Avalanches are rapid movements of large masses of snow down a slope that commonly occur in mountainous regions.
Despite what you may have seen in movies and on television, shouting cannot trigger an avalanche, according to the Utah Avalanche Centre. The UAC says that in 90% of avalanche deaths, it was the weight of the victim or someone in their group that triggered the avalanche.
In some countries the authorities monitor avalanche conditions and estimate risk levels. Specialists also intentionally trigger small snowslides with explosives so that the snow does not build up and is brought down the mountain in a controlled way when people are not present.
Image: An avalanche cascades down a mountain (credit: John Terence Turner)
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More info on: http://www.bbc.co.uk/science/earth/natural_disasters/avalanche