Fundamentals of Physical Geography

Interior of the Earth Notes

Interior of the Earth Class 11 Geography Notes

These Interior of the Earth Class 11 Notes explain the structure, composition and processes occurring inside the Earth. The chapter discusses sources of information about Earth’s interior, earthquakes, seismic waves, shadow zones, volcanoes and volcanic landforms in detail.

These notes are useful for UPSC, SSC, Railways, State PSC, CUET, CBSE Board Exams and other competitive examinations because earthquakes, seismic waves, Earth structure and volcanoes are among the most important topics in Physical Geography and Geology.

NCERT Pages: 18–26

Table of Contents

Chapter Overview

NCERT Pages: 18–26

This chapter explains how scientists study the Earth’s interior through direct and indirect sources. It discusses earthquakes, seismic waves, Earth’s layers, volcanoes and volcanic landforms. It also explains intrusive volcanic forms such as batholiths, lacoliths, sills and dykes.

Major Topics Covered

  • Interior of the Earth
  • Direct and indirect sources of information
  • Earthquakes
  • Seismic waves
  • Shadow zones
  • Structure of Earth
  • Crust, mantle and core
  • Volcanoes
  • Volcanic landforms
  • Intrusive forms

Sources of Information About the Interior

NCERT Pages: 18–19

These notes explain how scientists gather information about Earth’s interior.

Sources of Information

Earth’s radius is approximately 6,378 km, making direct observation of the interior impossible.

Two Main Sources

Source Type Examples
Direct Sources Mining, drilling, volcanic eruptions
Indirect Sources Seismic waves, gravity, magnetic field

Direct Sources of Information

NCERT Page: 18

Major Direct Sources

  • Mining activities
  • Deep drilling projects
  • Volcanic eruptions

Important Projects

Project Significance
Deep Ocean Drilling Project Exploration of crust
Integrated Ocean Drilling Project Oceanic crust studies
Kola Drilling Reached depth of 12 km
Important Fact: Volcanic eruptions bring magma to the surface for laboratory analysis.

Indirect Sources of Information

NCERT Page: 19

Major Indirect Sources

  • Temperature and pressure changes
  • Density variations
  • Meteor studies
  • Gravitation
  • Magnetic field
  • Seismic activity

Gravity Anomaly

  • Difference between expected and actual gravity values.
  • Helps determine distribution of materials inside Earth.

Earthquake

NCERT Page: 19

  • Sudden shaking of Earth due to release of energy.
  • Energy released along faults.

Important Terms

Term Meaning
Fault Break in crustal rocks
Focus/Hypocentre Point of energy release
Epicentre Point on surface directly above focus

Earthquake Waves

NCERT Pages: 19–20

Types of Earthquake Waves

Type Characteristics
Body Waves Travel through Earth’s interior
Surface Waves Travel along Earth’s surface

P-Waves (Primary Waves)

  • Fastest seismic waves
  • Reach first at surface
  • Travel through solids, liquids and gases

S-Waves (Secondary Waves)

  • Travel only through solids
  • Produce crests and troughs
  • Help identify liquid outer core

Surface Waves

  • Most destructive earthquake waves
  • Cause ground displacement and collapse of structures

Shadow Zone

NCERT Pages: 20–21

Shadow zones are areas where seismic waves are not recorded.

Wave Shadow Zone
P-Waves 105°–145°
S-Waves Beyond 105°
Importance: Proves outer core is liquid.

Structure of the Earth

NCERT Pages: 22–23

Layer Characteristics
Crust Outermost solid layer
Mantle Extends to 2,900 km
Core Innermost layer

Crust

  • Outermost solid layer
  • Brittle in nature
Region Thickness
Oceanic crust 5 km
Continental crust 30 km
Himalayan region Up to 70 km

Mantle

  • Extends from Moho discontinuity to 2,900 km depth
  • Asthenosphere is weak upper mantle zone
  • Main source of magma

Core

Part State
Outer Core Liquid
Inner Core Solid
  • Core mainly composed of Nickel and Iron
  • Called Nife layer

Volcanoes

NCERT Page: 23

  • Openings through which lava, gases and ash escape.
Term Meaning
Magma Molten material inside Earth
Lava Magma reaching surface

Types of Volcanoes

NCERT Pages: 23–24

Shield Volcanoes

  • Largest volcanoes
  • Mostly basaltic lava
  • Low explosivity
  • Example: Hawaiian volcanoes

Composite Volcanoes

  • Viscous lava
  • Explosive eruptions
  • Layers of lava and ash

Calderas

  • Explosive volcanoes collapse inward
  • Form large depressions

Flood Basalt Provinces

  • Fluid lava spreads over huge areas
  • Example: Deccan Traps

Volcanic Landforms

NCERT Pages: 24–25

Intrusive Forms

Intrusive forms develop when lava cools inside the crust.

