A Fragment–Flow Model of Dry–Snow Avalanches

Abstract

Abstract Field data on dry–slab avalanches obtained during the period 1975–79 from several snow climates suggest the following: (1) most of the mass of the typical avalanche studied consisted of fragments with lengths greater than 5 cm, (2) transverse and longitudinal shear planes formed during deceleration in the avalanche run–out zone, and (3) the flow height exceeded the slab height in most cases. No correlation was found between the run–out distance and the track or run–out zone slope, or between the run–out distance and the released slab height. The field data suggest that avalanche motion is best described as a flow of fragments in which boundary shearing stresses are sensitive to fragment size distributions and volumetric solids concentrations. These factors may be more important than the roughness of the avalanche boundary in determining maximum velocity and run–out distance.