Ice wedges on hillslopes and landform evolution in the late Quaternary, western Arctic coast, Canada

1995 ◽  
Vol 32 (8) ◽  
pp. 1093-1105 ◽  
Author(s):  
J. Ross Mackay
Keyword(s):  
Active Layer ◽  
Late Quaternary ◽  
Chronological Age ◽  
Bottom Slope ◽  
Thermally Induced ◽  
Landform Evolution ◽  
Ice Wedge ◽  
Western Arctic ◽  
Arctic Coast ◽  
The Mean

In rolling to hilly areas of the western Arctic coast of Canada, anti-syngenetic wedges, which by definition are those that grow on denudational slopes, are the most abundant type of ice wedge. Through prolonged slope denudation, hilltop epigenetic wedges can evolve into hillslope anti-syngenetic wedges, and some bottom-slope anti-syngenetic wedges, by means of deposition from upslope, can evolve into bottom-slope syngenetic wedges. The axis of a hillslope wedge is oriented perpendicular to the slope, so the wedge foliation varies according to the trend of the wedge with respect to the slope. Because the tops of hillslope wedges are truncated by slope recession, the mean chronological age of anti-syngenetic wedge ice decreases with time, so the growth record for an old wedge is incomplete. Summer and winter measurements show that a thermally induced net movement of the active layer of hillslope polygons tends to transport material from their centres towards their troughs independent of the trends of the troughs relative to the slope. Wedge-ice uplift, probably diapiric, has been measured. Some hillslope polygon patterns may predate the development of the present topography. Many Wisconsinan wedges, truncated and buried during the Hypsithermal period, have been reactivated by upward cracking.

scholarly journals Thermally induced movements in ice-wedge polygons, western arctic coast: a long-term study

2002 ◽  
Vol 54 (1) ◽  
pp. 41-68 ◽  
Author(s):  
J. Ross MacKay
Keyword(s):  
Active Layer ◽  
Term Study ◽  
Thermally Induced ◽  
Seasonal Movements ◽  
Long Term Study ◽  
Ice Wedge ◽  
Western Arctic ◽  
Arctic Coast

AbstractThermally induced seasonal movements of the active layer and subjacent permafrost have been measured in numerous ice-wedge polygons that have varied in age, type, crack frequency, and topographic location. The field observations show that, in winter, thermal contraction, which is inward, is constrained or vanishes at the polygon centres but, in summer, thermal expansion, which is outward, is unconstrained at the ice-wedge troughs. Therefore, there tends to be a small net summer transport of the active layer, to varying depths, into the ice-wedge troughs. The movement has been observed in all polygons studied. The slow net transport of material into the ice-wedge troughs has implications for: permafrost aggradation and the growth of syngenetic wedges in some troughs; the palaeoclimatic reconstruction of some ice- wedge casts; and the interpretation of polygon stratigraphy based upon the assumption that the polygon material has accumulatedin situ.

Air temperature, snow cover, creep of frozen ground, and the time of ice-wedge cracking, western Arctic coast

1993 ◽  
Vol 30 (8) ◽  
pp. 1720-1729 ◽  
Author(s):  
J. Ross Mackay
Keyword(s):  
Snow Cover ◽  
Active Layer ◽  
Air Temperature ◽  
Thermal Stresses ◽  
Temperature Drop ◽  
Frozen Ground ◽  
Air Temperatures ◽  
Ice Wedge ◽  
Western Arctic ◽  
Arctic Coast

The time of ice-wedge cracking is examined for several sites with young and old ice wedges along the western Arctic coast. The correlation between sharp air temperature drops and ice-wedge cracking is highest where the snow cover is thin and least where the snow cover is thick. The favoured duration and rate of a temperature drop that results in cracking is about 4 days, at a rate of about 1.8°C/d. Such temperature drops have a minimal effect in cooling the top of permafrost wherever there is an appreciable snow cover. Since short duration temperature drops often result in ice-wedge cracking, the thermal stresses that trigger cracking probably originate more within the frozen active layer than at greater depth in permafrost. Although most ice wedges tend to crack during periods of decreasing air temperatures, about one third of those monitored have cracked during periods of increasing air temperatures. Long-term measurements show that the active layer and top of permafrost move differentially all year in a periodic movement. That is, creep of frozen ground occurs all year, irrespective of whether ice wedges crack or do not crack. The presence of a snow cover and the creep of frozen ground are two major factors that confound a simple application of conventional ice-wedge cracking theory to air temperature drops and the time of ice-wedge cracking.

