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Process of weathering may be divided into three parts: 1. Physical Weathering 2. Chemical Weathering 3. Biological Weathering.
Process # 1. Physical Weathering:
In this type of weathering rocks are divided/disintegrated into different parts without any chemical change that is why it is known as mechanical weathering.
Three agents work on this type of activity:
a. Insolation:
This process takes place mostly in deserts as during day time rocks expand due to high temperature and contract during night with fall in temperature. Repetition of this activity results in disintegration of rocks. Sometimes rocks disintegrate into small pieces, which is known as Granular disintegration. Although main reason for physical weathering is heat of sun yet winds and air pressures can also cause such process.
b. Frost-Heaving:
Due to heat when cracks appear on rocks, rain water is filled in those cracks. At night, water freezes because of low temperature and expands due to which breakdown of rocks starts and they disintegrate into smaller parts. Mostly this process takes place in mountainous regions. Sometime small stones come out from soil because of frost heaving and these stones make ring like structure.
c. Exfoliation:
This activity takes place in desert areas. Rise and fall in temperature on daily basis leads to disintegration of layers of rocks and due to high speed winds these fine eroded layers get transported to far-flunged areas. This process is known as exfoliation.
Process # 2. Chemical Weathering:
In this weathering chemical structure of rock changes. Gases in Atmosphere and rain lead to disintegration of rocks which brings physical as well as chemical changes. This process is known as chemical weathering.
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Chemical weathering also has various types:
a. Oxidation:
In this process oxygen reacts with the iron particles present in rocks because of which ferrous (rust) is formed. Due to oxidation, rocks attain red or yellow colour. Rust leads to the disintegration of rocks in small particles.
b. Carbonation:
When regions with high lime content receive rainfall, the carbon-dioxide present in water reacts with lime and carbonic acid is formed. Because of carbonic acid cracks turn into enlarged deeps on rocks and continuity of this process disintegration of rocks takes place.
c. Hydration:
In this process in which rocks having metallic content absorb water which makes structural change in type of rocks. Some rocks expand due to water absorption like Feldspar changes into Kaolin. Vindheya Mountains situated near Jabalpur are formed by this process.
d. Solution:
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Some minerals are easily dissolvable in water and rock salt, silica and gypsum like soft rocks does not lose vanish by dissolving in water. Rock salt which is mostly found in desert areas, carries on its identity because of less or negligible rainfall in desert regions. Gypsum, which is not as dissolvable as salt continues with its identity in humid regions where rock salt dissolves.
Process # 3. Biological Weathering:
If activities of plants, animals and human beings result in to disintegration of rocks, weathering caused is known as biological weathering.
a. Plants:
Plants contribute important type in physical and chemical weathering. Expansion of roots with growth of plants, leads to cracking of rocks. Further expansion results in disintegration of rocks.
b. Bacterial Action:
Decomposition of leaves and roots form organic and nitric acids which on reaction cause chemical weathering. ‘Humus’ is also formed in such process only.
c. Weathering by Animals:
Cracks appear on rocks because of ‘burrows’ of animals. Many animals make their ‘Funnels’ by breaking rocks. All this results in the disintegration of rocks. Common animals and insects performing such acts are; Foxes, Rats, Rabbits, Earthworms, Mites, Ants etc.
d. Human Actions:
Activities like search for minerals, construction of buildings, leveling of land for agriculture, construction of roads results in disintegration of rocks. Deep quarrying for fulfilling need of stones is also one of the agents that causes weathering results.
Weathering effect is not same or similar for all types of rocks. Various factors like weather, atmosphere, structure etc. affect their process.
Mass wasting is also known as slope movement or mass movement, is a process by which soil, sand and rocks move downslope. This brings change in the structure of rocks. The structure itself indicates the change which weathering brings in parent rock. Weathering process may be quite fast on some rocks while slow on others.
Sometimes due to gravitational pull, the debris stops at higher spot on a slope. ‘Creep’ is the type when debris is creeping downslope while fall at high speed is known as ‘Fall’. Falling big parts of broken rocks are known as ‘Talus’ and smaller ones as ‘Scree’.
When these broken rocks fall at high speed, huge loss of life and property occurs. During rainfall these activities are very common in hilly regions. Mud flows downslopes at the speed of 80 km/hr/50 mph. This process is known as mud flow. In other words, movement of soil and regolith that more resembles fluid behaviour is called a ‘flow’.
