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A rapidly descending mass, usually of snow, down a mountainside. Powder avalanches consist of a moving amorphous mass of snow. Slab avalanches occur when a large block of snow moves down a slope and can cut a swathe through the soil and sometimes erode the bedrock if the snow is wet. See A. V. Briuchanov (1967).

Avalanches of other substances are forms of mass movement, and are distinguished by the type of material involved. Debris avalanches are typically triangular in shape, and are associated with morphological discontinuities, such as scarps and road cuts; see Guadagno et al. (2005) Geomorph. 66, 1–4 on man-made cuts and debris slides. Rock avalanches occur when a jointed rock loses internal cohesion, until some sections are held together only by the friction between blocks. If this frictional force is lessened through water seepage, or if lateral support is removed, failure will occur. See Mitchell et al. (2007) Landslides 4, 3.

Subjects: Meteorology and Climatology.

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