arête, (French: “ridge”), in geology, a sharp-crested serrate ridge separating the heads of opposing valleys (cirques) that formerly were occupied by Alpine glaciers. It has steep sides formed by the collapse of unsupported rock, undercut by continual freezing and thawing (glacial sapping; see cirque). Two opposing glaciers meeting at an arête will carve a low, smooth gap, or col. An arête may culminate in a high triangular peak or horn (such as the Matterhorn) formed by three or more glaciers eroding toward each other.