Water expands when it freezes. If water accumulates in
a crack and then freezes, its expansion pushes the rock
apart in a process called frost wedging. In a temperate
climate, water may freeze at night and thaw during the
day. Ice cements the rock together temporarily, but when
it melts, the rock fragments may tumble from a steep
cliff. If you hike or climb in mountains when the daily
freeze–thaw cycle occurs, be careful; rockfall due to
frost wedging is common. Experienced climbers travel in
the early morning when the water is still frozen and ice
holds the rock together.