Here are 20 long-answer questions based on Chapter 3, "Our Changing Earth," from the Class 7 CBSE Geography curriculum. Each question is followed by a comprehensive answer containing 5 to 6 key points.
1. Explain the different types of forces that cause movements on the Earth's surface.
Answer:
Endogenic Forces: These are internal forces that originate within the Earth's interior. They can lead to sudden movements like earthquakes and volcanic eruptions, causing significant changes to the Earth's surface.
Exogenic Forces: These are external forces that act on the Earth's surface. They include processes like weathering, erosion, and deposition, which gradually wear down and reshape landforms.
Sudden Movements: Caused by endogenic forces, these include events like earthquakes and volcanic eruptions that result in immediate and noticeable changes to the landscape.
Diastrophic Movements: These are slow movements caused by endogenic forces, leading to the formation of mountains and continents over extended periods.
Weathering: An exogenic process where rocks are broken down into smaller particles by atmospheric conditions, such as temperature changes, water, and biological activity.
Erosion and Deposition: Exogenic processes where agents like water, wind, and ice transport weathered materials and deposit them in new locations, forming various landforms.
2. Describe the formation and features of fold mountains.
Answer:
Definition: Fold mountains are mountains formed primarily by the folding of Earth's crust due to compressional forces.
Formation Process: When two tectonic plates collide, the accumulated sediments between them are compressed and pushed upward, creating folds.
Types of Folds: Includes anticlines (upward folds) and synclines (downward folds).
Examples: The Himalayas in Asia and the Alps in Europe are classic examples of fold mountains.
Characteristics: They often have complex structures with multiple folds and are associated with seismic activity.
Economic Significance: Rich in minerals and resources, making them important for mining and tourism.
3. How do volcanic activities shape the Earth's surface?
Answer:
Formation of Landforms: Volcanoes create various landforms, such as volcanic cones, plateaus, and islands.
Soil Fertility: Volcanic ash enriches the soil with minerals, enhancing agricultural productivity.
Creation of New Land: Lava flows can solidify to form new landmasses, as seen in the Hawaiian Islands.
Geothermal Features: Volcanic regions often have hot springs and geysers due to geothermal activity.
Hazards: Eruptions can lead to loss of life, destruction of property, and environmental changes.
Climate Impact: Large eruptions can inject ash and gases into the atmosphere, affecting global climate patterns.
4. Discuss the processes of weathering and their impact on the landscape.
Answer:
Mechanical Weathering: Physical breakdown of rocks without chemical change, caused by temperature fluctuations, frost action, and biological activity.
Chemical Weathering: Decomposition of rocks due to chemical reactions, leading to new mineral formations.
Biological Weathering: Involves living organisms, like plant roots and microbes, breaking down rocks.
Soil Formation: Weathering contributes to soil development by breaking down rocks into finer particles.
Landscape Alteration: Gradual weathering reshapes landforms, leading to features like rounded hills and valleys.
Influence on Human Activity: Affects agriculture by determining soil characteristics and stability of structures.
5. Explain the role of rivers in the formation of various landforms.
Answer:
Erosion: Rivers erode their banks and beds, creating valleys and canyons.
Transportation: They carry sediments downstream, which can be deposited elsewhere.
Deposition: Leads to the formation of floodplains, deltas, and alluvial fans.
Meandering: Rivers develop bends called meanders due to lateral erosion and deposition.
Oxbow Lakes: Formed when a meander is cut off from the main river, creating a separate water body.
Waterfalls: Occur where there is a sudden drop in the riverbed, often due to differential erosion.
6. How do glaciers transform the Earth's surface?
Answer:
Erosion: Glaciers erode the land through plucking and abrasion, carving out valleys.
U-shaped Valleys: Distinctive valleys with a U-shaped cross-section formed by glacial erosion.
Fjords: Deep, glacially carved valleys flooded by seawater, common in Norway.
Moraines: Accumulations of debris deposited by glaciers, forming ridges.
Drumlins: Smooth, elongated hills formed by glacial deposition.
Glacial Lakes: Lakes formed in depressions created by glacial erosion and deposition.
7. Describe the impact of wind as an agent of erosion and deposition in desert regions.
Answer:
Deflation: Wind removes loose particles, lowering the land surface.
