Shaping of the Earth – (Class 9, Chapter 2 )
Introduction
The Earth’s surface is not uniform. It is made up of various landforms such as mountains, plateaus, plains, valleys, and deserts. These landforms are continuously being shaped and reshaped by natural forces.
The shaping of the Earth refers to the processes that create and modify the physical features of the Earth’s surface. These processes operate both inside the Earth and on its surface.
There are two main types of forces responsible for shaping the Earth:
1. Internal Forces (Endogenic Forces):
These forces originate from within the Earth. They are responsible for building up landforms. Examples include movements that cause earthquakes, volcanic eruptions, and the formation of mountains.
2. External Forces (Exogenic Forces):
These forces act on the Earth’s surface. They wear down high landforms and fill up low areas. Agents like rivers, wind, glaciers, and sea waves play an important role in this process.
The continuous interaction between internal and external forces leads to the formation, destruction, and reshaping of landforms. This dynamic nature of the Earth makes its surface ever-changing.
In this chapter, we will study how these forces work and how different landforms are created and modified over time.
Interior of the Earth
The Earth is not a solid mass throughout. Its interior is made up of different layers, each with distinct composition, thickness, and properties. Since we cannot directly reach deep inside the Earth, most of our knowledge comes from indirect sources like earthquake waves (seismic waves).
Layers of the Earth:- The Earth is divided into three main layers:
1. Crust
- It is the outermost layer of the Earth.
- It mainly made up of rocks and minerals.
- It is the thinnest layer (about 5–70 km thick).
- It is where we live and includes land, oceans, soil, and minerals.
- Continental Crust (thicker, mainly granite)
- Oceanic Crust (thinner, mainly basalt)
2. Mantle
- Located below the crust, extending up to about 2900 km.
- It is the thickest layer of the Earth.
- Made up of semi-solid rocks (magma).
- The upper part of the mantle is soft and allows tectonic plates to move.
- Convection currents in the mantle are responsible for movements like earthquakes and volcanic eruptions.
3. Core:-
- The innermost layer of the Earth.
- It composed of Nickel and Iron (NIFE).
- Extremely hot (up to 5000°C or more).
- Responsible for generating the Earth’s magnetic field.
Divided into two parts:
- Outer Core – liquid state (mainly iron and nickel)
- Inner Core – solid state due to high pressure
Theory of Plate Tectonics:- The Theory of Plate Tectonics explains how the Earth’s surface is divided into large pieces called tectonic plates and how their movement shapes landforms like mountains, earthquakes, and volcanoes.
Movement of Plates:- The plates are not fixed; they are constantly moving, though very slowly (a few centimeters per year). Their movement is mainly caused by convection currents in the mantle.
Tectonic Plate Divisions:- The Earth’s lithosphere is divided into several tectonic plates. These plates vary in size and are classified into major plates and minor plates. There are seven major tectonic plates:
- Pacific Plate – The largest plate, mostly covered by the Pacific Ocean.
- North American Plate – Covers North America and parts of the Atlantic Ocean.
- South American Plate – Covers South America and part of the Atlantic Ocean.
- Eurasian Plate – Covers Europe and Asia.
- African Plate – Covers Africa.
- Indo-Australian Plate – Covers India, Australia, and surrounding oceans.
- Antarctic Plate – Covers Antarctica and surrounding oceans.
Types of Plate Movements
1. Divergent Boundary (Moving Apart)
- Plates move away from each other.
- It leads formation of new crust.
- it results in volcanic activity and rift valley.
- Magma rises to fill the gap and forms new crust.
- Example: Mid-ocean ridges.
2. Convergent Boundary (Coming Together)
- Plates move towards each other and collide.
- One plate may go below the other (subduction), or both may crumple to form mountains.
- Example: Formation of fold mountains like the Himalayas, earthquaks and sometimes volcanic activity.
3. Transform Boundary (Sliding Past Each Other)
- Plates slide past one another horizontally.
- Causes earthquakes but does not create or destroy crust.
