An overhanging mass of wind-deposited snow that breaks off of a ridgeline and tumbles down the slope. 

Credit: Utah Avalanche Center

Cornices typically form on the leeward side of a sharp, wind-exposed terrain break such as a ridge crest or summit.  Cornice falls can trigger additional slab avalanches on the slope below, or they can simply consist of the cornice and any additional snow entrained by the cornice blocks.  Accidents typically involve cornices breaking unexpectedly below ridgeline travelers, or occasionally from natural cornice falls that overtake travelers on slopes below.  

Aerial view of a cornice fall that swept several climbers down a steep chute. Credit: Colorado Avalanche Information Center

A cornice fall that triggered a narrow slab avalanche. Credit: Crested Butte Avalanche Center