An avalanche is a slide of a large snow down a mountainside, caused when a buildup of snow is released downward a slope, and is one of the major dangers faced in the mountains in winter. An avalanche is an example of a gravity present consisting of granular material.
In an avalanche, lots of material or mixtures of dissimilar types of material fall or slide rapidly under the force of gravity. Avalanches are often classified by what they are made of, for example snow, ice, rock or soil avalanches. A combination of these would be called a debris avalanche.
A large avalanche can run for many miles, and can create massive demolition of the lower forest and anything else in its path. For example, in Montroc, France, in 1999 300,000 cubic meters of snow slid on a 30 degree slope, achieving a speed of 100 km/h. It killed 12 people in their chalets under 100,000 tons of snow, 5 meters deep. The Mayor of Chamonix was convicted of second-degree murder for not evacuating the area, but received a suspended sentence.