Are avalanches caused by the shift from static to kinetic coefficient of friction? I was thinking about avalanches, and how they form, when it occurred to me to be quite likely that avalanches occur when a mass of snow gains enough momentum to push more snow through static friction into kinetic, gaining enough momentum to push even more snow through static friction into kinetic, and so on as a physical chain reaction.
Is this assessment of the cause of avalanches correct?
 A: My info on this comes from the book Snow sense: a guide to evaluating snow avalanche hazard, by Fredston and Fesler.
The physics of avalanches seems to be pretty complicated. Fredson and Fesler classify avalanches into four main types: "loose snow slides, slab avalanches, cornice collapses, and ice avalanches." They describe loose snow slides as arising through the sort of chain reaction you describe, while in a slab avalanche an entire slab starts sliding as a unit. Slab avalanches are often the most dangerous.
There seem to be a variety of reasons why the bond between a slab and the underlying bed can give way, leading to a slab avalanche. You get layers of snow with different properties, and they undergo changes such as metamorphosis (I guess analogous to geological metamorphosis) and melting. Often humans set off an avalanche, but the necessary weakness has to be present.
Although the question refers to the standard Coulomb-Amontons model of static and kinetic friction as taught in freshman physics courses, that model doesn't tend to work well for wetted surfaces, and it doesn't seem like it would naturally be able to explain some of the phenomena involved in avalanches. For example, in the Coulomb-Amontons model, stepping on a slab would never cause it to slide, because the critical angle is independent of the weight. (The added weight increases the normal force, which increases the maximum force of static friction exactly in proportion to the additional frictional force needed to support the greater weight.)
