🎓 Class 11 – Geography
📘 Chapter 3: Interior of the Earth
📚 Book: Fundamentals of Physical Geography
📅 Session: 2025–26
👨🏫 Presented by: Amresh kumar
🌍 Earth – The Unique Planet
🪐 Earth is the only planet in the solar system where life exists 🌱.
and is also known as the Blue Planet 🌊
because about 71% of its surface
is covered with water.
🌎 Internal Structure of the Earth (पृथ्वी की आंतरिक संरचना)
To understand what lies inside the Earth, we study two types of sources:
🔹 1. Direct Sources (प्रत्यक्ष स्रोत):
These are the actual things we can touch or study directly, such as:
•Materials from mining (खनन)
•Lava and gases from volcanic eruptions 🌋
➡️ These give real evidence about Earth’s interior.
🔸 2. Indirect Sources (अप्रत्यक्ष स्रोत):
These are the observations and effects that give us clues about Earth’s inner layers:
🌡️ Variation in temperature, pressure, and density (तापमान, दबाव और घनत्व में अंतर)
☄️ Meteorites (उल्कापिंड) – They come from space and resemble Earth’s deep interior.
🧲 Gravity (गुरुत्वाकर्षण) – Helps measure Earth’s shape and material.
🌍 Earthquake-related activities (भूकंप से जुड़ी घटनाएं)
🌐 Seismic Waves (भूकंपीय तरंगे):
Seismic waves are waves produced during earthquakes and help us understand Earth’s interior. There are two main types:
•Primary Waves (P-Waves) ➡️ Travel fastest
•Secondary Waves (S-Waves) ➡️ Slower, can't pass through liquid
🧠 These waves help scientists map the three main layers of Earth:
1.Crust (भूपर्पटी)
2.Mantle (मांटल)
3.Core (कोर)
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🌋 Volcanoes and Landforms
This chapter also helps us understand how volcanoes form landforms like mountains and islands by bringing out molten material (पिघला हुआ पदार्थ) from deep inside the Earth.
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🌍 Layers of the Earth's Internal Structure (पृथ्वी की आंतरिक संरचना की परतें)
The Earth’s interior is divided into three main layers:
🟤 1. Crust (भूपर्पटी)
Outermost layer of the Earth 🌐
Depth: ~30 km
Density: ~3 g/cm³ (घनत्व)
Made of solid rocks 🪨
🟠 2. Mantle (मेटल)
Found below the crust
Extends up to 2900 km deep
Upper Mantle + Crust = Lithosphere 🌎
Lower Mantle is in solid state
Density: ~3.4 g/cm³
🔴 3. Core (कोर)
•Located beneath the mantle
•Divided into:
•Outer Core – Liquid (द्रव अवस्था)
•Inner Core – Solid (ठोस अवस्था)
•Density: ~13 g/cm³
•Made of Nickel and Iron (निकेल और लोहा)
🪨 Parts of the Earth's Crust (पृथ्वी की भूपर्पटी के भाग)
The Earth’s crust is the outermost layer and extends up to about
30 km below the surface.
It is divided into two main parts:
🟤 a) Continental Crust or Sial
(महाद्वीपीय भूपर्पटी / सियाल)
Thickness: ~20 km
Made of silicate (सिलिकेट) and aluminium
Called Sial → Si = Silica, Al = Aluminium
Lighter in weight (density is low)
Found under continents 🌍
📌 So, Sial = Light Continental Layer | Sima = Heavy Oceanic Layer
🌍 Earthquake – A Natural Disaster (भूकंप – एक प्राकृतिक आपदा)
💥 Major Effects of Earthquakes
(भूकंप से होने वाले प्रभाव)
🌍 Land Shaking (ज़मीन का हिलना)
🌀 Ground Motion (धरातल का कंपन)
🏔️ Landslide / Mudslide (भूस्खलन / कीचड़ धंसकना)
💧 Soil Liquefaction (मिट्टी का तरल बन जाना)
🛤️ Surface Displacement (धरातल का खिसकना)
❄️ Avalanche (हिमस्खलन)
🌊 Floods due to Dam Breaks (बांध टूटने से बाढ़ आना)
🔥 Fire Ignition (आग लगना)
🏚️ Building Collapse (इमारतों का गिरना)
🌊 Tsunami Waves (सुनामी तरंगें उठना)
🪨 Falling Objects (वस्तुओं का गिरना)
📉 Ground Tilting (ज़मीन का एक तरफ झुक जाना)
🌍 Why Does the Earth Vibrate During an Earthquake? (पृथ्वी में कंपन क्यों होता है?)
