Class 9 Geography Chapter 2 Notes | Shaping of the Earth's Surface | New NCERT 2026–27 | Understanding Society: India and Beyond

Class 9 Geography Chapter 2 Notes | Shaping of the Earth's Surface | New NCERT 2026–27 | Understanding Society: India and Beyond

CBSE Class 9
Published on By Amresh Academy

 

Chapter 2: Shaping of the Earth's Surface

Part 1: Plate Tectonics and Earth's Internal Structure

Book: Understanding Society: India and Beyond (Class 9 NCERT 2026–27)

Introduction

The Earth on which we live is not a motionless planet. Its surface is continuously changing due to both internal (endogenic) and external (exogenic) forces.

Millions of years ago, the continents were joined together as one giant landmass. Over time, they slowly moved apart due to movements inside the Earth. These movements continue even today and are responsible for earthquakes, volcanoes, mountain formation and the creation of oceans.

The study of these processes helps us understand why the Earth's surface looks the way it does today.

Why Should We Study the Earth's Surface?

The Earth's surface provides everything necessary for life.

  • Land for agriculture and settlements
  • Rivers and lakes for freshwater
  • Minerals for industries
  • Forests for biodiversity
  • Mountains that influence climate
  • Plains suitable for farming
  • Oceans that regulate weather

Understanding the Earth's surface helps us:

  • understand natural disasters
  • use natural resources wisely
  • protect the environment
  • plan roads, dams and cities
  • reduce disaster risks
  • conserve ecosystems

Thus, Geography is not only about maps; it helps us understand the relationship between people and the Earth.

The Earth: A Dynamic Planet

The Earth is called a dynamic planet because its surface is constantly changing.

These changes may be:

Slow Changes

  • Mountain formation
  • River valley formation
  • Soil formation
  • Coastal changes
  • Glacier movement

These take thousands or millions of years.

Sudden Changes

  • Earthquakes
  • Volcanic eruptions
  • Landslides
  • Tsunamis

These occur within seconds or minutes.

What Is Plate Tectonics?

Definition

Plate Tectonics is the scientific theory which explains that the Earth's outer layer (Lithosphere) is divided into several large and small rigid plates that move slowly over the semi-molten Asthenosphere.

These moving plates constantly change the Earth's surface.

Simple Definition

Plate Tectonics is the movement of huge pieces of the Earth's crust.

Why Is Plate Tectonics Important?

Before this theory, scientists could not explain

  • Why continents move
  • Why earthquakes occur
  • Why volcanoes erupt
  • How mountains are formed
  • Why oceans continue to expand

Plate Tectonics explains all these processes through the movement of tectonic plates.

Continental Drift

In the early 20th century, Alfred Wegener proposed the Continental Drift Theory.

He suggested that all present-day continents were once joined together in a single supercontinent called

Pangaea

Meaning:

"Entire Earth"

Around 200–300 million years ago, Pangaea began breaking apart.

It slowly separated into today's continents.

Although Wegener could not explain the force behind continental movement, his idea later became the foundation of Plate Tectonic Theory.

Structure of Pangaea

               PANGAEA

                   │

     ┌─────────────┴─────────────┐

     │                           │

 Laurasia                   Gondwanaland

(North America,             (India, Africa,

Europe, Asia)               Australia,

                             Antarctica,

                             South America)

How Does Plate Tectonics Work?

Scientists discovered that the Earth's interior is extremely hot.

Heat from the Earth's core produces convection currents in the mantle.

These currents slowly drag the tectonic plates.

Plate speed is generally

2–10 cm per year

Although this movement is very slow, over millions of years it completely changes the Earth's surface.

What Drives Plate Movement?

Three major forces move tectonic plates.

1. Convection Currents

Hot molten material rises.

Cool material sinks.

This continuous circulation creates movement.

2. Ridge Push

At mid-ocean ridges, newly formed crust pushes older crust away.

3. Slab Pull

Dense oceanic plates sink into the mantle during subduction.

This pulling force moves plates further.

Evidence Supporting Plate Tectonics

Scientists accepted Plate Tectonic Theory because of several pieces of evidence.

1. Matching Coastlines

The east coast of South America fits closely with the west coast of Africa.

2. Similar Fossils

Identical fossils are found on continents now separated by oceans.

3. Similar Rocks

Rock layers of the same age occur on different continents.

4. Earthquake Distribution

Most earthquakes occur along plate boundaries.

5. Volcano Distribution

Most volcanoes lie along plate margins.

What Does Plate Tectonics Create?

Plate movements create many landforms.

Mountains

Example:

  • Himalayas
  • Andes
  • Alps

Ocean Trenches

Example:

  • Mariana Trench

Volcanoes

Example:

  • Mount Fuji
  • Mount Etna

Rift Valleys

Example:

  • East African Rift Valley

Islands

Example:

  • Japan
  • Indonesia

Earthquakes

When plates suddenly slip, stored energy is released.

This produces earthquakes.

Layers of the Earth

The Earth consists of three main layers.

Layer

Nature

Thickness

Main Composition

Crust

Solid

5–70 km

Rocks (Granite & Basalt)

Mantle

Semi-solid

~2,900 km

Silicate rocks rich in magnesium and iron

Core

Mostly iron & nickel

~3,500 km radius

Iron (Fe) and Nickel (Ni)

1. Crust

The crust is the outermost and thinnest layer.

It is broken into tectonic plates.

Two types:

  • Continental Crust
  • Oceanic Crust

Continental Crust

  • Thick
  • Less dense
  • Mainly granite
  • Forms continents

Oceanic Crust

  • Thin
  • Denser
  • Mainly basalt
  • Forms ocean floor

2. Mantle

The mantle lies below the crust.

