Abstract

An historic major rockslide has diverted John-John Creek northwards to its present channel flowing into Brazeau Lake in the Main Ranges of the Rockies in Jasper National Park, Alberta.The slide debris moved northeastwards from cliffs on the northeastern face of "Molard Mountain," an unnamed peak northeast of Flat Ridge in the Grand Brazeau. It reached the shores of Brazeau Lake.The debris occupies a plan area of 0.9 km2 with an average width of 500 m. An estimated average debris thickness of 5 m gives a volume of the displaced mass of 4.5 × 106 m3. The angle from the slide crown to the tip of the debris is about 18°. An approximate reconstruction of the depletion and accumulation of the slide suggests 23° as a lower bound for the angle of friction of the slide debris.The exposed rupture surface of the slide, a bedding plane in the lower portion of the Middle Cambrian Pika Formation, dips at 27° to the northeast. Dolostones, limestones, and shales from the Pika Formation form the slide debris. The slide site is in a panorama photographed in 1928. The slide shows on aerial photographs taken in 1951. A secondhand account of the slide places its occurrence in early July 1933. So the Brazeau Lake slide is the second major rockslide to occur in the Canadian Rockies this century and the first that is undoubtedly a natural event.

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