Weathering

What is Meant by Weathering?

Several naturally-occurring processes influence the world that we see around us, and that's why the terrain and the sea are diverse. Be it because of rains, snow, wind, or sunshine, the rocks break down or disintegrate into smaller units. Such a process, in its elaborate form, is called weathering. The causes of weathering can be the effect of continuous biological, chemical, and physical processes, as seen on rocks, wood, soils, and minerals. Often confused with erosion that occurs with the movement of rocks, soil, minerals via water, gravity, snow, wind, weathering, on the other hand, only occurs in rocks, soil, and minerals that stay in one place. 


There are primarily three different types of weathering process:

  • Chemical Weathering: Some prominent chemical weathering examples would include oxidation, the salinity of seawater, etc. 

  • Physical Weathering: Among the most commonly found tangible weathering examples are ice wedging, growing of plant roots in rock cracks.

  • Biological Weathering: As interesting as these types of weathering is, one example would be that of lichens that are found in rocks, causing it to open and be more vulnerable to weathering. 


Weathering Diagram

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There can be many weathering agents, like water, ice, acids, salts, plants, animals, and timely changes in temperature. There are no rocks present on Earth that are resistant to weathering, and the Grand Canyon in Arizona, USA, is one such example. 


Weathering of Rocks

Weathering is often observed as mechanical, chemical, and biological processes. However, the biological processes can come as a combining effect of both physical and chemical processes taking place via a living organism. The processes are:


Physical or Mechanical Weathering

In this type of weathering, the process can also be called disaggregation, where the rocks get disintegrated without undergoing chemical changes in them. Abrasion is one such process in which the clastic rocks get reduced in size, especially seen in the rocks near the shoreline that get washed away due to waves. 


However, physical weathering mainly occurs due to the result of extreme temperatures, pressure, frosting, etc. These can be found occurring in areas with lesser soil deposits, low vegetation, and arid regions. In the tundra, physical weathering can occur by continuous melting and freezing of water. In contrast, in hot deserts, the same can occur due to constant expansion and shrinking of the surface rocks. 


Chemical Weathering

The chemical weathering can take place due to change in rock compositions, as a result of several chemical reactions. Upon slow, gradual, and ongoing process, the rocks surface minerals now develop newer minerals allowing oxidation and hydration to occur subsequently. It is further enhanced by geological agents like water and oxygen that makes the microbial and plant-root metabolism acids. These occur rampantly in areas having high temperatures (in tropical climates) but are also found across the world. There are different types of chemical weathering:

  • Carbonation: The removal of rock in the form of acidic rainwater causes chemical weathering. Here the rain that contains dissolved Carbon dioxide can help in the weathering of Celestone.

  • Hydrolysis: It refers to the acidic water that breaks down rock into clay and several soluble salts.

  • Oxidation: It refers to the breakdown of rocks with the continuous effect of oxygen and water, thus providing it with a rust-like surface to rocks that are rich in iron constituents. 


Biological Weathering

This refers to the weakening and breakdown of rocks under the influence of microorganisms, plants, and animals. It can occur due to the growth of roots that can pressurize rocks, causing it to get weakened and exposed to further weathering. It can also come as a process favoring chemical weathering since the organic acids that get produced by the plant roots can provide the ground for the growth of several microorganisms and help in dissolving the minerals. 


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It is also due to the surge in microbial activity, that causes the alteration of the natural composition of rocks, making it more susceptible to weathering. In lichen, such symbiotic microbial growth is observed prominently between algae and fungi that release chemicals responsible for breaking down minerals present in the rocks. Such minerals are further consumed by algae and facilitate cracks in rocks, slowly breaking it down as a combined effect of physical and chemical weathering. 


Small rodents and other animals that live in burrows can dig up rocks and make them vulnerable to intense weathering because of the sudden exposure to sunlight, air, wind, and water.  


Humanity and Weathering

There are many ways in which humans facilitate the weathering process and cause it to occur faster than natural methods. An example of it would be due to distinct air pollutants that get into the atmosphere because the burning of fossil fuels can increase the overall composition of nitrogen oxide and sulfur dioxide in the air. Such chemicals can form acidic compounds upon reacting with sunlight and atmospheric moisture that falls on the surface as acid rains. 


Acid rains are primarily responsible for weathering of limestone, marble, and is often seen on gravestones, making the writings illegible.

FAQ (Frequently Asked Questions)

Q1. What is Spheroidal Weathering?

The spheroidal weathering is a sub-part of chemical weathering that takes place in any rectangular block, getting exposed to weathering from its three sides. Due to the effect on the two sides and along the edges, it gives the block a specific spherical weathering structure. Thus it's named spheroidal weathering. It is observed in onion skin weathering commonly.

Q2. What is the Difference Between Physical and Chemical Weathering?

Physical weathering is termed in cases that include the breaking down of any rock's physical structure and integrity. In contrast, the chemical weathering refers to the cases where the weathering occurs due to change in the chemical composition of the rock or minerals. The physical weathering uses natural forces like impact and friction to cause the weathering. The chemical weathering, on the other hand, occurs due to the exchange of ions and cations at the molecular level of rocks.