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THESII

 

This is to certify that the

thesis entitled

PATTERNED GROUND IN THE JUNEAU ICEFIELD REGION,
ALASKA - BRITISH COLUMBIA

presented by

Frederick Edward Nelson
has been accepted towards fulfillment

of the requirements for

M-S. degree in W

WW

Major professor
Date _1/_’[ZL_

0-7639

'aL'u‘ -

OVERDUE FINES ARE 25¢ PER DAY
PER ITEM

Return to Book drop to remove
this checkout from your record.

 

 

 

 

PATTERNED GROUND IN THE JUNEAU ICEFIELD REGION,
ALASKA - BRITISH COLUMBIA

By

Frederick Edward Nelson

A THESIS

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

MASTER OF SCIENCE
Department of Geography
1979

ABSTRACT

PATTERNED GROUND IN THE JUNEAU ICEFIELD REGION.
ALASKA - BRITISH COLUMBIA
By

Frederick Edward Nelson

Patterned ground is found in abundance only in the more continental
sectors of the Juneau Icefield region. Its concentration here is parti-
ally due to the Sporadic winter snowcover, which allows the subsurface
freezing required for effective frost sorting. In maritime sectors of
the icefield, the concurrent onset of annual precipitation maximums and
sustained subzero temperatures operate to produce a thick and relatively
uniform snowcover, which prohibits pattern-generating processes. Although
it was not possible to define a lower limit for patterned ground in the
western reaches of the icefield, this limit was found to lie slightly
below 1500 meters on the eastern margin. Owing to genetic differences,
it is suggested that both small- and large-diameter patterned ground not
be used in the definition of a singular lower limit.

Investigations of the internal structure of patterned-ground features
reveal that the lateral margins of sorted stripes exhibit a distinctive
fabric. characterized by a preferred azimuthal orientation parallel to
the axis of the stripe, and steeply dipping b-axes. This fabric results

from compression of the stone stripes as fine centers expand during the

Frederick Edward Nelson
autumn freeze. Field evidence indicates that cobble geometry is an impor-

tant factor influencing the efficacy with which frost-sorting operates.

@Copyright by
FREDERICK EDWARD NELSON
l978

ACKNOWLEDGMENTS

I have been assisted in this undertaking by so many people that it
is impossible to mention them all here. Nonetheless, I extend my deepest
appreciation to all those who helped in so many ways, both in the field
and at Michigan State University. Thanks go to the many 1975 and 1976
Juneau Icefield Research Program participants who undertook tedious tasks
in my behalf, often under adverse conditions. I am especially indebted
to Dr. Robert Nichols, Professor Emeritus at Tufts University, for
critical methodological comments and special insights into the study of
geomorphology in the field.

Dr. Maynard Miller, Dean of the College of Mines and Geology at the
University of Idaho, and Director of the Foundation for Glacier and
Environmental Research, provided much of the impetus for this thesis.

He has helped to guide my interest in cold-climate geomorphology from
its inception, and through his generosity I was provided with an excep-
tionally varied and high quality introduction to the field study of
periglacial landforms. I am furthen indebted to Dr. Miller for financial
support through F.G.E.R. in the 1975 and 1976 field seasons, and for
arranging additional assistance in 1976 from the Explorers Club. Dr.
Miller also provided many excellent criticisms and suggestions regarding
both fieldwork and preparation of the manuscript.

Mr. Harold Coolidge, past chairman of the Explorers Club Education

Committee, and the Explorers Club itself. deserve my heartfelt thanks

ii.

for a grant in 1976, without which this research would not have been possi-
ble. I sincerely hope that this thesis lives up to their expectations.
Dr. Dieter Brunnschweiler acted as supervisor of the research and
served as chairman of my academic committee at Michigan State University.
To Professor Brunnschweiler I owe my interest in periglacial and climatic
geomorphology. His great enthusiasm and encyclopedic knowledge of
geography have stimulated me in many ways. I especially wish to acknow-
ledge Dr. Brunnschweiler's patient and generous aid in translation of
foreign literature. This assistance, as well as his insightful criticisms
and accessibility for discussion, have greatly enhanced this thesis.
Finally, I wish to acknowledge the labors of Mr. Chris Cialek of
Michigan State, who executed almost all of the graphics for the thesis
and served as a sounding board for many of the ideas contained in it.
I also thank Mr. Cialek for permission to mutilate a copy of his fine
map of the Cathedral Massif, which appears as Figure 4-3.

The thesis is dedicated to the memory of Stan Zieminin.

iii

is this love...or is it just confusion?

- J. Hendrix

iv

TABLE OF CONTENTS

CHAPTER ‘Pagg
I. INTRODUCTION ....................... 1
1.1 Research Objectives ................ 1

1.2 Research Hypothesis ................ 2

1.3 The Study Area ................... 4

1.3.1 Bedrock Geology ............... 8

1.3.2 Climate and Vegetation ........... 11

1.3.3 Previous Periglacial Research ........ 14

1.4 Terminology .................... 15

II. INTENSIVE INVESTIGATIONS OF PATTERNED GROUND ....... 19
2.1 Small-Diameter Patterned Ground .......... 20

2.1.1 Type I Forms ................ 21

2.1.2 Type II Forms ................ 26

2.2 Large-Diameter Patterned Ground .......... 31

2.2.1 Size and Spacing of Patterned Ground . . . . 32

2.2.2 Effects of Moisture ............. 37

2.3 Fabric Analysis .................. 46

2.3.1 Previous Research .............. 46

2.3.2 Field Procedures and Data Analysis ..... 50

2.3.3 Origin of Fabrics .............. 55

2.4 Particle Shape Analyses and Frost Sorting ..... 63

2.4.1 Mechanisms of Stone Movement ........ 64

Table 9f_Contents (cont.)

Page
2.4.2 Field Procedures and Assumptions ...... 65
2.4.3 Data Analysis ................ 67

2.4.4 Interpretation of Shape Characteristics . . . 78

PERMAFROST DISTRIBUTION IN THE JUNEAU ICEFIELD REGION . . . 81

3.1 Literature Review ................. 81
3.1.1 Southeast Alaska and Coastal British

Columbia . . . . . . . . .......... 81

3.1.2 Interior British Columbia .......... 83

3.2 Permafrost Sites in the Juneau Icefield Region . . . 84

3.3 Calculated Permafrost Levels ............ 89
3.4 Conclusions .................... 93
DISTRIBUTION AND LIMITS OF PATTERNED GROUND ........ 95
4.1 Literature Review ................. 95

4.2 Distribution of Patterned Ground in the Juneau

Icefield Region .................. 100
4.2.1 Nest Slape ................. 100
4.2.2 Interior of Icefield ............ 101
4.2.3 Atlin Region (East Slope) .......... 102

4.2.4 Limits of Large-Diameter Patterned Ground . . 110
4.2.5 Local Variations .............. 111
4.2.6 Limits of Small-Diameter Patterned Ground . . 116

4.3 Conclusions and Recommendations .......... 117

BIBLIOGRAPHY ........................... 119

 

vi

LIST OF TABLES

Descriptive Statistics and Results of Spearman

Rank-Order Correlation for Frost Ridge Dimensional

Data ...........................
Stone Stripe Fabric Data .................

Analysis of Cailleux Flatness Values by
Kolmogorov-Smirnov Test .................

Analysis of Cailleux Roundness Values by
Kolmogorov-Smirnov Test .................

Descriptive Statistics for Frost Ridge Weathering
Rind Data ........................

Computed Permafrost Levels ................

vii

Page

36
53

90

FIGURE

1-1.
1-2.
2-1.

2-2.

2-3.
2-4.
2-5.
2-6.

2-7.

2-8.

2-10.
2-11.
2-12.

2-13.

2-14.

LIST OF FIGURES

The Northern Boundary Range ...............
Bedrock Configuration ..................

Type I small-diameter patterned ground, Cathedral
Massif .........................

Type II small-diameter patterned ground, Cathedral
Massif .........................

Overview of Frost Ridge patterned ground site ..... ..
Active "Zone A" sorted stripes .............
Inactive "Zone C" sorted stripes ............

Inactive patterned ground adjacent to Chapel Glacier.
Note lichenized borders and vegetated centers ......

Active patterned ground adjacent to Chapel Glacier.

This site is the lighter colored area in background of
Figure 2-6 .......................
Frost Ridge stone stripe fabrics ............

Cumulative frequency distributions, up- and downslope
dips ..........................

Histograms of a-axis dips ................
Histograms of b-axis dips ................

Cumulative frequency distributions, Cailleux flatness
values (Kolmogorov-Smirnov Test) ............

Cumulative frequency distributions, Cailleux roundness
values (Kolmogorov-Smirnov Test) ............

Histograms of weathering rind thicknesses ........

viii

Page
6

11

45

61
61

77

List gf_Figures (cont.)
FIGURE Page
4-1. View to west from Camp 10 in interior of Juneau
Icefield, showing predominance of steep slopes
typical of the area ................... 104

4-2. Polar diagram showing aspect and elevation of
patterned ground sites, Cathedral Massif ........ 106

4-3. Map of patterned ground sites in the Cathedral Massif . . 109

4-4. Sorted stripes at margin of Balcony Glacier, 1950 m,
Cathedral Massif. Note trim line on facing wall . . . . 114

4-5. Extrazonal patterned ground at 975 m, Fourth of July
Creek Valley ...................... 114

ix

CHAPTER I
INTRODUCTION

 

Over the past twenty years, a sizable North American contribution
tolthe periglacial literature has accumulated, although little attention
has been given to the traditional European theme of spatial variation in
periglacial phenomena. The frequently-mentioned but inadequately docu-
mented relationship between continentality and alpine geomorphological
features would appear to be particularly evident in the North American
cordillera. By means of a transect in the Juneau Icefield region, an
attempt is made in this thesis to clarify some of the questions regarding
the origin and distribution of cryogenic landforms.

There has been considerable discussion. primarily in the German-
language literature, regarding variations in the altitudinal threshold
of sorted patterned ground in mountainous regions. While there is general
agreement on a decrease in elevation of this limit poleward, Troll (1958,
pp. 5-9, 60) and Hastenrath (1960) contend that the boundary follows tree-
1ine and snowline, rising with increasing continentality. H6vermann
(1960; 1962), among others, maintains an Opposing viewpoint, arguing for
a decrease in threshold elevations with progression from maritime to
continental environments.

In a brief discussion of patterned-ground thresholds and related
problems, Hashburn (1973, p. 101) calls for detailed regional studies of

periglacial features. A diverse regional base is required if the

interrelationships and factors contributing to the occurrence of peri-
glacial phenomena are to be better understood. Since there appear to be
few regional periglacial studies from North America, such an undertaking
appears appropriate.

At a more local scale, much remains to be learned regarding the in-
ternal structure of patterned ground. Conflicting reports, often based
on casual observation. have been published on the nature and origin of
cobble fabrics in the borders of patterned ground cells. Similarly, it
has been suggested, without rigorous testing, that a given particle's
geometry may influence its propensity for movement in a frost-affected
soil matrix. The relationship between temporal and spatial aspects of
snowcover and the occurrence of patterned ground is also inadequately
documented. These problems are addressed in the present thesis.

1.1 Research Objectives

 

The primary goal of this study is determination and explanation of
the distribution of patterned ground and permafrost in the Juneau Icefield
region. Considerable selectivity is required, since such an objective is
obviously too large a goal to be realized by a single worker in two
field seasons. The study has therefore been limited by concentrating
observations on a 200 km transect in the Northern Boundary Range between
Juneau, Alaska (58° 22'N., 134° 35'H.), and Atlin. British Columbia (59°
35'N., 133° 38'N.). In this manner. the broad outline of the distribution
and controls operative on the features in question can be constructed, to
which subsequent observations may be added.

Because of its three-dimensional character, mountainous terrain
demands that considerable attention be given to topographic and altitudi-

nal factors influencing the distribution of small-scale landfOrm elements.

An important problem which this thesis seeks to resolve is the direction
assumed by the regional trend of the patterned ground and permafrost
thresholds. An attempt is also made to combine observations of climatic,
topographic, and edaphic factors controlling the distribution and thres-
hold with a review of literature in order to account for the empirically-
derived results. Explanation is offered in a largely deductive framework.

1.2 Research Hypotheses

 

It is hypothesized that the lower limit of large-diameter sorted
patterned ground falls in response to conditions of increasing continent-
ality. Furthermore, it is postulated that patterned ground is most likely
to develop at sites with the following characteristics:

1) Parent material characterized by heterogeneously-sized components

 

with high frost susceptibility. Such material is conducive to size-
sorting because ice segregation is presumably required for effective
frost sorting (Washburn, 1973, pp. 71-80). Many glacial tills have such
characteristics.

2) Low-angle slopes with north to northeast exposures, where late-

 

lying snowbanks provide sufficient moisture for ice segregation at the
time of the autumn freeze. It is possible that these snowbanks have the
effect of keeping the summer temperature centered about 0°C near their
margins, thereby maximizing the number of potent freeze-thaw cycles at
times when the ground is saturated. It is emphasized that the latter
point is applicable only to small-diameter forms, in that it is only
these that are affected by diurnal cycles.

3) A_mean annual temperature gf;1:§_gr_lower. This limit is sug-

 

gested by Williams (1961, p. 344) as a crude limit for widespread pat-

terned ground occurrence. Although it cannot be precisely determined

except by reliable microclimate observations, this boundary may be
approximated by applying lapse rates. Bird (1967, p. 197) suggests that
the southern limit of patterned ground in Arctic Canada may be identified
with a mean annual air temperature of -4° C. However. French (1976, p.
195) maintains that the effective limit of miniature frost-related forms
may be better approximated using William's limit. Since the elevation

at which such a mean annual temperature occurs may be expected to decrease
with increasing distance from oceanic influence, it should follow that

the lower altitudinal limit of patterned ground in the Boundary Range is
depressed inland. Another important factor in this regard is the effect
of snow cover on soil temperatures. Mountainous areas characterized by

a continental climate and sporadic snow cover are likely to experience

a wider range of subsurface soil temperatures than oceanic areas with
heavy snow accumulation, even though each locality may have identical

mean annual air temperatures (Outcalt, 1967, p. 10). Assuming that suffi-
cient moisture is available for frost sorting, as at the downslope edge
of a perennial snowbank, continentality should play an important role in
the development of widespread patterned ground.

1.3 The Study Area

 

The Juneau Icefield is the fifth largest area of continuous highland

2 northeast of

ice in North America. It covers an area of about 2700 km
the city of Juneau, in the northern Boundary Range on the Alaska - B.C. -
Yukon border. This icefield extends from the Taku River Valley at its
southern edge, to the vicinity of White Pass, northeast of Skagway,
Alaska (Figure 1-1). The icefield is a system of interconnected glaciers

and snowfields of variable elevation. Its main area may be regarded as

a broad ice plateau cresting near the International Boundary at

Figure 1-1. The Northern Boundary Range.

 

  
  
     
 
 

“M

x 1905
Ruby Mt.

 

"x 2616
Devils Paw

° TULSEOUAH

 

      
     
  
 
 

1373 X

\
ALASKA '. Cairn Pk.

v o
(v 'C.‘
GLACIERS 6‘4.
«7-.
0 5 IO 20
KILOMETERS

 

 

 

L- 58'

 

approximately 1950 meters (Miller, 1964. p. 261). In the central icefield
numerous nunataks protrude through the ice surface, some attaining heights
of up to 1200 m above the surroundings. The form of many is that of the
typical horn peak, although some having been overridden by ice, display
rounded profiles. Many of the nunataks contain cirque-glaciers, whose

ice flows out to merge with that of the plateau. The highest elevation

in the area is attained by Devil's Paw (2616 m), on the southeastern

flank of the Icefield.

In the southeastern sector of the icefield, the Taku-Llewellyn
transection glacier system extends from tidewater at Taku Inlet nearly
to the shores of Atlin Lake, some 100 km to the north (Figure 1-1).
Although the regime of most outlet glaciers is negative or close to
equilibrium, that of the largest, the Taku Glacier, is strongly positive.
This glacier has advanced almost 12 km since the 1890's. while its east
slope counterpart, the Llewellyn Glacier, has receded more than 3 km
since 1920 (Miller, 1976, p. 275). This contrast has been explained
with respect to the location of the zone of maximum accumulation on each.
The Taku's maximum area lies between 900-1375 m on the maritime west
slope. where conditions for accumulation of snow are optimal. However,
Llewellyn's maximum area lies on the eastern slope between 900-1500 m,
which is today well below the zone of maximum accumulation on this side
of the range (1919).