Abrasion: Wind-driven particles wear down rock surfaces, creating features like ventifacts.
Sand Dunes: Wind deposits sand in mounds or ridges, forming dunes.
Loess Deposits: Windblown silt accumulates to form fertile loess plains.
Mushroom Rocks: Wind erosion creates
8. What are earthquakes? Explain their causes and effects.
Answer:
Definition: Earthquakes are sudden movements of the Earth's crust caused by the release of energy from the lithosphere.
Causes:
Tectonic Plate Movements: Most earthquakes occur along plate boundaries.
Volcanic Activity: Some earthquakes happen due to volcanic eruptions.
Human Activities: Mining, construction, and reservoir-induced seismicity can trigger earthquakes.
Effects:
Destruction of Property: Buildings, roads, and bridges collapse.
Loss of Life: Strong earthquakes cause thousands of casualties.
Tsunamis: Underwater earthquakes trigger massive waves.
Landslides: Ground shaking can cause slope failure.
Economic Loss: Businesses suffer damages, and reconstruction costs are high.
9. Describe how tsunamis are formed and their impact.
Answer:
Formation:
Underwater Earthquakes: Seismic activity beneath the ocean displaces large water volumes.
Volcanic Eruptions: Submarine volcanic activity can generate tsunamis.
Landslides: Coastal or underwater landslides push water outward.
Meteoroid Impacts: Large meteors hitting oceans create massive waves.
Impacts:
Coastal Flooding: Tsunamis submerge land areas, displacing people.
Destruction of Property: Entire towns and villages get washed away.
Loss of Lives: Thousands perish due to drowning and debris impact.
Environmental Damage: Marine and coastal ecosystems suffer devastation.
Economic Crisis: Fishing, tourism, and local economies collapse.
10. Explain the importance of plate tectonics in shaping the Earth's surface.
Answer:
Definition: Plate tectonics is the movement of large lithospheric plates over the Earth's mantle.
Types of Plate Boundaries:
Divergent Boundaries: Plates move apart, creating new land (e.g., Mid-Atlantic Ridge).
Convergent Boundaries: Plates collide, forming mountains and deep-sea trenches.
Transform Boundaries: Plates slide past each other, causing earthquakes.
Effects on Earth's Surface:
Mountain Formation: The Himalayas resulted from the Indian and Eurasian plates colliding.
Volcanic Activity: The Pacific Ring of Fire has numerous volcanoes due to subduction.
Earthquakes: The San Andreas Fault is an example of tectonic movement causing earthquakes.
Island Formation: Oceanic volcanic activity creates islands like Hawaii.
11. How do river landforms change from the upper to lower course?
Answer:
Upper Course (Youth Stage):
Steep Gradient: The river flows rapidly with high energy.
Erosion Dominates: Valleys, waterfalls, and rapids form.
V-shaped Valleys: Formed due to vertical erosion.
Middle Course (Mature Stage):
Lateral Erosion: River widens its valley.
Meanders Develop: The river bends due to erosion and deposition.
Oxbow Lakes Form: Old meanders get cut off.
Lower Course (Old Stage):
Deposition Dominates: The river loses energy and deposits sediments.
Floodplains and Deltas: Rich, fertile lands form at the mouth.
Braided Channels: Multiple small river channels form due to deposition.
12. Explain the role of sea waves in coastal landform development.
Answer:
Erosional Landforms:
Cliffs and Wave-cut Platforms: Strong waves erode the base of cliffs.
Sea Caves, Arches, and Stacks: Continuous erosion forms caves, which develop into arches and eventually separate stacks.
Depositional Landforms:
Beaches: Sand and pebbles are deposited by waves.
Sandbars and Spits: Extended landforms created by longshore drift.
Lagoons: Enclosed water bodies formed behind spits.
Human Impact:
Coastal erosion leads to loss of land, affecting settlements and infrastructure.
13. How do lakes form, and why are they important?
Answer:
Natural Formation:
Tectonic Lakes: Created by Earth’s movements (e.g., Caspian Sea).
Volcanic Lakes: Formed in craters of extinct volcanoes.
Glacial Lakes: Carved out by moving glaciers.
Oxbow Lakes: Formed by river meanders getting cut off.
