Slab Avalanche Release: Data and Field Experiments

Starting zone sizes are shown to obey statistical laws, named “power laws”, stating that the recurrence time of an event of a given size increases in a precise proportion with its size. Extrapolation of such laws fitted on small-sized events allows a determination of recurrence times for big and uncommon events. The key role of the weak layer (WL) failure is illustrated by “Propagation Saw Tests” (PST), showing that the collapse of a WL zone of a few decimeters may act as a switch, triggering a very large scale spontaneous WL failure. However, the consequences of such a collapse may be damped down by sintering of broken WL grains. We analyze bridging indexes, often used to estimate WL resistance to collapse under loading. We define a new bridging index, extending the usual one to the case of elastic bending, and we discuss the validity domains of both of them.