III LANDFORMS | Class 11 Geography Notes

WEATHERING

Weathering is the in-situ breakdown of rocks and minerals at or near the Earth's surface through mechanical disintegration and chemical decomposition caused by atmospheric and climatic elements. It does not involve significant movement of materials, distinguishing it from erosion and transportation.

Weathering processes depend on geological, climatic, topographic, and biological factors. Climate is particularly important as it influences the depth and type of weathering mantle formed. Figure 5.2 shows the relationship between climatic regimes and the depth of weathering mantles, indicating deeper weathering in warm, humid climates and shallower weathering in cold or arid regions.

Weathering is classified into three major types:

1. Chemical Weathering: Involves chemical reactions such as solution, carbonation, hydration, oxidation, and reduction. These reactions decompose or dissolve minerals, facilitated by water, oxygen, carbon dioxide, and acids from decomposing organic matter. Chemical weathering is accelerated by heat and moisture.

2. Physical (Mechanical) Weathering: Caused by physical forces such as gravitational stresses, temperature fluctuations causing expansion and contraction, crystal growth, water pressures from wetting and drying cycles, and biological activity. These forces cause rock fracturing and disintegration through processes like exfoliation, frost action, and salt crystallization.

3. Biological Weathering: Involves the physical and chemical effects of organisms. Roots penetrate and break rocks, burrowing animals expose surfaces to chemical attack, and organic acids from decaying matter enhance mineral decomposition.

Special effects of weathering include exfoliation, where curved sheets peel off bedrock due to thermal expansion and unloading, forming smooth, rounded surfaces and features like exfoliation domes and tors.

Weathering is crucial as it prepares materials for erosion and mass movements, aids soil formation, and contributes to the concentration of economically important minerals through enrichment processes.

📊 Diagram: Figure 5.2 depicts climatic regimes and corresponding depths of weathering mantles, showing deeper weathering in humid tropical regions and shallower in cold or arid zones. Figure 5.3 illustrates exfoliation and granular disintegration with flaking sheets from bedrock.

🧪 Activity: Mark the latitude values of different climatic regimes in Figure 5.2 and compare the details.

🔗 Connection: Prepares for understanding mass movements which often follow weathering.