couloirs

A couloir is a narrow, steep gully on a mountainside. The term, from French, is widely used in mountaineering to describe a natural channel bounded by rock walls that channels snow, ice, or rockfall. Couloirs vary in width from a few meters to several tens of meters and in length from tens of meters to hundreds or thousands of meters. They form on high, cold faces where frost weathering and glacial action concentrate snow and ice into funnel-shaped passages.

Formation and types: Couloirs form where relief and climate favor snow and ice accumulation within a natural bowl or chute, with rock walls confining the flow. They are categorized as snow, ice, or mixed couloirs when rock is involved. Their angles often lie between 30 and 60 degrees, though some are steeper. Snow and ice conditions can change rapidly, making some couloirs stable routes and others hazardous.

Use and climbing approach: In alpine climbing, couloirs serve as routes for ascent or descent and can be the most direct line to a summit. They require technical gear and skills, including crampons, ice axes, ropes, and protection; climbers rely on route-finding and belayed protection. Hazards include avalanches, ice and rockfall, crevasse openings, and cornice collapse, making snow stability and weather assessment critical.

Geographic distribution and context: Couloirs are found in major ranges such as the Alps, Andes, Himalayas, and Karakoram. They are iconic features of alpine terrain and influence the difficulty and choice of routes. Conditions vary with sun exposure and temperature; many couloirs are more favorable in winter or spring when snow is consolidated, while others remain dangerous year-round.