In a humid, temperate area of central-western Alberta, a mudflow occurred along Hell's Creek, a short tributary of the Smoky River in July, 1962, during a heavy rainstorm. Flows had not occurred during the previous 3 years, even though rains of comparable intensity had fallen. The source area is a steep-sided rock amphitheater, cut in deformed shales and siltstones, and almost devoid of vegetation. The mud moved over a mile in a narrow stream valley and spread across the lower part of an alluvial cone. The exposed lithology of the cone suggests that mudflow is the principal agent in construction of this and other cones of the region. Deposition of the cone has diverted the course of a large river.

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