How do knife-edge ridges develop in glaciated mountains?
An arête is a narrow, sharp ridge between neighbouring glacial valleys or cirques. Its shape reflects erosion on both sides reducing the intervening mass of rock.
Erosion from two sides
As glaciers reshape valley floors and walls, cirque headwalls can retreat. Neighbouring hollows approaching one another narrow their dividing ridge. Freeze-thaw activity and rockfalls also shape exposed surfaces above the ice. An arête is therefore a combined product of glacial and slope processes rather than a line directly cut by ice alone. Rock fractures influence its continuity and sharpness.
Differences from pyramidal peaks
A ridge is an elongated feature; erosion by several cirques from different directions may instead leave a pointed summit, called a horn or pyramidal peak. Not every sharp mountain ridge has a glacial origin, because tectonic structure and river erosion can produce similar forms. Identification requires surrounding cirques, U-shaped valleys and other evidence together. Former arêtes can persist in mountains that no longer contain glaciers.