Ch 2 Shaping Of The Earth’s Surface Notes Class 9| Understanding Society India And Beyond

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Also Read| Ch 1 Understanding Social Science Notes Class 9 Social Science

Ch 2 Shaping Of The Earth’s Surface Notes Class 9

Why Should We Study the Earth’s Surface?

Earth’s surface is changing due to :
● Internal and External forces

Plate Tectonics
● Explains movement of large crustal plains over mantle
● This movement creates different landforms.

Importance of Plate Tectonics:
Explains :
● Earthquakes
● Volcanic eruptions
● Formation of continents and oceans.

What Is Plate Tectonics?

Plate tectonics is when giant pieces of Earth’s crust move and collide.

Plate Tectonics Theory
● By W. J. Morgan
● Explain- movement of the Earth’s crust.

How It Works
● Earth’s outer layer is divided into tectonic plates.
● These plates move slowly over the semi-molten mantle.

What It Creates
● Mountains
● Earthquakes
● Volcanoes

What are the Layers of the Earth?

● Lithosphere = Crust + upper part of mantle.
● Lithosphere broken into tectonic plates.
● Asthenosphere lies below the lithosphere, semi-molten and it lets plates move.

What are Tectonic Plates?

● Massive slabs of solid rock.
● Move very slowly– few centimeters per year.

Types of Tectonic Plates
● Continental plates: carry continents.
● Oceanic plates: carry ocean floors.
● Mixed plates: carry both continents and oceans.

Major Tectonic Plates of the World

What Causes Plate Movement?

What are Plate Boundaries?
= Edge where tectonic plates meet.
Three main types.

1. Convergent Boundary
● Two plates move towards each other.
● Continental + Continental collision → forms fold mountains (e.g., Himalaya).
● Oceanic + Continental collision → oceanic plate sinks beneath continental plate → causes volcanic activity and earthquakes.

2. Divergent Boundary
● Plates move away from each other.
● Magma rises from below. Forms new crust.
● Creates features like mid-ocean ridges.
Example: Mid-Atlantic Ridge.

3. Transform Boundary
● Plates slide past each other.
● No crust is created or destroyed.
● Mainly causes earthquakes.
Example: San Andreas Fault, United States.

Why is Plate Tectonics Important?

Impact on the Earth’s Surface
● Shapes the Earth’s surface.
Forms:
➢ Mountains, Valleys, Ocean basins. Volcanoes. Earthquakes
Explains– distribution of continents and oceans.
● Most earthquakes and volcanoes occur along plate boundaries.

Ring of Fire
● Surrounds the Pacific Ocean.
● Highest concentration of earthquakes and volcanoes.

Process of Weathering and Erosion

Weathering breaks down rocks. Erosion moves the broken material. Together they shape mountains, valleys, plains, caves, cliffs, and river deltas.

What Is Weathering?

Weathering is the process by which rocks break down into smaller pieces on the Earth’s surface.

How It Happens
● Breaks rocks into smaller fragments.
● Only breaking down occurs, not transportation.

Importance of Weathering
● Helps shape the Earth’s surface.
● Role in soil formation.

Common Confusion:
● Weathering breaks rocks in place.
● Erosion moves the broken pieces away. Don’t mix the two

What are the Types of Weathering?

1. Physical Weathering
● Rocks break into smaller pieces.
● Caused by temperature changes, frost, or wind.

2. Chemical Weathering
● Minerals in rocks change.
● Caused by reactions with water, air, or acids.
● Leads to the formation of new substances.

3. Biological Weathering
● Caused by plants, animals, or micro-organisms.
Example: plant roots grow into cracks in rocks and split them apart.

What Is Erosion?

Erosion is the process by which soil, rocks, and other surface materials are worn away and transported from one place to another.

Agents of Erosion
● Erosion is caused by:
➢ Water ➢ Wind
➢ Ice ➢ Waves

How Erosion Differs from Weathering
● Weathering only breaks down rocks.
● Erosion breaks down and transports the material.

Importance of Erosion
● Shapes landforms.
● Create and destroy features on the Earth’s surface.

What are the Types of Erosion?

How Does Erosion Affect Human Occupations?

1. Impact on Farming
● Removes fertile topsoil.
● Reduces crop yields.

2. Impact on Settlements
● Washes away land, houses, and roads.
● Causes property damage.

3. Impact on Construction and Mining
● Makes the land unstable.
● Increases safety risks.

4. Impact on Tourism and Fishing
● Damages beaches, rivers, and fertile land.
● Affects tourism and fishing livelihoods.

Agents of Gradation

What are Agents of Gradation?

Agents of gradation = natural forces that wear down, transport, and deposit materials on Earth’s surface.
They level or smooth the surface over time.

Main Agents of Gradation

How Does Running Water Shape Land?

Rivers shape land through erosion, transportation, and deposition.

River Course Stages

These landforms are important for :
Agriculture, Settlement, and Ecosystems.

What is a Waterfall?

● A waterfall = landform ↦ river flows over a steep cliff or vertical drop
● Forms in the upper course of rivers.
● Hard rocks resist erosion. Softer rocks below get worn away. This creates a sudden drop.

Importance of Waterfalls
● Attract tourists.
● Hydroelectric power generation.
● Recreation — trekking, photography.
● Cultural or religious significance in certain regions.

What is a Meander?

● A meander is a winding curve or bend in the middle or lower course of a river.
● The river erodes the outer banks of bends.
● The river deposits sediment on the inner banks.
● This gradually creates large loops.

Importance of Meanders

● Fertile soil deposited along banks supports agriculture.
● Influence settlement patterns — villages/towns develop on gentle slopes near meanders.
● Used for navigation, irrigation, and sometimes tourism.

