Weathering of Rocks


Weathering of Rocks

Weathering is the process that causes the rock to disintegrate physically and decompose chemically because of exposure near the Earth’s surface through the elements of weather.

Among these elements temperature, rainfall, frost, fog, and ice are the important ones.

In nature, generally both the disintegration and decomposition act together at the same time and assist each other.

In this process, no transportation or movement of material is involved.

 

Physical Weathering of Rocks (Mechanical Weathering)

Physical weathering is a process in which rocks are broken up into smaller particles without any chemical change.

This is a process of physical disintegration of rock into smaller pieces

Physical weathering is carried out in different ways in different types of areas.

Block disintegration

Physical weathering is carried out in different ways in different types of areas.

Successive heating and cooling cause rock expansion and contraction.

In hot desert regions, daytime temperatures are high, while nights are very cold.

This high diurnal temperature range causes rock expansion and contraction that tend to enlarge joints.

And then, rocks disintegrate into smaller pieces.

The process is termed as block disintegration.

Exfoliation

Rocks are usually weak heat conductors.

As a result of extreme heating, the rock’s outer layers expand quickly while the inner layers remain unchanged.

Due to this, the outer layer of the rock subsequently peels off from the rock’s main mass.

The process of rock peeling is very similar to the peeling of an onion’s successive layers.

This process is termed as Exfoliation.

Examples of exfoliation: Dolerite blocks of rocks in Singhbhum(Bihar), Granite domes of Mahabalipuram.

Frost Action:

This process occurred in cold climates.

The rocks get split into parts due to continuous freezing and melting of water inside their joints.

When water is converted into ice its volume increased by 10 percent.

In cold regions s, through this process rocks are broken down into small particles.

This process is termed as frost action.

 

Chemical Weathering of Rocks

The formation of new compounds in the rocks due to chemical change is called chemical weathering.

Chemical processes include oxidation, hydrolysis, and an acid solution.

Chemical weathering involves four major processes:

 

Oxidation:

In this process atmospheric oxygen reacts with the rock to produce oxides.

The process is called oxidation.

The greatest impact of this process is observed on ferrous minerals.

Humid-air oxygen combines with iron grains in the rocks to create a yellow or red iron oxide.

This is called rusting of the iron.

Rust decomposes rocks completely with the passage of time.

 

Carbonation:

This is the process by which various types of carbonates are formed.

Some of these carbonates are soluble in water.

For example, when rainwater containing carbon dioxide passes through limestone rocks, the rock joints enlarge due to the action of carbonic acid.

Joints are expanded and lime is dissolved in solution. 

This form of rock breakdown is called carbonation.

 

Hydration:

This is the process by which water is absorbed by the minerals of the rock.

The volume increases due to the absorption of water by the rock, and the grains lose their structure.

For example, the feldspar is converted into kaolin by hydration.

Kaolin on Vindhyan Hills near Jabalpur has been formed in this manner.

 

Solution:

This is the process in which some of the minerals get dissolved in water.

They are therefore removed in solution.

Rock salt and gypsum are removed by this process.

 

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