A snow cornice or simply cornice (from the Italian cornice meaning "ledge") is an overhanging edge of
snow
Snow consists of individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes.
It consists of frozen crystalline water througho ...
on a ridge or the crest of a
mountain
A mountain is an elevated portion of the Earth's crust, generally with steep sides that show significant exposed bedrock. Although definitions vary, a mountain may differ from a plateau in having a limited summit area, and is usually higher t ...
and along the sides of
gullies.
Formation
A snow cornice forms by wind blowing
snow
Snow consists of individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes.
It consists of frozen crystalline water througho ...
over sharp terrain breaks (e.g. the crest of the mountain) where it attaches and builds out horizontally. This build-up is most common on the steeper and
leeward
In geography and seamanship, windward () and leeward () are directions relative to the wind. Windward is ''upwind'' from the point of reference, i.e., towards the direction from which the wind is coming; leeward is ''downwind'' from the point o ...
sides of mountains. Cornices are extremely dangerous and travelling above or below them should be avoided.
When a cornice ''collapses'', it breaks in from the cornice to the top of the peak; even being on the snow on top of rock exposes the alpinist to hazard in this situation. The best practice in
mountaineering
Mountaineering, mountain climbing, or alpinism is a set of outdoor activities that involves ascending mountains. Mountaineering-related activities include traditional outdoor climbing, skiing, and traversing via ferratas that have become mounta ...
is to stay far enough back from the edge so as not to be able to see the drop, as an approximate metric of exposure.
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In
avalanche
An avalanche is a rapid flow of snow down a Grade (slope), slope, such as a hill or mountain. Avalanches can be triggered spontaneously, by factors such as increased precipitation or snowpack weakening, or by external means such as humans, othe ...
safety, cornices are a high avalanche danger as they often break and trigger larger avalanches that permeate several snow layers. Cornices are particularly vulnerable to collapse during periods of high
solar irradiance
Solar irradiance is the power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument.
Solar irradiance is measured in watts per square metre ( ...
.
Gallery
See also
*
List of climbing topics
*
Sastrugi
References
External links
"Cornice" from the Avalanche Encyclopedia*
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Aeolian landforms
Geographical terminology in mountaineering
Snow