Stress Concentrations in Weak Snowpack Layers and Conditions for Slab Avalanche Release

Dry-snow slab avalanches release due to the formation of a crack in a weak layer buried below cohesive snow slabs, followed by rapid crack propagation. The onset of rapid crack propagation occurs if stresses at the crack tip in the weak layer overcome its strength. In this study, we use the finite element method to evaluate the maximum shear stress tau(max) induced by a preexisting crack in a weak snow layer allowing for the bending of the overlaying slab. It is shown that tau(max) increases with increasing crack length, slab thickness, slab density, weak layer elastic modulus, and slope angle. In contrast, tau(max) decreases with increasing elastic modulus of the slab. Assuming a realistic failure envelope, we computed the critical crack length a(c) for the onset of crack propagation. The model allows for remote triggering from flat (or low angle) terrain. Yet it shows that the critical crack length decreases with increasing slope angle.