The release of an overhanging mass of snow formed by wind deposits. 

Credit: Utah Avalanche Center

Cornices grow through the winter on the leeward side of wind exposed ridges and summits. Cornices range from small wind lips of soft snow to overhangs of hard snow larger than a school bus. They can break off the terrain suddenly and unexpectedly and can sometimes be triggered from a distance.  Overhung cornices can pull back further than expected onto a flat ridge top and catch people by surprise. While large cornices are quite destructive by themselves, even a small cornice can be deadly if it carries you over a cliff or rocky terrain below.  The impact from a Cornice Fall can also easily trigger slab avalanches on steep slopes below.  Travel cautiously on corniced ridgelines, giving cornices or unknown edges a wide berth.  Limit your exposure to slopes below cornices. Cornice Fall is most likely during periods of significant temperature warm-up or rapid cornice growth due to wind loading.

Many Cornice Fall accidents are caused by people venturing too far out onto corniced ridgelines. Credit: Flathead Avalanche Center

Cornices can break further into a ridge crest than you might expect.

Cornices also pose dangerous overhead hazards. This Cornice Fall swept several climbers down a steep chute. Credit: Colorado Avalanche Information Center

Cornice Fall can trigger slab avalanches (as shown), or simply entrain large amounts of loose snow along with the cornice debris. Credit: Flathead Avalanche Center

Be cautious of obscured horizon lines like this one. Without the gaping cornice crack here, you wouldn’t know that you’re standing on an overhung cornice. Credit: Crested Butte Avalanche Center