Exogenous Forces - Weathering and Erosion

Exogenous Forces

Such actions by which a plane is established on the earth's surface are called exogenous forces. Exogenous forces try to remove inequalities created by endogenous forces. All those activities which try to bring the surface to normal rhythm are called processes of gradient balancing. By this, sea water, flowing water, glacier, wind etc. other activities come under it. Weathering and Erosion take place through these activities, due to which the sunken parts of the earth's crust are filled. As a result of weathering and erosion of exogenous forces, many shapes are formed, which mainly include U-shaped valley, V-shaped valley, alluvial wings, loess, barkhan etc.     

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Their details are as follows –

1. Weathering
   1. Physical or Mechanical Weathering
   2. Chemical Weathering
   3. Zoological Weathering
2. Erosion

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A. Weathering

Weakening of rocks by physical or chemical processes and breaking down, rotting and disintegrating at their own place is called weathering. Weathering is a static process, that is, this action takes place in its place. These are of three types –

1. Physical or Mechanical Weathering
2. Chemical Weathering
3. Zoological Weathering

1. Physical or Mechanical Weathering 

The process of breaking of rocks into pieces without any chemical change is called physical or mechanical weathering. Decomposition processes take place in physical weathering. Due to daily temperature difference in tropical areas and dry desert parts, due to the action of frost or frost in cold places, rocks start breaking. The main causes of physical weathering are heat and temperature difference, frost action or water penetration into rocks, friction and pressure action.

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Physical Weathering Process

1. Rocks are made up of different types of minerals. The rates of expansion and shrinkage of all these minerals are also different, due to which the rock breaks down into its mineral particles.
2. In hot deserts, there is a great difference between day and night temperature. Here the temperature is very high during the day, due to which the upper cover of the rocks expands, but due to the sudden drop in temperature at night, the upper layer of the rock starts shrinking. Due to the repetition of this process every day, cracks start appearing in the rocks and they break into large pieces.
3. In hot desert and semi-desert and monsoon climate regions, due to the daily temperature difference, the upper layers of the rocks get heated, while the inner layers remain relatively cold. Due to the difference between the inner layer and the outer layer, a crack occurs between them. In this way the upper layers of the rocks break apart.
4. In cold tropical regions, water fills the cracks and crevices of the rocks. This filled water keeps on freezing and melting. Due to this the rocks become weak and start breaking. This action is called Frost action.

2. Chemical Weathering

In this process, the fragmentation of rocks takes place due to chemical reasons. In this, due to various reasons, chemical changes occur in the components of the rocks, due to which their bond becomes loose and the rocks start breaking. The main causes of chemical weathering are oxidation, carbonization, decomposition and hydration etc.

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Chemical Weathering Process

1. Oxidation – This occurs especially in iron-rich rocks, where iron minerals react with oxygen and turn into oxides when the humidity increases. In this way the iron mineral becomes weak and starts breaking. Rusting of iron is the best example of this. This especially happens in the rainy season.
2. Carbonization – Water and carbon dioxide combine to form carbonic acid, which especially affects rocks containing elements like calcium, magnesium, sodium etc. These elements dissolve in carbonic acid, due to which the rocks made of these elements weaken and disintegrate.
3. Hydration – In this process, the minerals present in the rocks absorb water, as a result of which the bonds of the rocks become weak and start breaking. When the upper layers of rocks swell and separate from the lower surface, it is called spheroidal weathering.
4. Decomposition – When different types of minerals present in rocks dissolve in water, it is called decomposition. For example, rock salt, gypsum etc. dissolve easily in water.

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3. Zoological Weathering

The weathering caused by plants and animals is called zoological weathering. Under this mainly vegetative, biological and human activities are included.

B. Erosion

In this process, the boulders are broken and transferred from one place to another by moving media. In this, the transfer of weathered materials to other places is called erosion. Erosion is caused by exogenous forces such as running water, underground water, sea water, glacier, epiglaciation and wind etc. Its action takes place in the following stages –

Erosion Processes

1. Abrasion – In this process, the erosion of rocks that come in contact with flowing materials takes place.
2. Attrition – In the process of attrition, the flowing substances become smaller by colliding or rubbing with each other.
3. Solution or Corrosion - The process of separation of soluble substances like dolomite, limestone etc. from the rock by dissolving in water is called corrosion.
4. Hydraulic Action – Due to the high speed of water, the rocks are broken and moved separately, then it is called hydraulic action. It is mainly caused by ocean waves and fast river currents.
5. Water Pressure – The erosion caused by the pressure of water is called water pressure erosion.
6. Plucking – In this action, glaciers move forward by breaking the rocks coming in their flow path.
7. Deflation – The process of blowing away the sediments by wind from one place to another is called deflation.

Internal Structure Of The Earth