<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> <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> <P> Frost weathering, also called ice wedging or cryofracturing, is the collective name for several processes where ice is present . These processes include frost shattering, frost - wedging and freeze--thaw weathering . Severe frost shattering produces huge piles of rock fragments called scree which may be located at the foot of mountain areas or along slopes . Frost weathering is common in mountain areas where the temperature is around the freezing point of water . Certain frost - susceptible soils expand or heave upon freezing as a result of water migrating via capillary action to grow ice lenses near the freezing front . This same phenomenon occurs within pore spaces of rocks . The ice accumulations grow larger as they attract liquid water from the surrounding pores . The ice crystal growth weakens the rocks which, in time, break up . It is caused by the approximately 10% (9.87) expansion of ice when water freezes, which can place considerable stress on anything containing the water as it freezes . </P>

Exposure to which of these is the most common cause of chemical weathering