Snow avalanche


Avalanche at Samedan airport. Picture: Avalanche Samedan, Nicole Bischof SLF 2001

An avalanche is a process in the course of which snow or ice from the release zone moves suddenly and rapidly downwards along an avalanche track as a sliding mass or turbulent mixture of snow and air and comes to a halt in an avalanche accumulation area. Picture: Powder snow avalanche Leukerbad, Wolfgang Loretan 1999

Snow slabs can be recognized from the breaking off of a layer of snow. The rupture transverse to the slope is clearly identifiable in the photograph. Picture: Avalanche Furggentäli, Bernhard Krummenacher 1994

Wet snow avalanches are often triggered spontaneously and are frequently released during rain showers or after an increase in the day temperature. They mainly occur in spring. Picture: Slab avalanche Leukerbad, Bernhard Krummenacher 1991

Powder snow avalanches released from a large drop height can attain speeds of up to 300 km/h and, as a result, can cause very extensive damage. The masses of air that move along with the snow mass are a particular feature of this type of avalanche. Together with the snow crystals and larger lumps of snow, the air masses form "powder clouds" which can have destructive consequences for the surrounding area. Picture: Powder snow avalanche Grindelwald, K. Amacher 1996

Picture: Avalanche Rescue, SLF 1990

Just one winter sports enthusiast can trigger a slab avalanche. The risk of being carried along and buried by an avalanche is very high. Slab avalanches do not have to be very big to be dangerous. A typical slab avalanche caused by a skier is 70 metres wide and 200 metres long with a fracture depth of 50 centimetres. Picture: Slab avalanche Davos, SLF 1982

Avalanche deposit near Vallascia. What starts out as a snow avalanche eventually transports other solid materials with it. Picture: Avalanche Vallascia, SLF 1990


A snow avalanche is the rapid mass movement of deposited snow that exceeds 100 m3 in volume and 50 metres in lenght. Based on how they move, avalanches can be subdivided into flowing avalanches and powder-snow avalanches.

 

When avalanches meet an obstacle, buildings and infrastructure can be destroyed by the resulting compressive forces. The destructive effect of avalanches can be further increased by the transport of trees and rocks.

 

Video: Slab avalanche

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