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Permafrost conditions near shorelines of
oriented lakes in Old Crow Flats, Yukon
Territory
P. Roy-Léveillée & C. R. Burn
Department of Geography and Environmental Studies, Carleton University, Ottawa, Ontario, Canada.
ABSTRACT
Old Crow Flats is a 4300 km2 plain in the continuous permafrost of Northern Yukon. It contains over 2500 thermokarst
lakes, many of which have rectilinear shorelines and tend to be oriented either NE-SW or NW-SE. Previous
explanations of the shape and orientation of the lakes focussed on the underlying geological structure and the
propagation of faults through the sediments to cause the alignment of the lakeshores. Permafrost conditions and shore
erosion mechanisms observed at forested and tundra sites suggest that wind and patterns of ice-wedge development
may be contributing to the occurrence of rectilinear shorelines in the open tundra of Old Crow Flats.
RÉSUMÉ
La plaine de Old Crow est située dans la zone de pergélisol continu, au nord du Yukon. Le nombre de lacs
thermokarstiques situés sur cette plaine excède 2500, et plusieurs de ceux-ci ont des berges rectilignes et ont tendance
à être orientés soit nord-est-sud-ouest ou nord-ouest-sud-est. Jusqu’à maitenant, les explications avancées pour les
lacs d’Old Crow misent sur la structure geologique sous-jacente et la propagation de failles à travers les sédiments
forcant l’alignment des berges des lacs. Les conditions thermiques du pergélisol et les mecanismes d’érosion des
berges observés dans la tundra et la forêt de la plaine de Old Crow suggèrent qu’en fait le vent et la distribution des
coins de glace jouent un rôle important pour le dévelopment de berges rectilignes dans la tundra sur la plaine d’Old
Crow.
1 INTRODUCTION
Oriented lakes are groups of lakes possessing a
common, preferred, long-axis orientation (van
Everdingen 1998). They are common in arctic and
subarctic lowlands and have been described from the
lowlands of the Alaska coastal plain (Livingstone 1954;
Carson and Hussey 1962; Hinkel et al. 2005), from the
Canadian Beaufort Sea coastal lowlands (Mackay 1963;
Harry and French 1983; Côté and Burn 2002), from the
coastal lowlands of northern Siberia (Tomirdiaro and
Ryabchun 1978; Morgernstern et al. 2008), and from
other arctic regions including Old Crow Flats in the
northern Yukon (Price 1968; Allenby 1989). French
(2007) describes several distinct forms of oriented lakes
including D-shaped lakes, oval, elliptical, triangular, and
rectangular lakes. He divides lake profiles in two broad
categories: lakes with littoral shelves surrounding a
central deeper part, and shallow saucer-shaped lakes. In
most cases, the long axes of the lakes are perpendicular
to the prevailing wind direction (Seppälä 2004). The
hypothesis that wind-induced currents result in
preferential erosion of the ends of the lake and
redistribution of sediments along the long-axis shorelines
has been proposed to explain lake orientation (Black and
Barksdale 1949; Rex 1961; Carson and Hussey 1962;
Mackay 1963; Côté and Burn
2002). However, according to French (2007), this
hypothesis fails to explain the elongation of small lakes
where such currents cannot develop.
In Old Crow Flats, Y.T. (Fig.1), many of the 2500
lakes have rectilinear shorelines and tend to be oriented
either NE-SW or NW-SE (Fig 2). The morphology and
orientation of the lakes has been attributed to the
underlying geological structure (Price 1968; Allenby
1989; Morrell and Dietrich 1993). Allenby (1989)
suggested that the rectangular shapes reflect faults in the
underlying crystalline basement which have propagated
up through the overlying sediment. The hypothesis of
geological control on lake shapes is difficult to test in Old
Crow Flats, as the Quaternary sediments deposited over
the bedrock are over 40 m thick and very little evidence
of fault line propagation through the sediments can be
found (Morrell and Dietrich 1993). The area is difficult to
access, and as a result very little field-based information
is available regarding the lakes of Old Crow Flats.
In this paper we contribute to the discussion by
investigating permafrost conditions near rectilinear and
irregular shorelines in Old Crow Flats. We examine
possible relations between mechanisms of shore erosion
and lake morphology and orientation.
1509
Figure 1. Location of Old Crow Flats, northern YT
(modified from Lauriol et al. 2009, Fig.1, p. 213).
