An avalanche most commonly occurs in the 24 hours after a snow storm that dumps more than 30 cm of snow. There is a quick pile-up of snow that overloads the layers underneath. This causes the weak layers underneath to break.
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Storms,temperature,wind,steepness and direction of the slope,terrain,vegetation and snow pack conditions,all influence how the slope avalanches. Different combinations of these factors create different types of avalanches.