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Abstract

Avalanche fatalities mainly occur due to dry-snow slab avalanches. Their release is a multi-scale process. It starts with the formation of a localized failure in a highly porous weak snow layer underlying a cohesive snow slab, followed by rapid crack propagation within the weak layer. Finally, a tensile fracture through the slab leads to its detachment. The dynamics of crack propagation, which affects the size of avalanche release zones, is still rather poorly understood. To shed more light on this crucial process, we developed a 3D model based on the discrete element method (DEM) to simulate the so-called Propagation Saw Test (PST), a commonly used snow fracture test, in order to analyze fracture dynamics from a micro-mechanical perspective. Using cohesive and non-cohesive ballistic deposition, we numerically produce a highly porous, brittle weak layer underneath a dense cohesive slab. Our results show that crack propagation reaches a stationary velocity if the snow column is long enough. Elastic moduli of the slab and weak layer as well as weak layer shear strength are key variables affecting stress concentrations at the crack tip, the onset of crack propagation, and the crack velocity. Finally, DEM simulations on steep slopes showed the emergence of a so-called supershear crack propagation regime, driven by shear failure, in which the crack becomes intersonic. Overall, our results lay the foundation of a comprehensive study on the influence of the snowpack mechanical properties on the fundamental processes for avalanche release.