freeze–thaw

Active freeze-thaw on the chalk causes rockfalls on this section of the south Dorset coast, England. As the chalk is prized apart, it falls to the ground forming a scree slope. Active scree slopes are characterized by a very white colour (fresh chalk) as well as a lack of vegetation. In contrast, older freefalls and mass movements produce a darker colour and partly vegetated scree slopes.

Scree slopes are common in upland areas, such as the Lake District. The scree – broken fragments of rock – is usually formed by freeze-thaw activity. This breaks solid rock into smaller, often angular particles. Scree is common in mountainous areas, since night-time temperatures often fall below freezing point, and there is a ready supply of moisture to freeze. A typical lowland glaciated valley can be seen in the background.

Scree slopes are common in upland areas, such as the Lake District in northwest England. The scree, broken fragments of rock, is usually formed by freeze-thaw activity. This breaks solid rock into smaller, often angular particles. They are common in mountainous areas, since night-time temperatures often fall below freezing point, and there is a ready supply of moisture.

Compassberg Mountains in South Africa. Many geological processes are at work here, particularly freeze-thaw action in which rocks are broken apart by the expansion of frozen water and repeated heating and cooling.

Form of physical weathering, common in mountains and glacial environments, caused by the expansion of water as it freezes. Water in a crack freezes and expands in volume by 9% as it turns to ice. This expansion exerts great pressure on the rock, causing the crack to enlarge. After many cycles of freeze–thaw, rock fragments may break off to form scree slopes.

For freeze–thaw to operate effectively the temperature must fluctuate regularly above and below 0°C/32°F. It is therefore uncommon in areas of extreme and perpetual cold, such as the polar regions.