a) State four factors that promote weathering in the tropics.
(b) Explain the processes of mechanical weathering under the following:
- temperature changes;
- frost action.
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a) Factors that promote weathering in the tropics include:
1. High temperatures: The tropics experience high temperatures throughout the year, which accelerates chemical reactions and physical breakdown of rocks.
2. Heavy rainfall: The tropics often receive high amounts of rainfall, leading to increased moisture content in the soil and rocks. This moisture promotes chemical weathering reactions.
3. Biological activity: Tropical regions are known for their rich biodiversity. Plant roots, burrowing animals, and microorganisms play a role in breaking down rocks through physical and chemical processes.
4. High humidity: The high levels of humidity in the tropics facilitate the chemical reactions involved in weathering, leading to the breakdown of minerals in rocks.
b) Mechanical weathering is the physical breakdown of rocks into smaller fragments without changing their chemical composition. Two processes of mechanical weathering are temperature changes and frost action.
1. Temperature changes: Rocks expand when heated and contract when cooled. In areas with large temperature fluctuations, such as deserts or mountainous regions, rocks are subjected to repeated heating and cooling. This constant expansion and contraction cause stress on the rock surface, leading to the development of cracks and fractures. Over time, these cracks widen and deepen, eventually breaking the rock into smaller pieces.
2. Frost action: Frost action, also known as freeze-thaw weathering, occurs in areas where temperatures frequently fluctuate around the freezing point. When water seeps into cracks in rocks, it freezes and expands. The expansion of freezing water exerts pressure on the walls of the crack, causing it to widen. When the ice thaws, it contracts, leaving behind a larger crack. With repeated freeze-thaw cycles, the cracks expand and break the rock into smaller fragments.
Both temperature changes and frost action are examples of mechanical weathering, which can eventually lead to the disintegration of rocks into smaller particles.