The Atlin area, where much of the research for this thesis was con-
ducted, is northeast of the Juneau Icefield in the Cassiar District of
northwestern British Columbia. The region has been repeatedly occupied
by large north-flowing glaciers which have modified pre-existing struc-

tural and fluvially-cut depressions. resulting in precipitous valleys

of the familiar U-shape. Many of these lineaments are now occupied by
water bodies, the largest being Atlin Lake, which extends 105 km from the
terminus of the Llewellyn Glacier to the north side of the Yukon - B.C.
border. Based on palynological and stratigraphic evidences (Miller and
Anderson, 1974; Tallman, 1975), the last deglaciation in the Atlin area
is interpreted as having been well in progress by 10,000 years B.P.
(Miller, 1976, p. 286). With the exception of Icefield outlet glaciers,
glacierization is at present confined to small cirque glaciers in terrain
above 1550 m west of Atlin Lake.

The Cathedral Massif is an isolated mountain block occupying an
area of 8.25 km2 near the southwest end of Atlin Lake (Figure 1-1). The
highest point on the massif is Cathedral Peak (2118 m). The massif sup-
ports nine small cirque glaciers, which in recent decades have been down-
wasting and receding. A wealth of active and relict periglacial features
is also found in this small area. These features are the subject of part
of the research presented in later sections of this study. Jones (1975)
has presented an interpretation of the geology and glaciology of the
Cathedral Massif.

1.3.1 Bedrock Geology

 

The Juneau Icefield is within the area of the Coast Range Batholith,
a granitic emplacement of late Jurassic to Cretaceous age (Forbes, 1959;
Miller, 1959; Naff, 1972). This batholith extends from northern
Washington state to the vicinity of Skagway, Alaska, a distance of some
1760 kilometers. In the icefield area the bathdlith is composed of both
plutonic and crystalline rocks of granodiorite petrology. known as the
Coast Crystalline Complex. Less than one third of the exposed batholi-

thic rocks are composed of plutons, large-scale occurrences of which are

confined to the quartz monzonites and granites of the east marginal
pluton (v. Forbes, 1959, p. 3). Near the International Boundary, an
intrusive contact occurs between the plutonic rocks and the crystalline
schists. On the west margin, the transition is of a more gradational
nature (Forbes, 1959. p. 256).

Northwest of the icefield is a large fault-bounded area of primarily
Upper Paleozoic rocks known as the Atlin Terrane. This area is the
largest continuous occurrence of little metamorphosed rocks of this age
in the western part of the North American Cordillera (Monger, 1975, p. 1).
It has been suggested that the Atlin Terrane represents a large thrust
sheet, displaced to the southwest over Lower Mesozoic rocks during late
Jurassic time (191g, p. 38). To the southwest, the Atlin Terrane is in
contact with sedimentary rocks of the Intermontane Belt (Lower Jurassic).
which overlie the Coast Crystalline Complex. Figure 1-2 depicts the
general relationship between these areas. For detailed discussions of
the geology of the area and adjacent districts, the reader is referred
to the publications of Aitken (1955; 1959). Cairns. (1913), Forbes (1959),
Gwillim (1901), Miller (1956; 1959) and Monger (1975).

1.3.2 Climate agg_Vegetation

The western slope of the Boundary Range experiences a relatively
mild, marine cool summer climate (cfo in depen's classification). In
winter the area is subjected to numerous cyclonic storms which originate
in the Gulf of Alaska and the mid-Pacific. These moisture-laden depres-
sions result in great accumulations of snow at higher elevations on the
western slope of the Boundary Range. In summer, the Pacific high pres-
sure cell is displaced northward and effectively blocks much cyclonic

activity along the coast. The result is a precipitation maximum (55-60%)

10

Figure 1-2. Bedrock Configuration.

11

/
.//( YUKON

CRYSTALLINE

PLAT FORM

MOUNTAIN

ROCKY

!
/
BELT

 

   

     

INTERMONTANE

 

KILOMETERS

200 300

100

FLU LT

12

occurring between October and April. It will be noted that this winter
maximum is less pronounced than in coastal British Columbia or Washington,
where the influence of the Pacific anticyclone in summer is stronger
(Trewartha, 1961, pp. 267-273).

The presence of the cordillera exerts an important influence on the
climate of the area to the east. Although the mountains do not completely
block penetration of air from the Pacific, there is a distinct precipita-
tion shadow effect. The Pacific air that does reach the interior subsides
from high levels and is relatively dry (Bryson and Hare, 1974, p. 52).
Thus, while Juneau has a mean annual precipitation of 1387 mm, Atlin, 200
km to the northeast, experiences only 285 mm/year, although a similar
proportion of each falls during the October-April period.

The forest ecosystems Of the respective areas reflect this climatic
disparity. The abundant moisture at low elevations on the western flank

of the mountains supports a lush growth of sitka spruce (Picea sitchensis)

 

and its ecological successor, western hemlock (TSuga heterophylla). Near

 

timberline (600-700 m) mountain hemlock (Tsuga mertensiana) is common.

 

The dense understory is compared of rusty menziesia (Menziesia ferrunginea),

 

the aptly named devilsclub (Qplopanax horridus), bunchberry (Cornus

 

canadensis), and five-leaf bramble (Rubus pedatus), among other species

 

(Daubenmire, 1953; Viereck and Little, 1972).
The forest of the interior section near Atlin is basically unrelated
ecologically to that of the coast (Daubenmire, 1953. p. 134). The domi-

nant species are white spruce (Picea glauca). aspen (Populus tremuloides),

 

 

birch (Betula papyrifera). and various species of pine. A comprehensive

 

study of the vegetation of the Atlin region has been performed by

Anderson (1970). The treeline (1300 m) is significantly higher than in

13

the coastal area; this is attributable to a more sporadic snow cover and
greater summer warmth in the interior at comparable altitudes (Wardle,
1971; 1974).

Since it may be of considerable interest as regards observations
made later in this report, some attention is now focused on the problem
Of the continentality gradient between Juneau and Atlin. As noted by
McBoyle and Steiner (1972), the notion of continentality and its anti-
thesis, oceanicity, have long been the victims Of a bipartition Of
thought:

"on the one hand a concept derived from a hypothetical situation

Of a plane-surfaced land mass of regular shape where latitude

has no relevance and where the geometrical center of the land

mass would have the highest continentality; on the other a vision

Of continentality as the degree to which any part of that area

exhibits a climate typical Of being inland and away from the

sea's influence" (191g, p. 12)

It is in the latter sense that the continentality concept is applied-
here, i.e., the question is to what degree a station experiences large
annual and diurnal temperature ranges. Succinctly, continentality is

an inverse function of the influence on a station of the moderating
effects of large water bodies, which is in turn a function Of the dif-
ference in heat capacities of land and water, the atmospheric circulation,
and of mountain barriers.

There have been numerous attempts at quantification of continentality
through the use of indices (Zenker, 1888; Hann, 1903; Gorczynski. 1920;
Johansson, 1931; Conrad, 1946; Ivanov, 1959). Most of these rely primarily
upon the annual air temperature range. Since this range is to a large
degree influenced by the latitudinal position of a station, compensation

is made by dividing the annual temperature range by the sine Of the

station's latitude. Johansson's (1931) index of continentality has been

14

used in the construction of a continentality map of Canada (MacKay and
Cook, 1963) and in an interpretation of the glaciation level height in
northern British Columbia and southeastern Alaska (Ostrem, 1972). In the
interest of comparability, computations using this index were made for
Juneau and Atlin. It is recognized that this gives only a crude measure
of continentality and does not deal with the attenuating effects intro-
duced by elevational differences. The index does, however, give some
indication of the magnitude of the continentality gradient existing

between the two points. Johansson's index is given by

1.6A

 

K = sine ' 14
where:
K = continentality coefficient (values range from 0 to 100)
A = mean annual temperature range (°C)
0 = latitude

Values Obtained for Juneau and Atlin are, respectively, 17.7 and
38.6, confirming the existence of a pronounced continentality gradient
between the coast and the interior. A. Thompson (1975, p. 8) suggests
that this gradient attains its greatest steepness on the east slope of
the Boundary Range, i.e., on the inland flank of the Juneau Icefield.

1.3.3 Previous Periglacial Research

 

Although prior investigations in the study area have centered for
the most part on glaciological, botanical, and glacial geomorphological
topics, some periglacial research has been conducted, most notably in
the works of Hamelin (1964) and Tallman (1975).

Hamelin's investigations were of a reconnaissance nature, carried

out in the summer Of 1962 on the southern part of the icefield. His

15

study emphasized lithological control, in that the homogeneous granular
nature of many rocks in this region prevents the development of patterned
ground. The predominance of steep slopes further limits the occurrence
of many periglacial features. Where patterned ground was found, it was
Of the miniature type, imperfectly formed, and, as stressed by Hamelin,
occurred on morainic material, not in areas Of bedrock. The form of the
nunataks is attributed in part to frost shattering, although it was noted
that freeze-thaw cycles are minimal during summer. Frost-shattered
debris is, however, a frequent occurrence on many nunataks.

Tallman's investigations were carried out in the Fourth of July
Creek Valley northeast Of Atlin during the period 1971-1974. Research
centered around resistivity surveys of palsas and peat plateaus. In
addition, C-14 dates were obtained from material in the basal layer of
one peat plateau. Tallman also conducted reconnaissance-type research
on sorted circles and "nivation hollows." discussion of which is defer-
red tO a later section of this study.

Other periglacial-related studies include investigations on "tanks"
and tors on Ptarmigan Ridge near Juneau by Fleisher (1972) and Zwick,
gt, a1, (1974). The Atlin rock glacier has been the subject of recent
lichenometric and movement surveys by Juneau Icefield Research Program
personnel.

1.4 Terminology

 

a) Periglacial - Periglacial terminology has been described as

 

"irrational, imprecise, incomplete, and non-systematic" (Hamelin and
Cook. 1967, p. 11), a view to which this writer subscribes. The term

periglacial itself has been used to convey a variety of meanings. The

 

concept of a periglacial zone originated with Lozinski in 1909. who used

16

it to refer to the frost-rubble areas peripheral to Pleistocene ice

sheets (Jahn, 1954). The concept has now been extended so far that a
recent text uses the term to refer to "cold-climate, primarily terrestrial,
nonglacial processes and features regardless of data or proximity to
glaciers" (Washburn, 1973, p. 2). 0n the other hand, Embleton and King
(1975, p. 2) maintain that some semblance of the original meaning should
be preserved in that periglacial should be used to refer to "a zone of
indefinite width peripheral to the glacial ice of today or of any phases
of the Pleistocene."

Despite disagreement regarding strict definition of the term, its
imprecision seems appropriate when one views attempts to delineate the
boundaries Of the "periglacial environment." While most workers agree
that those areas underlain by perennially frozen ground are in the peri-
glacial realm, the problem of delineation becomes more difficult when
attention is focused on transitional zones, such as those under the in-
fluence of subpolar oceanic climate or the northern parts of the boreal
forests. These areas may lack perennially frozen ground, but the former
experience frequent shallow frost cycles, while the latter are subjected
to deep annual freezing and thawing of the ground. Although the paucity
of data may render this criterion difficult to apply over broad areas,
this writer considers the dominating effect of freezing and/or thawing
to be an essential requirement for categorization of an area as "peri-
glacial." In the absence of good microclimatic data to support this
definition, we may use morphological phenomena which require freezing
and thawing, usually in conjunction with water in the surficial material.
Despite a call for abandonment of the term periglacial (Linton, 1969).

its retention appears appropriate not only because its usage is so firmly

17

established in the literature, but because the very vagueness so Often
criticized corresponds to the imprecision with which the boundaries of
the periglacial realm are delineated. Following Brown and Kupsch (1974,
p. 25) periglacial is broadly defined as:

1) The area, geomorphological processes, and deposits charac-
teristic of the frost-affected immediate margins of existing
and former glaciers and ice sheets.

2) the environmentny(nonglacierized) cold regions in which
frost action is (dominant); the features resulting from
frost action.

It will be noted from the foregoing that no restrictive definition
of the periglacial climate can be advanced. Indeed, the term periglacial
denotes a variety of climatic types, ranging from the highly continental
interior of Siberia to moist environments with small annual temperature
range, typified by the subantarctic islands. Troll (1958) and Tricart
(1969, pp. 19-27) provide useful discussions Of the various periglacial
climates.

Mountainous areas at all latitudes may fall within the periglacial
realm if sufficient altitude exists. The threshold elevation Of the al-
pine periglacial zone declines poleward, but its trend is less well known
as one proceeds from oceanic to continental areas.

b) Permafrost - The merits of the term permafrost (Muller, 1947)
have been widely discussed (Bryan. 1946a; 1946b; Brown. 1970). Although
the expression has been severely criticized, its usage is so well en—
trenched that efforts to replace it have proven fruitless. An extended

definition of the term has been presented by Stearns (1966. pp. 1-2).

in which dry permafrost is defined solely on a temperature basis (0°C

 

for two or more years), while ice-rich permafrost (wet frozen, in Stearns'

 

terminology) occurs where enough of the existing pore water is frozen to

18

cement the previously unconsolidated mineral and organic constituents.
Thus, permafrost refers to a ground condition and is independent of the
type of material involved.

c) Features pf_Mass Movement - As stressed by Benedict (1970. PP.

 

170-176), gelifluction and frost creep Often operate in conjunction with
one another, the effects of each being separable only through detailed
instrumental observations. For this reason, descriptive terms such as

stone-banked and turf-banked lobes are preferable to genetic terms, such

 

 

as gelifluction lobes, since the latter may place undue emphasis on one

 

process while neglecting another.

Turf-banked lobes and terraces are defined as "lobate or bench-like

 

accumulations of slowly moving regolith with a continuous surficial mat
of grasses and organic material." These terms correspond to the German

"gebundene" (bound) gelifluction. Stone-banked lobes and terraces are

 

described as "lobate or bench-like accumulations of slowing moving regolith
overlain by or having crescentic banks Of stony material." These features
have their equivalent term in the German "ungebundene" (free) gelifluction.
Most of the remaining terminology used in this study is relatively
straight-forward and requires little further clarification. Wherever
possible, usage will conform to terminology in the glossary by Brown and

Kupsch (1974).

CHAPTER II
INTENSIVE INVESTIGATIONS QE_PATTERNED GROUND

 

Patterned ground is a phenomenon associated primarily with frost
action in polar, subpolar, and alpine environments. A number Of termi-
nological and classificatory schemes concerning patterned ground have
been developed in the last 65 years (v. J. Lundqvist, 1962, pp. 10-13).
This paper will utilize the widely accepted Washburn system, in which

the collective name patterned ground is used in reference to "the more

 

or less symmetrical forms, such as circles, polygons, nets, steps, and

 

stripes, that are characteristic of, but not necessarily confined to,
mantle subject to intensive frost action" (Washburn, 1956, p. 824).’
Each of these forms may be either sggtgg_(material within the feature is
segregated by grain size) or unsorted. As this classification is purely
descriptive, it sidesteps controversy while providing a basis for dis-
cussion among workers with conflicting views on the origin of patterned
ground. More recently, Washburn (1970) has developed a genetic classi-
fication based on his previous terminology. The classification is pre-
sented in matrix form and is based on the premises:

) patterned ground is polygenetic;

) similar forms may have differing origins;

) some processes may produce dissimilar forms;

) more processes may be responsible for patterned ground

than are presently recognized;
5) terminology should be kept as simple as possible.

DOOM-i

19

20

Large-diameter patterned ground is arbitrarily defined here as those
features whose unit cells average 0.50 meters or more in diameter or width;

small-diameter patterned ground has a mesh size less than 0.50 meters.

 

2.1 Small-Diameter Patterned Ground

 

Small-diameter or "miniature" forms of patterned ground are those
most frequently encountered in the study area; this was the only type
found in the Alaskan sector. The features are found at a wide range of
elevations and often occur in close proximity to, or within the cells of
larger patterns. Small-diameter forms are characterized by shallow (<10
cm) depths of sorting, and the rock fragments comprising their coarse
segments are proportional to the overall size of the features.

