<P> Thermal stress weathering, sometimes called insolation weathering, results from the expansion and contraction of rock, caused by temperature changes . For example, heating of rocks by sunlight or fires can cause expansion of their constituent minerals . As some minerals expand more than others, temperature changes set up differential stresses that eventually cause the rock to crack apart . Because the outer surface of a rock is often warmer or colder than the more protected inner portions, some rocks may weather by exfoliation--the peeling away of outer layers . This process may be sharply accelerated if ice forms in the surface cracks . When water freezes, it expands with a force of about 1465 Mg / m ^ 2, disintegrating huge rock masses and dislodging mineral grains from smaller fragments . </P> <P> Thermal stress weathering comprises two main types, thermal shock and thermal fatigue . Thermal stress weathering is an important mechanism in deserts, where there is a large diurnal temperature range, hot in the day and cold at night . The repeated heating and cooling exerts stress on the outer layers of rocks, which can cause their outer layers to peel off in thin sheets . The process of peeling off is also called exfoliation . Although temperature changes are the principal driver, moisture can enhance thermal expansion in rock . Forest fires and range fires are also known to cause significant weathering of rocks and boulders exposed along the ground surface . Intense localized heat can rapidly expand a boulder . </P> <P> The thermal heat from wildfire can cause significant weathering of rocks and boulders, heat can rapidly expand a boulder and thermal shock can occur . The differential expansion of a thermal gradient can be understood in terms of stress or of strain, equivalently . At some point, this stress can exceed the strength of the material, causing a crack to form . If nothing stops this crack from propagating through the material, it will result in the object's structure to fail . </P> <Table> <Tr> <Td> </Td> <Td> Parts of this article (those related to Conflating frost weathering and frost wedging and also not incorporating hydrofracturing, which makes the science here seem wrong . See paper referenced on Frost weathering page: Matsuoka, N.; Murton, J. 2008 . "Frost weathering: recent advances and future directions". Permafrost Periglac . Process . 19: 195--210 . doi: 10.1002 / ppp. 620 .) need to be updated . Please update this article to reflect recent events or newly available information . (January 2018) </Td> </Tr> </Table>

Which type of weathering is not a type of stress