Thermal stress weathering causes the outer layers of rocks to appear to peel off (exfoliation). Thermal stress weathering is a type of physical weathering. Thermal stress occurs when rocks are subjected to swings in temperature. For example, desert rocks experience significant solar heating during the day and cold night temperatures. Forest fires can also significantly heat rocks.
Heat will cause the minerals in the rock to expand. The outer layer receives more heat than the interior, thus the minerals in outer layers will expand more. Additionally, different minerals expand at different rates in response to heat. This uneven expansion causes stresses to build up in the rock. Eventually, these stresses will cause cracks to form in the material, and the outer layers of rock will peel off. The process will then occur again on the newly exposed rock surface.
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