Key takeaways
- A crevasse is a deep crack in a glacier, formed as the moving ice fractures over uneven ground.
- Hidden crevasses, masked by thin snow bridges, are the greatest danger — you can't see them.
- Falling into a crevasse is a major glacier-travel hazard and can be fatal.
- Protection comes from roped-team travel, crevasse-rescue skills, and reading the glacier surface.
From French 'crevasse' (crack), from 'crever' (to burst).
This is general educational information, not a substitute for glacier-travel and crevasse-rescue training. Take a course before traveling on glaciers.
How crevasses form
A glacier is a river of ice in slow motion. As it flows over bumps, steepenings, and bends in the bedrock beneath, the brittle surface ice can’t stretch and instead fractures, opening deep cracks — crevasses. They can be tens of meters deep and appear wherever the ice is under tension, often in predictable zones like icefalls and slope changes.
The hidden danger
The greatest hazard isn’t the open crevasse you can see and step around — it’s the hidden one. Wind-blown snow can bridge a crevasse with a thin, deceptive crust that looks like solid ground. Step onto a weak snow bridge and you can punch through into the gap below.
Crossing a snow-covered glacier, a roped team spaces out, keeps the rope snug, and probes ahead at a suspicious dip in the snow — finding a hidden crevasse under a thin bridge that looked like firm ground.
How climbers stay safe
Glacier travelers rope together as a team so a fall can be arrested, learn crevasse rescue to haul a fallen partner out, and read the surface for clues. The crevasse at the very top of a glacier, between moving and stationary ice, is a bergschrund — see crevasse vs bergschrund.
The bottom line
A crevasse is a deep glacier crack, and the hidden ones — masked by fragile snow bridges — are among the most serious hazards in mountaineering. The defense is never improvised: travel roped as a team, learn crevasse rescue, read the glacier's surface, and treat snow-covered glacier terrain with constant respect.
Frequently asked questions
What is a crevasse?
A crevasse is a deep crack in a glacier, created when the glacier's ice flows over changes in the underlying terrain and fractures under the stress. Crevasses can be very deep and wide, and they are a defining feature and hazard of glaciated mountain terrain.
Why are hidden crevasses so dangerous?
Snow can bridge over a crevasse, forming a thin, deceptive cover that hides the gap entirely. A climber can walk onto a snow bridge that looks like solid ground and break through, falling into the crevasse — which is why glacier travel demands roping up even when the surface looks safe.
How do climbers protect against crevasse falls?
By traveling as a roped team across glaciers, so that if one person breaks through, their partners can arrest the fall and perform a crevasse rescue to haul them out. Teams also probe suspect snow bridges, read surface clues (sagging lines, dips), and carry rescue gear like pulleys and prusiks.
Sources
- Glacier travel & crevasse rescue — American Alpine Club
- Glaciers & ice — USGS