Anticrack model for skier triggering of slab avalanches

Skiers caught in a slab avalanche often trigger the avalanche themselves. Preventing those accidents necessitates a better understanding of the factors contributing to the failure of the snowpack under the action of a skier. In the present work, a mathematical model based on the principles of mixed-mode anticracking is proposed for skier triggering. The respective influences of the slope-normal and slope-parallel components of the load exerted by a skier on the prospective fracture plane are taken into account. A criterion for fracture propagation under typical skier loads is derived. It manifests a small number of factors that, combined, multiply the risk of triggering an avalanche. The criterion indicates, contrary to a common perception, that fracture is not more difficult to trigger in gentle slopes than in steep slopes. This major result of the model is confirmed by data obtained from field experiments.