Chapter 2: Shaping of the Earth's Surface – CLASS - 9 New NCERT BOOK
Chapter 2: Shaping of the Earth's Surface –
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1. Introduction:- What Shapes the Earth's Surface?
The Earth's surface is not fixed. It is continuously changing due to the action of powerful internal and external forces.
Two Main Types of Forces
A. Internal (Endogenic) Forces:- These forces originate inside the Earth. They cause:
- Formation of mountains
- Earthquakes
- Volcanoes
- Folding and faulting
B. External (Exogenic) Forces:- These forces act on the Earth's surface. They include:
- Weathering
- Erosion
- Deposition
They slowly wear down and reshape landforms.
Why is this chapter important? Understanding the Earth's surface helps us:
- Explain earthquakes and volcanoes.
- Understand how mountains and plains are formed.
- Identify disaster-prone regions.
- Appreciate the dynamic nature of the Earth.
2. Plate Tectonics:- Plate Tectonics is a theory proposed by W. J. Morgan that explains the movement of the Earth's crust. According to this theory:
- The Earth's outer layer is broken into several tectonic plates.
- These plates move slowly over the semi-molten layer beneath them.
- Their movement causes mountains, volcanoes, earthquakes, and ocean basins.
Key Points
- Plates move only a few centimetres every year.
- Movement is caused by convection currents in the mantle.
- Plate movement continuously changes the Earth's surface.
Why Do Plates Move?:- Heat from the Earth's core creates convection currents in the mantle.
- Hot molten material rises.
- Cooler material sinks.
- Continuous circulation pushes and pulls tectonic plates.
- Heat from Earth's Core → Convection Currents → Plate Movement
3. Structure of the Earth:- The Earth has three main layers.
Layer Characteristics
- Crust Thin outer layer where we live
- Mantle Thick, hot layer beneath the crust
- Core Innermost, hottest and heaviest layer
Lithosphere
- Made up of the crust + uppermost mantle.
- Broken into tectonic plates.
- Asthenosphere
- Located below the lithosphere.
- Semi-molten layer.
- Allows tectonic plates to move.
Crust: 5–40 km thick.
Mantle: Thickest layer.
Core: Mainly iron and nickel; extremely hot.
Lithosphere: Rigid outer layer.
Asthenosphere: Semi-molten layer that enables plate movement.
4. Types of Tectonic Plates:- The chapter mentions three types of tectonic plates.
1. Continental Plates:- Carry continents, Thicker and lighter.
Example:- Eurasian Plate
2. Oceanic Plates:- Carry ocean floors, Thinner and denser.
Example:- Pacific Plate
3. Mixed Plates:- Carry both continents and oceans.
Example:-Indo-Australian Plate
Major Tectonic Plates:- Sven major plates:
- Pacific Plate
- Eurasian Plate
- African Plate
- North American Plate
- South American Plate
- Indo-Australian Plate
- Antarctic Plate
5. Plate Boundaries:- Plate boundaries are the edges where two tectonic plates meet. There are three types.
A. Convergent Boundary
- Movement:- Plates move towards each other.
- Results:- Fold mountains, Volcanoes, Earthquakes, Examples, Himalayas
- Oceanic plate subducting beneath a continental plate
B. Divergent Boundary
- Movement:- Plates move away from each other.
- Results:- New crust is formed., Magma rises., Mid-ocean ridges develop.
- Example:- Mid-Atlantic Ridge
C. Transform Boundary
- Movement:- Plates slide past each other.
- Results:- Frequent earthquakes, No crust is created or destroyed.
- Example:- San Andreas Fault (USA)
6. Ring of Fire:- The Ring of Fire is a region around the Pacific Ocean where most of the world's earthquakes and volcanoes occur. Because many tectonic plates meet around the Pacific Ocean.
Importance
- Earthquake-prone zone
- Volcano-prone zone
- Important for disaster management
7. Earthquakes & Volcanoes
Earthquake:- An earthquake is the sudden shaking of the Earth's surface caused by movement of tectonic plates.
Causes
- Plate collision
- Plate sliding
- Plate separation
Effects
- Loss of life
- Damage to buildings and roads
- Landslides
- Tsunami (in some cases)
Volcano:- A volcano is an opening in the Earth's crust through which magma, ash, and gases erupt.
