A crevasse is a deep crack, that forms in a
glacier or ice sheet that can be a few inches across to over 40 feet. Crevasses form as a result of the movement and resulting stress associated with the
shear stress generated when two semi-rigid pieces above a plastic substrate have different rates of movement. The resulting intensity of the shear stress causes a breakage along the faces.
Description
Crevasses often have vertical or near-vertical walls, which can then melt and create
serac
A serac (from Swiss French ''sérac'') is a block or column of glacial ice, often formed by intersecting crevasses on a glacier. Commonly house-sized or larger, they are dangerous to mountaineers, since they may topple with little warning. Even ...
s,
arch
An arch is a vertical curved structure that spans an elevated space and may or may not support the weight above it, or in case of a horizontal arch like an arch dam, the hydrostatic pressure against it.
Arches may be synonymous with vault ...
es, and other ice formations.
These walls sometimes expose layers that represent the glacier's
stratigraphy. Crevasse size often depends upon the amount of liquid water present in the glacier. A crevasse may be as deep as 45 metres and as wide as 20 metres.
Crevasse
by National Geographic
A crevasse may be covered, but not necessarily filled, by a snow bridge
Snow comprises 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 throughout ...
made of the previous years' accumulation and snow drifts. The result is that crevasses are rendered invisible, and thus potentially lethal to anyone attempting to navigate their way across a glacier. Occasionally a snow bridge over an old crevasse may begin to sag, providing some landscape relief, but this cannot be relied upon. Groups planning to travel on a glacier with hidden crevasses must be trained to move as a rope team The term rope team (german: Seilschaft), roped team or roped party, originally came from mountain sports, especially climbing, where it describes a group of people joined by a mountain or climbing rope and thus secured against falling.
Mountainee ...
and have proper equipment.
The presence of water in a crevasse can significantly increase its penetration. Water-filled crevasses may reach the bottom of glaciers or ice sheets and provide a direct hydrologic connection between the surface, where significant summer melting occurs, and the bed of the glacier, where additional water may moisten and lubricate the bed and accelerate ice flow.
Types of crevasses
*Longitudinal crevasses form parallel to flow where the glacier width is expanding. They develop in areas of tensile stress, such as where a valley widens or bends. They are typically concave down and form an angle greater than 45° with the margin.
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References
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{{Authority control
Glaciology
Glacial landforms
Mountaineering
Hazards of outdoor recreation