Cornice (climbing)

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This article is about the snow formation. For the architectural use, see cornice.

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The summit of San Jacinto Peak covered by a cornice formed by wind-blown snow.

Cornices can be very complex, allowing no safe route.

In climbing, a cornice is an overhanging edge of snow on a ridge or the crest of a mountain which are built up by drifting snow. Cornices are extremely dangerous and should never be walked on or under without adequate protection, or if other options are available and less hazardous.

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 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. Of course, this is not always possible. A good test for safety (in sunny weather) is to insert an ice axe and see if a blue glow comes out the hole. This indicates the ice is being lit from underneath, and that the climber should retreat to a safer location.

In avalanche 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 solar warming.