It is the thickest layer.

The upper mantle contains the Asthenosphere, where rocks behave plastically.

Tectonic plates move over this layer.

3. Core

The Earth's core has two parts.

Outer Core

  • Liquid iron and nickel
  • Generates Earth's magnetic field

Inner Core

  • Solid iron and nickel
  • Extremely hot (about 5,000–6,000°C)

Tectonic Plates

Tectonic plates are massive rigid slabs of the lithosphere.

Major plates include:

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

Indian Plate

India lies on the Indian Plate, which continues to move northward.

Its collision with the Eurasian Plate formed the Himalayan Mountains, which are still rising slowly today.

What Are Plate Boundaries?

Plate boundaries are places where two tectonic plates meet.

Most earthquakes and volcanoes occur here.

There are three main types.

1. Divergent Boundary

Plates move apart.

Creates:

  • New ocean floor
  • Mid-ocean ridges
  • Rift valleys

Example:

Mid-Atlantic Ridge

2. Convergent Boundary

Plates move towards each other.

Creates:

  • Mountains
  • Deep trenches
  • Volcanoes

Example:

Himalayas

3. Transform Boundary

Plates slide past each other.

Creates:

  • Earthquakes

Example:

San Andreas Fault (California)

Plate Boundary Comparison

Boundary

Movement

Landforms Created

Divergent

Plates move apart

Rift valleys, Mid-ocean ridges

Convergent

Plates collide

Mountains, Trenches, Volcanoes

Transform

Plates slide past

Earthquakes

Importance of Plate Tectonics

Plate Tectonics explains:

  • Formation of mountains
  • Formation of oceans
  • Earthquakes
  • Volcanoes
  • Continental movement
  • Ocean floor spreading
  • Distribution of minerals
  • Distribution of earthquakes and volcanoes

It helps governments identify earthquake-prone regions, prepare hazard maps and plan safer infrastructure.

Key Terms

Term

Meaning

Lithosphere

Rigid outer layer of Earth consisting of the crust and uppermost mantle.

Asthenosphere

Soft, semi-molten layer below the lithosphere on which tectonic plates move.

Plate Tectonics

Theory explaining the movement of Earth's plates.

Convection Current

Circular movement of heated material within the mantle that drives plate motion.

Pangaea

Ancient supercontinent from which modern continents separated.

Plate Boundary

Region where two tectonic plates meet.

Quick Revision

✅ Earth is a dynamic planet.

✅ Plate Tectonics explains changes in the Earth's surface.

✅ The lithosphere is divided into tectonic plates.

✅ Convection currents in the mantle move these plates.

✅ Three main boundaries are Divergent, Convergent and Transform.

✅ India lies on the Indian Plate, whose collision with the Eurasian Plate formed the Himalayas.

Chapter 2: Shaping of the Earth's Surface

Part 2: Process of Weathering and Erosion

Book: Understanding Society: India and Beyond (Class 9 NCERT 2026–27)

Introduction

The Earth's surface is constantly changing due to natural forces. Some forces build mountains, while others wear them down. The two most important processes responsible for breaking down and reshaping landforms are Weathering and Erosion.

Although these terms are often used together, they are different processes. Weathering breaks rocks into smaller pieces without moving them, whereas erosion removes and transports these broken materials from one place to another.

Together, weathering and erosion continuously modify landscapes, create fertile soil, shape valleys, form plains, and influence human activities.

Process of Weathering and Erosion

The transformation of Earth's surface occurs in three major stages:

Weathering

      ↓

Erosion

      ↓

Deposition

Step 1: Weathering

Rocks are broken into smaller fragments.

Step 2: Erosion

The broken materials are transported by water, wind, glaciers, or sea waves.

Step 3: Deposition

The transported materials settle in another place, forming new landforms.

What Is Weathering?

Definition

Weathering is the process by which rocks are broken down into smaller pieces at or near the Earth's surface without being moved from their original place.

Unlike erosion, weathering occurs in situ (at the same location).

Simple Definition

Weathering is the breaking of rocks without transportation.

Why Does Weathering Occur?

Rocks are exposed to different natural conditions such as:

  • Heat from the Sun
  • Rainfall
  • Wind
  • Ice
  • Plant roots
  • Flowing water
  • Living organisms

These factors gradually weaken rocks over thousands or even millions of years.

Importance of Weathering

Weathering plays a vital role in shaping the Earth.

It:

  • Forms soil for agriculture.
  • Supplies minerals to plants.
  • Helps in groundwater storage.
  • Shapes hills and mountains.
  • Supports plant growth.
  • Creates raw materials for sediments.

Without weathering, soil formation would not occur, making agriculture impossible.

Types of Weathering

Weathering is broadly classified into three types.

Weathering

      │

 ┌────┼────┐

 │    │    │

Physical Chemical Biological

1. Physical (Mechanical) Weathering

Definition

Physical weathering is the breakdown of rocks into smaller pieces without changing their chemical composition.

The rock remains the same; only its size changes.

Causes of Physical Weathering

Temperature Changes

During the day, rocks expand due to heat.

At night, they cool and contract.

Repeated expansion and contraction produce cracks.

Frost Action

Water enters rock cracks.

When temperature falls below 0°C, water freezes.

Frozen water expands by nearly 9%, widening the cracks.

Repeated freezing and melting eventually break the rocks.

This process is common in mountainous regions.

Pressure Release (Exfoliation)

Deep underground rocks are under high pressure.

When upper layers are removed by erosion, pressure decreases.

The rock expands and outer layers peel off like onion skins.

