Superficial and Full-Depth Avalanches

Abstract

This chapter is dedicated to two geometrically extreme and opposite cases of snow avalanches, respectively qualified as loose snow and full-depth ones. A general feature is the absence of a weak layer, which eliminates any basal crack initiation by collapse. The former type consists of superficial flows of low-cohesion snow grains, whereas the latter essentially involves the whole snow cover gliding on the bare ground. Superficial avalanches are often released on high-angle slopes, gradually gathering new snow grains as they propagate in fan-like shapes. The smallest ones are known as “sluffs”. Their release mechanism is reminiscent of Bak’s sand pile described in appendix A. Different types of full-depth avalanches can be defined in terms of water percolation through the snow cover or at the snow/ground interface. They correspond to different release processes. Their flow and arrest mechanisms are also analyzed in terms of grain sintering in a granular fluid.