Class 9 Geography Shaping of the Earth’s Surface Notes

Class 9 Geography Shaping of the Earth’s Surface Notes

Class 9 Geography Notes

Chapter 2: Shaping of the Earth’s Surface

Learning Objectives

After studying this chapter, you will be able to:

  • Explain plate tectonics.
  • Understand how landforms are formed.
  • Differentiate between weathering and erosion.
  • Identify landforms created by rivers, wind, glaciers, waves, and underground water.
  • Understand natural disasters related to landforms.

1. What are Landforms?

Landforms are natural features found on the Earth’s surface.

Examples

  • Mountains
  • Plateaus
  • Plains
  • Valleys
  • Deserts
  • Beaches
  • Deltas

Landforms are formed by:

  • Internal forces (inside the Earth)
  • External forces (acting on the Earth’s surface)

2. Layers of the Earth

The Earth has three main layers.

LayerDescription
CrustThin outer layer where we live
MantleThick middle layer made of hot rocks
CoreInnermost layer made mostly of iron and nickel

Important Terms

Lithosphere

  • Crust + upper mantle
  • Broken into tectonic plates

Asthenosphere

  • Semi-molten layer below the lithosphere
  • Allows tectonic plates to move

3. Plate Tectonics

Plate tectonics explains how huge pieces of the Earth’s crust move slowly.

Causes of Plate Movement

  • Heat from Earth’s core
  • Convection currents inside the mantle

Major Plates

  • Pacific Plate
  • Eurasian Plate
  • African Plate
  • North American Plate
  • South American Plate
  • Indo-Australian Plate
  • Antarctic Plate

4. Types of Plate Boundaries

A. Convergent Boundary

  • Plates move towards each other.
  • Forms fold mountains.
  • Causes volcanoes and earthquakes.

Example: Himalayas

B. Divergent Boundary

  • Plates move away from each other.
  • New crust is formed.
  • Creates mid-ocean ridges.

Example: Mid-Atlantic Ridge

C. Transform Boundary

  • Plates slide past each other.
  • Causes earthquakes.

Example: San Andreas Fault

5. Effects of Plate Movement

Plate movement causes:

  • Earthquakes
  • Volcanoes
  • Mountain formation
  • Ocean basins
  • Valleys

Most earthquakes and volcanoes occur near plate boundaries.

6. Ring of Fire

The Ring of Fire is the region around the Pacific Ocean where:

  • Most earthquakes occur.
  • Most volcanoes are found.

7. Weathering

Weathering is the breaking of rocks into smaller pieces without moving them.

Types of Weathering

Physical Weathering

Caused by:

  • Heat
  • Cold
  • Frost
  • Wind

Chemical Weathering

Caused by:

  • Water
  • Air
  • Chemicals

Biological Weathering

Caused by:

  • Plant roots
  • Animals
  • Micro-organisms

8. Erosion

Erosion is the wearing away and transportation of rocks and soil.

Agents of Erosion

  • Running water
  • Wind
  • Glaciers
  • Sea waves
  • Groundwater

Difference Between Weathering and Erosion

WeatheringErosion
Breaks rocksMoves broken rocks
No movementMaterial is transported
Forms soilChanges landscapes

9. Agents of Gradation

Agents of gradation reshape the Earth’s surface.

They include:

  • Rivers
  • Wind
  • Glaciers
  • Sea waves
  • Underground water

10. River Landforms

Waterfall

  • Formed where hard rock lies above soft rock.
  • Common in upper river course.

Uses:

  • Tourism
  • Hydroelectric power

Meander

  • Curved bend in a river.
  • Formed due to erosion and deposition.

Importance:

  • Fertile land
  • Farming
  • Irrigation

Delta

  • Formed at the river mouth.
  • Made by deposited sediments.

Importance:

  • Fertile soil
  • Rice cultivation
  • Fishing
  • Dense population

Example: Sundarbans Delta

11. Coastal Landforms

Beach

Formed by deposition of sand.

Importance:

  • Tourism
  • Fishing
  • Protects coast

Sea Cliff

Steep rocky coast formed by wave erosion.

Sea Cave

Created when waves erode weak rocks.

Sea Arch

Formed when two sea caves join.

Sea Stack

Rock pillar left after an arch collapses.

12. Glacial Landforms

Created by moving ice.

Examples:

  • U-shaped valley
  • Cirque
  • Arete
  • Hanging valley
  • Fjord
  • Moraine

Importance:

  • Tourism
  • Fresh water
  • Agriculture
  • Hydroelectric projects

13. Wind Landforms

Wind mainly works in deserts.

Landforms

  • Yardang
  • Ventifact
  • Oasis
  • Sand dunes

Types of Sand Dunes

  • Barchan
  • Longitudinal
  • Star
  • Parabolic

Importance

  • Protect against wind erosion
  • Tourism
  • Construction sand

14. Underground Water Landforms

Formed in limestone regions.

Examples

  • Cave
  • Sinkhole
  • Stalactite (hangs from roof)
  • Stalagmite (grows from floor)

Importance

  • Tourism
  • Fresh water
  • Religious sites

15. Landform-related Disasters

Landslides

Causes

  • Heavy rainfall
  • Earthquakes
  • Deforestation
  • Mining
  • Road construction

Prevention

  • Plant trees
  • Improve drainage
  • Avoid unsafe construction

Avalanches

Large masses of snow moving downhill.

Causes

  • Heavy snowfall
  • Rising temperature
  • Earthquakes
  • Human activities

Prevention

  • Weather monitoring
  • Warning systems
  • Controlled tourism

GLOF

(Glacial Lake Outburst Flood)

Causes

  • Melting glaciers
  • Heavy rainfall
  • Dam failure

Prevention

  • Monitor glacial lakes
  • Early warning systems
  • Safe settlements

Dust Storms

Causes

  • Strong winds
  • Dry soil
  • Drought
  • Deforestation

Prevention

  • Plant trees
  • Protect vegetation
  • Better farming methods

Importance of Landforms

Landforms influence:

  • Climate
  • Agriculture
  • Transport
  • Human settlements
  • Tourism
  • Trade
  • Natural resources

Important Definitions

Landform: Natural feature on Earth’s surface.

Plate Tectonics: Theory explaining movement of Earth’s plates.

Weathering: Breaking rocks without movement.

Erosion: Wearing away and transportation of materials.

Delta: Land formed at a river’s mouth by deposition.

Meander: Bend in a river.

Beach: Sandy shore formed by wave deposition.

Moraine: Deposits left by glaciers.

Sinkhole: Depression formed by collapse of underground rock.

Quick Revision (One-Minute Recap)

  • Earth has 3 layers: Crust, Mantle, Core.
  • Lithosphere is broken into tectonic plates.
  • Plates move due to convection currents.
  • Plate boundaries are Convergent, Divergent, and Transform.
  • Weathering breaks rocks; erosion moves them.
  • Rivers form waterfalls, meanders, and deltas.
  • Waves form beaches, caves, arches, and stacks.
  • Glaciers form U-shaped valleys and moraines.
  • Wind forms dunes and yardangs.
  • Underground water forms caves and sinkholes.
  • Common disasters: Landslides, Avalanches, GLOFs, Dust storms.

Exam Tips

Remember these key differences:

  • Weathering vs. Erosion
  • Convergent vs. Divergent vs. Transform boundaries
  • Stalactite vs. Stalagmite
  • Waterfall vs. Delta
  • Beach vs. Sea Cliff