This process is called Exfoliation.

Salt Weathering

In deserts and coastal regions, salty water enters cracks.

When water evaporates, salt crystals grow.

Growing crystals exert pressure and break rocks.

Characteristics of Physical Weathering

  • No chemical change occurs.
  • Rock composition remains unchanged.
  • Common in deserts and cold regions.
  • Produces large rock fragments.

2. Chemical Weathering

Definition

Chemical weathering changes the chemical composition of rocks through reactions with water, oxygen, and acids.

The original rock is transformed into new minerals.

Main Processes of Chemical Weathering

A. Oxidation

Oxygen reacts with minerals, especially iron.

Example:

Iron-rich rocks develop a reddish-brown colour due to rusting.

B. Carbonation

Rainwater absorbs carbon dioxide from the atmosphere.

This forms weak carbonic acid.

Carbonic acid dissolves limestone and marble.

This process creates caves and sinkholes.

C. Hydrolysis

Water reacts with minerals such as feldspar.

The minerals change into clay.

This process is common in humid regions.

D. Solution

Some minerals dissolve directly in water.

Examples include:

  • Rock salt
  • Gypsum

Characteristics of Chemical Weathering

  • Changes rock composition.
  • Common in hot and humid climates.
  • Produces fine particles and clay.
  • Leads to soil formation.

3. Biological Weathering

Definition

Biological weathering is caused by living organisms.

Plants, animals, and humans contribute to breaking rocks.

Agents of Biological Weathering

Plant Roots

Roots grow into cracks.

As roots enlarge, they force rocks apart.

Burrowing Animals

Animals such as rabbits, ants, termites, and rodents dig tunnels.

This loosens rocks and soil.

Human Activities

Mining

Road construction

Building construction

Quarrying

Deforestation

These activities accelerate weathering.

Characteristics of Biological Weathering

  • Caused by living organisms.
  • Can be physical or chemical.
  • Important in soil development.

Comparison of Types of Weathering

Feature

Physical

Chemical

Biological

Composition Changes

No

Yes

Sometimes

Main Cause

Temperature, Ice, Pressure

Water and Chemical Reactions

Plants, Animals, Humans

Climate

Dry or Cold

Warm and Humid

All Regions

Products

Rock Fragments

Clay and New Minerals

Soil and Broken Rocks

What Is Erosion?

Definition

Erosion is the process by which weathered rock materials are removed, transported, and deposited by natural agents.

Unlike weathering, erosion always involves movement.

Simple Definition

Erosion is the wearing away and transportation of rock materials.

Stages of Erosion

Rock

 ↓

Weathering

 ↓

Loose Material

 ↓

Transportation

 ↓

Deposition

Agents of Erosion

Four major agents cause erosion.

  • Running Water
  • Wind
  • Glaciers
  • Sea Waves

Each agent creates different landforms.

Types of Erosion

1. Water Erosion

Caused by:

  • Rivers
  • Rainwater
  • Streams

Produces:

  • Valleys
  • Gorges
  • Waterfalls
  • Deltas

2. Wind Erosion

Common in deserts.

Wind removes loose sand particles.

Produces:

  • Sand dunes
  • Mushroom rocks

3. Glacial Erosion

Occurs in high mountains.

Moving ice removes rocks.

Produces:

  • U-shaped valleys
  • Moraines

4. Coastal (Wave) Erosion

Sea waves continuously strike the coast.

Produces:

  • Sea cliffs
  • Sea caves
  • Beaches

Difference Between Weathering and Erosion

Weathering

Erosion

Rocks break at the same place

Rocks are transported

No movement

Movement occurs

Caused by heat, water, plants, chemicals

Caused by rivers, wind, glaciers, waves

First stage

Second stage

Produces loose material

Moves loose material elsewhere

How Does Erosion Affect Human Occupations?

Erosion has both positive and negative effects.

Positive Effects

Agriculture

Rivers deposit fertile alluvial soil.

Example:

The Indo-Gangetic Plain.

Tourism

Waterfalls, valleys, beaches, and caves attract tourists.

Mineral Resources

Erosion exposes valuable minerals.

Negative Effects

Soil Erosion

Loss of fertile topsoil reduces crop production.

Floods

Excessive erosion increases river sediment, reducing river capacity.

Landslides

Removal of vegetation increases slope instability.

Damage to Infrastructure

Roads, bridges, farms, and buildings may be damaged.

Soil Conservation Measures

To reduce erosion:

  • Afforestation
  • Terrace farming
  • Contour ploughing
  • Check dams
  • Shelter belts
  • Controlled grazing

These methods help conserve fertile soil.

Key Terms

Term

Meaning

Weathering

Breaking of rocks without movement

Erosion

Removal and transportation of rocks

Deposition

Settling of transported materials

Frost Action

Rock breaking due to freezing water

Oxidation

Chemical reaction with oxygen

Carbonation

Dissolving of rocks by carbonic acid

Exfoliation

Peeling of rock layers due to pressure release

Flowchart

Solid Rock

     │

Weathering

     │

Broken Rock Pieces

     │

Erosion

     │

Transportation

     │

Deposition

     │

New Landforms

Quick Revision

✅ Weathering breaks rocks without movement.

✅ Erosion removes and transports weathered material.

✅ Three types of weathering:

  • Physical
  • Chemical
  • Biological

✅ Four agents of erosion:

  • Running Water
  • Wind
  • Glaciers
  • Sea Waves

✅ Weathering forms soil, while erosion shapes valleys, beaches, plains, and deltas.

Exam-Oriented Questions

Very Short Answer

Q1. What is weathering?

