A crevasse is a deep, wedge-shaped opening in a moving mass of ice called a glacier.
Crevasses usually form in the top 50 meters (160 feet) of a glacier, where the ice is brittle. Below that, a glacier is less brittle and can slide over uneven surfaces without cracking. The inflexible upper portion may split as it moves over the changing landscape.
Crevasses also form when different parts of a glacier move at different speeds. When traveling down a valley, for example, a glacier moves faster in the middle. The sides of a glacier are slowed down as they scrape against valley walls. As the sections advance at different speeds, crevasses open in the ice.
A bergschrund is a special type of crevasse. Bergschrunds are cracks that appear between the moving ice of a glacier and the non-moving, or stagnant, ice of a mountain or cliff.
Crevasses may stretch across a glacier, run along its length, or even crisscross it. Some crevasses have measured as large as 20 meters (66 feet) wide and 45 meters (148 feet) deep.
Crevasses, which are usually deep, steep, and thin, are a serious danger for mountaineers. Sometimes, a thin layer of snow may form over a crevasse, creating a snow bridge. Snow bridges blend in with the surrounding landscape, hiding the crevasse. Thin snow bridges usually cannot hold a person's weight, so mountaineers secure themselves to each other with rope. All experienced mountaineers are trained in crevasse rescue.
The Khumbu Icefall, part of a massive glacier on the south slope of Mount Everest in Nepal, is one of the most difficult obstacles for mountaineers. The Khumbu glacier moves very rapidly, and crevasses open quickly. A series of ladders and ropes helps many climbers, but the area is still one of the most dangerous on the mountain.
Crevasses can create seracs, which are also dangerous to mountaineers. Seracs are tall pillars formed where several crevasses once met.
A serac can be as large as a house, and may topple with little warning. Icefalls often have dozens of seracs.
All experienced mountaineers are trained in crevasse-rescue techniques. Many crevasses are shallow, and victims can be rescued with ropes and other climbing equipment. However, high-altitude mountaineers can experience disorientation, and victims may be injured and unable to contribute to their own rescue. Many climbers who fall into crevasses die of hypothermia.
cracks that appear between the moving ice of a glacier and the non-moving, or stagnant, ice of a mountain or cliff.
fragile or easily broken.
deep crack, especially in a glacier.
emergency method to help victims who have fallen into cracks in glaciers.
mass of ice that moves slowly over land.
water in its solid form.
part of a glacier that falls over a steep slope, similar to a waterfall.
stiff or unable to bend.
the geographic features of a region.
someone who climbs mountains.
highest spot on Earth, 8,850 meters (29,035 feet). Mount Everest is part of the Himalaya range, in Nepal and China.
something that slows or stops progress.
a structure used for support.
large pillar of glacial ice formed by the meeting of two or more crevasses.
thin layer of snow or ice that forms over a crevasse.
depression in the Earth between hills.