Difference Between Chemical and Mechanical Weathering (With Table)

Weathering is a process through which rocks break into finer pieces. It is a strong process, which over time can change the whole landscape of a region. The soil that humans exploit for their purposes is formed through weathering of rocks. Weathering is a natural process but human activities can accelerate its pace.

Chemical vs Mechanical Weathering

The difference between chemical and mechanical weathering is that the former interacts with the rocks on their molecular level but the latter one weathers the rocks physically. Chemical weathering changes the chemical structure of the rock but mechanical weathering happens through friction and erosion.

Chemical weathering can be observed in hot and humid areas, which provide perfect space for chemical reactions. Chemical weathering leads to the formation of different and newer minerals. Moreover, recent studies have suggested that chemical weathering can help combat the issue of increased carbon dioxide in the atmosphere. Carbon dioxide gets trapped in sediment in the process of weathering, which helps in decreasing the CO2 levels.

Mechanical weathering is a physical process and can be observed in dry climate conditions. The rocks break down due to environmental conditions. Climate, temperature, water, wind are the major contributors to this process. Erosion is a part of this process, but excessive erosion can lead to degradation of the soil level.    

Comparison Table Between Chemical and Mechanical Weathering

Parameters of Comparison Chemical Weathering Mechanical Weathering
Interaction with rocksChemicalPhysical
Preferable Climate Conditions Hot and HumidDry and hot; with the temperature changing frequently.
Agents of weatheringOxidation, carbonation, and hydration Temperature, water, and winds
Action on rocksIt decays and softens them.It cracks and breaks them into finer pieces.
Formation of new mineralsLeads to the formation of new minerals.No new minerals are formed.
Effect on the molecular structureAlters the chemical structure of rocks and hence, of the soil too.Does not affect the molecular structure.

What is Chemical Weathering?

Chemical weathering is the process through which rocks are degraded by changing their molecular structure. Earth produces plentiful chemicals naturally through several processes. These chemicals react in nature and create either magical or horrifying things.

Through some chemical process, the composition of rocks changes, and sometimes they wither into minerals. The landscapes we live in, are formed by years of weathering and erosion. Oxidation is one of the most common processes of weathering. Rocks that contain iron or its substitutes get rusted due to oxidation.

Water is a major component in these chemical processes. Chemicals in the rocks come in contact with water, and they interact to form new chemicals and compounds. This process of chemical weathering is known as hydrolysis. For instance, Feldspar undergoes hydrolysis to form clay minerals, which weakens the rock and makes it more susceptible to breaking.

The reason for the salty nature of seawater is the result of years of chemical weathering. Further, through hydrolysis, many acids are formed, which in return reacts with the rocks. Carbon dioxide reacts with water, to form carbonic acid, which is the key agent for the formation of caves and huge holes in rocks. 

Acid rain is also another significant factor that changes the composition of rocks. But acid rain is caused by the result of human activities. The change in the color of the Taj Mahal is the result of acid’s interaction with the stones of the monument.

What is Mechanical Weathering?

Mechanical weathering is also referred to as physical weathering. The prominent agents of mechanical weathering are water, temperature, and changes in pressure. Other agents such as plants, animals, wind, earthquakes, and human interference also catalyze the process of weathering.

Mechanical weathering breaks down the rocks into smaller pieces. Water seeps into the smaller and deeper gaps between rocks and gradually erodes the rock, as it passes through them. Each time water passes through these holes, minute particles of the rock erode and washes away with water.

When water freezes between these gaps, due to a drop in temperature, then these gaps widen due to the expansion property of ice. Due to regular expansion and contraction, the strength of the rocks decreases. Such expansions weaken even the hardest rocks, and gradually they weather down.

Further, winds and earthquakes also create friction with the surface of the rocks, which eventually leads to weathering, yet again. Rocks, which have undergone rigorous weathering, look smoother. For instance, the rocks near the river bed are smoother than the ones found near a hill.

Mechanical weathering is a natural process – it helps in the production of soil which is beneficial for various human activities. But, extreme interference by humans in this process can lead to destructive results.

Main Differences Between Chemical and Mechanical Weathering

  1. Chemical weathering interacts with the chemical composition of the rocks. But mechanical weathering only affects the physical structure of the rocks.
  2. Chemical weathering is a slower process as compared to mechanical weathering. It takes years for the formation of new minerals but physical weathering is comparatively faster.
  3. Through chemical weathering, new minerals are formed, due to the interaction of other minerals. But, mechanical weathering does not result in any such formation.
  4. Chemical weathering includes chemical processes such as oxidation and hydrolysis. But, mechanical weathering is based on friction, abrasion, and thermal expansion.
  5. Mechanical weathering is accelerated in dry and hot climate conditions. But chemical weathering is more active in hot and humid climatic conditions.

Conclusion

Weathering is an essential process for the functioning of human life. But accelerating it can by human activities can gradually erode the essential resources. Weathering is observed on a physical as well as chemical level.

Both chemical and mechanical weathering are necessary for maintaining balance in nature. Through chemical weathering, new minerals are being formed constantly and gradually. And, mechanical weathering helps in forming a new layer of soil, while maintaining all the necessary minerals.

Physical and chemical weathering functions on different levels. Both the processes are gradual and it takes thousands of years to observe any prominently visible change. But chemical weathering is even slower than the other one because it involves modification of the components of minerals.  

Weathering decreases the stability of rocks. It has been affecting the monuments and historic works due to interference humans in its process.

References

  1. https://www.annualreviews.org/doi/abs/10.1146/annurev.earth.28.1.611
  2. https://www.questia.com/library/journal/1G1-192259700/how-does-mechanical-weathering-change-rocks-using
  3. https://www.sciencedirect.com/science/article/pii/S0012821X0800681X