How snow fails

Dry-snow slab avalanches start with a failure in a weak layer below a cohesive slab. Avalanche release models start with an initial crack which may propagate and, depending on the slope angle and the roughness of the fracture surface, lead to a whumpf or an avalanche. In order to investigate how the initial failure forms, we performed loading experiments with a weak surface hoar layer. We found that surface hoar strength decreased with loading rate and slope angle. Possible consequences for slab release are discussed.