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Weathering (UPSC Geography Notes)
Overview: Weathering is the process of breaking down rocks on the Earth’s surface by physical, chemical, or biological means. It plays a vital role in soil formation, landscape development, and rock cycle evolution — key topics for UPSC Geography.
Table of Contents
- 1. Introduction
- 2. Definition of Weathering
- 3. Types of Weathering
- 4. Physical (Mechanical) Weathering
- 5. Chemical Weathering
- 6. Biological Weathering
- 7. Importance of Weathering
- 8. Factors Affecting Weathering
- 9. UPSC Quick Revision Notes
- 10. Previous Year Question
1. Introduction
The rocks that form the Earth’s crust are constantly exposed to air, water, temperature variations, and living organisms. These external forces slowly break down rocks into smaller pieces and minerals — a process known as weathering.
2. Definition of Weathering
Weathering is the process of disintegration and decomposition of rocks in situ (i.e., without transportation). It differs from erosion, which involves movement of weathered materials by wind, water, or ice.
3. Types of Weathering
Based on the nature of the process, weathering is classified into three main types:
- 1. Physical or Mechanical Weathering
- 2. Chemical Weathering
- 3. Biological Weathering
4. Physical (Mechanical) Weathering
In physical weathering, rocks are broken down into smaller pieces without any chemical change. This process is more common in dry and cold regions.
Main agents of physical weathering:
- 1. Temperature Changes: Repeated heating and cooling cause rocks to expand and contract, leading to cracks and fragmentation (also called insolation weathering).
- 2. Frost Action: Water enters cracks, freezes, expands, and widens the cracks — a process known as frost wedging.
- 3. Exfoliation: Outer layers of rocks peel off due to pressure release or temperature changes.
- 4. Salt Crystal Growth: In desert and coastal areas, salt crystals expand in rock pores and cause disintegration.
5. Chemical Weathering
In chemical weathering, the chemical composition of the rock changes due to reactions with water, air, or other chemicals. It is dominant in hot and humid regions.
Major processes of chemical weathering:
- 1. Oxidation: Minerals (especially iron) react with oxygen to form oxides, giving rocks a reddish color (rusting effect).
- 2. Carbonation: Carbon dioxide in rainwater forms weak carbonic acid, which dissolves limestone and chalk (formation of caves and karst topography).
- 3. Hydration: Minerals absorb water and expand, causing the rock to weaken.
- 4. Hydrolysis: Reaction of minerals with water forming new, softer minerals such as clay.
- 5. Solution: Soluble minerals like rock salt and gypsum dissolve directly in water.
6. Biological Weathering
This involves the breakdown of rocks by living organisms such as plants, animals, and microorganisms.
- 1. Plant Roots: Roots grow into rock cracks and widen them.
- 2. Burrowing Animals: Organisms like rabbits, ants, and worms loosen rock material.
- 3. Microbial Activity: Lichens and bacteria produce acids that chemically decompose rocks.
7. Importance of Weathering
- Leads to soil formation — essential for agriculture.
- Releases minerals and nutrients from rocks.
- Shapes landforms like valleys, cliffs, and caves.
- Acts as the first stage of the rock cycle.
- Influences construction and engineering by affecting rock stability.
8. Factors Affecting Weathering
- Climate: Temperature and rainfall largely determine the type and rate of weathering.
- Rock Type: Permeability, mineral composition, and structure influence weathering patterns.
- Topography: Steep slopes favor physical weathering; flat areas favor chemical weathering.
- Vegetation: Plant cover can both protect and enhance weathering depending on conditions.
- Time: Longer exposure increases the degree of weathering.
9. UPSC Quick Revision Notes
Types – Physical, Chemical, Biological.
Physical → No chemical change (frost, heat, salt).
Chemical → Alteration of minerals (oxidation, carbonation, hydration).
Biological → Caused by plants, animals, microbes.
Important for soil formation and landform development.
10. Previous Year Question
Q. Which of the following weathering processes is most active in limestone areas?
(a) Oxidation
(b) Carbonation
(c) Frost Action
(d) Exfoliation
Answer: (b) Carbonation
Related Keywords
Weathering UPSC Notes, Types of Weathering, Mechanical and Chemical Weathering, Biological Weathering, Weathering and Soil Formation, Physical Geography UPSC Notes.
Sources: NCERT – Fundamentals of Physical Geography, Geological Survey of India, Britannica
