Cornices: A Pissed Off Rattlesnake
Cornices - Nature's Snowy Trap Door
Cornices are diving boards of snow that form when snow blows across a ridgeline and collects on the Leeward side of the ridge. After major windy periods and rapid warming cornices become more fragile and break more often. Yet, they can break at any time, so treat them like a pissed off rattlesnake. Best to stay back! I treat any ridge above treeline as guilty of having a cornice, until proven innocent with eyes on from a safe vantage point...which is sometimes possible and other times not possible.
UNPREDICTABLE when they will break
Minimize your time under cornices. Chunks of cornice can break off and trigger wind slab avalanches on the slope below...which causes a LOT more snow to come down the slope. Example of avalanche triggered by cornice fall
When will it avalanche?: Unpredictable
Tools to reduce risk: Avoidance, stay back!
Trends: Wind makes them grow. Wind, Sun, Warming can cause cornices to break
Habitat: on leeward sides of ridges
I just threw this clip in for fun. Jed Porter shot it of Janelle Smiley rappelling over a monster cornice in Peru.
We guessed that the cornices are stronger up high this close to the equator, but it was super scary regardless. The less time you spend under cornices the better.