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. ... Sometimes, a thin layer of snow may form over a crevasse, creating a snow bridge.

What causes crevasse?

A crevasse is a crack in the surface of a glacier caused by extensive stress within the ice. For example, extensive stress can be caused by stretching if the glacier is speeding up as it flows down the valley. Crevasses can also be caused by the ice flowing over bumps or steps in the bedrock.

What is in a crevasse?

Crevasse is a Glacial Fracture

Stress in the ice caused by the glacier's movement causes crevasses to open and close. Crevasses usually form in the upper 150 feet of a glacier where the ice is more brittle than deeper ice, which tends not to break and fracture as the glacier moves.