Model Answer
0 min readIntroduction
Weathering is the breakdown of rocks, soils, and minerals through direct contact with the Earth's atmosphere, water, and biological organisms. It is an *in-situ* process, meaning it doesn’t involve movement of the weathered material. It prepares the rock material for erosion and transportation. Weathering processes are broadly classified into physical (mechanical) weathering and chemical weathering, each operating through different mechanisms to disintegrate and decompose rocks. Understanding these processes is crucial for comprehending landscape evolution and soil formation.
Physical Weathering
Physical weathering, also known as mechanical weathering, involves the disintegration of rocks into smaller fragments without any change in their chemical composition. Key processes include:
- Freeze-Thaw Weathering: Water enters cracks in rocks, freezes and expands (by approximately 9%), exerting pressure and widening the cracks. Repeated cycles lead to rock fracturing. Common in mountainous regions with fluctuating temperatures. Example: Alpine regions of the Himalayas.
- Exfoliation (Pressure Release): As overlying rocks are eroded, the pressure on underlying rocks is reduced, causing them to expand and fracture in layers parallel to the surface. Example: Granite domes of Yosemite National Park, USA.
- Abrasion: The wearing away of rocks by the mechanical action of other rocks and sediments. This can be caused by wind, water, or ice. Example: Riverbeds carrying sediment, glacial abrasion.
- Thermal Expansion and Contraction: Repeated heating and cooling of rocks cause them to expand and contract, leading to stress and eventual fracturing. More effective in deserts with large diurnal temperature ranges.
- Salt Weathering: Salt crystals grow in pores and cracks of rocks, exerting pressure and causing disintegration. Common in arid and coastal regions.
Chemical Weathering
Chemical weathering involves the decomposition of rocks through chemical reactions, changing their mineral composition. Key processes include:
- Oxidation: Reaction of rock minerals with oxygen, often in the presence of water, forming oxides. Iron-rich minerals are particularly susceptible, resulting in rust formation. Example: Formation of reddish soils in tropical regions.
- Hydrolysis: Reaction of rock minerals with water, leading to the formation of new minerals, often clay minerals. Feldspar minerals are commonly altered through hydrolysis.
- Carbonation: Reaction of rock minerals (especially limestone and dolomite) with carbonic acid (formed from dissolved carbon dioxide in water), forming soluble bicarbonates. This leads to the dissolution of rocks and the formation of caves and karst landscapes. Example: Caves in Meghalaya, India.
- Solution: Dissolution of soluble minerals (like halite – rock salt) in water. This is particularly important in the formation of caves in limestone.
- Hydration: Absorption of water by minerals, causing them to expand and become weaker.
| Physical Weathering | Chemical Weathering |
|---|---|
| Disintegration without chemical change | Decomposition with chemical change |
| Examples: Freeze-thaw, exfoliation | Examples: Oxidation, hydrolysis |
| Effective in cold and arid climates | Effective in warm and humid climates |
Conclusion
Both physical and chemical weathering processes are integral to landscape evolution and soil formation. While physical weathering breaks down rocks into smaller pieces, chemical weathering alters their composition, making them more susceptible to erosion. The relative importance of each process varies depending on climate, rock type, and topography. Understanding the interplay between these processes is crucial for comprehending the dynamic nature of Earth’s surface and predicting future landscape changes.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.