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.
Crevasses often have vertical or near-vertical walls, which can then melt and create seracs, arches, and other ice formations. [1] 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 (150 ft) and as wide as 20 metres (70 ft) [2]
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, [3] where significant summer melting occurs, and the bed of the glacier, where additional water may moisten and lubricate the bed and accelerate ice flow. [4] [5] Direct drains of water from the top of a glacier, known as moulins, can also contribute the lubrication and acceleration of ice flow. [5]
Falling into glacial crevasses can be dangerous and life-threatening. [7] Some glacial crevasses (such as on the Khumbu Icefall at Mount Everest) can be 50 metres (160 ft) deep, which can cause fatal injuries upon falling. [8] Hypothermia is often a cause of death when falling into a crevasse. [2]
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. [9] : 343
The danger of falling into a crevasse can be minimized by roping together multiple climbers into a rope team, [9] : 340 and the use of friction knots. [10]