Intrusive Form Characteristics
Batholith Large dome-shaped body
Lacolith Dome-shaped intrusive body
Lapolith Saucer-shaped body
Phacolith Wavy intrusive mass
Sill Horizontal sheet
Dyke Vertical wall-like intrusion

Batholiths

  • Large granitic intrusive bodies
  • Exposed after denudation

Lacoliths

  • Dome-shaped intrusive bodies
  • Connected by pipe-like conduits
  • Example: Granite domes of Karnataka Plateau

Dykes

  • Vertical wall-like intrusive forms
  • Common in Maharashtra region

Important Topics

Important Topic NCERT Page
Sources of Earth interior 18–19
Earthquakes 19
Seismic waves 19–20
Shadow zones 20–21
Structure of Earth 22–23
Volcanoes 23–24

Important Concepts and Terms

Concept Explanation NCERT Page
Focus Point of energy release 19
Epicentre Point above focus 19
P-Waves Primary waves 20
S-Waves Secondary waves 20
Lithosphere Crust + upper mantle 23
Nife Layer Nickel + Iron core 23

Important Questions

Very Short Answer Questions

  1. What is an earthquake? (NCERT Page 19)
  2. Define focus and epicentre. (NCERT Page 19)
  3. What are body waves? (NCERT Page 20)
  4. What are P-waves? (NCERT Page 20)
  5. What are S-waves? (NCERT Page 20)
  6. What is shadow zone? (NCERT Pages 20–21)
  7. What is lithosphere? (NCERT Page 23)
  8. What is magma? (NCERT Page 23)
  9. What are dykes? (NCERT Page 25)

Short Answer Questions

  1. Explain direct sources of information about Earth’s interior. (NCERT Page 18)
  2. Explain indirect sources of information. (NCERT Page 19)
  3. Describe earthquake waves. (NCERT Pages 19–20)
  4. Explain shadow zones. (NCERT Pages 20–21)
  5. Describe structure of Earth. (NCERT Pages 22–23)
  6. Explain types of volcanoes. (NCERT Pages 23–24)
  7. Describe intrusive volcanic forms. (NCERT Pages 24–25)

Long Answer Questions

  1. Explain sources of information about Earth’s interior. (NCERT Pages 18–19)
  2. Describe propagation of earthquake waves. (NCERT Page 20)
  3. Explain effects of earthquakes. (NCERT Page 21)
  4. Discuss structure of Earth. (NCERT Pages 22–23)
  5. Describe types of volcanoes and volcanic landforms. (NCERT Pages 23–25)

FAQs

1. What are seismic waves?

Seismic waves are energy waves generated during earthquakes. (NCERT Pages 19–20)

2. Why are S-waves important?

S-waves travel only through solids and help identify liquid outer core. (NCERT Page 20)

3. What is lithosphere?

Lithosphere consists of crust and uppermost mantle. (NCERT Page 23)

4. What is the Nife layer?

Core composed mainly of nickel and iron is called Nife layer. (NCERT Page 23)

5. What formed the Deccan Traps?

Flood basalt eruptions formed the Deccan Traps. (NCERT Page 24)

Quick Revision Summary

  • Earth’s radius is about 6,378 km.
  • Direct sources include mining and drilling.
  • Gravity anomaly helps study Earth’s interior.
  • Earthquake energy released at focus.
  • Epicentre lies above focus.
  • P-waves travel through solids, liquids and gases.
  • S-waves travel only through solids.
  • Surface waves are most destructive.
  • Richter scale measures magnitude.
  • Mercalli scale measures intensity.
  • Oceanic crust is thinner than continental crust.
  • Mantle extends to 2,900 km depth.
  • Outer core is liquid; inner core is solid.
  • Lithosphere = crust + upper mantle.
  • Deccan Traps formed due to flood basalt eruptions.
  • Dykes are vertical intrusive structures.
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