A crevasse is a deep crack that forms in a glacier or ice sheet. 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 seracs, arches, 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 m and as wide as 20 m 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. Direct drains of water from the top of a glacier, known as moulins, can also contribute the lubrication and acceleration of ice flow.

Types

Dangers

Falling into glacial crevasses can be dangerous and life-threatening. Some glacial crevasses (such as on the Khumbu Icefall at Mount Everest) can be 160 ft deep, which can cause fatal injuries upon falling. Hypothermia is often a cause of death when falling into a crevasse. A crevasse may be covered, but not necessarily filled, by a snow bridge 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 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. The danger of falling into a crevasse can be minimized by roping together multiple climbers into a rope team, and the use of friction knots.