The Physics of Avalanches
Cornices

Formation
Triggering

Slabs

Bibliography

When a cornice attains enough mass that is extended out beyond the ridge line of the mountain it shears along a path that is straight up from the ridge and starts a large mass of snow moving down the mountain. These blocks can be as large as 10 meters tall and as long as ridge lines. There is a massive amount of potential energy stored in them and when they shear off all of the potential energy is transfered into kinetic energy. This is why they are so dangerous and cause so much damage to the mountain and anyone in its path. Cornices can also be triggered before they would fall naturally by humans if they walk to far beyond the ridgeline on the leeward side. Often times cornices can appear solid and stable to walk on when they are not. Therefore walking near or on cornices should be avoided when possible.

     
http://www.fsavalanche.org/encyclopedia/i-cornice/cornice-01.gif
http://ffden-2.phys.uaf.edu/212_fall2003.web.dir/Sarah_Schlichting/cornice.jpg