Abstract

A number of frost mounds of the frost blister type were observed at the site of a group of cold springs on the east side of Bear Rock, about 4 km west-northwest of Fort Norman, Northwest Territories, Canada. The mounds ranged in height from 2.0 to 3.0 m, with horizontal dimensions between 26 and 48 m. They contained a domed layer of ice, up to 85 cm thick, over an empty cavity up to 70 cm high, which was in turn underlain by frozen ground. Soil cover over the ice layer was 30–65 cm thick. The ice presumably formed from springwater injected under considerable hydraulic potential. New frost blisters are formed annually. Three recent frost blisters observed in June 1975 were partially destroyed by melting, slumping of the soil cover, and collapse of the ice dome by mid-September 1975. A portion of the ice lasted into summer 1976. Three new frost blisters, formed during the 1975–1976 winter, were observed in March 1976; two of these had completely collapsed by mid-June. An icing blister associated with one of them ruptured on March 21, 1976, producing a large flow of water, which lasted for several hours. A section of the icing blister subsequently subsided. Remnants of frost blisters have been observed in a spring area northeast of Turton Lake, Northwest Territories, and along the Dempster Highway in North Fork Pass and near the crossing of Blackstone River, Yukon Territory.

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