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(1) combined processes (such as sublimation, fusion or melting, evaporation) which remove snow or ice from the surface of a glacier or from a snow-field; also used to express the quantity lost by these processes (2) reduction of the water equivalent of a snow cover by melting, evaporation, wind and avalanches.


all processes by which snow or ice are added to a glacier, this is typically the accumulation of snow, which is slowly transformed into ice; other accumulation processes can include avalanches, wind-deposited snow, and the freezing of rain within the snow pack.

alpine layers

annual accumulations of snow and dust on a glacier.


mass of snow which becomes detached and slides down a slope, often acquiring great bulk by fresh addition as it descends.
An avalanche in motion. (Photograph courtesy of Richard Armstrong, National Snow and Ice Data Center.)


winds of at least 35 miles per hour along with considerable falling and/or blowing snow reducing visibility to less than one-quarter mile for a period of at least three hours (extremely cold temperatures are often associated with dangerous blizzard conditions, but are not a formal part of the modern definition).

blow hole

opening through a snow bridge into a crevasse or system of crevasses which are otherwise sealed by snow bridges; a snowdrift usuallly forms on the lee side.

blowing snow

an ensemble of snow particles raised by the wind to moderate or great heights above the ground; the horizontal visibility at eye level is generally very poor.

bottom temperature of snow cover

temperature measured at the base of the snow cover during mid- to late-winter (February/March).


an overhanging accumulation of ice and wind-blown snow, characteristically found on the edge of a ridge or cliff face.


a way that snow or ice can move by deforming its internal structure.