This article will provide you with the Class 11 Geography Chapter 3 Notes. Geography is a very important topic for students in class 11. They need to study it properly. So, I have prepared the handwritten style notes for them, which they can use easily. Interior of the Earth: Important topics and Notes can be helpful for everyone who wants to understand the chapter completely.

Chapter 3 – Interior of the Earth from Fundamentals of Physical Geography.

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Class 11 Geography Chapter 3 Notes

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🌍 Introduction

• Earth looks solid from outside, but inside it is layered (crust, mantle, core).
• We cannot directly reach Earth’s interior → so we use direct & indirect sources.
• Understanding interior is important to explain earthquakes, volcanoes, tsunamis, and landforms.

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Sources of Information about Earth’s Interior

Direct Sources

• Rocks from mining → only up to 3–4 km deep.
• Deep drilling projects → Kola (Russia) drilled ~12 km (deepest).
• Volcanic eruptions → magma/lava gives info about deep materials.

Indirect Sources

• Temperature & pressure → increase with depth.
• Density → increases as we go deeper.
• Meteors → similar composition to Earth.
• Gravity (g) → varies at poles/equator → indicates uneven distribution of mass.
• Magnetic field → tells about materials inside.
• Seismic waves → most important tool to study Earth’s layers.

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Earthquakes

• Definition: Shaking of Earth due to sudden release of energy along faults.
• Focus (Hypocentre): Point inside Earth where energy is released.
• Epicentre: Point on surface directly above focus.
• Seismograph: Instrument recording earthquake waves.

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Types of Earthquake Waves

Type	Nature	Travels through	Speed	Damage
P-waves (Primary)	Longitudinal (push–pull)	Solids, liquids, gases	Fastest	Least damaging
S-waves (Secondary)	Transverse (up–down)	Only solids	Slower than P	Cause crests & troughs
Surface waves	Move along surface	Crust	Slowest	Most destructive

Key Fact: S-waves cannot pass through liquids → proves outer core is liquid.

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Shadow Zone

• Region where no waves are recorded.
• P-wave shadow zone: Between 105°–145° from epicentre.
• S-wave shadow zone: Entire zone beyond 105° (≈40% of Earth’s surface).
• Helps scientists confirm liquid outer core.

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Types of Earthquakes

1. Tectonic → due to plate movement (most common).
2. Volcanic → linked to volcanic activity.
3. Collapse → roof of mines collapse.
4. Explosion → nuclear/chemical blasts.
5. Reservoir-induced → large dams/reservoirs.

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Measuring Earthquakes

• Richter Scale: Measures magnitude (0–10).
• Mercalli Scale: Measures intensity/damage (1–12).

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Effects of Earthquakes

1. Ground shaking.
2. Ground settlement.
3. Landslides, mudslides, avalanches.
4. Soil liquefaction.
5. Ground displacement/faults.
6. Floods (dam failure).
7. Fires, structural collapse.
8. Tsunami (if under ocean).

High magnitude (>5 Richter) → severe destruction.

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Class 11 Geography Chapter 3 MCQ | Interior of The Earth Important MCQ

Structure of the Earth

Crust (Outermost Layer)

• Brittle in nature.
• Thickness:
  • Oceanic: ~5 km (basaltic, denser).
  • Continental: ~30 km (granitic, lighter); up to 70 km in Himalayas.

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Mantle

• Extends from Moho Discontinuity → 2900 km depth.
• Upper Mantle:
  • Includes Asthenosphere (~400 km deep, weak, source of magma).
  • Lithosphere = Crust + Upper mantle (10–200 km thick).
• Lower Mantle: Solid state, extends further down.

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Core

• Begins at 2900 km depth → centre of Earth.
• Outer Core: Liquid (S-waves absent here).
• Inner Core: Solid (due to extreme pressure).
• Composition = Nickel + Iron (NIFE layer).

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Volcanoes

• Definition: Place where magma, gases, ash escape to surface.
• Active volcano: Currently erupting/recent past.
• Dormant: Sleeping, may erupt again.
• Extinct: No eruption in past & unlikely to erupt again.

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Types of Volcanoes

Type	Features	Example
Shield Volcanoes	Largest, gentle slopes, fluid lava (basaltic), non-explosive unless water enters.	Hawaiian Volcanoes
Composite Volcanoes	Alternating layers of lava & ash, viscous lava, often explosive.	Mt. Fuji (Japan)
Caldera Volcanoes	Very explosive, collapse after eruption → large depression (caldera).	Krakatoa (Indonesia)
Flood Basalt Provinces	Fluid lava spreads over vast areas → flat plateaus.	Deccan Traps (India)
Mid-Ocean Ridge Volcanoes	Found along mid-ocean ridges (70,000 km long system).	Mid-Atlantic Ridge

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Volcanic Landforms

A) Extrusive (formed on surface)

• Lava plains
• Volcanic cones (cinder cone, shield cone, composite cone).

B) Intrusive (formed inside crust, solidified magma)

Intrusive Form	Description	Example
Batholith	Huge cooled magma chambers, granitic, several km deep.	Himalayas (granite bodies)
Lacolith	Dome-shaped with flat base, source of lava.	Karnataka domal hills
Lapolith	Saucer-shaped concave intrusive mass.	–
Phacolith	Wavy masses along folds (anticline/syncline).	–
Sills	Horizontal sheet-like intrusions.	Deccan area
Dykes	Vertical wall-like intrusions, feeders for lava.	Western Maharashtra

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Table: Layers of the Earth

Layer	Depth	State	Composition
Crust	5–70 km	Solid	Basalt (oceanic), Granite (continental)
Mantle	70–2900 km	Solid (upper weak zone)	Silicate minerals
Outer Core	2900–5100 km	Liquid	Nickel, Iron
Inner Core	5100–6378 km	Solid	Nickel, Iron

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📌 Key Points to Remember

• Direct sources: mining, drilling, volcanoes.
• Indirect sources: seismic waves (most important), gravity, magnetic surveys, meteors.
• Earthquake focus = hypocentre; surface point = epicentre.
• P-waves → fastest, travel through solids & liquids.
• S-waves → only solids.
• Surface waves → slowest, most destructive.
• Shadow zones proved Earth’s liquid outer core.
• Earth has three main layers: Crust, Mantle, Core.
• Volcanoes are of different types → Shield, Composite, Caldera, Flood Basalt, Mid-Ocean ridge.
• Intrusive forms include Batholiths, Lacoliths, Sills, Dykes, etc.
• Understanding Earth’s interior = important for disaster management & sustainable living.

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