Experimental and theoretical study of the dynamics of powder snow avalanches

Abstract

A powder snow avalanche is referred to as the turbulent flow of a cloud of dense fluid (suspension of snow particles) in an ambient one (the air) down an incline. This buoyant cloud can be channeled in a couloir (two-dimensional or 2-D buoyant cloud) or spread laterally on an open field (three-dimensional cloud). Between these two extreme cases one can meet all kinds of flow depending on mountain relief. Previous laboratory experiments in a water flume concerned only 2-D flows. 3-D flows are the subject of the present paper. From ‘thermal theory’ it is possible to obtain laws about velocity and density of the flowing cloud. A hundred experiments were carried out in a large tank containing fresh water along a tilting plane. It was shown that the height, length, and width growth rates of the clouds, between 15° and 90°, were linear functions of the slope. On the other hand the variation of the front velocity was shown to be in accordance with the proposed theoretical analysis. The results of this modeling can be applied to a real case of a powder snow avalanche flowing down a slope if there is no entrainment of the snow from the ground. This ‘no entrainment assumption’ corresponds generally to the last stage of the flow. Some practical examples are proposed.