Several workers have regarded small-diameter patterned ground as
the result of processes differing in degree or kind from those Operative
on larger patterns. Some (e.g. Troll, 1958, p. 63) consider the two
types to be the products of different climatic regimes. The large and
small patterns are, however, remarkably similar in appearance, scale
expected, and the whole range of patterned ground forms is found in the
small-diameter variety. Occasionally, occurrences are found where the
transition from polygons to stripes can be clearly traced as declivity
increases. Troll (1958, Fig. 29, p. 44) has published a striking photo-
graph of this phenomenon.

Several investigators (e.g. R. Miller, gt, al,, 1954; Chambers,
1967) have remarked on the rapidity with which miniature forms can
develop. After destruction, patterns may re-form in as little as two
years.

It has been noted (Rapp and Rudberg, 1960, p. 149; J. Lundqvist,

1962, p. 76) that small-diameter forms are found only in areas devoid of

21

vegetation, Often on small patches where the plant cover has been removed
by the actions of wind, frost, animals or man. This proved true at all
sites investigated in the presently described field work.

2.1.1 Type _1_ Forms

 

The first type of small-diameter patterned ground (hereafter referred
to as "Type I") is associated with networks of cracks probably attribu-
table to desiccation. Several occurrences of sorted polygons were noted
on Cairn Peak, adjacent to the Lemon Creek Glacier on the west slope of
the Boundary Ridge. These occur at 1340 m on a flat site with southeast
exposure. Although imperfectly formed, the polygons are distinct, with
a fresh and active appearance. The fine centers were found to be 12-25
cm in diameter, while the coarse borders varied between 2-6 cm in width.
The stones comprising the borders occupied polygonal networks of cracks
which extended several tens Of cm below the surface, although rock frag-
ments occupy only the uppermost 2-3 cm of these. The centers consisted
of exclusively fine material in the surficial layer, but the soil was
heterogeneous with respect to particle size at greater depth.

A variation Of this type was found in abundance on the Cathedral
Massif in the inland section Of the Boundary Range. In some instances,
the transition from polygons to stripes was seen over a very short
distance (Figure 2-1). At 1620 m on the northeast slope of Frost Ridge,
networks of nonorthogonal cracks were observed in clayey material on the
treads of large stone-banked lobes. Where the microrelief on the lobes
steepened, the cracks transverse to the slope were compressed, but those
aligned parallel to the slope remained unaffected. Stones were found

in many of the latter cracks, giving rise to a crudely sorted effect.

22

Figure 2-1. Type I small-diameter patterned ground,
Cathedral Massif.

23

 

24

The first problem in the analysis of these patterns is the origin
of the fissures which form the basis of the patterning. Thermal contrac-
tion is discounted as a cause, since cracks initiated in this manner
reach their maximum width in midwinter and narrow as soil temperatures
rise. The depth of snow cover in this locale also tends to rule out
thermal contraction, by reason Of the damping effect of snow cover on
frost penetration. The patterns in question lie in an area which does
not emerge from below the snow until at least late June. The small
size of the patterns also militates against a thermal contraction origin.

Benedict (1966, p. 90) has drawn attention to the possibility that
certain cracks may result from tensional forces in areas of extending
flow in solifluction features. Such cracks would be oriented parallel
to the contour and thus need not be considered further here, since the
cracks in question form a regular polygonal pattern which is emphasized
at right angles to the contour in steep areas. Likewise, cracks due to
differential frost heave do not display regular polygonal patterning.

Desiccation appears to be the best explanation for these fissures.
The features are similar in size and form to desiccation polygons studied
in the field by Corte (1966b) and produced in laboratory studies (Corte
and Higashi, 1960). The arrangement of cracks in these patterns is of
the nonorthogonal type, indicating that all components of the systems
developed simultaneously, rather than sequentially, as is the case in
orthogonal systems. Most of the cells possess four or five sides, the
optimum numbers reported for desiccation features by Corte and Higashi
(1960, p. 21).

Corte (1966b, p. 131) notes that cracks are initiated at points

where stones are situated in a drying soil. Therefore, desiccation

25

cracking may of itself favor a sorted effect in a stone-rich soil. Stones
are also moved into cracks by the actions of wind and rain (191g,, p. 131)
and by frost creep. Once sorting has been initiated by these agents,
subsequent cracking events are likely to occur in exactly the same loca-
tions. Chambers (1967, p. 12) has documented the re-formation of desic-
cation cracks in their initial positions even after destruction of the
original networks.

The elongation of the polygonal micropatterns observed on Frost
Ridge appears to be related to gravitative slope processes. Suppression
of the transverse elements within the patterns may be indicative of
microsolifluction (used here in Troll's sense. i.e., movement within
the unit cell of each polygon). Such movement results in compression
and eradication Of transverse cracks, while the downslope-oriented
cracks remain relatively unaffected. Such movement may occur during the
thaw period when moisture from snowmelt is abundant, or it could result
from concentration of moisture at the surface due to formation and
ablation Of needle ice. Frost creep may be expected to play a similar
role. It is possible that rilling also accentuates the downslope-
oriented cracks.

Frost sorting of stones is not necessarily inoperative in the above
model, and indeed, probably takes place in limited fashion. This is
indicated by the lack of stones in the shallow subsurface layers of some
features. In Type I features, however, it is of secondary importance,
since they are initiated by azonal or extrazonal processes, and can occur
without the aid of primary frost sorting. It follows that Type I fea-
tures are not necessarily indicative of a periglacial environment and

should be excluded in attempts to establish frost-sorted patterned ground

26

limits. This conclusion is supported by the existence of small-diameter
sorted desiccation polygons in Illinois, documented by Corte (1966b, p.
131).

2.1.2 Iyp§_II.fggm§_

A second type of small-diameter patterned ground (Type II) was found
throughout the study area (Figure 2-2). This type appears similar to
the larger forms discussed in the latter part of this chapter and may
be fairly reliable indicator of periglacial conditions. Description
from two sites should suffice, but it is noted that these features are
also found on nunataks in the central icefield.

The first site is again on the southeast-facing slope of Cairn Peak
near Juneau. Here, sorted stripes occur in small patches of bare earth
devoid of the large schistose blocks found in the immediate surroundings.
The vegetative cover has been disrupted by frost heaving assisted by
wind; this slope is proximal with respect to prevailing wind direction
and is probably snow-free in winter. The effect produced is that of the
"turf exfoliation" described by Troll (1958, p. 34). When investigated
in early July, these sites were already snow-free, although considerable
depths Of snow remained on adjacent slopes with orientations other than
southeast.

The coarse stripes have a mean width of 13 cm and the fine stripes
average 23 cm. Lengths are variable, but the stripes are strictly
parallel and follow the fall line. The stone chips which compose the
coarse stripes are of the same biotite schist as the surrounding debris
and outcrops. Although some Of the chips exceed 8 cm, most are smaller.
Sorting is surficial, but the stone stripes occupy slight depressions.

Subsurface material consists Of rock fragments in a silty matrix, which

27

Figure 2-2. Type II small-diameter patterned ground,
Cathedral Massif.

28

 

29

is apparently unaffected by sorting processes.

Type II features were frequently encountered in the Cathedral Massif.
Noted occurrences were limited to stripes and were found at a wide range
Of elevations and exposures. One group of stripes, on a 17° slope at
1650 m was investigated in late August, 1975. The stony stripes averaged
2 m in length and 5-10 cm width. although larger stripes were also pre-
sent. The stones Of which these stripes were composed occupied slight
linear (down-slope trending) depressions. The rock fragments in each
were 0.5 to 5 cm diameter, but larger stones were scattered about the
site. Intervening fine stripes were 4-8 cm wide. Upon excavation,
sorting was evident to a depth of about 2.5 cm. At depths between 2.5
and 7.5 cm, the material consisted mainly of fines, indicating that the
stones had been heaved to the surface from this layer. A heterogeneous
mixture of fines and coarse material was found below 7.5 cm.

Needle ice may play an important role in producing the sorted effect
in these stripes. Similar to phenomena observed in England by Hay (1936)
and in New Zealand by Gradwell (1957), needle ice was formed during clear
nights in which temperatures at the Camp 29 station (1615 m) were re-
corded below 0°C. In addition to fine soil, numerous small stones were
lifted by the ice needles. During the following day, preferential abla-
tion of the needles adjacent to the coarser stripes was Observed. The
direction of collapse was toward these stony fractions, resulting in move-
ment of additional fragments into these stripes. R. B. King (1971, p.
381) has made a related Observation of some interest to this discussion.
Of 100 stones with an axial ratio of 2:1 or greater, 41 were upturned
during a needle ice event, as opposed to 42 lifted entirely and 17 which

were not affected. It is considered that such differential movements

3O

contribute to the formation and maintenance of small sorted stripes.
Since no cracks were found in association with these stripes, it is
probable that they are the result of a different initiating mechanism
than the Type I forms. Although somewhat smaller, the stripes bear
strong similarity to those described from the English Lake District by
Hay (1936; 1943) and Caine (1963). Hay (1943, p. 19) suggested that the
frequent heaving associated with needle ice events would prevent forma-
tion of a network of anastomotic rills. Surface drainage would, there-
fore, be restricted to a straight-line course down the steepest slope.
"Incipient hollows" thus formed would be natural sites for collection Of
coarser fragments heaved to the surface and overturned or uplifted by
needle ice. Caine (1963, p. 176) cited differential heaving as being
the initial patterning process but was unable to provide the precise
mechanism. Washburn (1969, p. 178) favored rillwash with subsequent
eluviation or washing in of stones as the initiator of some small stripes
in northeast Greenland. This appears to be a special case, however,
owing to the dendritic pattern displayed by the stripes. Troll (1958,
p. 64) favored the role of frost creep deforming initially polygonal
forms as a general explanation. Brockie (1968, pp. 197-198) was of the
Opinion that rill incision would result in stone accumulations, and
thereafter differences in the thermal characteristics between these and
the adjacent fines would promote inclined freezing fronts, which in turn
would lead to lateral sorting of subsurface stones into the stripes of
coarse fragments. J. Lundqvist (1962, p. 70) states that "there are pro-
bably no fundamental differences between the formation of miniature and
large patterns," except their dependence on the diurnal rather than annual

frost cycles.

31

Here the matter rests at present. Since no detailed investigations
were attempted on the Type II patterned grounds, a specific genetic in-
terpretation is not Offered. Nicholson's (1976, p. 341) comment that
"the initiation of patterns is more problematic than the mechanisms of
development" holds for small-diameter patterns as well as for their
larger counterparts, some aspects of which are discussed in the remainder
of this chapter.

2.2 Large-Diameter Patterned Ground

Occurrences of active large-diameter patterned ground were not noted
by this writer in the main icefield area, although some have been found
at high elevation near the International border (Miller, 1977). As dis-
cussed in a subsequent section, conditions suitable for the widespread
development of patterned ground are found primarily in the more conti-
nental parts of the Boundary Range. The Observations comprising the
remainder of this chapter were made at 1700 m on "Frost Ridge," situated
in the Cathedral Massif, where presently active patterned ground is found
in relative abundance. The intent of this section is not to provide a
comprehensive genetic explanation for these features, as such as approach
would require year-round instrumental Observation. Interest is focused
instead on some rather poorly known aspects of the internal structure
of the patterned ground. These observations are presented separately in
sections 2.2.1 through 2.2.4.

Site Description

The crest of Frost Ridge extends 1.5 km northeastward from its
juncture at 1700 m with Splinter Peak, to an elevation Of about 1200 m
(Figure 4.3). Detrital cover conceals a transition from the igneous and

metamorphic bedrock of the peak to thick layers of morainic material at

32

the downslope extremity of the ridge. Jones (1975, p. 35) interprets

this entire cover as a Wisconsin till, a view to which (with some reserva-
tion) this writer subscribes. The summit area of the ridge is gently
convex, with 30°-35° slopes on the northwest and southeast flanks.

In the upper reaches of Frost Ridge, near its confluence with
Splinter Peak, a field of well-developed sorted stripes occurs. The
stripes are nearly continuous over a large part of the ridge summit and
occupy primarily gentle (4°-10°) slopes with NE aspect. In places where
the gradient is negligible, an occasional sorted circle is found. A
view of the patterned area is presented in Figure 2-3. The general
trend of stripe axes reflects their adjustment to the microrelief. Stone
stripes are slightly sinuous and serve as channels for meltwater from
perennial snowbanks upslope. They often meet one another at low angles,
the intersections of which point downslope. The stripes are traceable
as coherent entities over distances as great as 75 m. Interspersed are
fine lobes composed primarily of silt.

Several stripe units were trenched normal to their long axes.
Sorting extends to a depth of approximately 80 cm, but the separation
Of fines and stones is incomplete. The features correspond to Poser's
(1932) "anchored" stone network. The largest particles were found near
the surface in the stone stripes; stone size decreases with depth.
Clasts of varying sizes are embedded within the fine stripes. Numerous
stones protrude through these surfaces, some possessing a cap of fine
soil. Details of these features are considered next.

2.2.1 Size and Spacing gf_Patterned Ground

 

Many workers (e.g. Goldthwait, 1976, p. 31; Nicholson, 1976, p. 339)

have commented on what they perceived to be a great regularity in the

33

Figure 2-3. Overview of Frost Ridge patterned ground site.

34

 

35

spacing of patterned ground unit cells. On the other hand, J. Lundqvist
(1962, p. 54) suggests that "the regularity seems to be somewhat overesti-
mated in the literature." Statistical analyses of Frost Ridge patterned
ground data indicate that the latter view is correct, even through casual
Observations had suggested Otherwise.

Three parallel sampling traverses normal to stripe axes were carried
out over the patterned area. Locations are shown in Figure 2-3. Data
were collected concerning width and length Of fine lobes and stone stripe
width. Spearman rank-order correlation coefficients (Nie, pt, 31,, 1975)
were computed for all combinations of these variables in each transect,
and for the entire set Of 65 Observations. Correlation coefficients are
low, indicating that stripe spacing is essentially random. Large standard
deviations for all variables tend to support this conclusion. The only
correlation coefficient that is statistically significant at the 0.05
level, while maintaining even moderate strength is the plot between
lobe width and length (.572) in Transect 3, where the features are thought
to have formed relatively recently due to a decrease in mean snowbank
size. This cannot, however, be construed as more than a low to moderate
correlation, and the lack of significance in the other plots suggests
that stripe spacing is indeed irregular.

The results of these analyses cast.some doubt on Nicholson's (1976,
p. 339) suggestion that the first cell to develop dictates the locations
of subsequently formed patterns. Numerous other controls on pattern size
and spacing have been proposed, including depths of frost penetration
and soil sorting (Troll, 1958, pp. 57-58), clast size within the parent
diamicton (Goldthwait, 1976, p. 33), and the spacing of blocks in the
initial material (Corte, 1966a, pp. 230-231). It is possible that a

36

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37

combination of these factors is responsible, and much work remains to be
done on this problem before its solution. It is suggested that further
research should be concentrated on circles, nets, or polygons, as the
slope factor associated with stripes may complicate interpretive efforts.
2.2.2 Effects 9: Moisture

Fundamental differences in the form of patterned ground and its
activity are related to temporal and spatial variations in moisture supply.
Figures 2-4 and 2-5 illustrate this point with respect to sorted stripe
morphology. The photos were taken at points within 75 m of one another
on Frost Ridge. Figure 2-3 divides the patterned area into horizontal
"zones" reflective of moisture supply. Each of these zones is discussed
below.
£01125

Zone A is at present the area of greatest apparent process intensity.
Here stone stripes stand 10 cm or more above the level of the intervening
fines, and carry minimal lichen cover. Vegetation, consisting primarily

of Carex spp., Potentilla, and occasional Cassiope tetragona, is restricted

 

 

to lobe margins and is in many places totally absent.1 This lack of lichen
and vegetation is partly attributable to late snow cover in this area.

In 1975, Zone A did not experience complete meltout until mid-July.
Probably more important in disruption of vegetation are cryogenic processes.
The fine lobes are subject to significant accretions Of segregation ice
(observed by B. Otto, personal communication, August 1976). Heave is
maximized at lobe centers (Jahn, 1970), so that vegetative colonization

is inhibited, except atlobe margins.

