A Melt-Freeze Crust or Rain Crust is a discontinuity between
snow
Snow consists of individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes.
It consists of frozen crystalline water througho ...
layers which can lead to
avalanche
An avalanche is a rapid flow of snow down a Grade (slope), slope, such as a hill or mountain. Avalanches can be triggered spontaneously, by factors such as increased precipitation or snowpack weakening, or by external means such as humans, othe ...
s.
The layer can be created in two ways:
*A temperature high enough to allow surface snow to melt, creating a layer of melt water which may later re-freeze.
*Rain falling and freezing on the surface of existing snow, also creating a frozen layer.
This layer is brittle, smooth and slippery, and does not bond with snow layers above it, allowing the overlying slab of snow to move down the mountain under
gravity
In physics, gravity (), also known as gravitation or a gravitational interaction, is a fundamental interaction, a mutual attraction between all massive particles. On Earth, gravity takes a slightly different meaning: the observed force b ...
when disturbed or if the accumulated snowfall exceeds a critical mass. The initial slab may be as large as 10,000m² and 10 metres thick.
References
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Snow