Artificial Lakes: Created by dams and reservoirs.
Importance:
Water Supply: Used for drinking, irrigation, and industries.
Hydroelectric Power: Dams generate electricity.
Biodiversity: Lakes support aquatic life and ecosystems.
Tourism and Recreation: Popular for boating, fishing, and tourism.
14. Describe the different types of mass movements.
Answer:
Landslides: Large rockfalls triggered by earthquakes, rain, or human activities.
Mudflows: Rapid movement of water-saturated soil, often during heavy rainfall.
Rockfalls: Individual rocks break off and fall due to gravity.
Creep: Slow downward movement of soil and rock over time.
Slumping: A large mass of soil suddenly slips along a curved surface.
15. How do deserts develop due to natural and human activities?
Answer:
Natural Causes:
Climate Change: Long-term dry periods cause desertification.
Wind Erosion: Removes topsoil, making the land barren.
Human Activities:
Deforestation: Cutting trees leads to soil erosion.
Overgrazing: Livestock eat vegetation, exposing soil to erosion.
Poor Farming Practices: Excessive cultivation depletes soil nutrients.
Urbanization: Expanding cities reduce arable land.
16. What is soil erosion, and how can it be controlled?
Answer:
Definition: Soil erosion is the removal of the topsoil layer by wind, water, or human activities.
Causes:
Deforestation: Reduces soil-binding roots.
Overgrazing: Exposes land to wind and rain.
Poor Farming: Plowing loosens soil, making it prone to erosion.
Control Measures:
Afforestation: Planting trees to hold soil.
Contour Plowing: Farming along land contours to reduce runoff.
Terracing: Steps cut into slopes slow down water flow.
Cover Cropping: Planting crops to protect soil from erosion.
17. How do human activities influence changes on Earth’s surface?
Answer:
Deforestation: Reduces vegetation cover, leading to erosion.
Mining and Quarrying: Disturbs land and increases landslide risk.
Urbanization: Expands cities, destroying natural landscapes.
Agriculture: Overuse of land leads to desertification.
Pollution: Industrial waste affects land, water, and air quality.
18. What are the different types of volcanoes? Explain with examples.
Answer:
Active Volcanoes: Frequently erupt lava, gases, and ash. Example: Mount Etna (Italy), Mount St. Helens (USA).
Dormant Volcanoes: Have not erupted in a long time but may erupt again. Example: Mount Fuji (Japan), Yellowstone (USA).
Extinct Volcanoes: Have no eruption history and are unlikely to erupt again. Example: Mount Kilimanjaro (Tanzania), Edinburgh Castle Rock (UK).
Shield Volcanoes: Have gentle slopes and fluid lava flows. Example: Mauna Loa (Hawaii).
Composite Volcanoes: Steep-sided, explosive eruptions. Example: Mount Vesuvius (Italy).
Cinder Cone Volcanoes: Small, steep, and formed from volcanic debris. Example: Paricutin (Mexico).
19. How do earthquakes affect human life and the environment?
Answer:
Human Impact:
Loss of Lives and Injuries: Thousands can die due to building collapses.
Destruction of Infrastructure: Roads, bridges, and homes are damaged.
Economic Collapse: Industries shut down due to structural damage.
Displacement of People: Many become homeless or refugees.
Psychological Effects: Trauma and stress increase after major quakes.
Environmental Impact:
Landslides: Hillsides collapse due to tremors.
Tsunamis: Earthquakes under the ocean generate massive waves.
Ground Deformation: Earth’s surface cracks and shifts.
Floods: Dam failures or changed river courses cause flooding.
20. What are the differences between erosion and deposition?
Answer:
Definition:
Erosion: The removal and transportation of rock particles.
Deposition: The settling and accumulation of transported materials.
Agents:
Erosion: Carried out by rivers, wind, glaciers, and waves.
Deposition: Happens when the carrying agent loses energy.
Landforms Formed:
Erosion: Creates valleys, cliffs, and caves.
Deposition: Forms deltas, sand dunes, and floodplains.
Effect on Landscape:
Erosion: Wears down the land.
Deposition: Builds up new landforms.
Examples:
Erosion: Grand Canyon (USA).
Deposition: Nile Delta (Egypt).