🪨 Deep inside the Earth, there are fault lines (भ्रंश रेखाएं) — where rock blocks on either side try to move in opposite directions.
💥 What Happens Next?
💨 A huge amount of energy is released
🌊 This energy travels as seismic waves (भूकंपीय तरंगे)
📉 These waves cause the Earth to vibrate — what we feel as an earthquake
📌 In short: Rock pressure → Friction fails → Sudden slip → Energy release → Earth shakes 🌍⚡
Main Types of Earthquakes (Part 1) (भूकंप के मुख्य प्रकार )
📌 Earthquakes are classified into five types based on their origin (उत्पत्ति के आधार पर):
🌍 1. Tectonic Earthquake
Most common type of earthquake
Caused by movement of rocks along fault lines (भ्रंश रेखा)
Occurs when continental or oceanic plates (महाद्वीपीय या महासागरीय प्लेटें)
👉 Collide with each other
👉 Or move away from each other
Example: Earthquakes in the Himalayan region
🌋 2. Volcanic Earthquake
A special type of tectonic earthquake
Occurs in active volcanic regions (सक्रिय ज्वालामुखीय क्षेत्र)
Caused due to magma movement and volcanic eruptions
🧠 These earthquakes are mostly natural and result from movements deep inside the Earth.
💥 Main Types of Earthquakes (Part 2) (भूकंप के मुख्य प्रकार)
🕳️ 3. Collapse Earthquake
•Happens in mining areas (खनन क्षेत्र)
•Caused by collapse of underground mine roofs
•Mild tremors felt on the surface
•Also called Fall Earthquakes (गिरावट वाले भूकंप)
•
💣 4. Explosion Earthquake
Caused by man-made explosions like:
Nuclear blasts (परमाणु विस्फोट)
Chemical explosions
Ground shakes due to shockwaves created
by the blast
🚧 5. Reservoir Induced Earthquake
Occurs in areas with large dams (बड़े बांधों वाले क्षेत्र)
Water pressure and weight of reservoir can trigger tremors Also called Dam Induced Earthquakes
•📌 So, not all earthquakes are natural – some are human-induced too! 🧨🌍
🌍 Types of Seismic Waves – Part 1 (भूकंपीय तरंगों के प्रकार)
🌀 1. Geologic Waves
🔹 A. P-Waves (Primary Waves)
Like a spring being stretched and released
Travel through solids, liquids, and gases
Fastest waves, reach first
Cause vibration in the same direction as wave
motion
🔸 B. S-Waves (Secondary Waves)
Like a rope twitching
Travel only through solids
Arrive after P-waves
Cause vibration at right angles to the direction of travel
🎯 P-waves = Pressure | S-waves = Shake | Both = Geologic Waves
Types of Seismic Waves – Part 2 (भूकंपीय तरंगों के प्रकार)
🌊 2. Surface Waves (सतही तरंगें)
Also called Ground Waves (भूमिगत तरंगें)
⚠️ Key Characteristics of Surface Waves
Slowest to arrive
Most destructive – cause heavy damage to buildings, dams, roads etc.
Velocity changes when passing through materials of different densities.
Cause effects like:
🏚️ Building collapse
🌊 Dam breaks
📉 Ground sinking
📌 These waves are recorded last on a seismograph but cause the most destruction on the surface.
