crevace

Old French crevace (crack, fissure) came from crever (to break, to burst), from Latin crepare (to crack, to burst, to make a cracking sound). English borrowed 'crevice' (a narrow crack, especially in rock) and 'crevasse' (a deep crack in a glacier) from the same French root — the difference in English usage distinguishes geological scale. A crevice is small; a crevasse is potentially fatal.

Glacier crevasses form where ice flows at different rates. As a glacier moves over uneven bedrock or around a bend, the surface ice stretches and cracks. Near the edges of glaciers, where ice moves more slowly than the center, longitudinal crevasses (running along the flow direction) form. Where a glacier steepens, transverse crevasses (perpendicular to flow) open. Seracs — towers of ice between crevasse systems — create the chaotic, dangerous terrain of a glacier's upper section.

Hidden crevasses — covered by snow bridges that can bear the weight of a person until they suddenly cannot — are the primary hazard of glacier travel. Mountaineers rope together precisely to arrest each other's falls into hidden crevasses. The 1991 discovery of Ötzi the Iceman in a melting glacier in the Alps was attributed to a shallow crevasse-like depression that preserved his body at high altitude for 5,300 years.

Climate change is changing glacier crevasse patterns. Warmer temperatures increase meltwater, which lubricates the glacier's base and accelerates flow, opening new crevasses in unexpected places. The Khumbu Icefall, the most dangerous section of the standard Everest route, has increased crevasse activity as the glacier accelerates. The frozen breaks are becoming more numerous as the ice moves faster toward its end.