An avalanche is when a whole lot of snow, rock, ice, soil, and other material slides quickly down a mountain. This is classified as a weather event.

Some features of an avalanche are a block (slab) of snow cut out from its surroundings by fractures. Elements of slab avalanches include a crown fracture at the top of the start zone, flank fractures on the sides of the start zones, and a fracture at the bottom called the stauchwall.