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.

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.

Active layer slope movement in a continuous permafrost environment, Garry Island, Northwest Territories, Canada

1981 ◽  
Vol 18 (11) ◽  
pp. 1666-1680 ◽  
Author(s):  
J. Ross Mackay
Keyword(s):  
Velocity Profile ◽  
Active Layer ◽  
Vertical Velocity ◽  
Late Summer ◽  
Organic Layer ◽  
Field Investigations ◽  
Permafrost Environment ◽  
Vertical Velocity Profile ◽  
Ice Wedge ◽  
Ice Content

Field investigations have been carried out at Garry Island, N.W.T. for the 1964–1980 period in order to study downslope active layer movement at sites with two-sided (downward and upward) freezing and active ice-wedge growth. Movements have been determined with reference to semi-flexible plastic tubes inserted vertically into the ground and by deformation of lines of stakes. The results show that the vertical velocity profile on the hillslopes with clayey hummocks is convex downslope; the movement is plug-like and occurs in late summer; the plug-like movement progressively buries the interhummock peat to form a buried organic layer; and most of the plug-like movement can be attributed to frost creep by thaw of an ice-rich layer at the bottom of the active layer. The ice-rich layer forms by upfreezing in winter and the ice content may be augmented by ice lensing in the summer thaw period. In a sedgy drainage swale, the vertical velocity profile is concave downslope. The active layer of ice-wedge polygons shows a net movement outwards from the centres to the troughs. These studies show that active layer movement at sites with two-sided freezing and active ice-wedge polygons may differ substantially from sites with only one-sided freezing and without active ice-wedge polygons.

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.

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.

Influence of ground ice and permafrost on coastal evolution, Richards Island, Beaufort Sea coast, N.W.T.

1996 ◽  
Vol 33 (5) ◽  
pp. 664-675 ◽  
Author(s):  
Scott R. Dallimore ◽  
Stephen A. Wolfe ◽  
Steven M. Solomon
Keyword(s):  
Coastal Erosion ◽  
Sediment Budget ◽  
Storm Event ◽  
Ground Ice ◽  
Coastal Evolution ◽  
Thermal Erosion ◽  
Ice Wedge ◽  
Mechanical Erosion ◽  
Sea Coast

A long-term sediment budget (1947−1985) for northern Richards Island shows that, when ground ice and offshore erosion are accounted for, there is a near balance between headland erosion and coastal deposition. Excess ice constitutes about 20% of the total volume of eroded material from the headlands, with massive ground ice contributing nearly 9% and segregated ice lenses and ice wedges making up the remainder. Coastal response to major storms in 1987 and 1993 suggests that erosion is episodic, with short periods of intense disruption followed by readjustment of cliff profiles. Processes characteristic of this environment include mechanical erosion of ice-bonded sediments creating unstable erosional niches, mechanical failure of niches along ice-wedge planes, and longer term thermal erosion of ice-bonded sediments. Where ice contents are high, localized thaw slumps initiated by coastal erosion may retreat at rates substantially higher than those observed at other sections of the coast. Cliff-top retreat rates may be out of phase with storm-event chronology.

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.

Climate and ground temperature relations at sites across the continuous and discontinuous permafrost zones, northern Canada1This article is one of a series of papers published in this CJES Special Issue on the theme of Fundamental and applied research on permafrost in Canada.2Earth Science Sector (ESS) Contribution 20110128.

2012 ◽  
Vol 49 (8) ◽  
pp. 865-876 ◽  
Author(s):  
Jennifer Throop ◽  
Antoni G. Lewkowicz ◽  
Sharon L. Smith
Keyword(s):  
Active Layer ◽  
High Arctic ◽  
High Elevation ◽  
Climatic Conditions ◽  
Yukon Territory ◽  
Ground Temperature ◽  
Air Temperatures ◽  
Discontinuous Permafrost ◽  
Heat Effects ◽  
Ice Content

Climate – ground temperature relations are examined under a range of conditions for 10 sites across northern Canada. The sites are located between 60°N and 83°N and at elevations of 40 to 1840 m above sea level. They encompass various environmental and climatic conditions, with permafrost temperatures that range from just below 0 to –15 °C. The substrates range from bedrock to fine-grained sediment with high ice content, and vegetation types include coniferous forests in the Mackenzie Valley, shrub tundra at high elevation in the southern Yukon Territory, and polar desert in the High Arctic. Permafrost conditions at all of these sites are determined primarily by air temperature, followed by snow and substrate conditions. The apparent thermal diffusivity is relatively high at colder sites and in bedrock and is lower at sites in sediment with high ice content. Snow has a greater influence on air–ground temperature relations at sites where mean annual air temperatures and active-layer moisture contents are relatively high, leading to physically significant latent heat effects and a slower freeze-back of the active layer.

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