An avalanche is a speedy flow of snow down a inclined surface. Avalanches are typically triggered in a initial zone from a automatic failure in the snowpack when the forces on the snow go beyond its strength but sometimes only with steadily widening .After instigation avalanches usually speed up rapidly and grow in accumulation and quantity as they entrain more snow. If the avalanche moves fast enough some of the snow may blend with the air forming a residue snow avalanche which is a type of gravity current.
The weight on the snowpack may be only due to gravity in which case breakdown may result either from fading in the snowpack or increased weight due to precipitation. Avalanches that take place in this way are known as spontaneous avalanches. Avalanches can also be triggered by other masses such as skiers, snowmobilers, animals or explosives. Seismic activity may also trigger the failure in the snowpack and avalanches. A popular myth is that avalanches can be triggered by piercing noise or uproar but the pressure from sound is small to start a avlanche
In this video there is a dry avalanche went down in Randa in the state of Valais and it is extremely dangerous but nobody got hurt.