Agents of Erosion
Short Questions
1. What is plucking in glacial erosion?
Answer: Plucking is when a glacier uproots rock fragments by exerting pressure as it moves.
2. Which process smoothens bedrock surfaces like sandpaper?
Answer: Abrasion smoothens bedrock by particles scratching or polishing the surface.
3. What is attrition in erosion?
Answer: Attrition is the breaking of rocks into smaller, rounded fragments during transport.
4. What landform results from wind removing loose sediments?
Answer: Deflation hollows are depressions formed by wind removing loose sediments.
5. What is a pothole in a riverbed?
Answer: A pothole is a depression formed by circular water flow and sediment drilling.
6. What is headward erosion?
Answer: Headward erosion is backward erosion at a river’s source, moving it upstream.
7. Which landform is formed by wave abrasion at a cliff base?
Answer: A wave-cut platform is a flat surface formed by wave abrasion.
8. What is a barchan?
Answer: A barchan is a crescent-shaped sand dune with a gentle windward slope.
9. What are stalactites in karst topography?
Answer: Stalactites are calcium carbonate deposits hanging from cave ceilings.
10. What is a U-shaped valley?
Answer: A U-shaped valley is a broad, flat-bottomed valley formed by glacial erosion.
11. What is a delta?
Answer: A delta is a triangular sediment deposit at a river’s mouth with high sediment supply.
12. What are moraines in glacial deposition?
Answer: Moraines are sediment deposits along the sides or front of a glacier.
13. What is a sea arch?
Answer: A sea arch forms when waves erode soft rock under hard rock, connecting caves.
14. What is saltation in transportation?
Answer: Saltation is the bouncing movement of pebbles or sand by water or wind.
15. What is a ventifact?
Answer: A ventifact is a smooth, polished rock formed by wind abrasion.
Long Questions
1. How does abrasion contribute to landform formation by different agents?
Answer: Abrasion by glaciers forms roche moutonnees by smoothing bedrock, while sea waves create wave-cut platforms by eroding cliff bases. Wind abrades rocks into ventifacts and mushroom rocks, and rivers smooth riverbeds, forming potholes. Each agent uses particles to wear down surfaces, shaping distinct landforms.
2. Why are deltas common on India’s Eastern coast but estuaries on the Western coast?
Answer: The Eastern coast has gentle slopes and rivers like the Ganga with high sediment loads, forming deltas in shallow seas. The Western coast’s steep slopes and deeper seas limit sediment deposition, leading to estuaries. This contrast is due to coastal topography and sediment supply.
3. Explain the process of pothole formation in rivers.
Answer: Potholes form when river water develops a circular flow around obstacles or joints in the bed, trapping sediments. These sediments grind the bedrock, deepening the depression through a drilling action. Continuous swirling enlarges potholes, as seen in rivers like Kukadi in Maharashtra.
4. How do sea waves create sea arches and stacks?
Answer: Sea waves erode softer rock beneath harder rock, forming sea caves on headlands. When caves on opposite sides meet, a sea arch is created. If the arch collapses, an isolated rock pillar called a sea stack remains.
5. What conditions are necessary for wind to be an effective erosional agent?
Answer: Wind erosion requires aridity with low precipitation, sparse vegetation to expose loose sediments, and high wind velocity to lift particles. Dry, unconsolidated materials on the surface are easily transported. These conditions are common in deserts like Rajasthan.
6. How do glaciers form U-shaped valleys?
Answer: Glaciers erode valley sides and bottoms equally through lateral and vertical erosion, creating broad, flat-bottomed U-shaped valleys. Unlike rivers, glaciers’ slow, massive ice flow reshapes valleys uniformly. These are common in the Himalayas.
7. What is the significance of floodplains for human activities?
Answer: Floodplains, formed by river sediment deposition, are fertile due to nutrient-rich alluvium, supporting agriculture in regions like the Ganga plains. They provide flat land for settlements and infrastructure. However, they are prone to flooding, requiring management.
8. How does groundwater create karst landforms like sinkholes?
Answer: Groundwater dissolves soluble rocks like limestone, enlarging joints and fractures into circular depressions called sinkholes. This solution process occurs underground, often concealing landforms. Sudden sinkhole collapses can pose natural hazards.
9. Why do sea waves work ceaselessly compared to other agents?
Answer: Sea waves operate continuously due to constant tidal movements and wind-driven forces, unlike rivers or glaciers, which are seasonal or geographically limited. This relentless action causes rapid erosion and deposition. Coastal landforms thus change quickly.
10. Explain the formation of barchans and their characteristics.
Answer: Barchans form where wind deposits sand in areas with limited supply, creating crescent-shaped dunes. The windward slope is gentle, while the leeward slope is steep. They are common in deserts like Rajasthan, shaped by consistent wind direction.
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