page_title: Avalanche
section_title: Human involvement
hierarchical_section_title: Avalanche / Human involvement
caption_attribution_description: Verbauungen Tanngrindel
context_page_description: An avalanche is an event that occurs when a cohesive slab of snow lying upon a weaker layer of snow fractures and slides down a steep slope. Avalanches are typically triggered in a starting zone from a mechanical failure in the snowpack when the forces of the snow exceed its strength but sometimes only with gradual widening. After initiation, avalanches usually accelerate rapidly and grow in mass and volume as they entrain more snow. 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.
  Slides of rocks or debris, behaving in a similar way to snow, are also referred to as avalanches. The remainder of this article refers to snow avalanches, because they are the ones that occur the most in the world.
  The load on the snowpack may be only due to gravity, in which case failure may result either from weakening in the snowpack or increased load due to precipitation. Avalanches initiated by this process are known as spontaneous avalanches. Avalanches can also be triggered by other loading conditions such as human or biologically related activities.
caption: Snow fences in Switzerland during summer.
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