Physical Weathering (Mechanical Weathering)—–
When the rocks are broken up into smaller fragments without any chemical change in their composition, it is called physical weathering.
Physical weathering takes place in different ways in different types of areas.
Successive heating and cooling causes expansion and contraction of the rocks.
In hot desert regions, day temperatures are very high while nights are very cold.
This high diurnal range of temperature causes successive expansion and contraction of the rocks which tend to enlarge the joints.
Finally the rocks disintegrate into smaller blocks.
This process is known as block disintegration.
Rocks are generally poor conductors of heat.
As a result of intense heating the outer layers of the rock expand rapidly while the inner layers remain almost unaffected by heat.
Due to successive expansion and contraction, the outer layer of the rock subsequently peels off from the main mass of the rock in the form of concentric shells.
The peeling of rocks in layers by this process is very similar to the peeling of successive layers of an onion.
The process is called exfoliation.
Almost all rounded forms of dolerite blocks of rocks in Singhbhum district of Bihar are due to this process.
Granite domes of Mahabalipuram, particularly ‘Krishna Ka Laddu’ and those near Jabalpur on Madan Mahal Hill are good examples, of exfoliation.
One of the most important physical weathering processes in cold climates is frost action.
The alternate freezing and melting of water inside the joints of the rocks, splits them into fragments.
This is because conversion of water into ice increases the volume of water by 10 percent.
In cold regions rocks are disintegrated into small particles through this process.
It is called frost action.