Causes
- Movement of tectonic plates
- Rising magma
Effects:-
- Formation of new landforms
- Lava flow
- Ash deposition
- Damage to life and property
The Mud Volcano at Baratang Island (Andaman & Nicobar Islands) as a unique natural feature in India.
Weathering:- Weathering is the process by which rocks on the Earth's surface break down into smaller pieces due to natural processes.
Important: In weathering, the broken material does not move from its original place.
Types of Weathering
A. Physical (Mechanical) Weathering:- Rocks break into smaller pieces due to:
- Temperature changes
- Frost action
- Wind
- Example: Rocks crack due to heating during the day and cooling at night.
B. Chemical Weathering:- Minerals in rocks change because of reactions with:- Water, Air, Acids
C. Biological Weathering:- Caused by living organisms such as:
- Plant roots
- Animals
- Micro-organisms
- Example: Tree roots grow into rock cracks and split the rocks.
Importance of Weathering
- Forms soil
- Breaks rocks into smaller particles
- Helps in the formation of landforms
- Supports agriculture by producing soil
2. Erosion:- Erosion is the process by which soil, rocks, and other materials are worn away and transported from one place to another by natural agents. Unlike weathering, erosion involves the movement of material.
Agents of Erosion
- Running water
- Wind
- Ice (Glaciers)
- Sea waves
Types of Erosion:-
Water Erosion, Caused by:- Rivers, Rain, Ocean waves
Wind Erosion:- Occurs mainly in: Deserts, Dry and sandy regions,
Glacial Erosion:- Moving glaciers scrape and carry rocks.
Coastal Erosion:- Sea waves wear away coastal land.
Effects of Erosion
- Removes fertile topsoil
- Reduces agricultural productivity
- Damages roads and houses
- Changes river and coastal landscapes
- Affects human occupations and livelihoods
Weathering = Breaking
Erosion = Breaking + Moving
4. Agents of Gradation:-Agents of Gradation are natural forces that:
- Wear down rocks
- Transport materials
- Deposit sediments
- Level or smooth the Earth's surface over time
Main Agents of Gradation
1. Running Water:- Creates:
- Valleys
- Plains
- Waterfalls
- Deltas
2. Glaciers:- Create:- U-shaped valleys, Moraines
3. Wind:- Creates:- Sand dunes, Yardangs
4. Sea Waves:- Create:- Beaches, Sea cliffs, Sea caves
5. Underground Water:- Creates:-
- Caves
- Sinkholes
- Stalactites
- Stalagmites
5. Running Water Landforms:- Running water shapes the land through erosion, transportation, and deposition.
Upper Course:- Forms:- V-shaped valleys, Waterfalls, Rapids
Middle Course:- Forms:- Meanders, Oxbow lakes, Floodplains,
Lower Course:- Forms:- Deltas, Levees, Alluvial fans
These landforms support agriculture, settlements, and ecosystems.
6. Waterfall:- A waterfall is a landform where a river flows over a steep cliff or vertical drop.
Formation
- Found mainly in the upper course of a river.
- Hard rock resists erosion.
- Softer rock below erodes faster.
- This creates a sudden drop.
Importance
- Tourist attraction
- Hydroelectric power generation
- Recreation (trekking, photography)
- Cultural and religious importance
7. Meander:- A meander is a winding bend or curve in the middle or lower course of a river.
Formation
- Outer bank → erosion
- Inner bank → deposition
- Continuous erosion and deposition create loops.
Importance
- Fertile soil for farming
- Supports settlements
- Used for irrigation
- Navigation
- Tourism
Example:- Grand Anicut (Kallanai), Tamil Nadu – use of rivers for irrigation.
8. Delta:- A delta is a landform formed at the mouth of a river where it deposits sediments before entering a sea, ocean, or lake.
Formation
- River slows down.
- Sediments settle.
- Deposits accumulate.
- Fan-shaped or triangular landform develops.
Importance
- Very fertile alluvial soil
- Suitable for rice and jute cultivation
- Rich fishing grounds
- Dense human settlements
- Centres of trade and transport
Limitation:- Flood-prone area
Example Mentioned:- Sundarbans Delta
9. Beach:- A beach is a landform made of sand, pebbles, or rocks along the shoreline, formed by the deposition of sediments by sea waves.
