An avalanche can last from a few seconds to several minutes. Usually it lasts for under a minute. The entire event takes place very quickly once the snow begins to role downhill. It can reach speeds in excess of 100 kilometer per hour
Sometimes several avalanches take place in quick succession making it look like one big avalanche.
An avalanche is triggered when several layers of snow pile up with a weak supporting layer beneath it. The snow may be fresh and powdery. The steep slopes of a mountainside and a lack of vegetation are factors that allow the snow to hurtle downwards. Being buried under an avalanche is a mountaineer’s worst nightmare, and he not many survive.