couloir

A couloir is a narrow gully on a mountainside, typically between steep rock faces, carved by glacial or water erosion. The term, from French for corridor, is used in mountaineering and backcountry skiing to describe a constrained passage that may be filled with snow, ice, or loose rock. Width and depth vary; some couloirs are straight, others curved, and walls are often high and sheer.

Formation and types: Couloirs form where frost weathering and erosion concentrate flow or snowfall, creating a channel that can accumulate snow and ice. They can persist year-round in high latitudes or elevations, or fill seasonally. Many are climbed or skied as routes, with snow couloirs, ice couloirs, and dry rock couloirs representing different conditions.

Hazards and assessment: Common hazards include rockfall and icefall from the walls, avalanches or cornices, crevasse openings, and sudden weather changes. Exposure and route-finding can be difficult, and decisions about risk are central to ascent and descent.

Notability and usage: Couloirs are sought for their aesthetic lines and technical challenge. They occur in major mountain ranges worldwide, including the Alps, the Rockies, the Andes, and the Himalaya, and may require specialized equipment such as axes, crampons, ropes, and protection.

See also: gully, chute, chimney.