The first 7 years (1978–1985) of ice wedge growth, Illisarvik experimental drained lake site, western Arctic coast

1986 ◽  
Vol 23 (11) ◽  
pp. 1782-1795 ◽  
Author(s):  
J. Ross Mackay
Keyword(s):  
Growth Rates ◽  
Linear Expansion ◽  
Temperature Dependent ◽  
Frozen Ground ◽  
Ice Wedge ◽  
Western Arctic ◽  
Arctic Coast ◽  
Coefficient Of Linear Expansion ◽  
Lake Site ◽  
Crack Widths

A large lake, measuring 600 m × 300 m and with a depth of nearly 5 m, was artificially drained on 13 August 1978. Observations on the formation, width, and depth of thermal contraction cracks for the first 7 years show that the crack profiles and ice wedge growth rates differ markedly from those of old ice wedges reported in the literature. The first winter's cracks had box-like profiles, with surface widths to 10 cm and depths to 2.5 m. Some cracks continued to widen and deepen, once opened in early winter, and then narrowed or even closed completely in summer. Mean growth rates for the ice wedges for the first few years have been as much as 3.5 cm/year. Temperature gradients at the time of first cracking have been in the range of 10–15 °C/m. The growth rate of young ice wedges is site specific and temperature dependent, varying with factors such as the temperature gradient, vegetation, and snow cover, so an estimate of the age of an ice wedge from its width will usually be impossible. A study of crack widths indicates that the apparent coefficient of linear expansion of frozen ground may be several times that of ice. Upward cracking has been proven.

Disturbances to the tundra and forest tundra environment of the western Arctic

1970 ◽  
Vol 7 (4) ◽  
pp. 420-432 ◽  
Author(s):  
J. Ross Mackay
Keyword(s):  
Active Layer ◽  
Clear Distinction ◽  
Forest Tundra ◽  
Thermal Erosion ◽  
Surface Disturbance ◽  
Ice Wedge ◽  
Western Arctic ◽  
Ice Content ◽  
Seismic Lines

The more important physical disturbances to the tundra environment are discussed with examples. Thermokarst subsidence, not thermal erosion, is shown to be the dominant result of man-induced disturbances, such as those caused by the bulldozing of seismic lines and firebreaks. It is shown that a clear distinction between thermokarst subsidence and thermal erosion is necessary, if the causes of the disturbances are to be prevented and minimized, or the results treated. The typical surface disturbance to the tundra results in a deepening of the active layer. Therefore, foreknowledge of the effect of a disturbance on deepening the active layer, together with information on the ice content of the permafrost affected, makes it possible to predict the amount of thermokarst subsidence likely to take place. Three practical examples of three types of ground disturbance are given: a fire near Inuvik, N.W.T.; a patch of vegetation trampled and killed by a dog at Garry Island, N.W.T.; and seepage down a walking trail in an ice-wedge area at Garry Island, N.W.T. The effects of the disturbances are illustrated and discussed.

The direction of ice-wedge cracking in permafrost: downward or upward?

1984 ◽  
Vol 21 (5) ◽  
pp. 516-524 ◽  
Author(s):  
J. Ross Mackay
Keyword(s):  
Ground Surface ◽  
Vertical Direction ◽  
Thermal Conditions ◽  
Field Studies ◽  
Field Instrumentation ◽  
Ice Wedge ◽  
Western Arctic ◽  
Arctic Coast ◽  
First Time ◽  
Continuous Temperature

Field studies have been carried out along the western arctic coast of Canada in an attempt to determine whether all ice-wedge cracks originate at the ground surface and therefore propagate downward or whether some cracks originate near the top of permafrost and then propagate both upward and downward. The field studies have been concentrated upon (1) low- and high-centred tundra polygons a few thousand years old; and (2) ice wedges, growing for the first time, on the bottom of a lake experimentally drained in 1978. The field instrumentation has included electronic crack direction indicators, electronic elapsed timers, and continuous temperature measurements. The field studies reveal that many of the ice-wedge cracks originated near the top of permafrost and then propagated upward to the ground surface as well as downward into ice-wedge ice. For the 1974–1982 period, the field observations showed that about 57% of the ice wedges cracked from the ground surface downward and 43% cracked both upward and downward. Furthermore, the vertical direction of ice-wedge cracking was not consistent for any given wedge, presumably because of year-to-year variations in the physical and thermal conditions of the polygons and their troughs.