Answer: Weathering is the process of breaking rocks into smaller pieces at their original place without transportation.

Q2. Name the three types of weathering.

Answer: Physical, Chemical, and Biological weathering.

Q3. What is erosion?

Answer: Erosion is the removal and transportation of weathered rock materials by natural agents such as water, wind, glaciers, and sea waves.

Short Answer (2–3 Marks)

Differentiate between weathering and erosion.

Answer:

  • Weathering breaks rocks at the same place, whereas erosion transports the broken materials.
  • Weathering is caused by physical, chemical, or biological processes, while erosion is caused by running water, wind, glaciers, and sea waves.

Long Answer (5 Marks)

Explain the types of weathering with suitable examples.

Answer: (Students should explain Physical, Chemical, and Biological weathering with causes and examples such as frost action, oxidation, carbonation, plant roots, and human activities.)

Excellent! Now let's continue with the next section.

Chapter 2: Shaping of the Earth's Surface

Part 3: Agents of Gradation (Running Water)

Book: Understanding Society: India and Beyond (Class 9 NCERT 2026–27)

Agents of Gradation

Introduction

The Earth's surface is constantly being modified by natural forces. After rocks are broken down by weathering, the loose materials are carried away and deposited by natural agents. These agents continuously wear down highlands and fill lowlands, making the Earth's surface more balanced.

This process is known as gradation.

Gradation is one of the most important geomorphic processes because it creates many landforms such as valleys, waterfalls, flood plains, meanders, deltas, beaches, sand dunes, and moraines.

What are Agents of Gradation?

Definition

Agents of Gradation are natural forces that wear away (erode), transport, and deposit weathered materials, thereby reshaping the Earth's surface.

Simple Definition

Agents of Gradation are natural agents that reduce high areas and fill low areas by erosion and deposition.

Major Agents of Gradation

There are four major agents:

Agent

Main Area of Action

Landforms Created

Running Water

Rivers & Streams

Valleys, Waterfalls, Meanders, Deltas

Sea Waves

Coastal Areas

Beaches, Cliffs, Sea Caves

Glaciers

High Mountains

U-shaped Valleys, Moraines

Wind

Deserts

Sand Dunes, Mushroom Rocks

Among these, running water is the most active and widespread agent of gradation.

How Does Running Water Shape Land?

Rivers are constantly flowing from higher elevations to lower elevations under the force of gravity.

During their journey, rivers perform three important functions:

  1. Erosion
  2. Transportation
  3. Deposition

These three processes together create a variety of landforms.

Flowchart

Running Water

      │

 ┌────┼────┐

 │    │    │

Erosion Transportation Deposition

      │

 Creation of Different Landforms

Stages of a River

Every river passes through three stages during its journey.

1. Upper Course (Youthful Stage)

The river flows rapidly down steep mountain slopes.

Characteristics

  • Very steep gradient
  • Fast flow
  • Strong erosion
  • Narrow valleys
  • Deep gorges
  • Waterfalls

Landforms

  • V-shaped valleys
  • Gorges
  • Rapids
  • Waterfalls

2. Middle Course (Mature Stage)

The river enters plains and the slope becomes gentle.

Characteristics

  • Moderate speed
  • Less vertical erosion
  • More sideways erosion
  • Wider valleys

Landforms

  • Meanders
  • Flood Plains
  • River Cliffs

3. Lower Course (Old Stage)

The river reaches flat plains before entering the sea.

Characteristics

  • Slow flow
  • Very gentle slope
  • Maximum deposition

Landforms

  • Deltas
  • Distributaries
  • Natural Levees
  • Estuaries (in some rivers)

River Journey

Mountains

     ↓

Upper Course

     ↓

Waterfalls & Valleys

     ↓

Middle Course

     ↓

Meanders & Flood Plains

     ↓

Lower Course

     ↓

Delta

     ↓

Sea

River Erosion

Definition

River erosion is the wearing away of rocks and soil by flowing water.

The force of flowing water removes materials from river banks and beds.

Types of River Erosion

1. Vertical Erosion

The river cuts downward into its bed.

Produces:

  • Deep valleys
  • Gorges
  • Canyons

2. Lateral Erosion

The river erodes sideways.

Produces:

  • Wider valleys
  • Meanders

3. Headward Erosion

The river extends backward toward its source.

This increases the river's length.

Transportation by Rivers

After erosion, rivers transport sediments.

Materials are carried in different ways.

Method

Description

Solution

Dissolved minerals carried in water

Suspension

Fine particles remain suspended

Saltation

Small particles bounce along the bed

Traction

Large stones roll along the river bed

Deposition by Rivers

When the river loses speed, it cannot carry heavy materials.

These materials settle down.

This process is called deposition.

Deposition forms fertile plains and many important landforms.

What is a Waterfall?

Definition

A waterfall is a steep vertical drop in the course of a river where water falls suddenly from a higher level to a lower level.

Formation of a Waterfall

Waterfalls usually develop where:

  • Hard rocks lie above soft rocks.
  • Soft rocks erode faster.
  • Hard rocks remain standing.
  • Water falls vertically.

Over time, waterfalls gradually move upstream because of continuous erosion.

Parts of a Waterfall

  • Hard Rock
  • Soft Rock
  • Plunge Pool
  • River Channel

Diagram

Hard Rock

──────────────

      ↓

      ↓ Waterfall

      ↓

~~~~~~~~~~~~~~

Plunge Pool

~~~~~~~~~~~~~~

River

Examples of Waterfalls

India

  • Jog Falls (Karnataka)
  • Athirappilly Falls (Kerala)
  • Dudhsagar Falls (Goa)

World

  • Niagara Falls (USA–Canada)
  • Victoria Falls (Africa)
  • Angel Falls (Venezuela)

Importance of Waterfalls

  • Hydroelectric power generation
  • Tourism
  • Freshwater ecosystems
  • Scenic beauty

What is a Meander?

