Key takeaways
- A cornice is an overhanging mass of wind-deposited snow on the lee edge of a ridge or cliff.
- It forms as wind carries snow over the ridge crest and deposits it past the edge.
- Cornices are weak and can break far back from the visible edge, dropping a person through.
- Stay well back from corniced edges, and beware cornice fall triggering avalanches on slopes below.
From Italian 'cornice' (ledge), via French.
This is general educational information, not avalanche or mountaineering training. Take a certified course before traveling in avalanche and cornice terrain.
How a cornice forms
A cornice forms when wind carries snow across a ridge crest and deposits it on the sheltered, downwind (leeward) side, building an overhanging shelf that juts out over empty space. Over a season these can grow huge — extending meters beyond the solid rock or ground beneath.
Why cornices are dangerous
- Hidden edge: the real edge of solid ground sits well back from where the snow appears to end, so people break through walking too close.
- Structural weakness: unsupported cornices can fracture far back from the lip.
- Avalanche trigger: a falling cornice can land on and release the slope below.
Traveling a corniced summit ridge, a team stays a body-length or more back from the apparent edge — well onto the windward side — knowing the snow they can see may be overhanging nothing but air.
Staying safe
Give corniced edges a wide margin, avoid traveling beneath them during warming or heavy snowfall, and treat the slopes below as avalanche terrain. In a whiteout, the cornice hazard multiplies — navigate by instrument and keep well back.
The bottom line
A cornice is wind-built snow overhanging a ridge edge — beautiful, deceptive, and dangerous. Because it can break far back from the apparent edge and trigger avalanches when it falls, the rules are simple: stay well back on corniced ridges and avoid lingering beneath them, especially during warming or storms.
Frequently asked questions
What is a cornice?
A cornice is an overhanging shelf of snow that builds up on the downwind side of a ridge or cliff edge, formed by wind blowing snow over the crest and depositing it past the edge so it juts out over empty space, sometimes for several meters.
Why are cornices dangerous?
Cornices are unsupported and structurally weak, and they can fracture far back from where the solid ground appears to end — so a person walking near the edge can break through and fall. When a cornice collapses it can also land on and trigger an avalanche on the slope below.
How do you stay safe around cornices?
Give corniced ridges a wide berth, staying well back from the edge — the true edge of solid ground is usually farther in than it looks. Don't travel below cornices when they're prone to failure (such as during warming or heavy loading), and treat the slopes beneath them as potential avalanche terrain.
Sources
- Avalanche & snow hazards — Avalanche.org
- Winter mountaineering — The Mountaineers