Crevasses are deep cracks in a glacier or snowpack. They typically have near vertical sides and can be very deep. They are extremely dangerous hazards for those crossing a glacier as snow can drift to cover them, forming a snow bridge, and hiding this sudden drop. Crevasses may lead to ice caves below. There may be perilous bridges connecting the two sides of a crevasse.

Those navigating a glacier often travel connected by ropes, so that if one member falls into a crevasse the others may attempt to stop their fall.

In fictional worlds, large crevasses may divide the landscape and separate two different regions or countries. They may mark the division between civilization and the wilds or the wastes. They may share similarities with canyons and chasms and there may be cliffside settlements and cliffside pathways. In game-oriented worlds, crevasses may act as either terrain hazards or terrain obstacles.