Definition

A meander is a winding or looping bend formed in a river flowing across a plain.

Formation of Meanders

When rivers enter plains:

  • Water flows more slowly.
  • Sideways erosion increases.
  • Deposition occurs on the inner bank.
  • Erosion occurs on the outer bank.

This creates curved river channels.

Parts of a Meander

Inner Bend

Outer Bend

Deposition

Erosion

Slow Water

Fast Water

Diagram

        Erosion

           )

          )

River     )

         (

        (

 Deposition

Importance of Meanders

  • Increase fertile floodplains.
  • Improve soil fertility.
  • Support agriculture.
  • Provide habitats for wildlife.

Oxbow Lake (Additional Concept)

Sometimes a meander becomes very curved.

During floods, the river cuts across the narrow neck.

The old bend gets separated.

This forms an Oxbow Lake.

What is a Delta?

Definition

A delta is a triangular or fan-shaped landform formed at the mouth of a river due to the deposition of sediments.

Formation of a Delta

As the river enters a sea or lake:

  • River speed decreases.
  • Sediments settle.
  • Deposits build up.
  • The river divides into smaller channels called distributaries.

Diagram

River

   │

   │

  \│/

  / \

 /   \

Delta

~~~~~~~

Sea

Conditions for Delta Formation

  • Large amount of sediments
  • Slow-moving water
  • Calm sea conditions
  • Wide river mouth

Examples of Deltas

India

  • Ganga–Brahmaputra Delta (World's largest)
  • Mahanadi Delta
  • Godavari Delta
  • Krishna Delta
  • Kaveri Delta

World

  • Nile Delta
  • Mississippi Delta
  • Mekong Delta

Importance of Deltas

  • Extremely fertile soil
  • Dense population
  • Rich fisheries
  • Agriculture
  • Mangrove forests

Example:

Sundarbans, located in the Ganga–Brahmaputra Delta, contain the world's largest mangrove forest.

Difference Between Waterfall, Meander and Delta

Waterfall

Meander

Delta

Vertical fall of river

Curved river bend

Depositional landform at river mouth

Upper course

Middle course

Lower course

Formed by erosion

Formed by erosion and deposition

Formed mainly by deposition

Conclusion

Running water is the most effective agent of gradation because it constantly reshapes the Earth's surface through erosion, transportation, and deposition.

From steep mountain valleys to fertile river plains and large deltas, rivers create landforms that support agriculture, settlements, biodiversity, and economic activities.

Understanding these processes helps us manage water resources, reduce flood risks, conserve fertile land, and protect natural ecosystems.

Key Terms

Term

Meaning

Gradation

Levelling of Earth's surface by erosion and deposition

Erosion

Wearing away of rocks

Transportation

Movement of sediments

Deposition

Settling of sediments

Waterfall

Vertical drop of a river

Meander

Curved bend in a river

Delta

Depositional landform at the river mouth

Distributary

Smaller channels into which a river divides near its mouth

Quick Revision

✅ Running water is the most active agent of gradation.

✅ Rivers perform erosion, transportation, and deposition.

✅ Waterfalls form in the upper course.

✅ Meanders form in the middle course.

✅ Deltas form in the lower course due to deposition.

✅ The Ganga–Brahmaputra Delta is the world's largest delta.

Excellent! Let's continue with Part 4.

Chapter 2: Shaping of the Earth's Surface

Part 4: Waves, Glaciers, Wind and Underground Water

Book: Understanding Society: India and Beyond (Class 9 NCERT 2026–27)

Waves and Currents

Introduction

Oceans cover about 71% of the Earth's surface. The movement of seawater through waves, tides, and ocean currents constantly changes the shape of coastlines. These natural forces erode rocks, transport sediments, and deposit sand, creating many beautiful coastal landforms.

What are Waves?

Waves are the rhythmic movements of seawater mainly caused by the blowing of wind over the ocean surface.

The energy of the wind is transferred to the water, creating waves that move towards the shore.

Main Characteristics of Waves

  • Formed mainly by wind.
  • Move continuously towards the coast.
  • Cause erosion, transportation, and deposition.
  • Become stronger during storms.

What are Ocean Currents?

Ocean currents are continuous streams of seawater flowing in a particular direction.

They are caused by:

  • Wind
  • Difference in water temperature
  • Difference in salinity
  • Earth's rotation (Coriolis Effect)

Ocean currents influence:

  • Climate
  • Fishing activities
  • Marine biodiversity
  • Navigation

Work Done by Sea Waves

Sea waves perform three major functions.

Sea Waves

      │

 ┌────┼────┐

 │    │    │

Erosion Transportation Deposition

What is a Beach?

Definition

A beach is a gently sloping landform made of sand, pebbles, shells, or small rocks deposited along the coast by sea waves.

Formation of Beaches

  • Waves carry sand and sediments.
  • As wave energy decreases, sediments are deposited.
  • Continuous deposition forms beaches.

Importance of Beaches

  • Protect the coast from strong waves.
  • Support tourism.
  • Provide habitat for marine organisms.
  • Help fishing communities.

Examples

India

  • Marina Beach (Chennai)
  • Juhu Beach (Mumbai)
  • Puri Beach (Odisha)

World

  • Bondi Beach (Australia)
  • Waikiki Beach (Hawaii)

What is Coastal Erosion?

Definition

Coastal erosion is the wearing away of rocks and land along the seashore by sea waves.

Strong waves continuously hit coastal rocks, gradually breaking them into smaller pieces.

Processes of Coastal Erosion

Hydraulic Action

