Freeze-thaw weathering, also known as frost weathering, is caused by water working its way deep into cracks in rock faces, expanding as it freezes and then driving deeper into the rock when it melts. Over time, this process can work large chunks of stone loose from rock faces and send the debris tumbling downhill into large scree piles.
Frost weathering is most effective in wet environments where the temperature routinely hovers close to the freezing point of water. A wet environment gives liquid water the chance to work down into sometimes microscopic cracks and imperfections in a stone face. A cold environment promotes the formation of ice crystals that put pressure on all sides of the crack and force the gap wider. If the temperature tends to fluctuate above and below zero degrees Celsius, the water has a chance to repeat the cycle multiple times, penetrating deeper with each freeze-thaw cycle and widening the crack like a wedge being driven deeper and deeper.
In contrast to stone that has been weathered by running water, frost-weathered rock typically shatters into sharp, angular fragments. Sometimes these fragments are of considerable size and shatter further when they drop from the living rock face.