Thermal expansion, or insolation, is a very important type of
weathering, which occurs particularly in desert type areas. It is
essentially very similar to freeze-thaw weathering, without the water. The
outer layer of the rock is heated greatly by the sun during the day,
causing it to expand. At night, the cooling of the rock causes it to
contract. After this expansion and contraction has been repeated many
times, the outer layer of the rock peels away

Heat spalling can be heat from forest fires and brush fires will cause the outer
surface layers of rock to expand quickly and break away in spalls. Natural
fires, although an infrequent occurence in human experience, occur on a
scale from yearly to hundred yearly, and are thus very frequent events
over geological time scales.