Powerful waves force water into cracks.

The pressure enlarges the cracks.

Eventually rocks break apart.

Abrasion

Sand and pebbles carried by waves strike coastal rocks like sandpaper.

Attrition

Rock fragments collide with one another.

They become smaller and smoother.

Solution

Sea water dissolves soluble rocks such as limestone.

Landforms Produced by Coastal Erosion

  • Sea Cliffs
  • Sea Caves
  • Sea Arches
  • Sea Stacks

Landforms Produced by Coastal Deposition

  • Beaches
  • Sand Bars
  • Spits
  • Lagoons

Glaciers

What is a Glacier?

A glacier is a large, slow-moving mass of ice formed from accumulated snowfall in cold mountainous and polar regions.

Glaciers move under the force of gravity.

They are often called "Rivers of Ice."

Formation of Glaciers

  1. Snow falls every winter.
  2. Snow accumulates over many years.
  3. Pressure compresses snow into ice.
  4. Thick ice slowly begins to move downhill.

Types of Glaciers

Valley Glacier

Moves through mountain valleys.

Example:

Gangotri Glacier

Continental Glacier

Covers huge land areas.

Example:

Antarctica

Greenland

What is Glacial Erosion?

Definition

Glacial erosion is the process by which moving ice removes rocks and soil from the Earth's surface.

Although glaciers move slowly, they have enormous power.

Processes of Glacial Erosion

Plucking

Ice freezes around rocks.

As the glacier moves, rocks are pulled away.

Abrasion

Rock fragments trapped under glaciers scrape the ground.

This smoothens and polishes rocks.

Landforms Created by Glaciers

Erosional Landforms

  • U-shaped Valleys
  • Cirques
  • Hanging Valleys

Depositional Landforms

  • Moraines
  • Drumlins
  • Eskers

What are Moraines?

Definition

Moraines are piles of rocks, soil, and debris deposited by glaciers.

Types of Moraines

Lateral Moraine

Found along glacier sides.

Medial Moraine

Formed where two glaciers join.

Terminal Moraine

Deposited at the glacier's end.

Ground Moraine

Spread beneath the glacier.

Importance of Glaciers

  • Freshwater storage
  • River source
  • Hydroelectric power
  • Climate regulation
  • Tourism

Wind

Introduction

Wind is an important agent of gradation in dry and desert regions where vegetation is scarce.

Wind can:

  • Erode rocks
  • Transport sand
  • Deposit sediments

What is Wind Erosion?

Definition

Wind erosion is the removal and transportation of loose soil and sand by moving air.

Processes of Wind Erosion

Deflation

Loose particles are lifted and carried away.

Abrasion

Sand particles strike rocks.

Rocks become smooth.

Attrition

Sand particles collide and become finer.

Landforms Produced by Wind

Mushroom Rocks

Lower part erodes faster.

Upper part remains broad.

Looks like a mushroom.

Yardangs

Long narrow ridges carved by wind.

Deflation Hollows

Depressions formed after removal of loose materials.

What are Dunes?

Definition

A sand dune is a hill or ridge of sand deposited by wind.

Formation of Sand Dunes

  1. Wind carries sand.
  2. Wind slows down.
  3. Sand is deposited.
  4. Gradually dunes develop.

Types of Sand Dunes

Barchan Dunes

Crescent-shaped.

Common in deserts.

Longitudinal Dunes

Long parallel ridges.

Transverse Dunes

Form across wind direction.

Importance of Sand Dunes

  • Prevent desert sand movement.
  • Protect farmland.
  • Support desert plants.
  • Provide habitat for wildlife.

Underground Water

Introduction

Rainwater does not always remain on the surface.

Some water enters the soil through tiny openings.

This is called infiltration.

The water stored below the Earth's surface is known as groundwater.

Work Done by Underground Water

Groundwater slowly dissolves rocks and forms unique underground landforms.

This process is especially common in limestone regions.

What is Karst Topography?

Definition

Karst Topography is a landscape formed due to the dissolution of soluble rocks such as limestone by underground water.

Characteristics of Karst Topography

  • Sinkholes
  • Limestone caves
  • Underground streams
  • Stalactites
  • Stalagmites

Formation Process

Rainwater absorbs carbon dioxide.

↓

Forms weak carbonic acid.

↓

Carbonic acid dissolves limestone.

↓

Underground caves develop.

↓

Karst landscape forms.

Stalactites

Hang from cave roofs.

Grow downward.

Stalagmites

Rise from cave floors.

Grow upward.

Diagram

 Cave Roof

     │

  Stalactite

      ▼

      │

      │

      ▲

  Stalagmite

 Cave Floor

Importance of Groundwater

  • Drinking water
  • Irrigation
  • Industries
  • Ecosystems
  • Freshwater supply

Comparison of Major Agents of Gradation

Agent

Main Region

Erosion

Deposition

Major Landforms

Running Water

Everywhere

High

High

Valleys, Deltas

Sea Waves

Coast

High

High

Beaches, Cliffs

Glaciers

Mountains

High

High

U-shaped Valleys, Moraines

Wind

Deserts

Moderate

High

Dunes, Mushroom Rocks

Underground Water

Limestone Regions

Chemical

Limited

Caves, Sinkholes

Conclusion

Different agents of gradation continuously reshape the Earth's surface.

  • Sea waves create beaches and cliffs.
  • Glaciers carve valleys and deposit moraines.
  • Wind builds dunes and erodes rocks.
  • Underground water forms caves and Karst landscapes.

Together, these natural processes produce the diverse landforms found across the world and play a crucial role in supporting ecosystems, human settlements, agriculture, tourism, and economic activities.

Key Terms

Term

Meaning

Beach

Depositional coastal landform

Coastal Erosion

Wearing away of coastal rocks

Glacier

Slow-moving mass of ice

