Ice movement
In small quantities, ice is brittle, and the uppermost layer of a glacier often cracks up into crevasses. However, pressure increases with depth, and below about 30 metres, the pressure makes the ice lose its rigidity – the ice becomes plastic. In this way, the ice can respond to gravity, and may spread – slowly – over a large area, or flow downhill.

A glacier may move by basal sliding, gliding downhill lubricated by meltwater and mud at its base. Movement is a key characteristic of a glacier