Crevasses

Crevasses are deep fractures that form on the surface of glaciers and ice sheets. They arise where the ice experiences extensional stress as it flows over irregular bed topography or around obstacles, causing the ice to crack and separate.

They commonly occur in areas of fast flow, such as along glacier tongues, near icefalls, and at constrictions where the ice is stretched. Cracks propagate from existing fractures and extend downward through the brittle upper layer, creating vertical or overhanging walls that expose the ice interior.

Open crevasses have visible, vertical faces and may reach the surface; snow and ice can bridge some crevasses, producing hidden or covered crevasses that are dangerous because their depth and width are not visible without probing. Snow bridges can collapse under load, unexpectedly opening a hazard.

Sizes vary widely: widths can range from a few centimeters to tens of meters, and depths from several meters to tens of meters; on large glaciers, crevasses can be very deep and long. The exact dimensions depend on local flow, bed conditions, and seasonal snow cover.

Hazards and safety: Crevasses pose major risks to mountaineers, researchers, and transport routes. Safe passage often requires rope teams, probing with poles, route planning to avoid known crevasse fields, and, in some cases, crevasse rescue training and equipment.

Glaciology and mapping: Crevasses inform glacier dynamics by indicating stress and flow patterns. They are mapped through aerial and satellite imagery, photogrammetry, and ground-penetrating radar, contributing to measurements of ice thickness and movement across glaciers.