Shaping of the Earth's Surface — Important Questions

Answers

• Convergent Boundaries: Plates move towards each other.
• Continental-Continental Collision: Forms fold mountains (e.g., Himalayas).
• Oceanic-Continental Collision: Oceanic plate subducts under the continental plate, leading to volcanic activity and earthquakes.
• Divergent Boundaries: Plates move away from each other. Magma rises to form new crust (e.g., Mid-Atlantic Ridge).
• Transform Boundaries: Plates slide past each other, causing earthquakes (e.g., San Andreas Fault). [5 marks]
  2. The Earth is composed of three main layers:
• Crust: The outermost solid layer, where we live. It is relatively thin, varying from 30-40 km under continents to 5-7 km under oceans.
• Mantle: The thick, hot, mostly solid layer below the crust, extending down to the outer core.
• Core: The innermost layer, extremely hot and dense, consisting of an outer liquid core and an inner solid core.
  The lithosphere is the rigid outer layer comprising the crust and the uppermost part of the mantle. Beneath the lithosphere is the asthenosphere, a semi-molten, mobile layer that allows the tectonic plates (lithosphere) to move. [3 marks]
  3. Convection currents are the continuous movement of molten material within the Earth's mantle. Heat from the Earth's core causes molten rock to rise, cool, and then sink back down. This circular motion creates currents that exert force on the tectonic plates above, causing them to move. [3 marks]
  4.
• Convergent Boundaries: Two plates move towards each other. When two continental plates collide, they crumple and fold to form massive fold mountains like the Himalayas. When an oceanic plate meets a continental plate, the denser oceanic plate subducts beneath the continental plate, leading to volcanic mountain ranges (e.g., Andes) and earthquakes.
• Divergent Boundaries: Two plates move away from each other. Magma from the mantle rises to fill the gap, cools, and solidifies to create new crust. This process forms features like mid-ocean ridges (e.g., Mid-Atlantic Ridge) and rift valleys on continents. [3 marks]
  5. Weathering is the process of breaking down rocks on the Earth's surface into smaller pieces by various processes without involving the movement of the broken material.
• Physical Weathering: Rocks break down due to changes in temperature, frost action, or wind. Example: Temperature expansion and contraction causing rocks to crack.
• Chemical Weathering: Minerals in rocks react with substances like water, air, or acids, causing them to change and break down. Example: Oxidation of iron-bearing minerals.
• Biological Weathering: Caused by living organisms. Example: Plant roots growing into rock cracks and widening them, or burrowing animals breaking rocks. [5 marks]
  6. Erosion is the process by which soil, rocks, and other surface materials are worn away and transported from one place to another by natural agents like water, wind, ice, or waves. Unlike weathering, which only breaks down rocks in place, erosion involves the movement of these weathered materials.
• Agents of Erosion and their impact:
• Running Water: Carves valleys, transports sediment, forms deltas.
• Wind: Shapes deserts, forms dunes, causes dust storms.
• Ice (Glaciers): Carves U-shaped valleys, transports large debris.
• Waves and Currents: Erodes coastlines, creates beaches, cliffs, and sea caves. [5 marks]
  7. Running water shapes land through erosion, transportation, and deposition:
• Waterfalls: Form where a river flows over a steep cliff or vertical drop. This occurs when hard rock resists erosion while softer rock below is worn away, creating a sudden drop.
• Meanders: Winding curves or bends in the middle or lower course of a river. They form due to lateral erosion on the outer banks and deposition on the inner banks of bends.
• Deltas: Fan-shaped landforms created at the mouth of a river where it enters a sea, ocean, or lake. Sediments carried by the river are deposited here. [5 marks]
  8. Sea waves and currents are powerful agents shaping coastlines.
• Beaches: Formed by the deposition of sand and pebbles by waves and currents along the shoreline.
• Sea Cliffs: Steep rock faces formed when waves undercut the base of the coast, leading to the collapse of the overlying rock.
• Sea Caves: Formed when waves erode weak parts of the rock along the base of a cliff.
• Arches: Created when sea caves on opposite sides of a headland meet and erode through.
• Stacks: Isolated pillars of rock left standing after the collapse of a sea arch. [3 marks]
  9. Glacial erosion occurs as glaciers move slowly over land:
• U-shaped Valleys: Glaciers widen and deepen existing river valleys, smoothing their sides to form a characteristic 'U' shape.
• Cirques: Bowl-shaped depressions formed at the head of a glacier where ice has eroded the rock.
