”The process of of mechanical disintegration and/ or chemical decomposition of rocks that destroys their coherence and breaks them into smaller components/ fragments is called weathering.”
Weathering is the decomposition of rocks, soils and their minerals through direct contact with the Earth’s atmosphere. Weathering occurs with no movement and thus it should not be confused with erosion, which involves the movement and disintegration of rock particles and minerals by agents such as water, ice, wind and gravity. Three important classification of weathering processes exist.
Mechanical or Physical Weathering
Biologically produced chemical weathering
01. Mechanical/ Physical Weathering:
Mechanical Weathering involves the physical disintegration of rock material without any change in its chemical composition. Mechanical weathering is the cause of disintegration of rocks. The primary process in mechanical weathering is abrasion – the process by which clasts and other particles are reduced in size. However, chemical and physical weathering often goes hand in hand. For example cracks exploited by mechanical weathering will increase the surface area exposed to chemical action. Furthermore, the chemical action at minerals in cracks can aid the disintegration process.
02. Biological Weathering:
Biological weathering occurs in three ways.
a). Through agency of Living Organisms (Fauna Based):
Living organisms may contribute to mechanical weathering. Lichens and mosses grow on essentially bare rock surface and create a more humid chemical micro-environment. The attachment of these organisms to the rock surface enhances physical as well as chemical breakdown of the surface of the rock. On a large scale seeding sprouting in the crevice of and plant roots exert physical pressure as well as providing a pathway for water and chemical infiltration. Borrowing animals and insects disturb the soil layer adjacent to the bed rock surface thus further increasing water and acid infiltration and exposure to oxidation processes.
b). Through agency of Plants (Flora Based):
It is also called root wedging. Root wedging occurs when the root of a plant begins to grow into a crack or pore in a rock. As the plant grows larger, so too does its roots, until the rocks breaks apart.
c). By Human Action:
The following human actions also results in disintegration of rocks:
- Air pollution
- Quarrying and Mining
- Road cut, dam construction, and underground atomic explosions etc.
- Ploughing for agriculture
Chemical weathering involves the decomposition of rocks by alteration of rock forming minerals. Chemical weathering involves the change in the composition of rocks, often leading to a break-down in its form. This type of weathering happens over a period of time.