Tundra lakes and permafrost, Richards Island, western Arctic coast, Canada

2002 ◽  
Vol 39 (8) ◽  
pp. 1281-1298 ◽  
Author(s):  
C R Burn
Keyword(s):  
Snow Cover ◽  
Active Layer ◽  
Open Water ◽  
Active Layer Thickness ◽  
Equilibrium Conditions ◽  
Lake Bottom ◽  
Near Shore ◽  
Western Arctic ◽  
Arctic Coast ◽  
Average Size

Lakes, of average size 33 ha, occupy a quarter of the surface area of Richards Island, Northwest Territories. Most of the lakes have a central pool deeper than the thickness of winter ice, and many have prominent, shallow, littoral terraces. The relatively warm lake bottoms cause considerable disturbance to the surrounding continuous permafrost. Water and lake-bottom temperatures, the configuration of permafrost, and active-layer thickness were measured at a tundra lake between 1992 and 1997. The lake is oval, 1.6 km long, 800 m wide, and as deep as 13 m. Sandy terraces, covered by less than 1 m of water, extend over 100 m from the shore. The terraces are underlain by permafrost, which terminates almost vertically at their edge. The annual mean temperature measured at lake bottom in the central pool ranged between 1.5°C and 4.8°C, depending on depth, and between –0.2°C and –5°C on the terraces, due to differences in snow cover and proximity to the central pool. In consequence, the temperature of permafrost at 7 m depth in the terraces also varied, from –2°C near shore to –5°C in mid-terrace. The active layer in the terraces was uniformly 1.4 m deep. Geothermal modelling of talik configuration indicates that there is no permafrost beneath the central pool of the lake. The modelling indicates that, under equilibrium conditions, about one quarter of the lakes on Richards Island have taliks that penetrate permafrost, and at least 10–15% of the island is underlain by talik. Short-term climatic changes predicted for the region imply a small increase in summer lake-water temperature and an extension of the open-water season, accompanied by thicker snow cover in winter. Following such changes, with longer freeze-up and warmer terrace temperatures in winter, permafrost may not be sustainable in the lake terraces.

The frequency of ice-wedge cracking (1967–1987) at Garry Island, western Arctic coast, Canada

1992 ◽  
Vol 29 (2) ◽  
pp. 236-248 ◽  
Author(s):  
J. Ross Mackay
Keyword(s):  
Air Temperature ◽  
Classification System ◽  
Environmental Reconstruction ◽  
Wide Range ◽  
Ice Wedge ◽  
Western Arctic ◽  
Arctic Coast ◽  
The Common ◽  
A Site ◽  
Observation Period

The frequency of ice-wedge cracking has been studied at Garry Island, Northwest Territories, for the 1967–1987 period. Sites have included low-centre polygons, intermediate-centre polygons, and polygons that do not fit any classification system. Analyses of crack frequency have included trough characteristics, polygon characteristics, and ice-wedge types. The results show that crack frequencies are highly variable within one site and also between two adjacent sites. The correlation between crack frequency and a low air temperature is poor. Crack frequencies for a site with 59 wedges ranged from 8 to 42% between 1967 and 1979 and for a nearby site with 32 wedges from 22 to 75% between 1967 and 1987. In view of the wide range in crack frequencies at a given site, the use of mean ice-wedge growth rates for estimating ages of ice wedges and their casts in environmental reconstruction may be hazardous. The data show that the common twofold classification into active and inactive wedges is difficult to apply because crack frequencies are gradational and dependent on such factors as the number of ice wedges being monitored, the size of the area, the types of ice wedges, and the length of the observation period. A system for classifying crack frequency is proposed.

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