Crevasses often have vertical or near-vertical walls, which can then melt and create seracs, arches, and other ice formations.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.[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.Occasionally a snow bridge over an old crevasse may begin to sag, providing some landscape relief, but this cannot be relied upon.
The glacier Taschachferner below the
Wildspitze
(left, 3.768 m) in Tyrolia in
Austria
in April 2005. There are some zones with large open crevasses, e.g., the spot-shaped area below the middle of the image and most right. The line marks the ascent track of
mountaineers on skis
which intentionally avoided these dangerous areas.