Crevasses are deep fissures or cracks in a glacier that can be up to 100m or more. Crevasses are formed, when the brittle ice on top of the glacier fractures as the underlying ice continues to flow under the force of gravity.

On snow-capped mountains, it is very common to encounter crevasses. Crevasses that are visible on the snow surface can usually be avoided by going round it. But it is the hidden crevasses that are covered by snow or a thin layer of ice that poses the greatest dangers to climbers. Thus, when crossing a crevasse field, climbers are usually roped-up to one another so that if one is to fall into a crevasse, the other team members on the same rope can set up a system to pull the fallen climber out.