 

1I am indebted to Ruth Magnuson of Boulder, Colorado, for identi-
fying vegetation samples.

38

Figure 2-4. Active "Zone A" sorted stripes.

Figure 2-5. Inactive "Zone C" sorted stripes.

39

‘ year an? 4 .
“5* Mix,“ ”ME-fall...

 

40

Strong evidence for active mass movement processes in the lobes is
provided by plant roots. Excavation revealed that these trail off in an
upslope direction, indicating that movement is most rapid in the surfi-
cial layer of fines. With a decrease in slope, fines spread laterally
and bury neighboring stone stripes, which is suggestive of more rapid
movement in the former. Movement within the coarse stripes is not dis-
counted, however, as the stones comprising these are very sparsely
lichenized.

Apparently, the major factor responsible for the activity of stripes
in Zone A is their abundant water supply. As can be seen in Figure 2-3,
the trend of water-channeling stone stripes is such that Zone A is pro-
vided with a constant supply of moisture from snowbanks upslope. This
condition was noted to persist throughout the summer, so that the features
were still moist at the time of the autumn freeze. Heave and frost creep
are maximized in such a situation. This relationship is a critical fac-
tor in the formation and maintenance of patterned ground.

2219.3.

Zone 8 is characterized by rather heavily lichenized stone stripes
and bulging turf-banked lobes. Here the lobes have a nearly continuous
vegetative cover and occupy slopes of 6°-12°, steeper than those of the
Zone A stripes. Some lobes spill over the sides of the ridge to continue
as thin strips of fines for as much as 40 m downslope. In Zone 8, soli-
fluction probably exceeds frost creep, since fine lobes tend to override
and bury stone stripes. In 1975, snow had largely disappeared here by
23 June, although the area still received an abundant supply of melt-
water from upslope. This was attested by extreme saturation Of the lobes,

by their bulging profiles, and evidences Of overridden vegetation at lobe

41

fronts. Meltwater is channeled through stone stripes to points on the
lepe where the stones comprising them have been buried by soliflual debris.
The high frost table in early summer prohibits percolation of water to
depth, and promotes saturation of the upper layers. Water emerges at
the base of each riser, flows overland short distances, and saturates
the next lobe downslope. On some of the largest features, smaller lobes
are superimposed, this probably being reflective of the area of maximum
saturation.

Frost creep in the autumn is probably a less important process here
than in Zone A, because this area is snow-free at a much earlier date,
and because the snowbanks upslope have largely disappeared by the summer's
end. Movement in the stone stripes themselves, therefore, is minimal,
as indicated by their lichen cover. The net effect in this zone is eradi-
cation of preexisting patterns through burial by the active turf-banked
lobes.
A1922

This "zone" lies in the northwest part of the patterned area and is
comprised of inactive sorted stripes. This conclusion is based upon
several lines of evidence which presented themselves during the course
of the investigation.

Stone stripes in this area are heavily lichenized and stand below
the level of the intervening fine lobes. The latter have a subdued
appearance and are covered with a nearly continuous mat Of vegetation
whose roots penetrate the soil vertically. This plant community is

dominated by Salix, spp., Hierochloé alpina, and, particularly, Cassiope

 

tetragona. Raup (1965, p. 27) indicates that Hierochloé alpina prefers

 

dry sites, and that it is found only in stable soils. Kershaw (1976, p.

42

108) and Hulten (1968, p. 724) mention that Cassiope tetragona is also

 

indicative of dry conditions, but Raup (1965, pp. 98-99) found it in a
fairly wide range of moisture situations. This plant is not particularly
tolerant Of disturbance, however. Raup found that on stable heaths in
Northeast Greenland, it had coverages of up to 90%, but on disturbed
sites coverage fell to 1-6%. Since this plant is found in great abun-
dance in Zone C, it is concluded that the site is indeed stable.

The factor responsible for this apparent lack of cryogenic activity
is the paucity of moisture supply to this zone. Several spot checks in
late August, 1976, revealed that fines in Zone A contained up to 55%
greater water content (by weight) than did those of Zone C. Several
small areas of bare soil on lobe treads display polygonal networks of
desiccation cracks, also attesting to the relative summer dryness of this
area. This dryness is partly due to lack of winter snow cover. At the
time of the writer's first visit to the site in 1975, when the Camp 29
research facility was opened for the field season (23 June), this area
was devoid of snow and already quite dry, while adjacent parts of Zone A
had as much as l m of snow remaining. Winter winds probably keep the
area snow-free. Possibly more important is the trend of meltwater-
channeling stripes. The orientation of these is such that little moisture
is delivered to Zone C from the perennial snowbanks upslope during the
summer months, so that the entire area is desiccated by the time of the
annual freeze. Even though winter frost penetration is probably greatest
in Zone C, its effects are minimal in the absence of soil moisture.

Conclusions

 

From these observations it appears that the Frost Ridge patterned

ground develOped during a period when annual snowfall was greater and/or

43

summers were cooler than at present, allowing preservation of late snow-
banks in strategic positions through the summer. Evidence that such a
situation has existed on Frost Ridge is provided by the poorly developed
"incipient" patterned ground emerging from beneath snowbanks during
August at this and many other late snow sites in the Cathedral Massif.

It is possible that these have formed since the 1750 advance (Jones, 1975)
of cirque glaciers in this area. Since patterned ground could not be ex-
pected to develop beneath thick perennial snowbanks, it is likely that it
has formed at the margin of retained snowpacks whose mean sizes diminish
over the course of a long-term warming trend. As these new forms are
developing, those farther from the moisture source become progressively
less active.

Similar situations are found elsewhere in the Cathedral Massif.

One striking example is illustrated in Figure 2-6. This site is adjacent
to the Chapel Glacier, and overlooks Nelson Lake. Inactive, heavily
lichenized polygons were found on a small knoll, the top of which becomes
dry early in the summer. 0n the knoll's flanks, where late snowbanks
persist, active patterned ground was found (Figure 2-7). The relation-
ship is presumed to be identical to that described for the Frost Ridge
site. indicating a past period of cooler temperatures and/or greater
snowfall.

Every other active patterned ground site examined was provided with
moisture originating in a lingering snowbank uplepe, usually on north-
facing slopes. These relationships suggest that patterned ground occur-
rence and activity are governed by a delicate balance between snowbank
thickness and location, and the timing of moisture release. As noted by

Benedict (1965, pp. 23-24). the Optimal locations for patterned ground

44

Figure 2-6. Inactive patterned ground adjacent to Chapel Glacier.
Note lichenized borders and vegetated centers.

‘ Figure 2-7. Active patterned ground adjacent to Chapel Glacier. This
site is the lighter colored area in background of Figure
2-6.

45

 

46

formation (and maintenance) are sites with thin or negligible winter snow-
cover and which receive summer meltwater from late-lying snowbanks upslope.
In such areas cryogenic activity is maximized by deep frost penetration
into saturated regolith. This point is crucial to arguments made later
regarding patterned ground distribution and will be taken up again in
Chapter Four.

2.3 Fabric Analyses

 

Little research has been carried out on the arrangement of stones in
sorted patterned ground features. There have been numerous and often
conflicting casual observations, but very few precise surveys. In this
section orientation data from a sorted stripe border are presented. It
is hoped that statistical analysis of the data, combined with literature
review, will help to relate observed fabrics to process in a meaningful
way.

2.3.1 Previous Research

 

In order to appreciate such significance as exists in the fabrics
of borders, some discussion must first be concentrated upon the orienta-
tion of blocks within the features' centers. Several studies (G. Lundqvist,
1949, pp. 345-346; Schmertmann and Taylor, 1965, pp. 23-24; Furrer and
Bachmann, 1968, p. 9) have shown that there is usually a radial or centri-
fugal pattern of stone orientation in the centers of sorted circles and
polygons. The long axes of the stones tend to be oriented at right
angles to the nearest border and are Often vertical (Corte, 1962, p. 16),
or steeply dipping (Furrer and Bachmann, 1968, p. 9). The mechanism re-
sponsible for this orientation remains to be investigated, but it appears
that the pattern may be due to one or both Of two factors. The first

may be a confirmation Of the mass displacement hypothesis of patterned

47

ground formation, which has been demonstrated experimentally by Diulynski
(1963) and Anketell, pt, 91, (1970). In this model, patterned ground
results from an upwelling of fine particles into overlying coarser material
due to "moisture controlled changes in density and intergranular pressure"
(Washburn, 1973, p. 145). Such movement would probably result in stone
orientations reflective of radial movement. A second process which could
operate alone or in conjunction with mass displacement is reorientation
of stones by repeated freezing and thawing. Such reorientation has been
demonstrated (v. Washburn, 1973, pp. 76-79; French, 1976, pp. 32-33),

and results from differential heave between the taps and bottoms of
elongate stones during freezing. The inclined freezing fronts associated
with sorted patterned ground (Schmertmann and Taylor, 1965, p. 62) may
Operate to promote rotation of stones into the radial pattern. The sub-
ject of stone reorientation will be taken up in more detail later in

this chapter.

Sorted stripes are generally regarded as slope-induced variants of
circular or polygonal forms. Initial sorting is thought to produce such
concentrations Of fines that the material becomes vulnerable to solifluc-
tion, with subsequent elongation of the patterns. This mechanism would
operate in such a way as to destroy a radial fabric and replace it with
one characteristic of solifluction deposits. Fabrics Of the latter are
well known (Benedict, 1966, pp. 26-27; 1970a, p. 205; 1976, pp. 63-64;
Washburn, 1973, p. 189), and are characterized by upslope-dipping long
axes aligned parallel to the direction Of movement. Near lobe fronts, a
transverse orientation becomes dominant. G. Lundqvist (1949, p. 342)
presents a diagram suggesting a radial orientation pattern near the fronts

of "stone banked flow earth cones." Furrer and Bachmann's (1968, p. 11)

48

diagrams show that stones near the lateral margins of the fines possess
long axis orientations oblique to lines Of flow. This is suggestive of
stone rotation during outfreezing as described above, or of lower rates
of movement close to lobe margins. Stones undergoing ejection from the
lateral margins Of fine stripes were noted in the present study area.
However, only further process-oriented study can pinpoint exactly the
factors responsible for this oblique orientation.

The centrifugal pattern is not translated to the borders of patterned
ground. These is some mechanism by which stones become rotated to posi-
tions paralleling the outlines of the features during or after ejection
from the fine centers. This will be discussed more fully after literature
review and presentation Of field observations and data from the present
study.

Many workers have made parenthetical reference to the orientation
Of blocks in patterned ground borders. Among these researchers there
appear to be two contradictory lines of thought. The first regards long
axes Of stones as being predominantly vertical. Huxley and Odell (1924,
p. 209) characterized the stones of polygon borders as "usually upended,"
as did Ahlmann (1963, p. 11), and Richmond (1949, p. 145), the latter
commenting that stones are usually found "with their longer axis vertical."
Bunting and Jackson (1970, p. 201) describe stones in the borders as
"vertically oriented, but with no preferred directional orientation ex-
cept in adjacent situations."

A second viewpoint is represented by Sharp (1942, p. 276), who found
that "platy fragments lie flat in the central area and are set gg_eggg in
the borders" ("on edge“ would indicate that intermediate or 'b' axes are

vertical or near vertical). Sharp is corraborated in this by Benedict

49

(1965, p. 24) who states that "where tabular stones are present in the
borders of polygons, they tend to stand on edge and to be oriented paral-
lel to the sides of the polygons." Regarding sorted stripes, French
(1976, p. 189) comments "the stones and boulders are commonly on edge
with a long axis parallel to the line of movement of the stripe."

To the writer's knowledge, only a very few detailed investigations
have been published which deal with the fabric of patterned ground peri-
pheries. The first such study was made by G. Lundqvist (1949), whose
diagrams suggest a near perfect agreement between the trend of the border
and the blocky material within it, although he does mention that some
of the fragments lie obliquely, or at right angles to the border.

Studies in the Alps and in Spitsbergen by Furrer (1968) and Furrer
and Bachmann (1968) convinced them that the fabric of patterned ground
is "form-specific," i.e., typical Of the features. This conclusion has
enabled them to identify fossil forms through fabric analysis. Their
studies show a maximum (50%) number Of stones parallel to the border, but
a large minority (30%) transverse to it. Long-axis dips are much lower
in the borders than in the central areas of fines.

G. Lundqvist (1962, p. 54) asserts that "the orientation of the
boulders in the (coarse) stripes is directed strictly down the slopes,
parallel to the stripes themselves,".and presents diagrams to this effect.
Brockie (1964, p. 98), commenting on "stone streams" in New Zealand re-
marks that "the orientation and dip of the major axis of individual
rocks...reveals a markedly preferential orientation and dip in the direc-
tion of the stream...it is believed that the large surface rocks demon-
strate a less perfect arrangement than the smaller material near the

base.“ Brockie felt that the data were not amenable to statistical

50

treatment due to close packing of the stones.

R. 8. King (1972, p. 162) found that no preferential orientation
existed in areas where rounded boulders formed "stone garlands," but
where the garlands were comprised of platy phyllite blocks "circum-
ferential orientation" did exist, apparently because of interaction be-
tween neighboring lobes.

2.3.2 Field Procedure and Data Analysis

On Frost Ridge, orientation data were Obtained from a sorted stripe
representative of Zone A stripes. This feature has an average slope of
3°-4°, a length Of 13.7 m, and a mean width of 1.14 m (narrowing uplepe,
widening downslope). Three samples of 50 Observations each were taken,
one in each of the stone stripes bordering the fine lobe, and one from
the "stone garland" at the feature's downslope margin. Measurements of
a-axis azimuth, as well as a and b-axis dip were made with the Brunton
compass. Only tabular blocks with axial ratios 2:1 were used for the
analysis. Measurements were made in the smallest area possible, involv-
ing no more than 4 m of length in each stone stripe.

Orientation and a-axis dips were analyzed using a computer program
developed by Mark (1971). Fabric diagrams are presented in Figure 2-8,
and details of the analyses are summarized in Table 2-2. Diagrams were
contoured by the Kalsbeek (1963) method. Although visual inspection in
the field had suggested a random azimuthal orientation, vector analysis
reveals that both stone stripe samples have preferred orientations signi-

ficant at the .01 Ievei.2 The trend of the stripe was 55° while azimuths

 

2Since the analysis was completed, it has come to the writer's atten-
tion that there are problems inherent in the statistical test used in
Mark's program. The correction term

51

Figure 2-8. Frost Ridge stone stripe fabrics. Ploted on Schmidt Net,
Lower Hemisphere. Direction of local slope and inter-
section Of plane of lepe with hemisphere are indicated.

52

 

 

53

 

 

 

 

 

 

 

 

 

 

m.m~ m.nm m.m~ mHo mwxmin

onH<H>uo om<oz<em

om.mm om.o¢ om.~m aHo mwxmin z<mz

~.m_ m.mp N.m_ aHo mwxmum

.onP<H>uo om<oz<pm

0mm.MN 0N.N_. om.m_. QHD mwXfllm Z<m2

mm.m_ ow.m_ mm.FF Amy mozmaHmzou

do nzHo<m 4<uHmmzam

w¢.~ op.m mm.m Axv mmhmz<m<a

onmHomma no mp<thmm

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emep epm cum onp<hzmHmo achom> z<mz
Aucocuv Amawcum pmmzv Amapgum ammuv

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<H<a u~mm<m mmumhm szHm

.NIN m4m<H

 

54

of the maximum mean vector for the east and west stripes are 62° and 81°
respectively, demonstrating a strong preferred orientation subparallel to
the axis of the stripe. These samples approximate a spherical-normal
distribution since "k" values exceed 3.0 in both cases (Andrews and
Shmizu, 1966, p. 156). The spherical radius of confidence (6) indicates

a 5% probability that the true mean direction of all stones in the stripes
is more than 11.8° from the calculated sample mean for the east stripe,
and 13.9° in the west stripe (Mark, 1971, p. 2663).

