In an avalanche, a large volume of material falls or slides rapidly under the force of gravity. Avalanches are often classified by the type of material they are made of, for example snow, ice, rock or soil avalanches. Natural avalanches occur because new or windblown snow overloads weak-layers or because of rapid warming. Avalanches are also triggered by humans, due to additional weight, kicks during skiing, or intentionally by explosives, slope-cuts and other means.
For example, in Montroc, France, in 1999 300,000 cubic metres of snow slid on a 30 degree slope, achieving a speed of 100 km/h. It buried and killed 12 people under 100,000 tons of snow, 5 meters deep. The Mayor of Chamonix was charged with manslaughter.