📊 Difference Between Primary Waves (P-Waves) and Secondary Waves (S-Waves)
📌 P-Waves = Fast + All Mediums | S-Waves = Slow + Only Solids
🌍 Seismic Shadow Zones (भूकंपीय छाया क्षेत्र)
🔎 Key Observations:
'P' and 'S' waves are clearly recorded up to 105° from the epicenter (भूकंप केंद्र).
From 105° to 145°, no waves are recorded — this is the shadow zone for both P and S waves.
After 145°, only P-waves are recorded.
S-waves disappear completely beyond 105°, so they have a larger shadow zone.
📌 Why this happens?
•P-waves bend (refract) but still pass through
•S-waves get blocked (as they can't travel through liquid)
📊 Comparison Table: P-Waves vs S-Waves Shadow Zone
📊 Difference Between Batholith and Lacolith
What is a Volcano? (ज्वालामुखी क्या होता है?)
A Volcano is a sudden natural event (प्राकृतिक घटना) in which:
⚡ Lava, gas, ash, smoke, pebbles, and rocks burst out from within the Earth.
📤 All these materials escape through a natural tube called the vent or drain channel (निकासी नली).
🕳️ The opening through which lava comes out is called a crater (मुख या ज्वालामुखी मुख).
📌 Volcano = Lava explosion from Earth's crust due to internal pressure
Types of Volcanoes (ज्वालामुखी के प्रकार)
Volcanoes are classified into three main types:
🔥 1. Active Volcano (सक्रिय ज्वालामुखी)
Frequently erupts
Mouth always open
Example: Mount Etna, Italy
🌡️ 2. Dormant Volcano (सुप्त ज्वालामुखी)
Has not erupted for a long time, but can become active anytime
Sudden eruption can cause huge damage
Example: Mount Vesuvius, Italy
❄️ 3. Extinct Volcano (निष्क्रिय ज्वालामुखी)
No activity for a long time
No chance of future eruption
Example: Mount Popa, Myanmar
📌 Active = Erupting | Dormant = Sleeping | Extinct = Dead 🌋🛌💀
🌋 Volcanic Landforms: Caldera & Cinder Cone (ज्वालामुखी से बनी आकृतियाँ)
🔴 1. Caldera (कैलडेरा)
•Formed during very explosive volcanic eruptions 💥
•Instead of building a high mountain, the top part of the volcano blasts off
•This creates a large, bowl-shaped crater (गहरा कटोरे जैसा गड्ढा)
•This crater is called a Caldera
📌 Caldera = Huge crater formed after explosion
🟤 2. Cinder Cone (सिंडर कोन) (Commonly mistaken as “Cinderella”)
Formed during less explosive eruptions
Lava flows out like a fountain (फव्वारे की तरह) from the vent
The lava cools down and piles up near the opening
It forms a cone-shaped hill made of ash and small rocks — called a Cinder Cone
📌 Cinder Cone = Cone of lava fragments formed by mild eruption
🎯 In short: Explosion = Caldera 💥 | Fountain lava = Cinder Cone ⛰️
🌋 Intrusive Volcanic Landforms (अन्तःस्थ ज्वालामुखीय आकृतियाँ)
These landforms are created when lava cools and solidifies inside the Earth
Let’s look at the major types:
🧱 1. Sill and Sheet (सिल और शीट)
When lava spreads and cools horizontally (क्षैतिज रूप से) inside the Earth's layers:
If the layer is thick ➡️ it's called a Sill (सिल)
If the layer is thin ➡️ it's called a Sheet (शीट)
📌 Both are formed parallel to the rock layers
🧩 2. Dyke (डाइक)
Lava enters a vertical crack (ऊर्ध्वाधर दरार) and cools down
It cuts across rock layers at right angles (समकोण पर)
This forms a wall-like structure called a Dyke
📌 Dykes are perpendicular (लंबवत) to rock layers
🧠 Sill/Sheet = Horizontal layers | Dyke = Vertical wall of cooled lava
🚀 Keep Learning, Keep Growing! See you next time! 👋
