Pyramidal peak

Apyramidal peak,sometimes called aglacial hornin extreme cases, is an angular, sharply pointedmountainpeak which results from thecirque erosiondue to multipleglaciersdiverging from a central point. Pyramidal peaks are often examples ofnunataks.

Formation

Cross-section of cirque erosion over time

Kinnerly PeakinGlacier National Parkin theU.S.state ofMontana

Glaciers,typically forming in drainages on the sides of a mountain, develop bowl-shapedbasinscalledcirques(sometimes called ‘corries’ - fromScottish Gaeliccoire[kʰəɾə] (a bowl) - orcwms). 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, theheadwalland ridges between parallel glaciers calledarêtesbecome more steep and defined. This occurs due tofreeze/thawand mass wasting beneath the ice surface. It is widely held^{[by whom?]}that a common cause for headwall steepening and extension headward is thecrevassesknown asbergschrundthat occur between the moving ice and the headwall.Pluckingand 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 theWeissmiesand theMönch.^[1]A peak with four symmetrical faces is called aMatterhorn(after theMatterhorn,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 theAlps,"horn" is also the name of very exposed peaks with slope inclinations of 45-60° (e.g.Kitzbüheler Horn).^{[citation needed]}