Snow as a Material

sagging and deforming. Unlike most materials we come in contact with snow is within 95% Kevin (K) of its melting point. To contrast this, the steal alloys in your car are within roughly 18% K of their melting point.  Molecules in the snow pack are, there for, very mobile and subject to change.  The layer of snow out side your door may appear static and unchanging throughout the winter, when in fact, the snow reacts quickly and easily to atmospheric changes (temperature and relative humidity).  The changes snow undergoes once it’s on the ground can either make the snow pack more stable (less likely to avalanche) or weaker (more likely to avalanche) 

A more useful property of snow for the understanding avalanche formations is the way in which snow deforms.  Snow can react bridaley or plastically, much like a glob of silly pudy, depending on the rate of the applied load.  When a large load is applied to the snow pack in a short period of time it can break (brittle reaction) much like an over stretched rubber band.  Appling the same load over a longer period of time can result in the snow pack slowly

Rapid loading resolts in a brittle fracture.
The same load applied over a longer period of time resolts in a plastic deformation

When a 600lbs. snow machine high marks up a slope or a skier “drops in” off a cornice do you think that this is slow or rapid loading?  Will the snow pack react plastically or brittly? Will it slowly deform or shatter into an avalanche?

Slab Avalanche Release Dynamics

Slab Avalanche Formation

Forces on the Snowpack