The arrangement of blocks at the front of the fine lobe is funda-
mentally different from that in the lateral stripes. The orientation of
the mean vector is 148°, normal to the trend of the feature itself, as
was also reported by G. Lundqvist. However, corrected values in the
vector analysis and the results of the Tukey X2 test indicate that pre-
ferred orientation is weak or nonexistent, confirming what is suggested
by visual inspection of the plotted values (Figure 2-8, Sample 3). The
lack of fabric strength detected by these tests may be more the result
of poor sampling than absence of preferred orientation, however. Acquisi-
tion of 50 observations necessitated taking some measurements from blocks
close to or within the area in which the garland changes orientation as
it grades into the lateral stripes. This probably introduced some dis-

tortion in the azimuth values.

 

S] = 1.24(R/N) - 0.302

suggested by Mark (1973, p. 1372) was used to enter a significance table
(ibid.). The stone stripe samples were found to remain significant at
the .01 level, but the garland was so only at the 0.1 level. As an addi-
tional check, a Tukey X test (Harrison, 1957) was run using 20° class
intervals and a 180° distribution. This test yielded results similar to
the vector analysis (significant at the .05 level) in the cases Of the
stone stripes, but the null hypothesis of a uniform distribution could
not be rejected for the garland.

55

2.3.3 Opigjg_gf_Fabrics

It can be seen that the results of this analysis support the conclu-
sions of the earlier workers cited above, who reported preferred orienta-
tions in the stones of patterned ground borders. The mechanisms responsi-
ble for this orientation are, however, still somewhat Obscure. In this
section the various hypotheses that have been suggested are reviewed, and
data on a and b-axis inclination and orientation are used as a partial
basis for deduction concerning processes responsible for observed fabrics.

Some investigators (e.g., R. 8. King, 1971, pp. 383-384) explain
the fabric of stone stripes as related to slope processes, usually soli-
fluction, in the adjacent fine stripes. Although this explanation
initially appears credible, several lines Of evidence militate against
it:

1) The blocks of sorted circles and polygons are also oriented in
circumferential manner, parallel to the outline of the features. There
must be a connective process Operating to produce analogous fabrics in
the various geometrical forms of patterned ground, as was recognized by
G. Lundqvist (1949, p. 346).

2) If solifluction were the main control behind the orientation
pattern, rates Of movement would necessarily be greater in the fine lobes
than in the stone stripes. Although movement surveys were not a part of
the writer's present undertaking, various studies have established that
movement may be greater in either the fine stripes (Chambers, 1966, pp.
29-30; 1970, p. 93; MacKay and Mathews, 1974) or the coarse stripes
(Antevs, 1932, pp. 57-58; Washburn, 1947, pp. 87-88). Some investigators
have found evidence for relative movement of both types within the same

locality (Benedict, 1970a. PP. 203 & 207; Washburn, 1969, p. 187). This

56

apparent discrepancy can be explained by the predominance of solifluction
in moist microenvironments, resulting in greater movement in the fine
stripes. Where conditions are relatively dry, frost creep predominates
and the stony stripes move more rapidly than the fines, owing to the
latter's cohesion on resettling. In both cases, however, similar fabrics
apparently exist (compare Benedict, 1970a, Figure 44, p. 204; with
Benedict, 1966, Figure 3, p. 26). It therefore seems that creep is
also a factor in producing downslope-oriented fabrics.

3) Forces exerted by differential downslope movement between coarse
and fine stripes may not be sufficient to produce preferred downslope
orientations in blocks near the centers of wide stone stripes. In King's
discussion Of stone orientation within stripes, he suggests that soli-
fluction in “soil stripes" would operate in such a manner as to produce
gentle inclinations in downlepe-dipping stones projecting from adjacent
stone stripes. Conversely, stones with upslope dips would tend to have
their inclinations steepened by such movement. Unfortunately, the data
presented by King in support of this hypothesis, which show maxima at
both low and high dip angles, do not include the §gg§g_of the dips. This,
in the writer's view, makes his supposition rather speculative.

King's assertion was tested using data available from the Frost Ridge
stripes. Since the long-axis dips of stones with azimuthal orientations
normal or subnormal to the stripe axis were of little use for this analysis,
the dips of b-axes were substituted in these cases (the b-axis is perpen-
dicular to the a-axis by definition). In this way, a sample of 100 stones
was made available, 47 dipping between south and west (upslope), and 53
with dips between north and east. If the solifluction hypothesis were to

be substantiated, we would expect the former group to display higher

57

inclination angles, since the stripe trends N55°E. The two-sample
Kolmogorov-Smirnov test was applied to the data. The cumulative frequency
distributions are presented in Figure 2-9; a between-sample difference Of
26.5% within any class interval is required to establish statistical signi-
ficance at the 0.05 level. It can be seen that the null hypothesis of

"no significant difference" between samples should be retained, making
King's suggestions improbable, at least in the present study area.

It seems that the major clue to the origin of patterned ground
border fabrics lies not so much in the azimuthal orientation (which could
be produced by a variety of processes) as in the dips, particularly of
the b-axes. Figures 2-10 and 2-11 show the frequencies Of a and b-axis
dips in 15° intervals. From these it can be seen that the blocks within
stone stripes have more steeply inclined b than a-axes. This supports
the Observations of those workers cited above who remarked on the large
number of stones lying "on edge." In both the east (Sample #1) and west
(Sample #2) stripes, more than 50% of the stones are inclined 3_45°. By
contrast, the great majority of a-axis inclinations are <30°. There is
no apparent preference for either axis to dip predominantly up or down-
slope.

This pattern Of inclinations seems to suggest that the stone stripes
are subjected to compressive forces. A mechanism which may account for
both the preferred azimuthal orientation and the large proportion Of
edgewise blocks in all geometric forms of sorted patterned ground has
been suggested by Goldthwait (1976, p. 31). "Squeezing" of the coarse
borders by expansion Of saturated fines during the fall freeze could be
expected to set stones on edge, and may also account for aligned a-axes

in situations where adjacent centers exert compressive forces. The

58

Figure 2-9. Cumulative frequency distributions, up- and downslope dips.

59'

 

PERCENT

 

I'NE

 

60

Figure 2-10. Histograms of Figure 2-11. Histograms of
a-axis dips. b-axis dips.

61

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

a-AXIS DIPS b-AXIS DIPS

sow 507

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8 sol» SAMPLE I a 30+ SAMPLE I
a: (I
3‘ ‘a‘

201» 20-

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Go 15 30 45 60 75 50 CO 15 30 45 so 75 90

DIP (°) 0”” 1°)

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40' 40(7

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507 50v

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20» 20

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O 15 30 45 60 75 9O 0 15 30 45 60 75 90

 

62

rigidity Of the frozen fines would effect reorientation of stones by
pushing them into as compact an area as possible during expansion.

Lateral displacement within patterned ground features has been docu-
mented, and in some cases measured by other workers, although Goldthwait
was apparently not aware of these works. Jahn (1966, p. 144; 1970, p.
120), working in Spitsbergern, measured heave amounting to about 5 cm
in the lateral margin of a sorted circle's fine area, while in the center,
he found heave as much as 15 cm. He remarks that "the movement of the
central area pushes against the inside Of the border causing the stones
to slide down the steep slope " (Jahn, 1966, p. 144).

Taylor (Schemertmann and Taylor, 1965, p. 27), found horizontal
heave Of about 1.4 cm in a sorted circle near Thule, Greenland. He was
not satisfied with the survey method used however, and strongly recom-
mended that this problem be pursued in future work through the use of
horizontal photography (jpjg, p. 74).

Benedict (1970a, p. 201) used painted connecting lines to detect
movement of adjacent stones in polygon borders. In One "frost-disturbed
area," he found that 15 of 20 such marked stones had been displaced
during one winter, apparently by "the influence of fine-textured centers."

It would seem, therefore, that expansion of fine centers is a plauSi-
ble explanation for the fabrics that have been observed. A further indi-
cation lieS in the b-axis inclination Of blocks within the downslope
margin of the fine lobe. Here, compression is minimized since forces
are exerted from one direction only. Both the a and b-axis inclinations
are relatively low, lending further support to the compression hypothesis.

It must be stressed that much more work is required to establish an

adequate link between form and process. Recorded horizontal displacements

63

are not of great magnitude, and careful study should be made of the effect
of such movement on stone orientation and inclination. The influence of
stone shape on orientation may also be Of some significance, and should

be considered in future studies, as indicated by King's (1972, p. 162)
Observation that rounded boulders show no preferred orientation. Finally,
it should be emphasized that the suggestions presented here are based on

a rather small number of samples. More observations are required before
truly firm conclusions can be drawn. The writer hopes to extend these
studies in the near future.

2.4 Particle Shape Analysis and Frost Sorting,

It has long been suspected that "upfreezing" of stones from an ini-
tially heterogeneous mixture Of fines and rock fragments may be at least
partially responsible for the striking particle size segregation charac-
teristic of sorted patterned ground. Detailed laboratory studies by
Corte (1961; 1962; 1966) have shown this theory to be viable. That the
shape of a stone may be an important factor influencing its propensity
for migration and separation from a fine soil matrix has been touched
upon by several workers (Price, 1970, p. 109; Taber, 1943, p. 1453;
Washburn. 1973, p. 76), but to this writer's knowledge has not been
rigorously tested, except by Corte (1966a, p. 200), whose work involving
freezing of soil samples from the bottom up indicates that "particles
Of similar material...with less sphericity and greater contact area Show
a greater migration.” It, therefore, seems reasonable to suspect that
different shape characteristics predominate in the coarse and fine frac-
tions of patterned ground, and that the shapes in these fractions may
provide a partial basis for deduction of the particular processes in-

volved.

64

2.4.1 Mechanisms gf_$tone Movement

 

 

There are two commonly-accepted mechanisms, dubbed the "frost-pull"
and "frost-push" hypotheses (Washburn, 1973, pp. 71-80), by which differ-
ential movement between fines and stones may be explained, although there
is a notable lack of field evidence to indicate the relative importance
of each. In the frost-pull model, a stone within a freezing soil body
is raised in association with expansion of the saturated fines surround-
ing it, leaving a void in its original position. The stone is not able
to return to this position when thaw occurs because lateral thrusting
during freezing narrows the void, and because thawing soil tends to slump
into the cavity. Through repetition of this process a stone can gradually
work its way to the surface.

According to the frost-push hypothesis, upward movement of stones
occurs as ice lenses form around and at their bases. The fact that rock
fragments are better heat conductors than fine soil results in the former
acting as loci for development of segregation ice, which forces them up-
ward. An important factor controlling the magnitude of movement by
frost-push is the amount of unfrozen pore water in the fines overlying
the migrating stone. High unfrozen water content results in relatively
low soil strength, so that stone migration may not be significantly
impeded.

In both models the magnitude Of the movement increases with the
effective vertical height Of the stone. Washburn (1973, p. 71) cites
empirical work by Kaplar (1969, p. 36) in which the maximum heave experi-
enced by a stone due to frost-pull is a function of the stone's vertical
height. A similar situation exists with the frost-push mechanism, where

movement is proportional to the total thickness of segregated ice lenses

65

at the base of, and surrounding the stone.

As noted in the section dealing with patterned ground fabrics, there
is a process associated with upfreezing which Operates to maximize the
effective height of coarse particles and thereby to increase their capa-
city for movement. Stones are first gripped in their upper portions by a
descending freezing front. Heave is directed upward, causing reorienta-
tion Of elongate stones into positions of higher angle than the original
postures. With repeated cycles, the long axis of a stone is rotated so
that it becomes oriented normal to the frost line. Washburn (1973, p.
79) and French (1976, p. 32) provide diagramatic representation of this
phenomenon. It appears that this process should not be restricted to
horizontal freezing fronts, but may also be Operative in conjunction with
the inclined freezing fronts associated with lateral sorting. The end
result in all cases would be rotation Of the long axis to a position
approximately parallel to the direction Of heat flow, thereby maximizing
the effectiveness of the sorting process, independent of the orientation
assumed by the freezing plane.

2.4.2 Field Procedures and Assumptions

 

Four point samples of 50 stones each were Obtained from a representa-
tive "Zone A" sorted stripe on Frost Ridge. The samples were taken from
the uppermost 10-15 cm, and from near the depth of sorting (=80 cm) in
both the fine lobe and one adjoining stone stripe. Some effort was made
visually to obtain stones of approximately the same Size. Although there
is a tendency for the largest rock fragments to be positioned near the
surface in the stone stripes, many smaller stones were found throughout
these rather tightly packed features so that sampling represented no

apparent difficulties. All stones were Of a relatively coarse-grained

66

granodiorite type common in this area.

Stones were measured for computation of the Cailleux Roundness and
Flatness Indices (Tricart and Schaeffer, 1950). The former is given by
(g?) 1000, where R is the minimum radius of curvature in the principal
plane, and a is the length of the long axis. This index calculates the
degree to which the corners of a stone have been rounded, and is not an
expression of geometrical shape. Values can range from near zero for
very angular stones, to 1000 for extremely rounded particles.

Cailleux's flatness index is computed by (%§?) 100, where a, b, and

c are the long, intermediate, and short axes of the stone. Lithologies
such as slate can produce values of 1000. King and Buckley (1968) have
shown that this index is inversely related to the sphericity index, (3%) .
proposed by Krumbein (1941), and that it is therefore unnecessary to com-
pute both. The Cailleux index was used in this study for its ease of
computation.

These indices have the advantage of comparability, since they have
been used by many investigators. The roundess index, in particular, has
proven to be of value as an indicator of depositional mode and/or environ-
mental conditions (King and Buckley, 1968), although the indices were
used to somewhat different effect in this study.

As discussed in an earlier section, it is likely that the Frost
Ridge patterned ground is developed in till, so that stones comptising
the features were deposited under more or less uniform conditions. Dif-
ferences between stones are, therefore, inherited and diffused through-
out the till sheet due to glacial "mixing." Furthermore, the processes
of mass movement associated with the features (frost creep and solifluc-

tion) arethoughttn be incapable of affecting the angularity of particles

67

(Benedict, 1976, p. 61), and analysis of weathering rind thicknesses
showed no statistical difference between samples (see below). Thus, it
would appear that such dissimilarities in shape and roundness as might
be found in the stones of the various sorted stripe fractions would be
attributable more to the propensity of the particles for movement under
the influence of frost than modification by environmental parameters or
depositional incongruity.

2.4.3 Data Analyses

 

Values for roundness and flatness were computed for each sample and
comparison made by the KOlmorgorov-Smirnov test. Each sample was com-
pared with all other samples. Results are presented in Tables 2-3 and
2-4.

An interesting spatial arrangement of shape characteristics is re-
vealed by examination Of the data. In the sample from depth in the
fine stripe, the mean value for flatness is lower, but higher for round-
ness, than for any other sample. Comparison by the Kolmogorov-Smirnov
statistic confirms this. There is a statistically Significant difference
(.05 level) in roundness for the plots of lobe depth against both lobe
surface and stone stripe surface. Direction is such that higher round-
ness values occur at depth in the fines.

Even more interesting are the results of the flatness analyses.
Although computed values are not particularly high in any sample (as
might be expected with the rock type), there are statistical differences
at the .05 level between lobe depth and both lobe surface and stone
stripe surface. It will be noted that the plot between lobe depth and
stone stripe depth is significant at a level somewhat above .10, but does

not reach the critical limit at the .05 level, a situation which also

68

Figure 2-12. Cumulative frequency distributions, Cailleux flatness
values (Kolmogorov-Smirnov test).

69

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70

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mm34<> mmmzp<4n x2m44H<u no mHm>4<z< .muw m4m<h

71

Figure 2-13. Cumulative frequency distributions, Cailleux roundness
values (Kolmogorov-Smirnov test).

72

 

 

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73

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74

occurs in the same plot Of the roundness analysis.

What emerges is a pattern of higher flatness and lower roundness
values in stones situated where classic theories of patterned ground
formation suggest that the stones should be segregated out of the fine
center. As a check to insure that differential movement of stones is
not attributable to discrepancy in stone size between samples, a-axis
lengths for each sample were plotted against all other samples. These
plots yield only one between-sample difference, that of lobe depth
against stone stripe surface. Since different shape characteristics
occur between several other combinations Of samples, it appears that we
can discount the possibility that stone size is the primary factor re-
sponsible for the observed differences between samples. The one differ-
ence that does occur indicates that more care should be taken to obtain
stones within strictly defined size categories in future studies, since
the dimensions Of a stone are partially responsible for the magnitude
of its movement.