Example:
Grand Anicut (also called Kallanai), Tamil Nadu — example of rivers used for irrigation.

What is a Delta?

● A delta is a landform formed at the mouth of a river, where it flows into a sea, ocean, or lake.
● Rivers deposit sediments carried from upstream.
● Over time, deposits form a fan-shaped or triangular area of land.

Importance of Deltas
● Highly fertile due to rich alluvial soil. Good for agriculture (rice, jute).
● Fishing — fresh + saltwater = diverse aquatic life.
● Dense human settlements.
● Trade and transportation
● Risk: prone to flooding

Waves and Currents

Waves and currents reshape coastal land. They create beaches, sand bars, sea cliffs, caves, arches, and stacks.

What is a Beach?

Landform made up of sand, pebbles, or rocks along the shoreline.

● Created by deposition of sediments by waves.
● Shaped continuously by wave action, tides, and currents.

Importance of Beaches
● Tourist destinations
● Boosts local economy.
● Fishing areas.
● People collect sand and shells.
● Natural barriers against strong waves and coastal erosion.

What is Coastal Erosion?

● Occurs when waves, tides, and currents wear away land along the coast.
● Creates unique landforms.

Landforms of Coastal Erosion

“Cliff
▼
Platform
▼
Cave
▼
Arch
▼
Stack”
This is the order of formation; one leads to the next.

Glaciers

Moving ice is called a glacier

What is Glacial Erosion?

● Occurs when glaciers slowly move over land.
● Carves and shapes the landscape.

Landforms of Glacial Erosion

Importance to Humans

● U-shaped valleys & cirques: Tourist attractions — trekking, skiing, mountaineering.

● Fjords: Used for harbors and fishing.

● Glacial soil: Supports agriculture in some valleys.

● Glaciers: Crucial source of fresh water, feed rivers.

What are Moraines?

● Landforms created by deposition of rocks, soil, and debris (called till).
● Formed when a glacier melts and deposits eroded material.

Types of Moraines
● Lateral moraines: form along the sides of glaciers.
● Terminal moraines: found at the end of glaciers. Mark the furthest advance.
● Medial moraines: formed when two glaciers meet. Their lateral moraines join in the middle.

Importance of Moraines
● Create fertile soil for agriculture.
● Form natural dams and lakes.
● Used for water supply, irrigation, sometimes hydroelectric power.

Wind

What is Wind Erosion?

● Occurs when strong winds pick up and carry away loose sand and soil particles.
● Gradually shapes the landscape.

Landforms of Wind Erosion

Importance to Humans
● Influence settlement patterns and agriculture in arid regions.
● Ventifacts and yardangs attract tourists and geologists.

What are Dunes?

● Dunes are hills or ridges of sand formed by wind.
● Found in desert areas or along sandy coasts.

Types of Dunes

● Barchan dunes: crescent-shaped. Form with limited sand, a single wind direction.
● Longitudinal dunes: long ridges. Parallel to the prevailing wind.
● Star dunes: multiple arms. Form where winds come from different directions.
● Parabolic dunes: U-shaped. Often stabilised by vegetation.

Importance of Dunes
● Natural barriers against desertification and wind erosion.
● Tourism and adventure sports.
● Protect coastal settlements from strong sea winds and waves.
● Sand used for construction purposes.

Underground Water

What is Karst Topography?

● Underground water, especially in limestone or soluble rocks, creates Karst topography.
● Formed through chemical weathering and erosion.

Landforms of Underground Water

Importance to Humans

● Fresh water.
● Tourism opportunities.
● Cultural or religious significance .
● Stalagmites/stalactites attract geologists and adventurers.

Landforms and Disasters

Different landforms can cause disasters. Four common ones are landslides, avalanches, GLOFs, and dust storms.

What Causes Landslides?

Natural Causes

● Heavy and continuous rainfall — water seeps into soil/rocks. Increases weight. Reduces friction.
● Earthquakes and volcanic eruptions — shake ground. Weaken slopes.
● Steep slopes with loose or weathered rocks — increase risk.

Human Causes

● Deforestation, mining, road construction — disturb slope balance.
● Unplanned construction on hillsides.
● Poor drainage systems and improper land use — water accumulates. Leads to slope failure.

What Causes Avalanches?

● Sudden instability of snow on steep slopes.
● Weak or loosely bonded layers of snow make snowpack unstable.
● Sudden temperature rise — causes partial melting. Reduces friction holding snow together.
● Strong winds — pile up snow unevenly. Creates fragile layers.

Triggers
● Natural: earthquakes and vibrations.
● Human: skiing, trekking, construction in mountainous areas.

What are GLOFs?

● GLOFs = Glacial Lake Outburst Floods.
● Caused by sudden release of large volumes of water from glacial lakes.

How GLOFs Happen

Formation of a GLOF
● Rising temperatures cause rapid glacier melting.
● Glacial lakes grow larger and their water level rises.
● The increased water puts pressure on natural dams made of ice or moraines.
● Heavy rainfall or snowfall adds more water.
● Earthquakes, avalanches, or landslides can weaken or breach the dam.
● The dam suddenly collapses.
● The stored water rushes downstream, causing a Glacial Lake Outburst Flood (GLOF).

What Causes Dust Storms?

Caused by strong winds lifting large amounts of loose, dry soil and sand into the air.

Contributing Factors

● Prolonged drought and low rainfall
Dries out soil. Makes it easy for wind to lift particles.
● Desert and semi-arid regions
Soil is loose and dry.
● Sparse vegetation cover
Due to deforestation, overgrazing, poor farming practices. Leaves land exposed.
● Climate change and extreme weather
Increases frequency and intensity.

Disaster Comparison Table

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