arête

An arête is a narrow, knife-edged ridge that separates two glacial valleys or cirques. The term, from the French arête meaning edge, describes a crest that is typically sharp and elongated, often rising dramatically above the surrounding terrain.

Formation: Arêtes form where two or more glaciers erode the sides of a mountain valley; as ice moves between parallel valleys, rock is worn away by abrasion and plucking, leaving a residual ridge between them. With continued erosion on both sides, the ridge becomes narrow and sharp. In some landscapes a horn forms when three or more arêtes radiate from a common summit.

Appearance and significance: Arêtes are typically composed of resistant bedrock and may be snow-covered for part of the year. They can be several hundred meters to several kilometers long, and their width is often narrow relative to their length. Arêtes are diagnostic of past glaciation and are common in high mountain regions around the world, such as the European Alps, the Himalayas, and the Andes. They are part of a system including cirques (to the rear), cols or passes (at their ends), and horns if the ridge is truncated by multiple glaciations.

Understanding arêtes helps explain alpine landscape evolution and the legacy of glaciation.