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Avalanche

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An avalanche is caused when a build up of snow is released down a slope, and is one of the major dangers faced in the mountains in Winter. An avalanche is a type of gravity current.

Table of contents
1 Human Survival
2 Causes
3 Contributory Factors
4 Avalanche Avoidance
5 See Also
6 External Links

Human Survival

Even small avalanches are a serious danger to life, even with properly trained and equipped companions who avoid the avalanche.

Research carried out in Italy based on 422 buried skiers indicates that survival drops very rapidly from 92% within 15 minutes, to only 30% after 35 minutes, and near zero after two hours - Nature vol 368 p21. Consequently it is vital that everyone surviving an avalanche is used in an immediate rescue operation, rather than sending for help.

(Historically, the chances of survival were estimated at 85% within 15 minutes, 50% within 30 minutes, 20% within one hour).

Causes

Avalanches occur naturally when the weight of snow becomes so heavy that a layer of snow looses its bond with the layer beneath. However most avalanches that involve humans are caused when the additional weight or the action of the equipment (e.g. skis) of the traveller causes the loss of bond.

Contributory Factors

There are very many factors that cause a snow slope to be avalanche prone:

Snow

Terrain

Weather

Avalanche Avoidance

Due to the complexity of the subject, winter travelling in the backcountry (off-piste) is never 100% safe. Risks can best be minimised by employing the service of a local qualified mountain guide, by carrying the right equipment and knowing how to use it properly, and by minimising the number of people on the avalanche prone slope to ensure that, should an avalanche occur, immediate help is available.

Equipment

The Group

See Also

External Links