ABSTRACT
Active-layer detachment slides were mapped at three locations on the Fosheim Peninsula. Most occur on the upper and middle parts of slopes within plan form concavities, and generally they appear unrelated to undercutting by streams or to geological structure. The failure histories of individual slides range from simple, involving the movement of a single slab, to complex, with progressive failure from the base upslope as blocks become unsupported. At all sites, the process involves sliding of relatively rigid, strong soil masses over a thawing layer with minimal shear strength.
The average rate of activity in an area of 5.3 km2 within the valley of lower Black Top Creek is 3.5 failures per year (1950–1990), but 75 slides were initiated during July and August 1988. During this time thaw depths at nearby Hot Weather Creek were 56 to 65 cm, and the same levels were attained in the following two years, confirming that failure took place within the active layer where sampling showed ice contents and liquid limits were moderate. The importance of thaw rates was demonstrated by values for the basal part of the active layer in 1988, which were approximately double those in 1989 and 1990 when no failures occurred. The high density of active-layer detachment slides on the Fosheim Peninsula compared to most of the Canadian Arctic Archipelago is linked to the enhanced probability of substantial 224surface energy inputs in late summer when the thaw front is encountering segregated ice near the base of the active layer.