The possibility was also considered that the observed differences
in stone shape are attributable to intensified chemical weathering with-
in the relatively moist fine lobe. Thorn (1975), in a study of nivation
processes. suggests that rock weathering rind thickness is a good indi-
cator of the intensity of chemical weathering at a site. This assumption
is also made here.

Micrometer calipers were used to measure weathering rind thickness
to the nearest 0.5 mm on each of the particles for which Cailleux indices
were calculated. Descriptive statistics and histograms of these data
are presented as Table 2-5 and Figure 2-14, respectively. Although it

would be desirable to examine the null hypothesis that the samples were

75

 

 

 

 

 

 

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00<02<Hm

 

 

 

 

 

 

 

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.mum m40<~

 

76

Figure 2-14. Histograms Of weathering rind thicknesses.

15

80

 

 

 

 

 

 

 

 

 

 

 

 

 

77

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

”I
”I
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0
a
giei I81
0
:‘ IO' .0.
S . I I
o I I I I I0 I: o I 4 I I 10 II M II
Imp ‘IIIIcIIIIEss (mm)
LOBE SURFACE LOSE DEPTH
25 ‘
to ‘
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Per—m F—r—i—l—I
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STONE STRIPE DEPTH STONE STRIPE

SURFACE

78

drawn from the same population by the difference of means test or analysis
of variance, the distinctly non-normal data distribution does not allow
use of these techniques. Transformation is not possible, since many
particles displayed no visible weathering rind. Unfortunately, neither
of the nonparametric alternatives to the above tests (Mann-Whitney U and
Kruskal-Wallis nonparametric analysis of variance) are appropriate, due

to a large number of tied ranks. The observations were therefore treated
as nominal-scale data by partitioning each sample into three arbitrary
weathering rind classes, "thin," “medium," and "thick." Samples were

then compared by means of the X2 statistic. Although a considerable
amount of information was undoubtedly lost by this procedure, X2 appears
to be one of the few tests whose uSe is valid in this situation. Compari-
son Of each sample with every other failed to define a statistical dif-
ference between any pair at the 0.05 level of significance. Visual inspec-
tion of histogramed data tends to support this conclusion. The null
hypothesis of no difference in chemical weathering intensity between
samples is, therefore, retained. It should be noted, however, that
coarse-grained rocks such as the granodiorite used here are not as desir-
able for this type of analysis as those of finer grain size. This is
because chemical weathering tends to attack the bonds between coarse
grains, which are removed with little retention of surficial discolora-

tion on the rock (Birkeland, 1974, p. 75).

 

2.4.4 Interpretation pf_$hape Characteristics

 

The data presented seem to confirm that the arrangement of stone
concentrations relative to the fine SOil results from frost sorting.
This conclusion is perhaps unspectacular in light of the widespread

acceptance of this process as a factor in the formation of patterned

79

ground, but it nonetheless provides additional support for the concept.
The demonstrated coincidence of high flatness and low roundness values

in the stone stripes, where stones are assumed to have been sorted out
from the fines, indicates that shape plays an important role in governing
a given stone's likelihood of being segregated. Since there appears to
be no significant difference in chemical weathering in any fraction Of
the sorted stripe, it is difficult to explain the Observed distribution
of shapes in terms of any mechanism other than frost sorting.

A possibly more interesting conclusion is that the distribution of
shape characteristics provides evidence for the importance of the frost-
push mechanism. High flatness characteristics should be effectual in
minimizing resistance Offered by overlying frozen soil as a stone is
forced upward by formation of segregation ice at its base. This would
be particularly true if the stone has been subject to the rotational
mechanism, so that its major axis becomes normal to the freezing plane,
as discussed above. On the other hand, both sphericity and roundness
would tend to prevent, or at least inhibit, movement by frost-push since
the resistance offered would be greater with these traits. Theoretically,
frost-pull should not discriminate between stones of different shapes
(assuming equal sizes), so it appears that frost-push must play an impor-
tant role in the sorting. Further evidence for the operation of this
mechanism comes from the occasional “silt-capped" stones noted to be
protruding from the fine lobes. As discussed by Washburn (1969, p. 56),
these are indicative of rapid upfreezing caused by the formation of
relatively thick ice lenses at the bases Of stones.

Since it would be difficult to verify the above interpretations in

the field, further study of the effect of stone shape on movement might

80

be studied most profitably under controlled laboratory conditions. If

the suggestions made here were shown by experimentation to be tenable,

the analysis Of shape characteristics may prove to be a valuable indicator
of the relative efficacy Of the frost-push mechanism under field condi-
tions. That fragments of certain lithologies may be more susceptible to
frost sorting is also suggested, since those with high flatness values

may move more rapidly.

CHAPTER III
PERMAFROST DISTRIBUTION IN_THE JUNEAU ICEFIELD REGION

 

 

Although the occurrence of patterned ground is not strictly dependent
upon the presence Of permafrost, large-diameter forms are characteristic
of a permafrost environment (Jackli, 1957, p. 21; Washburn, 1973, pp.

112, 123, 134, 241-242), and for this reason some attention will be
focused on permafrost within the Juneau Icefield Region.
3.1 Literature Review

In the high mountains of most of the world, the extent of permafrost
is very poorly known (Ives, 1974). There have been several attempts to
portray the distribution of alpine permafrost through the use of theore-
tical calculations, but data derived from actual Observations are few.

The Boundary Range is no exception, although some investigations have
been made on its eastern margin. The permafrost literature for the study
area is reviewed below, and known occurrences are compared with calculated

permafrost levels.

 

3.1.1 Southeast Alaska and Coastal British Columbia

Baranov (1964, pp. 10-13, 22-23) has discussed the distribution Of
permafrost in the high mountains of the world, basing his calculations
on the mean January air temperature and the duration of subzero tempera-
tures at various sites. Using these criteria, he speculates that the
lower boundary of permafrost along the Pacific Coast of North America

rises from 75 m in the vicinity Of the Gulf of Alaska to 2500 m at 50°N.

81

82

He also suggests that this lower limit rises with increasing continentality.

Ferrien's (1965) map shows southeastern Alaska in its entirety as
being "generally free of permafrost, but a few small isolated masses of
permafrost (exist) at high altitudes." Further searching of the litera-
ture revealed no confirmed report of permafrost anywhere in southeast
Alaska, although its existence in the high peaks of the Fairweather Range
(Mt. Fairweather, 4663 m) can hardly be doubted. Ugolini (1966, p. 53)
suggests that permafrost may exist above the 900 m level in the locality
of Muir Inlet. This postulation is partially based upon the presence of
turf-hummocks, a rather poor indicator of permafrost conditions (Washburn,
1973, p. 126).

Since Observations of permafrost in mountainous areas under oceanic
influence are extremely rare, Mathews' (1955) notes from the southern
Coast Mountains of British Columbia assume a special significance.
Several occurrences of frozen ground surviving throughout the summer
were found at 1830 m on the Cinder Cone at Garibaldi Park (49°, 58'N,
123°, OO'W). One of the sites was within the walls of a natural tunnel
in which no marked air circulation was observed; it is possible that this
exposure is attributable to Balch ventilation. However, several occur-
rences more satisfactory for diagnostic purposes were found in the walls
of channels being cut by meltwaters frOm a nearby glacier. Mathews em-
phasized that this permafrost had been very recently exposed by the
glacier's retreat and that it was relict, and degrading under present
climatic conditions. This conclusion is underscored by the more recent
studies of MacKay and Mathews (1974, p. 354) in the same locality. Ex-
periments using vials designed to burst upon freezing indicate that

frost does not penetrate beyond 5 cm depth in winter, even at elevations

83

above the level of an adjacent glacier. This situation is no doubt attri-
butable to the damping effect of a heavy snow cover on the depth of winter
freezing.

3.1.2 Interior British Columbia

 

Brown's (1967a) map of permafrost distribution in Canada portrays
widespread alpine permafrost in northwestern British Columbia, but
coverage does not extend into Alaska. Extensive permafrost in the
southern Coast Ranges is shown, however, and a more limited distribution
is indicated in the Kitimat and Pacific Ranges. The cordilleran section
of this map was developed using lapse rates (1°C/164 m) to approximate
the elevation of the 30°F (-1.11°C) mean annual air isotherm at 169 sta-
tions in the Canadian Cordillera; a least-squares regression line was
then fitted to the data. By this method he estimates the lower limit of
permafrost to be 1866-2139 m at 49°N., falling to 1159-1432 m (:J35 m)
at 54°N. Brown's (1976b, p. 20) field observations indicate that the
lower limit of permafrost is "uniform" at about 1220 m throughout north-
ern British Columbia. He estimates that the discontinuous zone lies
between 1220 and 2440 m, and that above 2440 m permafrost is continuous.

Crampton (1977) has recently carried out investigations in north-
western British Columbia and found that permafrost thickness increases
on a transect between Fort Nelson and the N.W.T. - Alberta - B.C. border.
During August, scattered islands of ground ice were present at 425 m near
Snake River, 55 km northeast of Fort Nelson. At a similar latitude, but
435 km to the west, Brown (1976b, p. 28) found no permafrost at the
Cassiar townsite (1065 m). Just below 1370 m permafrost is sporadic;

above this elevation it is widespread.

84

3.2 Permafrost Sites jg_the Juneau Icefield Region

 

There have been several permafrost sites noted in the Juneau Icefield
Region, but their representativeness is not known, and no ground tempera-
ture data are available. Based upon these occurrences and glaciothermal
investigations, Miller (1975, p. 119) has suggested that permafrost is
widespread above 1675 m in the Atlin region, and above 1825 m in the
central icefield. The known permafrost locations in this region are out-
lined below.

Fourth gr_July Creek Valley

 

At this location, palsas are found in a Sphagnum bog at elevations
down to 915 m (Miller, 1977, p. 475). It is well known that palsas may
occur in the southernmost part of the discontinuous permafrost zone,
since the thermal properties of the peat of which they are composed are
particularly favorable for the development perennially frozen ground
(v. Brown, 1966. p. 21). J. Lundqvist (1962, p. 93) suggests that the
southern limit of palsa development coincides roughly with the -2° to
-3°C mean annual air isotherm. Tallman (1975, pp. 111-132) has done
extensive research on the Fourth of July Creek palsas and demonstrates
that many are developing under present conditions. Applying a lapse
rate Of 1°C/164 m indicates a mean annual air temperature at 915 m of
around -l.7°C in this vicinity. It therefore seems probable that this
is the lowest level Of aggrading permafrost; below about 900 m existing
permafrost would appear to be relict.

Atlin Road

 

During construction of this highway an isolated occurrence of perma-
frost was discovered between Mileposts 5.5 and 6.5, on a slope below the

road (Brown, 1976b, p. A-6). This permafrost is probably relict, since

85

Brown's investigations along the same road disclosed no other permafrost
sites. According to the l:250,000 Teslin map (Sheet 105C), elevations
in this segment of the highway do not exceed 915 m.

Atlin Mountain

 

A rock glacier is situated on Atlin Mountain, immediately southwest
of the Atlin townsite. It issues from an east-facing cirque at the
1500-1800 m level, and terminates well below 900 m. Movement in its
lower part has been recently demonstrated by J.I.R.P. personnel (R.
Flanders, personal communication, 1975), indicating retention of inter-
stitial or relict glacier ice at low levels. However, Since rock glaciers
are mobile, ice within their lower portions cannot be taken as evidence
of widespread jg_§jrg_permafrost development at these levels.

Rubngountain

 

An excellent indication Of extensive high level permafrost comes
from this location 23 km northeast Of the Atlin townsite. Here the adit
of an abandoned tungsten mine at 1825 m contains large accretions of
sublimation ice; a detailed description of the site is given by Tallman
(1975, p. 107). It should be noted that this occurrence is not likely
to have resulted from Balch ventilation, owing to the horizontal nature
of the mine shaft. Furthermore, this site has a southwesterly aspect,
which indicates that permafrost is widespread at similar elevations
throughout this area.

Cathedral Massif

A number of direct and indirect evidences for permafrost existence
are found here. These are outlined briefly below.

a) Ice-Cored Talus

On the shadowed, north-facing slope Of "Mt. Edward Little," solid

86

ice was Observed at 1490 m, just below the surface of a scree mantle.
A hummocky microtopography characterizes this site and is probably re-
lated to differential ablation of the ice core. Where the debris cover
is thin, meltwater was abundant in late August, but where the cover
exceeded 20 cm, the ice was apparently stable. It appears likely that
this ice is relict from the last advance of the Cathedral Glacier, and
was preserved by the insulating effect of scree accumulations derived
from the steep slopes above, as suggested by Jones (1975, p. 128).

b) Torres Rock Glacier

This feature lies on the shaded side of the valley just southeast
of the Cathedral Glacier. It is immediately below, and derived from, an
unnamed cirque glacier terminating in an ice fall at 1660 m. The rock
glacier itself extends from 1550 m to about 1225 m at its lowest point.
and is separated from the clean ice by a steep bedrock wall. The rock
glacier appears to have been derived through detachment of a segment of
the true glacier above, with subsequent burial and preservation of the
ice. This interpretation is based upon the discovery of a meltwater
tunnel in the upper reaches Of the rock glacier. Meltwater derived from
the glacier ice upslope flows down the bedrock face and disappears below
the upper surface of the rock glacier. Investigation of this tunnel re-
vealed debris-entrained shear planes within solid ice, not far below the
surface. Despite this discovery, it remains to be demonstrated whether
this core of glacial ice persists in the lower reaches of the feature,
or if these portions consist of interstitial ice of secondary origin.
The insulating cover of rock debris appears to be derived from talus
cones on flanking slopes, and may be partially due to debris entrainment

to the surface along shear planes, in the manner suggested by Carrara (1973).

87

Jones (1975, pp. 124-128) has suggested, but not demonstrated, the
existence of a similar ice core in a segment of the Cathedral terminal
moraine. Excavation of this feature by this writer in late August re-
vealed no ice, and positive temperatures were found at a depth slightly
greater than one meter. While some of Jones' evidences do indeed sug-
gest the existence of an ice core, its conclusive demonstration awaits
further excavation or geophysical investigation.

c) Frost Ridge

Evidence for the existence of conditions favorable for the develop-
ment or at least the persistence of permafrost, comes from the shaded
north-facing slope of Frost Ridge. Here, perennial snowbanks remain at
elevations down to 1550 m, and late-lying snowbanks and large-diameter
patterned ground occur as low as 1490 m. Small ponds also persist on
flatter sites.

A large perennial snowbank at 1585 m was investigated during the
last week of August, 1975. Snow depth in its central part was 2.75 m,
with numerous ice glands and lenticular inclusions. A sharp boundary
was observed between this firn and infiltration ice (Shumskii, 1964, pp.
276-303) below. The latter's thickness was at least 3 m, but difficulty
with the SIPRE drill bit prevented penetration to greater depth. The
propensity displayed by the drill corer to freeze into the ice indicates
that at depth the ice retains a reserve of cold, even at this late date.
It is therefore possible that this site is within the "infiltration
congelation zone“ (Shumskii, 1964, pp. 427-431), where the cold reserve
from winter freezing exceeds the heat expended on melting, and that de-
rived from liquid precipitation. According to Shumskii, such conditions

presume the presence of permafrost in adjacent terrain. This

88

interpretation must be considered tentative for the study area, however,
until more detailed thermal data are available. Miller (1975, p. 95)
suggests that on the adjacent but more exposed Cathedral Glacier, the
upper limit of temperate conditions (isothermal at 0°C) is approximately
1735 m. Above 1825 m, subpolar conditions exist. If subzero tempera-
tures can be conclusively demonstrated at the snowpatch Site described
above, a good illustration of the influence of aspect will have been
provided.

Central Icefield

 

Miller (personal communication, 1976) has noted the occurrence of
springs on nunataks near Camp 8 (2195 m) in the upper reaches of the
Juneau Icefield. He interprets this as evidence for meltout from ground
ice, and puts the lower limit of permafrost at about 1825 m in the central
icefield (Miller, 1975, p. 119). Andress (1963) and Freers (1966) have
documented slightly negative temperatures 45 m below the surface of the
upper Taku Glacier at the 1980 m level. On the same glacier at 2135 m,
negative temperatures exist 150 m below the surface (M. M. Miller, written
communication, 1977). In the highest reaches of the icefield (2164-2435 m)
subpolar glacier conditions exist, and infiltration by meltwater hastens
the densification process (Miller, 1975, p. 79). Although there appears
to be a notable lack of literature connecting glaciothermal data with
permafrost occurrence, it seems probable that the conditions described
are indicative of widespread perennially frozen ground on the nunataks of
the higher parts of the icefield. Study of the relationship between the
thermal characteristics of glaciers and permafrost distribution in the
surrounding terrain is a promising line of investigation, and could be

of great use in the solution of the alpine permafrost problem, as indicated

89

by the work of Haeberli (1975).

