1) Terrain: The slope must be steeper than about 30
degrees.
Slopes less
than about 30 degrees are not steep enough to avalanche.
2) Snowpack: The snow must be unstable. Mountain
snowpacks are a series of layers. Some layers are strong, and some are weak. The
snowpack is unstable when a strong layer rest on top of a weak layer.
3) Trigger: Extra stress on the weak layer can cause it to collapse and produce an avalanche.
A trigger
could be additional weight from a snowmobile or simply more snow.
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In the above diagram, the buried weak layer has
collapsed and the overlying slab layer has fractured and
avalanched. |