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Each type of snow avalanche
has distinct characteristics:
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The loose snow avalanche, or sluff, generally
occurs at the surface in new snow or wet spring snow. This type of
avalanche often begins at a point and spreads out as it goes. Sluffs
seldom entrain enough snow to bury a person deeply and the chief danger
to winter recreationists from this type of avalanche is from being
pushed over a cliff or rock band. |
Ice fall avalanches occur when a glacier
encounters a steep drop. Chunks of ice "calf" off as the glacier slowly
flows downhill under the force of gravity. Ice fall avalanches are
unrelated to temperature, time of day or any other factors, despite
conventional wisdom to the contrary. The best way to avoid these avalanches
is to not travel beneath ice cliffs and through ice falls, or if necessary,
roll the dice and travel through quickly.
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Roof avalanches can be deadly for the unwary
and will often release as the inside of the house or cabin warms up.
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Cornice fall avalanches
occur when cornices break loose from the lee side of ridges.
Cornices look like frozen ocean waves
stretched along mountain ridges. They form their characteristic "eaves"
of cantilevered snow when prevailing winds remove snow from slopes
on one side of a ridge and deposit it on the other side of the ridge.
The snow that forms cornices is very
dense and hard, yet can be extremely fragile. It is often difficult
to determine from the ridge top where the ground ends and the overhanging
cornice is not supported.
This type of avalanche is easily avoided
by staying back from the peak of ridges, but can be deadly as the
victim tumbles downhill amid massive, hard and heavy chunks of snow
which often trigger secondary slab avalanches as they pass.
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The most dangerous type of avalanche is the slab avalanche. The
slab is difficult to see and avoid and will often allow a person to travel
well out onto it before failing.
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