Figure 2. Landsat 7 orthoimage of Old Crow Flats and
surrounding areas acquired on August 30th 2001
(reproduced with permission of Natural Resources
Canada. All rights reserved). Number 1 and 2 indicate
the primary and secondary study areas, respectively.
2 OLD CROW FLATS
Old Crow Flats is surrounded by mountains, with British
and Barn Mountains to the north, the Old Crow Range to
the west, Richardson Mountains to the east, and the
Keele Range to the south. The Flats have a mean
elevation of 327 m, with remarkably little elevation
change except for the Holocene incision by the Porcupine
and Old Crow rivers which are 20 to 50 m below the plain
today (Lauriol et al. 2002).
Old Crow Flats was not glaciated during the
Wisconsinian period, but advances of the Laurentide Ice
Sheet about 30 and 17 ka BP blocked eastward drainage
and resulted in the flooding of the Bell-Old Crow-Bluefish
basins. These flooded basins formed glacial lake Old
Crow which deposited up to 10 m of unfossiliferous
glaciolacustrine sediment over the thick (near 40 m)
layered sands and silts which accumulated in the basin
during the Pleistocene (Lichti-Federovich 1973; Hughes
et al. 1981; Matthews et al. 1987; Duk-Rodkin et al. 2004;
Zazula et al. 2004).
Permafrost developed in the freshly exposed
glaciolacustrine sediments following the drainage of
Glacial Lake Old Crow (Lauriol et al. 2009).
Measurements of permafrost thickness have not yet been
made in the peatlands of Old Crow Flats, nor has
ground-ice content been assessed. However, surface
features indicative of ice-rich permafrost can be observed
in the area, such as high and low centre ice-wedge
polygons and retrogressive thaw slumps along river
bluffs.
3 STUDY SITES
A number of sites were selected to examine shore
erosion and permafrost conditions near rectilinear and
irregular lake shorelines. These sites were grouped in 2
study areas (Fig. 2). The first study area (Fig. 3a) is
located east of Old Crow River. It includes several small
and large lakes with rectilinear shorelines oriented both
NE-SW and NW-SE. It also includes several old
shorelines and drained lake basins of various ages most
of which also have rectilinear shorelines. It is located in a
portion of Old Crow Flats characterised by open tundra
with patches of shrubs up to 2 m high. The second study
area (Fig. 3b) is located in an open spruce shrubland
north of Old Crow River, and includes numerous small
and irregularly shaped lakes.
4 METHODS.
4.1 Shoreline surveys
Relations between shoreline morphology, local
conditions, and erosion mechanisms were observed on
all accessible shorelines during two open water seasons
(June to September). Randomly located benchmarks
were used to assess short-term erosion rates along
shorelines.
1510
Fig. 3 SPOT satellite imagery (summer 2007) of a) the
primary study area and b) Landsat 7 orthoimage of the
second study area, located approximately 35 km to the
northwest.
4.2 Measurement of permafrost temperatures and snow
depth
In both study areas, representative shorelines of different
orientation, height, slope, and vegetation cover were
equipped with temperatures sensors (Onset Computing,
TMC6-HD) installed in the top of permafrost at a depth of
1.25 m below the ground surface. Temperature was
recorded at 2-hour intervals with HOBOTM two-channel
data loggers (Onset Computing). The thermistors used
had a range of -40ºC to 100ºC, an accuracy of ±0.5ºC,
and a resolution of ±0.41ºC at 20ºC.
Snow-depth measurements were collected along
transects perpendicular to the shoreline, and snow-
stratigraphy was described at each instrumented site.
5 SHORELINE EROSION
5.1 Shoreline erosion mechanisms and shore
morphology
Three processes of permafrost degradation, as defined in
the Russian literature (Aré 1973, 1988), were observed
along the lake shorelines: 1) thermal abrasion, which is
erosion caused by the thermal and mechanical energy of
moving water in contact with permafrost; 2) thermal
erosion, which is ground subsidence due to conduction of
the thermal energy of water through the ground to the
thawing front; and 3) thermodenudation, which is the
destruction of shore cliffs under the effect of air thermal
energy, solar energy, and gravity.
High banks (> 2 m) are more susceptible to thermal
abrasion and thermodenudation due to the exposure of
mineral soil in the bank face. As a result, the morphology
of high banks can change rapidly in response to varying
conditions. Thawed soil slumps to the bottom of the bank
and can accumulate if the conditions are calm. This
accumulation reduces the bank gradient and insulates
the permafrost from the warm air (Fig.4a). If the lake
water level is high and the shoreline is exposed to the
wind, wave action removes thawed sediments from the
slope bottom and prevents accumulation (Fig. 4b). As a
result the bank steepens, permafrost remains exposed to
the warm air and shoreline recession occurs more
rapidly. Under windy conditions, wave action removes
material from the bottom of the bank faster than thawed
material slumps to the bottom, resulting in the
development of niches in the bank (Fig. 4c).