3.3 Calculated Permafrost Levels

 

Furrer and Fitze (1973), in an attempt to delimit permafrost distri-
bution in the Swiss Alps, have applied three climatically defined approxi-
mations developed by investigators working in the Arctic. Two of the
methods resulted in "nonsensical' values with respect to known occur-
rences of frozen ground. Although there are obvious problems involved
in applying lowland arctic permafrost parameters in a highland situation,
these workers found that Pihlainen's (1962) approximation yielded results
consistent with known occurrences in the Alps. The present writer has
made similar computations for the Juneau Icefield region, using the
Pihlainen method. Temperature data are based on records from Juneau
and Atlin (National Oceanic and Atmospheric Administration, 1976; Kerr
and Kendrew, 1955, respectively), a decrease of 1°C/164 m is assumed.
Because Of the dangers involved in applying lapse rates to mountainous
terrain (e.g., Brazel, 1974), and because variations in surface cover
are not taken into consideration by this index, it is strongly emphasized
that these computations are only a gross approximation of possible perma-
frost occurrence.

Pihlainen's approximation was derived by plotting mean annual air
temperature on the y-axis against the thaw index (the sum of daily mean
temperatures greater than 0°C on the x-axis). Values for stations in
the Canadian Arctic and Subarctic with reliable climatic data were then
plotted on this grid, and straight lines fitted to delineate the perma-
frost free, discontinuous, and continuous zones. The appropriate cate-

gory for a location can be found by the equations:

90

MAAT+_T_=0 (l)
780

MAAI+—T—=O (2)
270

where MAAT is the mean annual air temperature (°C), and T is the thaw
index (Furrer and Fitze, 1973). If equation (1) yields a value less than
zero, climatic parameters are suitable for permafrost. If equation (2)
produces values below or equal to zero, continuous permafrost is possible.
The effects of tOpography and local conditions are so great in the alpine
case, however, that the resulting quiltwork of perennially frozen and
permafrost-free sites requires replacing the term "continuous" with
"widespread." Truly continuous permafrost probably exists only at very
high elevations.

The computations yield the following boundaries:

TABLE 3-1. Computed Permafrost Levels

 

West Slope East Slope

 

Lower limit of
permafrost (M.A.S.L.) 980 900

 

Permafrost widespread
above (M.A.S.L.) - 1220

 

 

 

 

 

It can be seen that there is a remarkable agreement between the lower-
most occurrence of palsas in the Atlin locale and the calculated lower
limit of permafrost. For the case of the "boundary" of widespread perma-
frost, the calculation yields a value that appears at least 250 m too low,
if compared with available morphological evidences commonly associated
with permafrost.

For coastal sector, we may infer that permafrost is climatically

possible close to the 1000 m level. For reasons discussed below, a value

91

for "widespread" permafrost in the coastal sector would be rather meaning-
less. The similarity in the calculated lower limits between the maritime
and continental sectors is in fundamental agreement with the conclusions
of Williams (l96l, pp. 339-343), who shows that the depth of frost pene-
tration and develOpment of frozen ground phenomena is essentially inde-
pendent of winter cold intensity. Williams indicates that the mean annual
temperature is a far more important factor. Alternatively stated, in a
comparison of two locations with similar mean annual air temperatures,

one maritime, the other continental, nearly accordant depths of frost
penetration can be expected. This is because the summer heat flux into
the ground at the continental site offsets the correspondingly greater
heat loss of winter.

3.4 Influence gf_Ground Cover

 

An important factor that has not been considered until this point
is the effect of the ground cover on frost penetration. In particular,
snow cover may cause drastic discrepancies in the thermal regimes of
snow-covered and snow-free sites, even in immediately adjacent locations.
Both the depth of frost penetration (Atkinson and Bay, l940) and the
magnitude of negative temperatures (Lachenbruch, l959) may be damped.
For these reasons, permafrost may not develop at sites which experience
appreciable snow accumulations, even-if other climatic parameters are
favorable for its formation. Some aspects of the snow accumulation
patterns are discussed below.

l) Snowfall Amounts and Ground Loads

As was noted previously, the mountains of the coastal sector are
subject to substantial snow accumulation, while snowfall in the interior

is far less. Schaerer (l970) has investigated the variation of ground

92

snow loads in southern British Columbia. He shows that ground snow load
increases exponentially with elevation in the west coast situation of
Mt. Seymour, while the relationship is approximately linear farther in-
land. A similar situation may be expected across the northern Boundary
Range, although the difference is probably not as great due to the
smaller distances involved. It should also be noted that the interval
between the elevation of the 0°C mean annual air isotherms and the zone
of maximum precipitation is rather small in the coastal sector. Such
patterns of ground cover are obviously more amenable to permafrost develOp-
ment in the interior than in coastal locations.

2) Timing of Snow Accumulation

Marcus (l964, pp. 6l-65) has approximated the onset of accumulation
conditions on the Lemon Creek Glacier for the years l947-l957 through
the use of radiosonde data. His computations show that accumulation
usually begins in mid-to-late October at the l000 m level, although it
is occasionally delayed until early November. At l400 m, accumulation
conditions generally develop during early October. Therefore, at high
levels, the onset of snow accumulation coincides with that period of the
year during which precipitation is greatest. Heavy snow loads in the
coastal sector during the autumn transition period effectively protect
the ground from frost penetration. Although similar timing of accumu-
lation onset and precipitation maximum may be expected farther inland
(v. Chapter l), absolute amounts of snowfall are far lower.

3) Density of the Snow Cover

As stressed by Kudryavtsev (l965, pp. l0-19), the effect of the snow
cover can be correctly evaluated only if other climatic factors are taken

into consideration. Given similar thicknesses of snow cover and identical

93

mean annual air temperatures, the mean annual soil temperature will be
higher in a continental than in a maritime climate. This is true not
only because the density of snow under continental conditions is lower,
but because removal of much of the summer heat stored in the soil will
be prevented by the snow. Although the disparity in snow depths between
the interior and coastal sectors is probably more than sufficient to off-
set the differences in density, the latter are not so great as would be
the case if only snow thicknesses were considered.

0n the other hand, the lower density of snow in the interior renders
it vulnerable to drifting (Shumskii, l964, pp. 230—239), so that many
sites may have thin or negligible snow cover and are subject to deep
frost penetration. Examination of air photos taken of the Cathedral
Massif in December, l948, confirms the existence of many snow-free sites,
particularly on topographic highs such as ridge crests. Snow-free
sites in winter are probably not as common under marine west coast
conditions, by reason of the absolute amounts of snow involved, and be-
cause snow density is rather high. There are probably some winter snow-
free sites in the coastal sector, especially where steep slopes predomi-
nate, but their frequency is undoubtedly more limited than in the interior.

3.5 Conclusions

 

l) Theoretically, if only air temperatures are taken into account,
the lower limit of permafrost would appear to be at only slightly higher
elevations on the western slope of the Boundary Range than in the interior.
This remains to be demonstrated, however, since no reference to permafrost
can be found in the literature and ground temperature data are not avail-
able in the study area.

2) The effects of the snow cover are probably so great in the

94

maritime sector that permafrost development is inhibited, and much less
widespread than in the interior. Permafrost in the coastal sector, if
it exists, is confined to wind-swept topographic highs where winter snow
cover is minimal.

3) At lower elevations, under both maritime and continental condi-
tions, permafrost occurrence is in large part controlled by aspect (re-
stricted to ubac slopes), ground cover characteristics (snow and vegeta-
tion), and the thermal properties of the substratum.

4) The lower limit of permafrost is in equilibrium with present
conditions in the Atlin area. We can, with some confidence, put the
permafrost limit at about 9l5 m. This is under particularly favorable
local conditions, however, and permafrost is widespread only at higher

levels.

CHAPTER IV
DISTRIBUTION AND LIMITS QE_PATTERNED GROUND

4.] Literature Review

 

The question of the elevational threshold of patterned ground has
been so widely addressed in the German-language literature (e.g., Troll,
l958; Hastenrath, l959; Hovermann, 1962; H6llermann, l967; l972a; l972c)
that the latter investigator considers the problem "well worn" (Hollermann,
l972c). Most of these investigations were undertaken in Eurasia and
North Africa, and it is in this region that the patterned ground limits
are best known. Troll (l947) and Graf (l973) have synthesized most of
this information in small-scale maps of patterned-ground occurrence for
Eurasia.

As far as the situation in North America is concerned, Troll (l958,
p. 8) remarked in his classic paper that the continent was so poorly
studied that he could not attempt even a general descriptive account of
the trend of patterned ground limits. In recent years there has been
no shortage of patterned ground investigations on this continent, but
few are concerned with delimitation of altitudinal zones of its occur-
rence. While many authors cite the elevation at which their studies were
conducted, there is no assurance that these altitudes are the lowermost
sites in any locality. The probability is strong that they often are
not, since detailed site work is usually carried out on well-formed

occurrences, and these are likely to be found well above the elevational

95

96

threshold. To this writer's knowledge there has been only one detailed
study published on the lower boundary of patterned ground in any area of
North America. This investigation was performed by Hollermann (1972b)
in the White Mountains of California/Nevada.

Studies of the patterned ground distribution were initiated in
Europe by the l930's (e.g., Poser, l933). Troll's l944 synthesis
(Troll, l958) went far toward making known the various types of patterned
ground and their general world distribution. Troll (1919, p. 7) believed
that a climatic limit for patterned ground (Strukturbodengrenze) could
be determined and that this limit "has a regular course which rises and
falls with the forest boundary on the one hand and with the snow line on
the other." Soon afterwards he published a map of Eurasia showing ob-
served and theoretical patterned ground limits (lloll, l947, Fig. l, p.
l64).

Hastenrath (l959; l960) has examined regelation frequencies at vari—
ous locations in the Alps and concluded that the number of freeze-thaw
cycles is not the determining factor in patterned ground distribution.

He considers vegetation as directly attributable to climate, and the
crucial control over the lower limits. His conclusion is similar to
Troll's in that he perceived this limit to follow the tree- and snowlines,
increasing in elevation from the poles to the equator and from oceanic

to continental regions.

A different viewpoint is maintained by Hovermann (l960; l962), whose
investigations convinced him that the lower limit of patterned ground
descends with increased distance from oceanic influence therefore
opposing the general trend of the tree and snowlines. He contends that

on a continental scale, the amount of precipitation is not a primary

97

control over patterned ground distribution. Instead, he considers ther-
mal considerations more important, especially the number of freeze-thaw
cycles. Hovermann believes that the magnitude of frost events also
controls their morphologic effectiveness, and states that temperatures
-4° to -5°C are needed for effective sorting to occur.

More recent investigations support the views of Troll and Hastenrath.
Hollermann (l972a) studied patterned ground in the Pyrenees and found
that its lower limit rises from west to east in response to decreasing
oceanic influence. Graf (1973, p. l45) has published an isopleth map of
thresholds of patterned ground for Eurasia whose trends are in agreement
with Troll's (l947), although numerical values differ somewhat. Graf
(i_bi_d_, pp. l49-l50) also presents profiles along the 65th and 38th paral-
lels, which show a general west-east increase in patterned ground and
solifluction limits. Hollermann (1972b) makes the significant observa-
tion that patterned ground limits are not determined by thermal condi-
tions so much as by vegetation cover in humid regions. Under arid condi-
tions the relationship between soil moisture and the temporal occurrence
of frost action is the critical factor. In most areas the solifluction
limit is well below the patterned ground boundary, but in dry regions
these limits coincide.

J. Lundqvist (l962, pp. 95-96; l966, p. l48) concluded that edaphic
and vegetative factors determine, respectively, the upper and lower
limits of patterned ground in the Swedish Caledonides. These controls
operate within a broad climatic framework in which local conditions are
most important. The upper limit coincides with a lack of soil at high
levels, while occurrences are prohibited at lower levels by "thick vegeta-

tion." Lundqvist also found that sorted features are most common in the

98

southern Caledonides, where the climate is most continental.

It should be noted that these authors all have taken the occurrence
of small-diameter patterned ground as their lower limit. Troll (92, 915.,
p. 83) believed that large-diameter forms generally occur below the level
of the miniature features in the Alps. However, the more detailed subse-
quent observations of Kelletat (l969) in Italy, H6llermann (l967), Furrer
(l965), and Furrer and Dorigo (l972) in the Alps and Preusser (l973) in
Iceland show that not only is the threshold for the miniature forms lower,
they may also occur over a wider range of elevations. According to
Furrer and Dorigo (l972, p. 104), large-diameter patterned ground is found
above the "permafrost boundary," while small-diameter forms lie closer to
or may straddle it.

Furrer (l965) is cited by Washburn (l973, p. lDl) as having outlined
a characteristic altitudinal sequence of patterned ground forms in the
Alps. This sequence is, in ascending order:
zone of plowing blocks;
zone of garlands;
zone of earthflows;
zone of miniature patterned ground;

zone of sorted or stony lobate forms;
zone of large sorted patterned ground.

01 U'l h (.0 N -'
vvvvvv

An interesting approach to the study of patterned ground distribu-
tion was taken by Caine (l972), who statistically analyzed 79 small-
diameter occurrences in the English Lake District to determine the rela-
tive importances of lithology, elevation, and orientation. The lower
limit was taken to be 2600 m, while modes occurring at the 700 and 820 m
levels are related to low-angle slopes. Aspect appears not to be an im-
portant factor here, since application of Rayleigh and X2 tests to orienta-

tion data failed to define a preferred azimuthal class. The climatic

99

control was, therefore, interpreted to be that of temperature effects
induced by elevation, rather than radiation or wind effect. Nearest
neighbor analysis and examination of reflexive links show that occurrences
are more tightly clustered on slates than on volcanic rocks. This asso-
ciation was thought to be more a function of the frost susceptibility of
weathering products than of the rock itself. Caine concludes the study
by emphasizing the need for multivariate analysis of the problem, parti-
cularly when large geographic areas are investigated.

The classic view that patterned ground limits are determined by the
macroclimate is not sufficient; in recent years the importance of meso-
and microenvironmental parameters have become increasingly appreciated.
Exemplary in this regard are the works of Hollermann (1972b) and Furrer
(l965b), who show that the lower boundary of the "subnival" zones ascends
400 m in the 85 km between Lake of Thun and the Matterhorn. It is also
clear that patterned ground may be found over a wide range of climatic
situations. Unfortunately, the polygenetic nature of patterned ground,
and the fact that forms occurring under different climatic regimes may be
so dissimilar in size, appearance, and/or genesis, indicate that synthesis
on a global or continental scale can be quite misleading. This problem
may be at the root of disagreements over the trend of patterned ground
elevational thresholds in mountainous regions. It is this writer's opinion
that study of the effects of latitude or continentality of patterned
ground distribution should be pursued with only comparable forms consi-
dered in a given study area. As was shown above, some forms of small and
large-diameter patterned ground, although similar in appearance, may not
be merely reflections of the opposing ends in a continuum of process in-

tensity or frost cycle duration. Rather, they may be unrelated genetically

100

and both should not be used indiscriminately for defining a singular
lower limit of patterned ground occurrence.

4.2 Distribution of Patterned Ground ifl_the Juneau Icefield Region

 

Since no large-diameter patterned ground was discovered on the
west slope of the Boundary Range, the prerequisite for homogeneous forms
to be used in defining regional trends of the Strukturbodengrenze is not
fulfilled. If only small-diameter patterned ground is considered, the
lower limit rises inland, as discussed below. The distribution of large-
diameter patterned ground in the Juneau Icefield region may be similar
to that of permafrost, but is subject to the same uncertainties.

