Pyramidal peak

From Wikipedia, the free encyclopedia
  (Redirected from Glacial horn)
Jump to: navigation, search
The Matterhorn, a classic peak.

A pyramidal peak, sometimes in its most extreme form called a glacial horn, is an angular, sharply-pointed mountain peak which results from the cirque erosion due to multiple glaciers diverging from a central point.

Formation[edit]

Glaciers, typically forming in drainages on the sides of a mountain, develop bowl-shaped basins called cirques (sometimes called corries 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.

Erosional action of a cirque glacier.

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)[2]

Cross-section of cirque erosion over time.
Top view of stages in the enlargement of cirques (C) and their recession into an upland.
Stage Description Key Description
I Grooved upland A Aréte
II Early fretted upland C Cirque
III Mature fretted upland H Horn
IV Monumented upland M Monument

Preglacial surface shaded

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]

Examples[edit]

Examples of horns include:

See also[edit]

References[edit]

  1. ^ a b Embleton, Clifford; King, Cuchlaine A. (1968). Glacial and Periglacial Geomorphology. New York: St. Martin's Press. p. 193. LCCN 68-20348 Check |lccn= value (help). 
  2. ^ "Glossary of Glacier Terminology". US Geological Survey. Retrieved October 12, 2012. 

Bibliography[edit]

  • Easterbrook, Don J. (1999). Surface Processes and Landforms (2nd ed.). Upper Saddle River, NJ: Prentice Hall. pp. 334–336. ISBN 978-0138609580. 

External links[edit]