Thermal abrasion seems to play an important role on
many shorelines in the open tundra of the first study
area, and thermal erosion of permafrost seems to
dominate in the second study area (Fig. 4d). However,
both processes were observed in both study areas.
5.2 Effects of ice wedges on patterns of shore recession
The erosion of shorelines tends to follow ice wedges. In
the case of low shorelines, peat sediments are resilient to
wave action and ice wedges are eroded first, resulting in
the formation of polygon-shaped peat islands near
A
B
1511
Fig. 4 a) Thaw slumping under calm or low water conditions leads to the accumulation of sediments; b) wave action
can prevent the accumulation of sediment and cause a steepening of the bank; c) niches develop when wave action
removes material from the bottom of the bank faster than thawed material slumps to the bottom; d) the slow
subsidence of lake shores due to thermal erosion is most visible in areas sheltered from wave action and causes trees
to lean towards the lake in forested areas, as they respond to mass movement of the bank.
eroding shores. In the case of high shorelines, ice
wedges erode more slowly than the largely
unconsolidated sediments due to their higher latent heat
content, and form a lubricated surface against which
thawed sediments can slide.
5.3 Ice push
Shorelines exposed to strong winds in late spring are
periodically subject to ice push, which can contribute to
accelerating erosion by detaching and removing the
vegetation cover (Fig. 5a). Peninsulas and protruding
features of the shoreline are particularly vulnerable to the
erosive effects of floating ice pushed along or against
shorelines by wind action (Fig. 5b). Ice push may
contribute to the development of rectilinear shorelines by
accelerating the erosion of irregularities in the shoreline.
Observed rates of erosion varied between 0 and 3.5
m/yr. Shorelines receding most rapidly were located
where fetch and orientation result in exposure to more
aggressive wave action.
5.4 Discussion and implications
The lakes of Old Crow Flats are expanding by
thermokarst processes, in some cases rather rapidly.
High water levels, wave action, ice push, and the
presence of ice wedges accelerate erosion. It is difficult
to conceive how the shape of a lake could be determined
by underlying geological features and yet be maintained
despite permafrost degradation and movement of the
shorelines. For example, the 400 m shoreline which is
eroding at an average rate of 3.5 m per year is
maintaining its rectilinear shape despite its rapid
recession. This implies that the rectilinear shape of the
shorelines is controlled by something other than
underlying fault lines propagating through sediments.
A
B
C D
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Fig. 5. Ice-push a) accelerates shoreline erosion by damaging or removing the protective vegetation cover and b)
protruding features of the shoreline are most easily overridden by the moving ice.
6 PERMAFROST CONDITIONS NEAR
SHORELINES
6.1 Permafrost temperatures and snow conditions
Tundra sites were characterised by a vegetation cover of
tussocks and ericaceous shrubs over sphagnum peat.
Their mean top of permafrost temperature ranged
between -5.1ºC and -5.8ºC. In the open spruce shrubland
of the second study area, the mean annual temperature
at the top of permafrost was between -3.4ºC and -3.7ºC
(Table 1). These differences in mean temperature are
likely associated with differences in snow conditions
observed at each location. The snow cover is generally
thicker and has a lower density at the second study area,
providing better ground insulation than the thinner and
denser snow cover found at the tundra sites in the first
study area (Table 1).
6.2 Ice wedge abundance
Ice-wedge polygons are well developed and
omnipresent in the tundra of the first study area. They
are clearly visible from the air (Fig. 6), and along
the
shorelines where they are either exposed in rapidly
eroding banks, or form depressions in the bank on slowly
eroding shorelines. In the second study area, ice wedges
are rare, and have been observed only in patches of
tundra with a low vegetation cover. No ice wedges were
found in forest in Old Crow Flats during two summers of
fieldwork. No ice wedges were visible along forested
shorelines and in patches of forest we found no troughs
and no trees tilting towards each other (Kokelj and Burn
2005). The difference in ice-wedge abundance between
the two study areas may be related to the difference in
snow cover and ground temperature.