4.2.l West Slope

 

No occurrences of large-diameter forms were noted on the west slope,
but ithas not possible to investigate terrain above l375 m in this area.
The assemblage of small-scale cryogenic forms (plowing blocks, small turf-
banked lobes, miniature patterned ground) here indicates that between
l200-l375 m the lowermost periglacial étage (v. Rundberg, 1972) is
reached. It is therefore possible that large-diameter patterned ground
may indeed exist at higher levels, for example in the Fairweather Range.
However, this writer found no references to such sites in the geomorpholo-
gical literature dealing with southeast Alaska. It appears certain,
however, that far fewer occurrences are likely under maritime conditions
than continental, owing to the depth of the winter snow cover and timing
of the onset of the accumulation season (v. section 3.4), and their
attendant influence on soil freezing and the depths of frost penetration.
A similar relationship has been suggested by W. Thompson (l962) for rock
glaciers in the Olympic and Cascade Ranges of Washington. These features

are absent throughout the area of oceanic conditions, but rock glaciers

101

were discovered where the climate is of a more continental nature, as on
the eastern slope of the Cascades adjacent to the Dkanogon region.
Thompson attributes this distribution to the effects of heavy ground snow
loads on the Balch ventilation process. Where show cover is thin, Balch
ventilation is unimpaired, and rock glaciers may form. A similar distri-
bution of rock glaciers was observed in the Juneau Icefield Region. None
are found in the coastal sector, but they become increasingly frequent

in the Atlin region, as well as in the area of the Haines Cutoff, both

of which are orographically sheltered. Hansen (1976) has also noted a
greater frequency of turf-banked terraces in the continental parts of

the Olympic Mountains than on the seaward side. It seems likely that the
distribution of all these features is controlled by the depth and timing
of the snow cover.

4.2.2 Interior 9f_Icefield

In the central icefield area, widespread occurrence of large-diameter
patterned ground is prevented by edaphic, lithological, and gradient fac-
tors, as well as by a heavy snow cover.

Lietzke and Whiteside (l972) estimate that on the nunataks of the
cnetral icefield, only 2% of the surfaces snow-free in summer possess a
soil mantle, while the rest are composed of bedrock or rubble. Since
effective frost sorting requires an appreciable percentage of fines and
a wide range of grain sizes, little patterned ground development can be
expected, on this basis alone.

The predominantly granitic character of the nunataks in this area
is also a factor preventing formation of sorted patterned ground. The
homogeneous gravelly nature of the weathering products of these granular

lithologies effectively prohibits both frost sorting and solifluction

102

processes. Furthermore, the predominance of steep slopes dictates that
most have a positive denudation balance (Jahn, l968), so that topographic
sites suitable for patterning are both rare and limited in extent (Figure
4-l). Also pertinent in this regard is the general observation that on
the occasional flat sites, covers of perennial snow and ice persist,
especially in the more maritime sectors of the icefield and at shadowed
sites. With increasing elevation and continentality, and decreasing snow
cover, conditions for patterning become more favorable, and some occur-
rences of large-diameter patterned ground have been noted on relatively
level topographic sites above 2l35 m in the vicinity of Mt. Nesslerode
near the international border (Hamelin, l964; Miller, l977). At these
elevations, we are well into the "frost-shatter zone" of Rudberg (l972),
where blockslopes and blockfields occupy large areas, a situation much
less pronounced on nunataks in the vicinity of Camp lO.

4.2.3 Atlin Region (East Slope)

 

Patterned ground in the interior has a much wider distribution than
in any other area investigated. In addition to sites in the Cathedral
Massif described above, patterned ground has been found on Teresa Island,
in relative abundance above l925 m adjacent to the Fourth of July Creek
Valley (Tallman, l975, pp. llO-lll), and elsewhere (Miller, l977).

The writer's investigations were concentrated in the Cathedral Massif,
where 22 separate patterned ground sites were mapped. The mapping proce-
dure was to follow contours in the study area at 50 m intervals. Occur-
rences were plotted on a preliminary edition of the present base map by
compass and map triangulation, with the assistance of a pocket altimeter.

Figure 4-2 illustrates the elevation and aspect of the 22

103

Figure 4-1. View to west from Camp 10 in interior of Juneau Icefield,
showing predominance of steep slopes typical of the area.

104

 

105

Figure 4-2. Polar diagram showing aspect and elevation of patterned
ground sites, Cathedral Massif.

 

 

 

107

sites.1 The diagram suggests that patterned ground is most likely to
occur on slopes in the NE guadrant; a X2 test on a null hypothesis of a
uniform azimuthal distribution was used to examine this assumption. The
results indicate a strong (significant at the .00] level) preference for
the NE quadrant. S. Buttrick (personal communication, 1975) has noted
that patterned ground is similarly situated with respect to aspect on
nearby Teresa Island. This control appears to be strongest at lower
elevations, and decreases somewhat at higher levels. Screening of the
horizon by local topography may counteract the influence of slope orien-
tation, however, by shielding a site from incoming insolation. All
patterned ground sites with aspect other than N-NE occurred at such
locations. At these sites, snowbanks are preserved throughout the summer,
inhibiting vegetation and providing moisture for autumn frost heaving.

A prime example is the anomalous occurrence in the southwest quadrant at
1575 m. This site is situated in Chapel Valley, juSt below Alcove
Glacier's cirque; it is effectively shielded from the afternoon sun.

Most patterned ground sites investigated were developed in glacial
till. This material is not a prerequisite, however, since if other factors
are conducive to its development, patterned ground may occur wherever the
local bedrock has been converted by weathering processes into a fairly
wide range of grain sizes.

Another factor contributing to the relative abundance of patterned
ground in the Atlin area is the high frequency of low-angle slopes at

relatively high elevations (i.e., above 1500 m), where other conditions

 

1It is emphasized that a greater number of cells was found in terrain
above 1600 m, but that many of these were large systems of individual cells,
and were therefore tallied as single occurrences. Inspection of Figure 4-3
will clarify the distribution of cells in absolute numbers.

108

Figure 4-3. Map of patterned ground sites in the Cathedral Massif.

109

 

110

are optimal for patterned ground develOpment. Comparison of topographic
maps from the west slope and interior icefield sectors with those of the
Atlin area makes this point evident. The more intense past glaciations
in the former sectors have resulted in extremely precipitous topography,
which is not conducive to patterned ground development.

Finally, the interval between the elevation of the 0°C mean annual
air isotherm and the level of maximum precipitation is greater in the
interior than areas nearer the coast. The lighter ground snow loads and
the drifting associated with continental conditions also contribute to
the frequency of patterned ground in the interior.

4.2.4 _L_im_it§_ 9: Large-Diameter Patterned Ground

According to the writer's observations, the lower limit of presently.
active patterned ground is slightly below 1500 m in the Atlin area.
Derived from lapse rates, the mean annual air temperature at this altitude
is about -5°C, which agrees rather well with Bird's (1967, p. l97) sug-
gestion that the southernmost limit of "conspicuous" patterned ground in
arctic Canada corresponds with the -4°C isotherm. If the -5° to -4°C
isotherm is indeed a good indicator of the large-diameter Strukturboden-
grenze, it probably falls slightly from SW to NE, since computations indi-
cate a somewhat lower mean annual air temperature at any given elevation
in the interior. Lapse rates are, however, not particularly accurate for
representing local conditions in mountainous terrain. Furthermore, the
latitudinal difference of about 135 km between Juneau and Atlin has not
been taken into consideration and is probably of some importance. There
are at present too many unknowns for a definitive statement on the trend

of large-diameter patterned ground thresholds in this area.

111

4.2.5 Local Variations

 

While in a very broad sense, the regional climate may be viewed as
the primary control over patterned ground occurrence, microenvironmental
parameters are of great importance at the local level. This is well
illustrated by the presence of active and inactive features in immediately
adjacent situations, as discussed in Chapter 11. Furthermore, once the
critical elevational threshold has been reached (determined over a broad
area by the mean annual air temperature and hence the macroclimate)
patterned ground occurs over a wide range of elevations.

Benedict (1976) has made a strong case for distinguishing between
environments conducive to the present development of solifluction
features and those environments that serve only to maintain forms devel-
oped previously during a more rigorous climatic interval. This also
appears true for patterned ground, and the relationship is not restricted
to large-scale climatic change and accompanying vertical adjustments of
the altitudinal zones. Also important are subtle changes in local condi-
tions, such as snowmelt patterns.

Above the 1600 m level in the Cathedral Massif, the patterns appear
to be still in developmental stages, as evidenced by silt-capped stones
and minimal lichenization at the more suitable sites. It also seems likely
that patterned ground has developed rather recently near the Balcony
Glacier (Figure 4-4) at 1950 m. Moderately well-developed sorted stripes
are found near the lower margin of this small glacier. The stripes have
probably formed since the waning of the 18th century neoglacial maximum,
when the Balcony's ice covered a much larger area than at present.

On the other hand, below 1600 m and descending to what appears to

be the lower limit of presently active patterned ground at about 1490 m,

112

the features have a more subdued appearance, although they are not neces-
sarily heavily vegetated or lichenized. It would be most instructive to
obtain comparative movement data from sorted stripes at various elevations,
in order to determine differences in process intensity and to ascertain

the lower boundary of activity within patterned ground. On the basis of
morphological evidences, observed during the 1976 field season (in which
summer ablation on nearby glaciers exceeded the average of most years),

the latter "boundary" lies approximately 100 m below the lower level at
which perennial snowbanks survive.

0f considerable interest to the delineation of altitudinal sequences
of patterned ground are the large sorted circles found on the shore of a
small unnamed lake at 975 m in the Fourth of July Creek Valley (Figure
4-5). Since large-diameter patterned ground is usually found only at
considerably higher levels in this area, Tallman (1975, p. 110) and
Miller (1976, p. 267) have interpreted these features as relicts from
the early Holocene (7000-9000 years B.P.). This assumption is based on
C-l4 dates obtained from organic material within the basal layers of ad-
jacent bogs, and by the discovery of similar features at low elevation
on the west slope of the Boundary Range.

In the writer's opinion, these features are to be considered extra-
zonal and recently active, although their present inactivity is not
disputed. The difference of opinion in this matter thus involves the
length of time involved since cessation of activity in the patterned
ground. The present interpretation is based on the following points:

1) It is unlikely that these features have remained inactive since
the early Holocene (as was recognized by Tallman) since such a situation

would almost certainly result in their eradication by sedimentation in

113

Figure 4-4. Sorted stripes at margin of Balcony Glacier, 1950 m,
Cathedral Massif. Note trim line on facing wall.

Figure 4-5. Extrazonal patterned ground at 975 m, Fourth of July Creek
Valley.

114

 

19..
WT...

115

this topographically depressed site.

2) The patterned ground is in close proximity to the palsa bogs
discussed in Chapter III, and are, therefore, at present in the lower
part of the discontinuous permafrost zone. It is possible that only a
slight depression of the mean annual air temperature would be sufficient
to reactivate them.

Troll (1958, p. 41) has discussed "azonal" patterned ground attribu-
table to "nonclimatic intensification" of frost processes. One such
group is patterned ground on lakeshores, often found far below the
"climatic limit" for a particular locale. Conditions especially condu-
cive for the development of patterned ground are induced by seasonal
(summer) soaking of the soil. By autumn, when lake levels have fallen,
the saturated sediments are subjected to deep freezing, a condition
favorable to the development of patterned ground. This summer saturation
provides a high effective "precipitation," so that large accretions of
segretation ice and associated sorting processes are possible. Tallman
(1975, p. 110) has noted that these circles are frequently under water
in summer, and concluded that this condition has resulted in termination
of their growth, a view with which this writer does not concur. Troll
(92, £13,, p. 41) has cited a large number of localities where pattern
formation was enhanced at lakeshore sites, and J. Lundqvist (1962, pp.
78-82) reports a number of similar situations in Sweden. The Fourth of
July circles bear striking similarity to those in photographs presented
by Lundqvist, and it seems reasonable to conclude that their development
is the result of nonclimatic intensification of pattern-generating pro-
cesses. It may be that cessation of their activity is due not only to a

recent warming trend, but to lower mean summer lake levels. When viewed

116

by this writer in early July, 1975, the Fourth of July patterned ground
already lay above lake level. Tallman (1975, pp. 107-110) documents

the existence of a number of "nivation hollows" nearby, which in recent
years have experienced complete meltout during summer. The dearth of
lichen within these hollows testifies to their occupation by late lying
snow and ice within very recent times. An increased snowpack, and the
presence of snow at lower levels than at present would undoubtedly re-
sult in the lake maintaining high levels until later in the summer.

Under such conditions we may expect a higher moisture content at the on-
set of the autumn freeze, with a corresponding increase in susceptibility
to cryogenic processes. Since the features have not been buried by sedi-
mentation, it appears likely that the patterned ground at this location
suffered termination of its activity with the climatic warming and rise
in the regional snow line following the demise of the 18th century neo-
glacial maximum.

These observations show that even though patterned ground may in
the future be a useful tool in environmental reconstruction, its sensi-
tivity to changes in local conditions warrants extreme caution in inter-
pretation. Much remains to be learned about the many factors affecting
its behavior under changing climatic regimes.

4.2.6 Limit§_9f_5mall-Diameter Patterned Ground

It has been previously shown that small-diameter forms of sorted
patterned ground are to be regarded as extrazonal or even as azonal
phenomena, owing to their distribution over a wide range of latitudes
and altitudes. However, conditions for their development are probably
optimal at sites marked by frequent small-magnitude frost heave cycles

and lacking a restrictive vegetation cover. Even though the delimitation

117

of the range of small-diameter patterns was not a primary objective of
this study, it may be concluded that these features can form under less
severe conditions than the large-diameter variety, although the two types
may coexist at a given site.

It is certain that small-diameter forms exist at lower elevations
in the martitime sector than in the interior. Their development appears
to be dependent upon, or coincident with, the presence of bare patches
of soil. While the lowermost site investigated by this writer was at
1325 m on Cairn Ridge near Juneau, Ugolini (1966, pp. 34-35) found simi-
lar features at 800 m near Muir Inlet. In the same locality, Goldthwait
(written communication, 1977) discovered active miniature polygons at
760 m. By contrast, the lowest site noted in the Cathedral area was
about 1490 m, although they are widespread at this level, and may exist
below. It appears likely that the situation is similar to that observed
in Europe, where miniature, but not large-diameter forms are found at
anomolously low elevations in oceanic situations. For this reason - and
other stated in Chapter II - it seems wise to separate small and large-
diameter forms when attempting to trace the regional threshold of pat-
terned ground. Even though the Strukturbodengrenze of the small-diameter
forms rises in response to increasing continentality, it is possible
that the threshold of the large-diameter variety has an opposite trend.
This is particularly likely to be true if the "lower limit" of the pat-
terned ground is taken not as the lowest of isolated occurrences, but as
the arithmetic average of the lowest sites in an area, as suggested by
Furrer and Dorigo (1972).

4.3 Conclusions and Recommendations

 

Data on the lower limits of large-diameter patterned ground are too

118

few at present to delimit a regional trend in its elevational threshold
across the northern Boundary Range. Other aspects of the research hypo-
thesis do appear to be substantiated, however. It is apparent that
occurrences are more widespread in the interior, primarily due to conti-
nental conditions of solid precipitation and ground cover, as well as a
high frequency of flat sites at high elevation. The trend of the small-
diameter variety may be traced from relatively low levels under maritime
conditions near Juneau to higher elevations in the interior. The
genetic differences between these two varieties is stressed, however,
and it is possible that their lower boundaries have opposite trends.

At a particular site, patterned ground develops only where conditions
allow for saturation of the regolith at the time of the autumn freeze.
Such conditions are optimal at the downslope edge of late-lying or peren-
nial snowbanks. Aspect is a very important control because snowbanks are
most likely to persist on slope facing north to northeast. Relatively
low-angle (<15°) slopes and heterogeneously-sized parent material are
also prerequisites to the develOpment of large-diameter patterned ground.

It is recommended that the problem of the trend of elevational thres-
holds of patterned ground be pursued further in the Alaska-Yukon-British
Columbia area, since the north-south trending coastal ranges provide an
exceptionally steep continentality gradient not often found on other con-
tinents. If windswept topographic highs remain snow-free in winter, the
high peaks of the Fairweather Range must provide sufficient elevations
for the development of both permafrost and patterned ground. It is sug-
gested that this area be investigated for the occurrence of both phenomena,
discovery of which would greatly enhance our knowledgeeof maritime and

alpine periglacial conditions.

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