An arête ( / ə ˈ r ɛ t / ə- RET ; French: [aʁɛt] ) is a narrow ridge of rock that separates two valleys . It is typically formed when two glaciers erode parallel U-shaped valleys . Arêtes can also form when two glacial cirques erode headwards towards one another, although frequently this results in a saddle-shaped pass, called a col . The edge is then sharpened by freeze-thaw weathering , and the slope on either side of the arête steepened through mass wasting events and the erosion of exposed, unstable rock. The word arête is French for "edge" or "ridge"; similar features in the Alps are often described with the German equivalent term Grat .
7-404: Where three or more cirques meet, a pyramidal peak is created. A cleaver is a type of arête that separates a unified flow of glacial ice from its uphill side into two glaciers flanking, and flowing parallel to, the ridge, analogous to an exposed mid-channel bar in a braided river . Cleaver gets its name from the way it resembles a meat cleaver slicing meat into two parts. A common situation has
14-502: A glacial horn in extreme cases, is an angular, sharply pointed mountain peak which results from the cirque erosion due to multiple glaciers diverging from a central point. Pyramidal peaks are often examples of nunataks . Glaciers , typically forming in drainages on the sides of a mountain, develop bowl-shaped basins called cirques (sometimes called ‘corries’ - from Scottish Gaelic coire [kʰəɾə] (a bowl) - or cwm s). Cirque glaciers have rotational sliding that abrades
21-637: A horn depends on the number of cirques involved in the formation of the peak: three to four is most common. Horns with more than four faces include the Weissmies and the Mönch . A peak with four symmetrical faces is called a Matterhorn (after the Matterhorn , a mountain in the Alps). The peak of a glacial horn will often outlast the arêtes on its flanks. As the rock around it erodes, the horn gains in prominence. Eventually,
28-451: Is the crevasses known as bergschrund that occur between the moving ice and the headwall. Plucking and shattering can be seen here by those exploring the crevasses. A cirque is exposed when the glacier that created it recedes. When three or more of these cirques converge on a central point, they create a pyramid-shaped peak with steep walls. These horns are a common shape for mountain tops in highly glaciated areas. The number of faces of
35-455: Is usually the case on those summer routes to the summit whose lower portions are on the south face of Mount Rainier , where climbers traverse the flats of Ingraham Glacier but ascend Disappointment Cleaver and follow its ridgeline rather than ascend the headwall either of that glacier or (on the other side of the cleaver) of Emmons Glacier . Notable examples of arêtes include: Pyramidal peak A pyramidal peak , sometimes called
42-400: The floor of the basin more than walls and that causes the bowl shape to form. As cirques are formed by glaciation in an alpine environment, the headwall and ridges between parallel glaciers called arêtes become more steep and defined. This occurs due to freeze/thaw and mass wasting beneath the ice surface. It is widely held that a common cause for headwall steepening and extension headward
49-452: The two flanking glaciers melting to their respective ends before their courses can bring them back together; the exceedingly rare analogy to which is a situation of two branches of a braided river drying up before recombining. The location of a cleaver is often an important factor in the choice of climbing routes. For example, following a cleaver up or down a mountain may avoid travelling on or under an unstable glacial, snow, or rock area. This
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