In physical weathering, rocks are disintegrated due to rain water, temperature, frost etc. without changing any chemical composition of the rocks. There are several processes of Physical Weathering described below.
1. Insolation weathering
Insolation Weathering is related to temperature. Temperature varies from season to season and also day to day that is related to variation of annual range of temperature and diurnal range of temperature. Temperature variation affects the rocks. During the day time temperature is higher than night time. Thus, during day time the upper part of the rocks are expanded and during night time due to fall of temperature rocks are getting contracted. These expansion and contraction is going on repeatedly and everyday. Due to this process rocks are broken down or disintegrated into several fragments. These type of weathering is called as insolation weathering. The rock fragments are remain the same place until and unless any exogenetic forces remove these particles from one place to other.
Insolation weathering is of five types –
Block Disintegration This type of physical weathering is generally found in dry region and on homogenous rocks. Due to high temperature during day time, the upper part of the rock received more heat than the lower part and expanded. But, during night time similarly the upper part of the rock radiate the heat rapidly and cool down and contracted. Due to variation of length of day and night, little bit of heat is always remain inside the rocks layer, which may cause for turbulence inside the rock. Thus, lots of parallel cracks are developed over the rocks and after sometime these rocks are disintegrated along these cracks like a block. This is known as block disintegration.
Granular disintegration: It is also found in dry region and on heterogeneous rocks. As the rocks are composed of different types of minerals, thus, all the minerals don’t have the same ability to receive and radiate the heat. Some mineral receive more heat than the other mineral. So the rocks are affected by differential expansion and contraction which create excessive stress inside the rocks. Thus the rocks are disintegrated into smaller particles. Such type of shattering of rocks is called as granular disintegration.
Exfoliation: The term exfoliation means ‘peeling away’. Rocks are generally bad conductor of heat. In desert region during day time the upper part of the rocks receive more heat than the lower later. Thus the upper part of the rocks expanded than the lower layer. Similarly during night time upper part of the rocks contracted rapidly due to rapid radiation of heat than lower layer. If these expansion and contraction goes on for long time, then a heat gradient is developed inside the rocks. After sometime the upper part of the rocks peel off like onion shell. Thus, exfoliation is also known as onion weathering. this type of weathering is very common in granite rock. The remnant part of the main rocks look like spheroid, thus it is also called spheroidal weathering.
Boulder cleaving: In the mountainous region when boulders are exposed to the sun, due to rapid expansion and contraction lots of cracks are developed, which may separate the upper part of the boulder from its intruded portion of the mountain slope. This type of weathering is called as Boulder cleaving.
Dirt cracking: The rocks with several cracks, lots of smaller particles enter in between the cracks. During day time as temperature rises, these smaller particles expanded in its volume and it creates more pressure to the cracks to be widen. But during night time the particles contracted due to fall of temperature. Continuation of these process may cause for the break down of the main rocks into smaller fragments. This process is called as Dirt cracking.
2. Frost Action
Frost action also cause for the disintegration of rocks. It generally occurs in the high mountainous region accompanied with freezing and thawing. Three types of frost action is described below.
Frost weathering: In the mountainous region rain water and ice water enter the cracks of the rocks. During night time due to fall of temperature water turns into ice crystal and create stresses in between the rocks to enlarge the cracks. But, during day time ice melted and reduce the stresses. Freezing and thawing enlarge the cracks and after sometime the rocks become disintegrated into several block. This process of weathering is called as frost weathering.
Frost shattering: This is the same process of frost weathering and occurred at high mountainous region. But due to frost shattering rocks are broken down into lots of sharp edges small fragments, which is known as talus or scree. This talus or scree sometime accumulated at the base of foot hill zone, at that time it is called as felsenmer or blocksped.
Frost heaving: In the temperate region when rain water passes through the soil and enter the pore space of the rocks. During the winter this water turn into ice and break down the rocks into smaller fragments. this process is called as frost heaving.
3. Rainwater weathering
Rainwater is also responsible for disintegration of rocks. These are of two types.
Flaking: This type of weathering is found in humid region, specially in equatorial region. Rain water passes through the porous sedimentary rocks and makes them wet and expanded which become dried up and contracted due to evaporation. This process also leads to break down the rocks like a flakes. Thus, this process is called as flaking.
Splitting: This type of weathering is also found in equatorial region and more or less same process of flaking. But, in this process rocks are breaking down along the cracks without any changes of chemical composition. This process is called as splitting.
4. Pressure weathering
This type pf physical weathering rocks are disintegrated due to pressure. When a homogeneous granite rocks are subjected to huge load of sedimentary rock debris or under pressure with accumulation of ice, then rocks are breaking down in angular fragments. again, when these rock debris are washed away by any exogenetic forces, then pressure releases that also cause for breaking down of the rocks like sheet.
Pressure weathering are of two types.
Sheeting : Rocks are disintegrated due to unloading of the pressure.
Spalling: Rocks are disintegrated due to huge load of pressure.