An arête is a thin, crest of rock left after two adjacent glaciers have worn a steep ridge into the rock. A horn results when glaciers erode three or more arêtes, usually forming a sharp-edged peak. Cirques are concave, circular basins carved by the base of a glacier as it erodes the landscape.

The Matterhorn in Switzerland is a horn carved away by glacial erosion. —Credit: Photograph by Harry Fielding Reid. 1894. Zmutt Glacier: From the Glacier Photograph Collection. Boulder, Colorado USA: National Snow and Ice Data Center. Digital media

The “Garden Wall” formation in Glacier National Park, Montana, shows the sharp, knife-like ridge of rock characteristic of arêtes. —Credit: United States National Park Service

Iceberg Cirque in Glacier National Park, Montana, features a large circular bowl shape typical of glacial cirques. —Credit: United States National Park Service

These cirques on Disko Island in Greenland exhibit the circular bowl shape, and are separated by an arête. —Credit: Ole Mikkelsen