- As seen aloong the San Andreas Fault in the USA.
Effects of Plate Tectonics
- Formation of mountains, valleys, and ocean basins
- Occurrence of earthquakes and volcanic eruptions
- Continents slowly changing position (continental drift)
Weathering and Erosion :- The Earth’s surface is continuously changing due to external forces like water, wind, and ice. Two important processes responsible for these changes are weathering and erosion.
1. Weathering:- Weathering is the breaking down of rocks into smaller pieces at or near the Earth’s surface without movement.
Types of Weathering
(a) Physical (Mechanical) Weathering
- Breaking the rocks into smaller pieces without chemical process.
- Rocks break due to temperature changes, frost, or pressure.
- Example: Cracking of rocks in deserts due to heat.
(b) Chemical Weathering
- Rocks break down due to chemical reactions with water, oxygen, or acids.
- Example: Formation of caves in limestone areas.
(c) Biological Weathering
- Caused by plants, animals, and microorganisms.
- Example: Roots of plants growing into cracks and breaking rocks.
Importance
- Helps in soil formation
- Shapes landforms like valleys, deserts, and coastal features
- Plays a role in agriculture and natural resource distribution
- It helps in releasing minerals into the soil.
- It helps to natural recycling of materials on the earth
2. Erosion:- Erosion is the removal and transportation of weathered materials from one place to another. This continous process leads to the formation of various landforms such as valley, river plains, delats and coastal.
Importance of Erosion:- Erosion is a natural process that plays a significant role in shaping the Earth’s surface. Though it can sometimes cause damage, it is also very important for maintaining natural balance.
1. Formation of Landforms
2. Soil Formation and Fertility
3. Redistribution of Materials
4. Creation of Plains
5. Exposure of Minerals
6. Natural Cycle Maintenance
Agents of Erosion
1. Running Water (Rivers)
- Rivers are the most powerful agents of erosion.
- They erode land by cutting, transporting, and depositing materials.
- In upper courses, rivers form V-shaped valleys, gorges, and waterfalls.
- In lower courses, they deposit sediments to form plains and deltas.
- Example: Formation of fertile plains due to river deposition.
2. Wind
- Wind is an important agent in dry and desert regions.
- It erodes rocks by lifting and carrying sand particles.
- Wind shapes landforms like:
- Sand dunes
- Mushroom rocks
- It also deposits fine soil called loess.
3. Glaciers (Ice)
- Glaciers are slow-moving masses of ice found in high mountains and polar regions.
- They erode land by plucking and scraping rocks.
- They form landforms such as:
- U-shaped valleys
- Moraines (deposited debris)
- Glaciers carry large rocks and deposit them far away.
4. Sea Waves
- Sea waves continuously hit the coast and cause erosion.
- They shape coastal landforms like:
- Sea cliffs
- Sea caves and arches
- Beaches (by deposition)
- Strong waves can gradually wear away coastlines.
5. Underground
- Rainwater seeps into the ground through cracks and pores.
- It mixes with carbon dioxide to form a weak acid (carbonic acid).
- This acidic water dissolves rocks, especially limestone.
- Over time, it creates underground features.
Difference Between Weathering and Erosion
Weathering Erosion
Breakdown of rocks Carry away of weathered materials
Occurs at the same place Involves movement
No movement Includes movement
Temperature, air, water, plants and microorganisms Runnig water,wind,glaciers,waves etc.
Major Landforms and Their Formation :- The Earth’s surface is made up of three major landforms: mountains, plateaus, and plains. These landforms are formed due to internal and external forces acting over millions of years. This ongoing process maintains balance on the Earth's surface.
Formation of Mountains:- Mountains are mainly formed by internal (endogenic) forces such as movements of tectonic plates.
(a) Fold Mountains
- Formed when tectonic plates collide and compress the Earth’s crust.
- This compression causes rocks to fold and rise, forming mountains.
