Weathering and Mass Wasting
Short Questions
1. That are the three types of rocks found on Earth?
Answer: Igneous, sedimentary, and metamorphic rocks.
2. Which type of rock is formed first in the rock cycle?
Answer: Igneous rocks.
3. How are sedimentary rocks formed?
Answer: Sedimentary rocks form from the accumulation, compaction, and cementation of sediments under pressure.
4. What is weathering?
Answer: Weathering is the physical or chemical breakdown of rocks due to weather conditions in-situ.
5. Name the two main types of weathering.
Answer: Physical and chemical weathering.
6. What causes freeze-and-thaw weathering?
Answer: Water in rock cracks freezes, expands, and breaks the rock due to temperature changes.
7. Which rocks are most affected by freeze-and-thaw weathering?
Answer: Sedimentary rocks like sandstone, grit, and conglomerate.
8. What is oxidation in chemical weathering?
Answer: Oxygen reacts with minerals like iron in rocks, forming oxides and changing their size and color.
9. How does carbonation affect limestone?
Answer: Carbon dioxide reacts with limestone, detaching calcium and carbonate ions, leading to its decomposition.
10. What is the role of salt in weathering?
Answer: Salt expands in rocks, splitting grains and causing physical weathering, often forming honeycomb structures.
11. What is block disintegration?
Answer: Heat causes jointed rocks to break into blocks due to repeated expansion and contraction.
12. How does biological weathering occur?
Answer: Plant roots and microorganisms break rocks by widening cracks or secreting chemicals.
13. What is mass wasting?
Answer: Mass wasting is the down-slope movement of soil, land, and rock particles under gravity.
14. Name one factor that increases the likelihood of mass wasting.
Answer: Steep slopes increase the likelihood of mass wasting.
15. What is solifluction?
Answer: Solifluction is the slow downhill creep of oversaturated soil in periglacial regions over permafrost.
Long Questions
1. Explain how water contributes to both physical and chemical weathering of rocks.
Answer: Water physically weathers rocks through freeze-and-thaw cycles, where it enters cracks, freezes, expands, and breaks the rock apart, especially in high-altitude regions. Chemically, water causes hydrolysis by reacting with minerals like silicates in igneous rocks, forming new compounds that disintegrate the rock. It also facilitates solution, dissolving minerals like calcium in limestone to form acids that decompose the rock.
2. Describe the process of exfoliation and where it is commonly observed.
Answer: Exfoliation occurs when underlying rocks, previously under high pressure, are exposed to lower surface pressure, causing their outer layers to expand and peel off. This process is common in homogeneous igneous rocks like granite, forming dome-shaped structures. It is often observed in the Deccan Plateau regions such as Karnataka, Andhra Pradesh, and Telangana.
3. How does heat contribute to physical weathering in hot desert regions?
Answer: In hot deserts, high diurnal temperature ranges cause minerals in rocks to expand during the day and contract at night, creating internal stresses. This leads to granular weathering, where individual mineral grains break free, and shattering, where rocks break with a pistol-like sound. Additionally, in jointed rocks like granite, heat causes block disintegration by widening joints through repeated expansion and contraction.
4. Discuss the role of biological weathering in breaking down rocks.
Answer: Biological weathering involves living organisms like plants and microorganisms breaking down rocks. Plant roots penetrate rock cracks, widening and deepening them as they grow, eventually splitting the rock apart, while plants in fissures also contribute to disintegration. Microorganisms such as lichens and bacteria secrete chemicals that erode the rock surface, creating moist environments that enhance both chemical and physical breakdown.
5. What is the significance of weathering in the formation of landforms?
Answer: Weathering breaks down rocks into smaller particles, providing materials for erosion, which shapes landforms like deltas, beaches, and plains. It also facilitates soil formation by disintegrating rocks, which mix with organic matter to create fertile layers. Additionally, weathering enriches ores like bauxite in high-rainfall areas through leaching, contributing to resource formation.
6. Explain the role of gravity and water in mass wasting processes.
Answer: Gravity is the primary force in mass wasting, pulling soil, rocks, and debris downslope, especially on steep slopes where movement is rapid. Water increases the weight of slope materials through rainfall or snowmelt, making them heavier and more prone to sliding. It also reduces friction by seeping into the soil, lubricating sliding surfaces and triggering movements like slides and flows.
7. How does the structure of rocks influence the rate of weathering?
Answer: Rocks with joints or fractures weather faster as water, heat, and pressure can easily penetrate and break them apart, as seen in sedimentary rocks. Homogeneous rocks like granite are more resistant because they lack such weaknesses, making them harder to disintegrate. Larger grain sizes in rocks also increase weathering rates by allowing more space for water entry, accelerating the process.
8. Describe the types of mass wasting movements based on their speed and water content.
Answer: Mass wasting includes falls, where rocks rapidly free-fall down cliffs, and flows, where water-saturated materials move quickly, potentially burying villages. Slides involve a single mass of soil or rock moving downslope along a slippery zone, occurring on moderately steep slopes. Creep, the slowest movement, involves gradual soil displacement over years, often in dry conditions, while solifluction occurs in wet periglacial regions.
9. Why are landslides more frequent in the Himalayan foothills compared to flat regions like Marathwada?
Answer: The Himalayan foothills have steep slopes and high elevation, making them prone to rapid mass movements like landslides, especially during heavy monsoon rainfall that saturates soils. Vegetation loss due to deforestation further destabilizes slopes by removing root systems that anchor soil. In contrast, flat regions like Marathwada lack significant slopes and receive less rainfall, reducing the likelihood of landslides.
10. How does human activity accelerate weathering and mass wasting processes?
Answer: Human activities like mining, quarrying, and blasting for construction physically break rocks, exposing them to weathering agents, a process called anthropogenic weathering. Deforestation removes vegetation that stabilizes slopes, increasing the risk of mass wasting events like landslides, as seen in the Malin village mudslide. Additionally, air pollution from burning fossil fuels creates acid rain, which chemically weathers limestone structures, damaging historical monuments like the Taj Mahal.
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