

varves.—-(l) any sedimentary bed or set of rhythmites or

laminations deposited within one year's time; (2) more
usually defined as a pair of contrasting laminae
representing seasonal sedimentation as summer (light)
and winter (dark) within a single year.

viscotplastic flow.--flowage within a solid body that takes

 

place without shearing or cracking.

 

   

 

 

 

l 7‘ ~ ‘ if 1'» "r ‘k n ... O Piezometers
13* * J" ‘F * * * ¥ ..‘t * 9‘ ¥*‘)( 0 soil sample sites
*L “- * "‘ "K "k k x * ’2 firiié‘ecifiilas
*J‘ * ‘ * X’ 4“ ‘* ’Is * 7‘ ’3 studied
41 ¥ # 1
:1 3,4 ’6 ¥~ X ‘3. -)< * 4, ‘K *- " legging
it -)t ‘3" " ’6 ¥ . / roads
9' ‘( x ‘ * * >(' ¥
'X- ‘X 3.}: 7‘ .. * Hmbered
1 .fi- ‘l‘ 4% areas
/C' 3230 * fl * “K 4
'I""” g- (
.\ \ CEO“ 7 8 - 7“ 3" ¥¥ * Scale: 1/19 ‘
k\’ ‘\ 00009 firearm}, .gw.
. .. ‘ D '4’
\‘\/—‘|~/‘\DO DO ‘6*¥*):< * *4:
i ‘ ‘3 0 ¥ x 4. "‘ ac
‘ >k ' \" 2 -\ ‘3 x x a<
* ¥ 4‘ ,‘4
7:.
2 ’" ...
IT"
! ‘K
K
; 9r
[7'6
3 "K
[x-
1)‘ -X-
, 9‘
I 7‘1‘
1 1'-
ix *
l 2;.—

 

‘k

 

 

MAP 3

Planimetric map of a portion of Maybeso Creek valley showing locations of
principal slide areas studied and sample and instrument locations.

 

' _‘ 3 R at!

l}. 5 gflfiiifii ... ‘

llllllllll

W

‘ .....i».
«will

"
‘d
H“

Wfi'

«p
,h

 

 

 

GEOLOGIC MAP OF MAYBESO CREEK VALLEY AND
VICINITY PRINCE OF WALES ISLAND. ALASKA
Scale. 1:31.680
0 V4 1/’2 3‘ 1Mile
contour interval 1 100 feet
datum: mean sea level
Jurassic or
undifferentiated igneous rocks

largely quartz diorite Cretaceous

predominantely grey—green
greywacke. shale and conglomerate '
with interbedded andesites and middle _
3 black slatey argillite Ordoviclan

 

 

lo lower
Silurlan

‘w, V base
framUiSGSTopographic
'3eries,CraigB2,83.C2.C

. predominanlely black.sha|ey to
slatey argillites highly folded
and locally silicifie

 

strike and dip of bedro‘ck

faulting—dc shed where
approximately located

lithologic Contacts,dashed
where approximate y
logging roads
U upthrown side

: D downthrawn side

 

 

 

 

MAP'I

move omvno mam
i

_

  

rm

  

 

i

 

 

_
wm_m<mm_i_ >Cwmm>_23 whdkw Z<0_IU_E

 

 

ex
PM

'l‘él u g

    

' v

 

Ar: 3mm»

 

   
  
 
 
  

       

l5

     
  
 
  
 

Ill
1

I) ”\ r V.,/~-\\\%:. p“ “Q

lllr \

,2

ll.

\

ill ‘5) :4 ' 1

 
  

    
    
 

   

      
 
       
    
    
    
 
 
  

 
  

  

Efi§' . , "fin, ,(/ 3.37415 a; ..‘ll I , I / r [f 'K.

w W

  

idly» ffillllafi/ ‘ V
'll‘sl. f‘ M “i” C2 §
lat“: ll“

‘ .
JQ-«w

     

  
 
  

\

. - f , g: 'N/I .,
. I A - f\, ‘ i F
‘ . .. \ . x ”I /’ ".

  
   
 
 
    
   

       
  
   
   

 

’

Ea

 

 

 

MAP or THE GLACIAL GEOLOGY or MAYBESO‘
CREEK VALLEY AND PART or HARRIS RIVER I
VALLEr PRINCE or WALEs_I5LANq ALASKA

alluvium )

younger till

 

 

 

 

Scale, 131,680
0 ‘A ‘fi ' 56

older till

 

. . raised beach
contour intervalleO feet

 

end moraine l

l

datum: mean sea level

 

 

 

 

 

 

 

 

 

 

MAP2

 

o‘mo one

 

mwu—‘nwwg m

  

wm_m<mm_._ >._._wmm>_ZD m._.<._.w Z<0_IU:>_

 

 

 

 

 

 

 

 

MAP 4

Isosinal contour

   
  
  

map of the Maybeso
Experimental
Forest

scale 1 inch :1? mile

l/31680

>.3<4

 

road
/

...a
”

experimental forest

boundary
.--3.-->--.

critical conlour

.5
J
J
//
t‘ /
/
/
/

slide SlUdY
Sites

  

 

 

 

 

 

 

 

MAP

l/O (kc’f’ [may ,‘ /:

 

//////

"lllllllllllllllllllll