- Example: Himalayas(Asia), Alps(Europe), Rocky Mountains(North America)
Features:
- Very high and rugged
- Young and still rising in some cases
(b) Volcanic Mountains
- Formed due to volcanic activity.
- When magma erupts onto the surface, it cools and solidifies, forming a mountain.
- Example: Mount Fuji (Japan), Mount Kilimanjaro(Africa), Mount Vesuvius (Italy)
Features:
- Cone-shaped
- Found near volcanic regions
2. Plateaus:- Plateaus are flat-topped elevated areas of land. They are sometimes called tablelands because their top surface is relatively level like table. It can be very large and are often referred to as the Roofs of the world when they occur at very high elevations.
Formation of Plateaus:- Plateaus are formed in different ways:
(a) Tectonic Activity
- Uplift of large areas of the Earth’s crust due to internal forces.
- Example: Deccan Plateau
(b) Volcanic Activity
- Lava spreads over large areas and solidifies, forming flat surfaces.
- These are called lava plateaus.
Plains:- Plains are low-lying, flat or gently sloping areas of land. They are among the most suitable regions for human settlement, agriculture, and transportation due to their level surface and fertile soil.
Types of Plains
1. River Plains (Alluvial Plains)
- Formed by the deposition of sediments (alluvium) carried by rivers.
- When rivers slow down, they deposit fertile soil in floodplains.
- Example: Indo-Gangetic Plain
Features:
- Very fertile soil
- Densely populated
- Suitable for agriculture
2. Coastal Plains
- Formed by the deposition of sediments by sea waves and rivers along coastlines.
- Found between the sea and nearby highlands.
- Example: Eastern Coastal Plains along the way of Bay of Bengal
Features:
- Flat and narrow
- Important for trade, ports, and fishing
3. Glacial Plains
- Formed by the deposition of materials (till) carried by glaciers.
- When glaciers melt, they leave behind sediments that form plains.
- Example: North European Plain
Features:
- Covered with fine and coarse materials
- Found in cold and high-latitude regions
Importance of Plains
- Ideal for agriculture and settlements
- Easy construction of roads, railways, and cities
- Support economic activities
Valley:- A valley is a low-lying area between hills or mountains, usually formed due to erosion by natural agents like rivers and glaciers. Types of Valleys
1. River Valley
- Formed by the erosion of running water (rivers).
- Rivers cut downwards into the land, creating valleys over time.
Features:
- V-shaped cross-section
- Steep sides and narrow bottom
- Found in the upper course of rivers
- Example: Valleys formed in mountainous regions.
2. Glacial Valley
- Formed by the movement of glaciers (ice).
- Glaciers erode land by plucking and scraping rocks.
- U-shaped cross-section
- Wide and flat bottom
- Steep and straight sides
- Common in high mountain and cold regions.
Deserts:- A desert is a region that receives very little rainfall (usually less than 25 cm per year). It has dry climate, sparse vegetation, and extreme temperatures. Some example are Sahara Desert (Africa) Largest hot desert in the world and Thar Desert (India).
Formation of Deserts:- Deserts are formed due to various natural factors:
1. Low Rainfall
- Deserts form in areas where rainfall is very low or absent.
- Lack of moisture prevents plant growth and keeps the land dry.
2. Distance from the Sea (Continental Effect)
- Areas located far from oceans do not receive enough moisture-laden winds.
- By the time winds reach these regions, they lose their moisture.
3. Rain Shadow Effect
- When moist winds hit mountains, they drop rain on the windward side.
- The leeward side receives very little rainfall, forming a desert.
- Example: Thar Desert
4. Cold Ocean Currents
- Cold ocean currents cool the air, reducing its ability to hold moisture.
- This leads to dry coastal deserts.
5. High Pressure Areas
- Some regions have high atmospheric pressure, where air sinks and becomes dry.
- This prevents cloud formation and rainfall.
Role of Wind in Deserts:- Wind is the main agent shaping deserts. It removes loose sand and dust through erosion and deposits them elswhere.
Coastal Landforms:- Coastal landforms are features formed along the coastline, where land meets the sea. These landforms are mainly shaped by the action of sea waves, tides, and currents.