The ice-wedge networks surrounding the lakes are
strikingly orthogonal over extensive areas in Old Crow
Flats (Fig. 6). Orthogonal ice-wedge networks develop
where sediments undergo their initial freezing under
conditions of anisotropic thermal contraction stress
where a source of heat reduces the thermal stress in one
direction and cause ground cracking to occur at 90o to
the edge of the heat source (Lachenbruch 1962).
Extensive orthogonal networks such as seen in Old Crow
Flats (Fig. 6) may have developed where lakes slowly
regressed or drained in stages.
Table 1. Annual mean ground temperature (2008-09) and snow conditions (April 2010) in the two study areas, for
different vegetation covers.
Study area Vegetation # of sites TTOP
(ºC)
Median Snow depth
(cm) Snow density
(g/cm3)
1
Dwarf
shrubs
5 -5.1 to -5.8
(n=5)
26
(4 transects) 0.29
(n=8)
2
Open spruce
shrubland
4 -3.4 to -3.7
(n=4)
52
(4 transects) 0.19
(n=4)
A
B
1513
Figure 6. Ice-wedge networks are orthogonal over
extensive areas in Old Crow Flats.
6.3 Discussion and implications
The lakes of Old Crow Flats that are square and
oriented tend to be concentrated in areas characterised
by open tundra, where extensive orthogonal ice-wedge
polygons have been observed. The effects of ice
wedges on shoreline erosion described above and the
association of rectangular ice wedge networks and
rapidly expanding rectangular lakes suggests that
patterns of ground-ice development may contribute to
the evolution of rectilinear shorelines in the open
tundra of Old Crow Flats.
It is important to note that rapidly eroding
rectilinear shorelines have also been observed in areas
where the ice wedges are not orthogonal, highlighting
the probable importance of other factors in shaping
straight lake edges.
7 WIND REGIME AND SHORE EROSION
7.1 Wind direction and lake orientation
The dominant wind directions during the open water
season (June to September) at the first study area are
NE and ENE, while at the Old Crow Airport dominant
wind directions are NE and NNE (Fig. 7). The small
difference in orientation may be due to effect of local
topography between Old Crow and Old Crow Flats.
The lakes of Old Crow Flats are oriented both
perpendicular and parallel to this direction. The
consistency between the long-axis orientation of many
elongated lakes and wind direction in Old Crow Flats
indicates that lake orientation is not due to the wind-
driven processes associated with orientation of lakes
on Tuktoyaktuk Peninsula and the North Slope of
Alaska. However, observation of shore erosion
mechanisms clearly indicates that wind is an important
factor in the development of the lakes of Old Crow
Flats.
Figure 7. Wind speed and direction distribution for the
open water season (June to September) 2008 and
2009 a) in the first study area, and b) at the Old Crow
airport.
8 CONCLUSIONS
Field observations confirm that the lakes of Old Crow
Flats expand by thermokarst processes and the rapid
recession rates of some rectilinear shorelines indicate
that their morphology is not controlled by the structural
geology of the area. The form of the rectilinear lakes
may be associated with the orthogonal networks of ice
A
B
1514
wedges in the study area. While lakes with irregular
shorelines tend to be clustered in open spruce forest,
oriented lakes with rectilinear shorelines are clustered
in the open tundra, where the snow is thinner, the
ground colder, and orthogonal ice-wedge polygons are
abundant. Ice-wedges clearly affect shore erosion
patterns, but the occurrence of rectilinear shorelines in
areas where ice-wedge polygons are not orthogonal
indicates that other factors also contribute to lake
shape.
The relation between the local wind regime and the
bi-modal orientation of the lakes indicates that the
relation between lake orientation and wind regime
described at other arctic locations does not apply here.
The effect of the wind is likely still crucial to lake
development considering the importance of ice push
and wave action to shore erosion.
ACKNOWLEDGEMENTS
The research would not have been possible without the
financial support of the National Science and
Engineering Research Council Northern Chair
program, the Government of Canada International
Polar Year program, and the Northern Scientific
Training Program, Indian and Northern Affairs Canada.
The Aurora Research Institute and the Vuntut Gwitchin
First Nation Government provided essential logistical
support to the project. The SPOT imagery for the
YNNK project was provided jointly by The Government
of Yukon Department of Environment, McGill
University, and University of British Columbia. Several
residents of Old Crow contributed their help and
expertise during data collection including George
Nukon, Renee Charlie, Kibbe Tetlichi, Stephen Frost,
Douggie Charlie, Stanley Njoutli, Samantha Frost,
Erika Tizya-Tramm, Lance Nukon, and Marvin Frost
Jr. This paper is PCSP contribution 01310.
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