Moraine

Deposited glacial debris

Wind Erosion

Removal of sand by wind

Sand Dune

Hill of wind-deposited sand

Groundwater

Water stored beneath Earth's surface

Karst Topography

Landscape formed by dissolution of limestone

Stalactite

Mineral deposit hanging from cave roof

Stalagmite

Mineral deposit rising from cave floor

Quick Revision

✅ Waves constantly reshape coastlines through erosion and deposition.

✅ Beaches are formed by the deposition of sand and sediments.

✅ Glaciers are called "Rivers of Ice."

✅ Moraines are deposits left behind by glaciers.

✅ Wind is the main agent of erosion in deserts.

✅ Sand dunes are formed by wind deposition.

✅ Underground water dissolves limestone to form Karst Topography.

✅ Stalactites hang from cave roofs, while stalagmites rise from cave floors.

Chapter 2: Shaping of the Earth's Surface

Part 5: Landforms and Disasters | The Dynamic Earth

Book: Understanding Society: India and Beyond (Class 9 NCERT 2026–27)

Landforms and Disasters

Introduction

Natural processes that shape the Earth's surface can sometimes become natural disasters when they threaten human life, property, and the environment.

Earthquakes, landslides, avalanches, floods, volcanic eruptions, and dust storms are all linked to the dynamic nature of our planet. Understanding these disasters helps us reduce risks and prepare for emergencies.

What Causes Landslides?

Definition

A landslide is the sudden downward movement of rocks, soil, and debris along a slope due to gravity.

Landslides are common in mountainous and hilly regions.

Causes of Landslides

1. Heavy Rainfall

Excess rain makes the soil loose and unstable.

2. Earthquakes

Earthquakes shake mountain slopes, causing rocks to collapse.

3. Volcanic Activity

Volcanic eruptions weaken surrounding slopes.

4. Deforestation

Tree roots hold soil together.

Cutting forests reduces slope stability.

5. Human Activities

  • Road construction
  • Mining
  • Quarrying
  • Building construction

These activities weaken mountain slopes.

Effects of Landslides

  • Loss of life
  • Destruction of houses
  • Damage to roads and bridges
  • Blocking of rivers
  • Soil erosion
  • Loss of forests

Landslide-Prone Areas in India

  • Jammu & Kashmir
  • Himachal Pradesh
  • Uttarakhand
  • Sikkim
  • Arunachal Pradesh
  • Western Ghats

Prevention of Landslides

  • Afforestation
  • Proper drainage systems
  • Avoid construction on steep slopes
  • Controlled mining
  • Retaining walls
  • Early warning systems

What Causes Avalanches?

Definition

An avalanche is the sudden and rapid movement of a large mass of snow, ice, and rocks down a mountain slope.

Avalanches mainly occur in high mountain regions during winter.

Causes of Avalanches

  • Heavy snowfall
  • Rise in temperature
  • Earthquakes
  • Strong winds
  • Human disturbances (skiing, explosions)

Effects of Avalanches

  • Burial of villages
  • Death of people and animals
  • Damage to roads
  • Blocking of rivers
  • Destruction of forests

Prevention

  • Avalanche forecasting
  • Controlled explosions
  • Snow barriers
  • Avoiding high-risk zones

What are GLOFs?

Definition

GLOF stands for Glacial Lake Outburst Flood.

It occurs when a lake formed by melting glaciers suddenly bursts, releasing a huge amount of water.

Formation of GLOFs

  1. Glacier melts due to rising temperature.
  2. Meltwater collects to form a glacial lake.
  3. A natural dam of ice or rocks breaks.
  4. Massive floodwater rushes downstream.

Causes of GLOFs

  • Climate change
  • Rapid glacier melting
  • Earthquakes
  • Heavy rainfall
  • Weak natural dams

Effects of GLOFs

  • Flash floods
  • Destruction of bridges
  • Damage to villages
  • Loss of agricultural land
  • Death of people and animals

Prevention

  • Monitoring glacial lakes
  • Early warning systems
  • Controlled drainage
  • Satellite observation
  • Disaster preparedness

What Causes Dust Storms?

Definition

A dust storm is a strong wind carrying large amounts of dust and sand over long distances.

Dust storms are common in dry and semi-arid regions.

Causes

  • Strong winds
  • Loose dry soil
  • Lack of vegetation
  • Drought
  • Desert conditions

Effects

  • Poor visibility
  • Breathing problems
  • Crop damage
  • Road accidents
  • Soil erosion

Prevention

  • Plantation of trees
  • Shelter belts
  • Soil conservation
  • Better land management
  • Early weather warnings

Disaster Comparison Table

Disaster

Main Cause

Common Region

Major Impact

Landslide

Gravity, rainfall, earthquakes

Mountains

Loss of life and property

Avalanche

Heavy snowfall

Snow-covered mountains

Burial under snow

GLOF

Glacial lake burst

Himalayan region

Flash floods

Dust Storm

Strong winds

Deserts

Poor visibility and soil erosion

Relationship Between Landforms and Disasters

Many landforms are closely connected with natural disasters.

Landform

Possible Disaster

Mountains

Landslides, Avalanches

River Valleys

Floods

Coastal Areas

Cyclones, Tsunamis, Coastal Erosion

Deserts

Dust Storms

Glacier Regions

GLOFs

Disaster Risk Reduction

Disasters cannot always be prevented, but their impact can be reduced.

Important Measures

  • Scientific planning
  • Afforestation
  • Strong buildings
  • Disaster education
  • Early warning systems
  • Community awareness
  • Emergency response teams

The Dynamic Earth

What is a Dynamic Earth?

The Earth is called a dynamic planet because its surface is continuously changing due to internal and external forces.

No part of the Earth's surface remains exactly the same forever.

