Crevasses and Seracs
Glacier ice is a strange material. It flows like a liquid at depth but behaves like a brittle solid near the surface. The result of this two-personality behaviour is the dramatic crevasse and serac landscape that defines so many of the photographs we associate with glaciers.
How crevasses form
When a glacier flows over uneven bed terrain — a steep step, a corner, a constriction — the ice surface stretches. Below about 30 m depth, the ice is plastic enough to deform without cracking. Above that, it is brittle. The result: surface cracks open into deep crevasses.
Typical crevasse depths are 20-40 m. They can be wider than 10 m on fast-flowing glaciers. Most glacier accidents are crevasse falls through snow bridges that hide them.
Snow bridges
A fresh snowfall covers crevasses with a fragile bridge. Walking on a glacier in poor visibility, in fresh snow, or off marked routes is dangerous because you cannot see what is hidden. Roped travel is the basic safety system: if one rope-team member falls in, the others hold and pull them out.
Seracs
Seracs are towering columns or blocks of ice that form where two or more crevasses intersect. They are common on icefalls — fast-flowing, steep sections — and on the steeper margins of bigger glaciers. Seracs collapse unpredictably and have killed many climbers, including on the Khumbu icefall.
Reading a crevasse field
From a balcony viewpoint above a glacier you can read flow direction and bed geometry from crevasse patterns:
- Transverse crevasses (perpendicular to flow) indicate steepening.
- Longitudinal crevasses (parallel to flow) indicate widening valleys.
- Diagonal "splaying" crevasses near margins mark the friction between ice and rock walls.
Safety summary
If you are not roped up, you should not be on glacier ice past the guide markers. End of summary.
Explore on the map
The interactive map flags major crevasse zones and icefalls on monitored glaciers — useful pre-trip context, but no substitute for a local guide.