Temperature variations in glacial regions

In glacial regions of the world or during forest fires the rocks are exposed to extreme temperatures. Since the conduction of heat is very slow, the temperatures at the surface and the interior of the rock are quite different thereby a kind of lateral stress is generated which may cause the peeling off of the external layers of the rock. This phenomenon is called as exfoliation and is accelerated by freezing of water trap ped inside the rock  crevices and  unloading i.e., the removal of  overlying rocks or sediments causing the release of pressure.