Questions that are specifically about avalanche situations are supposed to be tagged with this tag.
Avalanche is a mass of snow, ice, and rocks falling rapidly down a mountainside. Avalanches are typically triggered in a starting zone from a mechanical failure in the snowpack when the forces on the snow exceed its strength but sometimes only with gradually widening. After initiation, avalanches usually accelerate rapidly and grow in mass and volume as they tend to drag more snow with them. If the avalanche moves fast enough some of the snow may mix with the air forming a powder snow avalanche, which is a type of gravity current.