crevassing

Crevassing is the formation of crevasses, deep fractures that develop in the surface ice of glaciers and ice sheets. Crevasses arise when the ice is subjected to tensile or shear stresses beyond its strength, typically as it flows over bedrock obstacles, encounters bed slope changes, or experiences differential motion within the glacier. The result is brittle fracture of the upper ice, producing visible fissures that can extend many meters downward and across large areas of the glacier.

Causes and mechanics include spatial variations in ice velocity, bending around turns or over steps in the terrain, and compression in some zones followed by extension in others. As ice accelerates or slows, or as it encounters rough topography, internal stresses concentrate at the surface and fracture planes propagate toward the air. Snow can accumulate in crevasses, concealing their depth and making travel hazardous. Some crevasses close during cold periods or refreeze at depth, while others widen with sustained flow or retreat.

Types of crevasses include transverse crevasses that cut roughly perpendicular to the flow direction, longitudinal or shear crevasses that run parallel to flow, and marginal crevasses near glacier edges. The pattern and size of crevasses reflect the underlying stress field and bed topology.

Hazards are a major concern for mountaineers and expeditions, since snow bridges over crevasses can collapse without warning. In glaciology, crevasse patterns help map ice flow, characterize stress regimes, and indicate changes in glacier dynamics over time.