Pyramidal peak

A pyramidal peak, sometimes called 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.

Formation edit

Cross-section of cirque erosion over time

Kinnerly Peak in Glacier National Park in the U.S. state of Montana

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 cwms). Cirque glaciers have rotational sliding that abrades 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^{[by whom?]} that a common cause for headwall steepening and extension headward 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.^{[citation needed]}

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 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.^[1] A peak with four symmetrical faces is called a Matterhorn (after the Matterhorn, a mountain in the Alps).^[2]

The peak of a glacial horn will often outlast the arêtes on its flanks.^[1] As the rock around it erodes, the horn gains in prominence. Eventually, a glacial horn will have near vertical faces on all sides.^{[citation needed]} In the Alps, "horn" is also the name of very exposed peaks with slope inclinations of 45-60° (e.g. Kitzbüheler Horn).^{[citation needed]}