Formation of Coastal Landforms:- Coastal landforms are formed by two main processes:
1. Erosion
- Strong sea waves continuously hit the coast and wear away rocks.
- This process breaks down coastal land.
2. Deposition
- Sea waves also deposit sand, pebbles, and sediments along the shore.
- This leads to the formation of new landforms.
Major Features of Coastal Landforms
1. Sea Cliffs
- Steep rocky faces formed due to continuous erosion by waves.
- Waves cut the base of rocks, causing them to collapse.
2. Sea Caves:- Hollow spaces formed inside coastal rocks due to wave erosion.
3. Sea Arches:- Formed when sea caves enlarge and cut through a rock, creating an arch-like structure.
4. Spits:- A spit is a long, narrow ridge of sand or shingle that extends from the coast into the sea. It is formed by the process of deposition by sea waves.
5. Beaches
- Formed by the deposition of sand and pebbles along the shore.
- Popular for tourism and human activities.
6. Sandbars and Lagoons
- Sandbars are ridges of sand formed by wave deposition.
- When water gets trapped behind sandbars, it forms a lagoon.
- Example: Chilika Lake
Landforms and Natural Disasters:- Natural processes that shape landforms can sometimes become natural disasters, causing damage to life and property. Major disasters related to landforms include earthquakes, landslides, avalanches, and GLOF, Dust Stroms.
1. Earthquakes
- Sudden shaking of the Earth’s surface due to movement of tectonic plates.
- Energy is released from inside the Earth, creating seismic waves.
Causes:
- Plate movements
- Volcanic activity
Effects:
- Damage to buildings and infrastructure
- Loss of life
- Changes in landforms (cracks, uplift)
2. Landslides:- Sudden downward movement of rock, soil, and debris on slopes.
Causes:
- Heavy rainfall
- Earthquakes
- Deforestation
- Human activities (construction, mining)
Effects:
- Destruction of roads and houses
- Blocking of rivers
- Loss of life and property
3. Avalanches
- Rapid flow of snow and ice down mountain slopes.
- Common in cold and mountainous regions like the Himalayas
Causes:
- Heavy snowfall
- Sudden temperature changes
- Vibrations or human activity
Effects:
- Burial of people and settlements
- Disruption of transport and communication
4. GLOF (Glacial Lake Outburst Flood):- Sudden release of water from a glacial lake due to the breaking of natural dams (ice or moraine).
Causes:
- Melting of glaciers
- Weak natural dams
- Earthquakes or landslides
Effects:
- Flash floods in downstream areas
- Severe damage to villages, roads, and bridges
Dust Storms:- A dust storm is a strong windstorm that carries large amounts of dust and sand particles over a wide area. It is common in dry and desert regions.
Causes
- Strong winds
- Dry and barren land
- Deforestation and overgrazing
- Drought conditions
Effects
- Health problems (breathing issues, eye irritation)
- Damage to crops and property
- Disruption of transport (road, air)
- Loss of top fertile soil
Importance of Disaster Mitigation:- Disaster mitigation means taking steps before a disaster occurs to reduce its impact on people, property, and the environment. It is very important for safety and development.
1. Identify Disaster-Prone Areas
- Helps in locating areas that are at risk of disasters like earthquakes, floods, or landslides.
- Mapping these areas allows better preparedness and planning.
- Example: Mountain regions prone to landslides or coastal areas prone to cyclones.
2. Reduce Risk Through Planning:- Proper planning can minimize damage caused by disasters.
Includes:
- Safe construction (earthquake-resistant buildings)
- Land-use planning
- Early warning systems
3. Protect Human Life and Property
- Main aim is to save lives and reduce injuries.
- Ensures safety of houses, schools, roads, and infrastructure.
- Quick response and preparedness reduce loss.
4. Promote Sustainable Development
- Encourages development that is safe and long-lasting.
- Avoids construction in risky areas.
- Protects natural resources and environment.
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