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G. V. Douglas Memorial Award - 1977

During the 1979 field season, a large number of measurements of active layer thickness were obtained at a number of locations in the Tuktoyaktuk Peninsula/Richard鈥檚 Island area, N.W.T., by probing the ground surface with a stainless steel rod until the firm resistance of frozen soil was met. The various data sets were analyzed to determine the effect of late snow cover, microrelief, soil type and slope orientation on active layer development.

Generally, thaw in the study area began sometime in May but active layer development in areas covered by remnant snow was delayed by at least two to three weeks, dependant on the extent of late snow cover. The effect of this delay in initial thawing was not observable in late summer active layer thicknesses for the Illisarvik southeast slope transect. Final snow melt on the Illisarvik southeast slope and an associated short lived period of rapid thaw, in the previously snow covered area, resulted in a water saturated downslope active layer.

Active layer thicknesses in areas surrounding late snow cover are dependant on a number of factors including soil type, soil moisture, vegetation type and abundance, microrelief and slope orientation within each area. Generally, a thicker active layer is encountered in sandy soils and unvegetated areas with a moderate and thin active layer associated with clay soil and peat soil, respectively.

The time required for propagation of daily maximum soil temperature through the active layer results in a delay between the time of daily maximum solar radiation (i.e. maximum ground surface temperature) and the period of daily maximum thaw. In early summer (June 17 to June 23), when the active layer was relatively thin, maximum diurnal thaw was recorded between 2000 hours and 0500 hours.

In hummocky terrain, late summer frost table was a crude mirror image of surface topography. This is caused by: the higher conductivity of silty clay soil beneath the hummock versus peaty soil in the interhummock depression, greater evaporation of soil moisture from interhummock peat soil, greater net direct radiation received on hummock tops, higher ice content in interhummock depression soils, and possible vegetational differences between the hummock top and the interhummock depression. On larger scale relief features (i.e. pingos), direct radiation affects active layer development in that south facing slopes tended to have a thicker active layer than north facing slopes while east and west facing slopes had intermediate average active thicknesses.

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Pages: 104
Supervisors:聽 D. J. W. Piper