Since differential movement within the ice causes tension and shearing, the surface of a glacier develops deep fissures or cracks. These fissures on the glacier surface are called crevasses. They can be either transverse or longitudinal.
Transverse crevasses form when the glacier passes over a steep slope. Longitudinal crevasses pointing up the glacier are produced because the central part of the glacier moves faster than its sides, or when the valley enclosing the glacier broadens causing it to spread laterally.
It is in these fissures that melt-water debris and other loose materials from the valley sides make their entry. On steeper slopes the crevasses intersect forming a series of ice pinnacles called seracs.
Where the slope increases abruptly, there is a cataract of ice called ice fall, characterized by many crevasses and ice pinnacles. The Khubu Ice-fall beneath Everest is a typical example.