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Types of Weathering

Ratnashri Dutta
The following write-up briefly explains the different types of weathering and their working mechanisms.

Process of Weathering

Weathering is a term in Geology, which means or indicates the 'natural decaying away of the rocks and minerals.' This process mainly takes place near the Earth's surface. The rocks are either broken down by physical forces or by chemical processes, and sometimes by both. Their exposure to water, air, or to living organisms, often leads to weathering.
Due to this, the minerals usually break down into small pieces, which are easily carried away by water and air. With time, these rocks are converted into sand and clay. The duration of weathering often depends upon the climate or the area, where the rock is present. Here are different types of weathering.

Physical/Mechanical Weathering
It does not involve the action of chemicals during the whole process of rock disintegration. Abrasion is the main process, by which physical weathering takes place. It is mainly seen in areas characterized by less vegetation, where the temperature fluctuates around 0° C, and also in those places where the diurnal range of temperature is high.
Physical and chemical weathering goes hand in hand. The former increases the surface area so that the latter can take place. Physical weathering can occur due to the following actions.

Frost Shattering

This takes place in areas where the temperature goes above or below the freezing point. Water present in the cracks or joints of the rocks, freezes during the night and thaws during the day. This repeated process leads to breaking up of the rock into several smaller fragments.

Crystallization

This process is also known as Haloclasty, and it occurs when salt water seeps into the cracks and joints of the rocks, and then evaporates leaving behind the salt crystals. Pressure is exerted on the rocks, which leads to weathering, as these crystals expand due to the increasing heat.

Exfoliation

This process mainly takes place in the desert regions, where the daytime temperature goes up to more than 40° C, and at night, the temperature goes below 10° C.
Due to this everyday constant change, the rocks start to expand and contract, causing stress within themselves, which in turn leads to the formation of cracks. Finally, the top layers of the rocks are peeled off.

Release of Pressure

This occurs due to removal of the top layer through erosion. Now, since the pressure that was earlier exerted is released, the rocks gets a chance to expand, and this causes interior stress that creates cracks. With time, the top layer breaks away.

Biological Weathering

Due to plants and animals, physical weathering may take place. The roots might grow into the cracks of the rocks, or sometimes during cultivation, the rocks are exposed to weathering agents like air and water. Other organisms also help in weathering by making underground tunnels.

Chemical Weathering
It takes place due to various chemical reactions in the rocks. The minerals start getting dissolved, thus transforming the whole rock, and also changing the physical characteristics. The whole process mainly depends on the warm climate or temperature, and also on the moisture present in that particular area.
The main agents of chemical weathering usually are water, air, and rainfall (most important agent). Rainwater contains a small amount of acid in it, and when it mixes with carbon dioxide in the air, it forms carbonic acid. This chemical compound is mainly responsible for the dissolution of various minerals in the soil, which causes its weathering.
The rocks are made up of different minerals, and hence, the chemical reactions on each mineral will vary. Some rocks like quartz do not break down due to chemical weathering, while some like limestone react strongly.