Geomorphic Work of Snow Avalanches in the Canadian Rocky Mountains^∗

Abstract

Snow avalanches are a major agent of debris transfer above tree line in the Canadian Rockies. At many sites they are a subsidiary rather than the dominant geomorphic process; therefore, landforms produced mainly by avalanche activity have a restricted and often strongly localized distribution. Optimal sites are slopes of 25 to 50° above tree line with plentiful debris cover. Talus slopes may often be strongly modified by avalanches. Debris accumulation by avalanches at experimental sites in Surprise Valley averages 0.6 to 4.8 mm yr^–1 over an 8-yr period. The morphological effects of avalanches are discussed with particular reference to the formation and distinctive characteristics of avalanche boulder tongues. The morphology of avalanche boulder tongues ranges from widespread thin fans of debris (fan tongues) to massive flat-topped or asymmetric tongues (roadbank tongues), depending on avalanche characteristics, debris supply, developmental history, and the morphology of the avalanche track. Vegetated, cone-shaped debris accumulations at the mouths of gullies or small stream valleys may also be formed by avalanches and are called avalanche cones.