Thaw slide west of King Point camp, Yukon Coast, July 10/99.

Landslides are common in the region of the Beaufort Sea coast. Retrogressive thaw flows, also known as retrogressive thaw slumps or ground ice slumps, are the main form of slope failure. They are found along the ice rich cliffs of the Tuktoyaktuk Peninsula, Richards Island, the islands north of the Mackenzie Delta, parts of the Yukon coast, and along the shores of thermokarst lakes in these areas. Large debris flows are restricted to the Caribou Hills bordering the East Channel of the Mackenzie River. They form large debris fans and periodically supply sediment to the river and the coast. Other forms of mass movement significant to cliff and coastal retreat include block falls and topples. These are common processes of coastal erosion and retreat that can remove several metres of the coast each year. The debris is usually quickly eroded by waves.

An inventory of landslides, based mainly on airphoto interpretation of photos taken in 1982, has been compiled. Within the Beaufort Coastlands about 3450 landslides ranging from very small features to large coalescing failures have been identified. Of these, fully 99% are retrogressive thaw flows and the final 1% are debris flows in till on the Caribou Hills or small rotational slides. Active layer detachment failures and block falls and topples, although locally significant in coastal retreat and in development of retrogressive thaw flows, are too small to be detected on air photos and are not included in the inventory.

Retrogressive thaw flow slide.

Rotational shear slide.

Authors: J.M. Aylsworth and J.A. Traynor
Geological Survey of Canada