Formation:- Created by:- Wave action, Tides, Ocean currents
Importance
- Tourism
- Recreation
- Fishing
- Natural barrier against coastal erosion
- Protects coastal settlements
- Formed by deposition of sand, pebbles, and shells.
- Found along the seashore.
- Popular tourist destinations.
- Examples: Marina Beach (Tamil Nadu), Juhu Beach (Mumbai)
- A steep rocky coast formed by continuous wave erosion.
- Waves strike the base of the cliff and gradually wear it away.
- Formed when waves erode weaker parts of coastal rocks.
- Over time, caves may enlarge into arches.
- Tourism
- Fishing
- Ports and harbours
- Marine biodiversity
- Protection from strong sea waves (in some areas)
- Formed by glacier erosion.
- Broad bottom with steep sides.
- Wider than river valleys.
- Bowl-shaped hollow at the head of a glacier.
- Usually contains snow or a small lake.
- Lake formed when glacier ice melts.
- Water collects in depressions created by glaciers.
- Source of freshwater
- Tourist attractions
- Support hydropower generation
- Feed rivers throughout the year
- Hills or mounds of sand formed by wind deposition.
- Continuously change shape with wind direction.
- Example: Thar Desert
- Fine dust deposited by wind.
- Forms fertile soil in some regions.
- Importance of Wind Landforms
- Support desert tourism
- Help understand climatic conditions
- Influence vegetation and settlement patterns
- Tourist attractions
- Scientific research
- Groundwater storage
- Natural heritage sites
- Fertile plains support farming.
- River valleys have rich alluvial soil.
- Deltas are ideal for rice cultivation.
- Plains are suitable for large cities.
- Mountains have scattered settlements.
- Coastal areas support ports and trade.
- lains provide easy road and railway construction.
- Mountains make transportation difficult.
- Rivers provide drinking water.
- Glaciers feed rivers.
- Groundwater supports irrigation.
- Mountains contain valuable minerals.
- Rivers help produce hydroelectric power.
- Beaches
- Waterfalls
- Mountains
- Caves
- Glaciers
- Sacred rivers
- Holy mountains
- Pilgrimage caves
- Landform Related Disaster
- Mountains Landslides, Avalanches
- Glacial Regions GLOFs (Glacial Lake Outburst Floods)
- Deserts Dust Storms
- Coastal Areas Coastal erosion, Storm surges
- Natural Causes
- Heavy rainfall
- Earthquakes
- Volcanic activity
- Weak rock structure
- Deforestation
- Road construction
- Mining
- Unplanned construction on hill slopes
- Loss of human life
- Damage to houses and roads
- Blocking of rivers
- Destruction of forests and farmland
- Disruption of transport and communication
- Plant more trees.
- Avoid cutting slopes unnecessarily.
- Build proper drainage systems.
- Restrict construction on unstable slopes.
- Use retaining walls where necessary.
- Follow landslide warning systems.
- Heavy snowfall
- Earthquakes
- Rising temperatures
- Human activities (trekking, explosions)
- Loss of life
- Damage to roads and buildings
- Destruction of forests
- Blocking of transport routes
- Monitor snowfall regularly.
- Avoid travel during avalanche warnings.
- Construct avalanche barriers.
- Develop early warning systems.
- Conduct rescue and awareness programmes.
- Rapid melting of glaciers
- Heavy rainfall
- Earthquakes
- Weak moraine dams
- Sudden floods downstream
- Damage to villages and roads
- Destruction of bridges
- Loss of agricultural land
- Threat to human life
- Regular monitoring of glacial lakes.
- Install early warning systems.
- Prepare evacuation plans.
- Avoid settlements in high-risk flood zones.
- Poor visibility
- Road accidents
- Respiratory problems
- Damage to crops
- Soil erosion
- Plant shelter belts and trees.
- Protect exposed soil with vegetation.
- Stay indoors during storms.
- Wear masks and protective eyewear.
- Follow weather advisories.
- Stay informed through weather forecasts and official warnings.
- Identify safe shelters and evacuation routes.
- Keep an emergency kit ready.
- Follow instructions from local authorities.
- Move to safer places if advised.
- Avoid risky areas such as unstable slopes or flood channels.
- Help injured people if it is safe.
- Avoid damaged buildings and roads.
- Use clean drinking water.
- Cooperate with rescue teams.
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