• Moraines: Ridges or mounds of rock, soil, and debris (till) deposited by a melting glacier. They can be found along the sides (lateral moraines), at the end (terminal moraines), or in the middle (medial moraines) of former glaciers. [3 marks]
  10. Wind erosion in arid regions creates distinctive landforms:
• Yardangs: Streamlined rock ridges carved by wind, often shaped like ships' keels, oriented parallel to the prevailing wind.
• Ventifacts: Rocks that have been polished and shaped by wind-blown sand (sandblasting).
• Dunes: Hills or ridges of sand piled up by the wind. Types include crescent-shaped Barchan dunes, long longitudinal dunes, and star dunes formed where winds blow from multiple directions. [3 marks]
  11. Underground water, particularly in limestone regions (Karst topography), creates unique landforms through chemical dissolution:
• Caves: Hollow spaces formed as acidic groundwater dissolves soluble rocks like limestone.
• Stalactites: Icicle-shaped formations hanging from the ceiling of caves, formed by the deposition of calcium carbonate from dripping water.
• Stalagmites: Conical formations rising from the floor of caves, also formed by calcium carbonate deposition.
• Sinkholes (Dolines): Depressions formed when the roof of an underground cavity collapses or when surface material is dissolved and washed into underground passages. [3 marks]
  12.
  (a) The landslides are likely caused by a combination of factors:
• Heavy rainfall: Water saturates the soil and rocks, increasing their weight and reducing the friction between them, making the slope unstable.
• Deforestation: Tree roots help bind the soil. Removing trees reduces this binding effect, making the soil more prone to sliding. It also reduces the interception of rainfall, leading to more water reaching the soil.
• Steep slopes: The natural steepness of the terrain makes it more susceptible to mass movement.
  (b) Mitigation measures could include:
• Afforestation/Reforestation: Planting more trees to help stabilize the slopes and bind the soil.
• Constructing retaining walls or terraces: Building structures to support the slope and prevent soil from sliding down.
• Improving drainage systems: Ensuring water is channelled away effectively to prevent saturation of the soil. [3 marks]
  13. The Mid-Atlantic Ridge is formed at a divergent plate boundary. Here, the North American and Eurasian plates are moving away from each other. As they separate, magma from the mantle rises to the surface, cools, and solidifies, creating new oceanic crust and forming the ridge. [2 marks]
  14. The 'Ring of Fire' is a horseshoe-shaped zone around the Pacific Ocean where a large number of earthquakes and volcanic eruptions occur. This is because it is a region dominated by convergent plate boundaries where the Pacific Plate is subducting beneath other surrounding plates. This subduction process leads to intense seismic and volcanic activity. [2 marks]
  15. (a) Both A and R are true and R is the correct explanation of A. [1 mark]
  16. Human activities can destabilize slopes and increase landslide risk by:
• Deforestation: Removing trees reduces soil stability as roots no longer bind the soil.
• Mining and Construction: Excavations and building on hillsides can alter the natural slope angle and remove support.
• Improper land use and drainage: Blocking natural drainage pathways can lead to water accumulation, increasing pore pressure and reducing friction in the soil. [2 marks]
  17. GLOFs (Glacial Lake Outburst Floods) are caused by the sudden release of large volumes of water from glacial lakes. Factors contributing to their occurrence include:
• Increased glacial melt: Rising global temperatures lead to faster melting of glaciers, increasing the size and water volume of glacial lakes.
• Weakening of natural dams: The dams holding these lakes are often made of ice or loose moraine material, which can be eroded or weakened.
• Triggers: Events like earthquakes, avalanches, or landslides can destabilize the dam, causing it to burst. [3 marks]
  18. River deltas are formed at the mouth of a river where it deposits the sediments it has carried from upstream. This deposited material is primarily silt and clay, which are rich in nutrients. This alluvial soil is highly fertile and ideal for agriculture, supporting crops like rice and jute. [2 marks]
  19. The presence of underground rivers can:
• Provide a crucial source of fresh water for human settlements.
• Create unique tourist attractions (caves, underground waterways) that can boost local economies.
• Pose risks of flooding if surface areas collapse into underground cavities or if the river's course changes.
• Be utilized for irrigation or water supply systems. [2 marks]
  20. Two landforms shaped primarily by deposition are:
• Deltas: Formed at the mouth of rivers where they deposit sediments as they enter a larger body of water. The deposition of nutrient-rich silt creates fertile land.
• Moraines: Deposited by glaciers. They are ridges of rock, soil, and debris left behind as a glacier melts, often creating uneven terrain that can form natural dams or fertile soil over time. [3 marks]