Mountains rise, rivers change course, coastlines shift, glaciers melt, and new landforms continue to develop.

Internal (Endogenic) Forces

These forces originate inside the Earth.

Examples:

  • Plate movements
  • Earthquakes
  • Volcanic eruptions
  • Mountain building

These forces mainly create new landforms.

External (Exogenic) Forces

These forces act on the Earth's surface.

Examples:

  • Running water
  • Wind
  • Glaciers
  • Sea waves
  • Underground water

These forces wear down existing landforms and create new ones through erosion and deposition.

Endogenic vs Exogenic Forces

Endogenic Forces

Exogenic Forces

Originate inside Earth

Act on Earth's surface

Build landforms

Wear down landforms

Plate movement

Rivers

Volcanoes

Wind

Earthquakes

Glaciers

Mountain building

Sea Waves

Why Does the Earth Keep Changing?

Several natural processes continuously reshape our planet.

  • Plate movement
  • Weathering
  • Erosion
  • Deposition
  • Climate change
  • River action
  • Glacial movement
  • Ocean waves
  • Wind action

These processes have been operating for millions of years and will continue in the future.

Why It Matters

Studying the Earth's surface helps us understand:

1. Natural Disasters

We can reduce disaster risks through better planning.

2. Resource Management

Knowledge of landforms helps in mining, agriculture, and water conservation.

3. Environmental Protection

Understanding erosion and climate helps protect ecosystems.

4. Sustainable Development

Land should be used wisely to meet present needs without harming future generations.

5. Human Settlements

Knowledge of landforms helps us decide where to build cities, roads, and dams safely.

Chapter Flowchart

                 EARTH

                    │

        Internal & External Forces

                    │

     ┌──────────────┴──────────────┐

     │                             │

Endogenic Forces            Exogenic Forces

     │                             │

Mountains                 Weathering

Earthquakes               Erosion

Volcanoes                 Deposition

     │                             │

     └───────────┬─────────────────┘

                 │

          Different Landforms

                 │

       Human Life & Environment

Complete Chapter Summary

  • The Earth's surface is constantly changing.
  • Plate tectonics explains the movement of continents and the formation of mountains, volcanoes, and earthquakes.
  • Weathering breaks rocks into smaller pieces.
  • Erosion transports weathered materials.
  • Running water forms valleys, waterfalls, meanders, and deltas.
  • Sea waves create beaches and coastal landforms.
  • Glaciers shape U-shaped valleys and deposit moraines.
  • Wind forms sand dunes and erodes desert landscapes.
  • Underground water creates caves and karst topography.
  • Natural disasters such as landslides, avalanches, GLOFs, and dust storms are linked to Earth's dynamic processes.
  • Understanding these processes helps us protect lives, manage resources, and promote sustainable development.

One-Page Quick Revision

Remember These Keywords

  • Plate Tectonics
  • Lithosphere
  • Asthenosphere
  • Weathering
  • Erosion
  • Deposition
  • Waterfall
  • Meander
  • Delta
  • Beach
  • Coastal Erosion
  • Glacier
  • Moraine
  • Sand Dune
  • Karst Topography
  • Landslide
  • Avalanche
  • GLOF
  • Dust Storm
  • Dynamic Earth

Important Board Questions

1 Mark Questions

  1. What is Plate Tectonics?
  2. Define Weathering.
  3. What is a Meander?
  4. What is a Delta?
  5. Define Glacier.
  6. What is Karst Topography?
  7. What is a GLOF?
  8. What is Coastal Erosion?

2–3 Mark Questions

  1. Differentiate between Weathering and Erosion.
  2. Explain the types of Plate Boundaries.
  3. How are Waterfalls formed?
  4. Describe the formation of Sand Dunes.
  5. Explain the causes of Landslides.

5 Mark Questions

  1. Explain the Plate Tectonic Theory with suitable diagrams.
  2. Describe the processes of Weathering and Erosion.
  3. Explain the work of Running Water as an Agent of Gradation.
  4. Discuss the role of Glaciers and Wind in shaping the Earth's surface.
  5. Explain different natural disasters associated with landforms.
  6. Why is the Earth called a Dynamic Planet? Explain with examples.

Mind Map

               SHAPING OF THE EARTH'S SURFACE

                          │

     ┌──────────────┬───────────────┬──────────────┐

     │              │               │              │

Plate Tectonics Weathering      Erosion     Deposition

     │              │               │              │

Earthquakes     Physical       Rivers      Deltas

Volcanoes       Chemical       Wind        Beaches

Mountains       Biological     Glaciers    Moraines

     │              │               │

     └──────────────┴───────────────┘

                    │

          Dynamic Earth & Landforms

                    │

          Human Life and Environment

Chapter Conclusion

The Earth's surface is alive with change. Internal forces such as plate movements build mountains and trigger earthquakes, while external forces like rivers, glaciers, wind, and sea waves continuously reshape the landscape through weathering, erosion, transportation, and deposition. Understanding these processes enables us to appreciate the formation of diverse landforms, reduce disaster risks, use natural resources responsibly, and work towards sustainable development.

 

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Amresh Academy

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