Physical Weathering Processes
Freeze Thaw (Frost Shattering)
Temperatures need to fluctuate above and below freezing. When the temperature drops below 0 degrees, water collected in rock cracks freezes and expands. When temperatures rise again the ice melts. Pressure created by expansion results in progressive weakening of the rock. At high altitudes frost-shattered material forms scree slopes. Heating & Cooling
Thermal expansion & contraction of rock in response to rising and falling temperatures. The daily cycle of heating and cooling sets up stresses in the rock that cause it to disintegrate. Occurs mostly in deserts where there is the greatest diurnal temperature range. Also occurs during bush fires. Wetting & Drying (Slaking)
Rock is alternately wetted then dried. Minerals which make up clay rocks expand when wetted, then contract on drying-out. The stresses from repeated expansion and contraction cause the rock to disintegrate. This process commonly occurs on the intertidal zone of coasts. Exfoliation (Onion weathering/Spheroidal)
Under warm conditions rock surfaces heat up and expand more than the main mass of the internal body of the rock. Eventually the surface layers split off or spall from the lower layers, sometimes in slightly curved sheets like the layers of an onion. Seen especially in granite. Crystal Growth (Salt Weathering)
Salt crystals, such as sodium carbonate and magnesium sulphate grow within spaces in a rock. It happens when saline water enters cracks in rocks then evaporates. The growing crystals prise the rock apart and small pieces break off. This process is especially effective in semi-arid areas and coastal regions. Pressure Release (Dilation)
Not caused by elements of weather. Occurs either when erosion removes a heavy covering of rock or when large ice sheets melt. The removal of great weight allows the rock layers beneath to expend. As they expand they also fracture to produce bedding...