GRANULATION OF SNOW: EXPERIMENTS AND DISCRETE ELEMENT MODELING

ABSTRACT: The flow dynamics of snow avalanches can strongly differ for individual avalanches even if the release conditions are similar. The development of different flow regimes, e.g. whether a plug flow or a sheared flow is formed, strongly depends on the snow properties in the avalanche. Depending on whether the avalanche was dry, moist or wet, typical granular structures and size distributions can be observed in the deposition zone. These are then often interpreted as indirect indicators of the internal flow dynamics of an avalanche. In order to understand under which circumstances granules form, we used a concrete tumbler to examine the granulation, the generic name for particle size enlargement, of snow with different properties. Our experiments show that granulation of snow only occurred when a snow temperature of-1◦C was exceeded. No granule formation could be observed below this temperature threshold. To better understand the physical processes involved in the granule formation, cohesive discrete element simulations were performed, allowing to correctly reproduce the size distributions of granules as measured in the tumbler and in real-scale avalanches. The results of this paper confirm recent studies that the snow temperature plays a crucial role on granulation and thus on the flow dynamics of avalanches since it may strongly change the structure of the flowing snow. This investigation provides a first step for more complex and real-scale modeling of flowing cohesive avalanches and shows that granulation has the potential to link snow cover properties with avalanche dynamics