Volcanoes and Earthquakes – Causes and Effects
Delhi Police & SSC Exams
1. Introduction
The Earth's interior is dynamic — constantly moving and changing due to internal heat. This leads to volcanic eruptions and earthquakes, two of the most powerful natural phenomena on our planet.
Key Concepts:
- Volcanic processes and types
- Earthquake mechanisms and measurement
- Geographical distribution patterns
- Safety measures and impacts
Memory Tricks:
Volcano = Fire from Earth's belly
Earthquake = Earth's sudden shake
2. What Is a Volcano?
Definition:
A volcano is an opening or vent in the Earth's crust through which molten rock (magma), gases, and ash come out.
Important: When magma reaches the surface, it is called lava.
Volcano Structure:
Cone (built by lava & ash)
Crater (Opening at top)
Vent (Passage for magma)
Magma Chamber (source of molten rock)
3. Types of Volcanoes
| Type | Description | Example |
|---|---|---|
| Active | Erupts regularly | Mt. Etna (Italy), Stromboli |
| Dormant | "Sleeping" — hasn't erupted for long but can erupt again | Mt. Vesuvius, Mt. Fuji |
| Extinct | No eruption in recorded history | Mt. Popa (Myanmar) |
Exam Trick: "ADE → Active, Dormant, Extinct"
4. Types of Volcanic Eruptions
| Type | Description | Example |
|---|---|---|
| Effusive | Gentle lava flow | Hawaiian volcanoes |
| Explosive | Violent eruptions with ash & gases | Krakatoa (Indonesia) |
5. Distribution of Volcanoes
Major Volcanic Zones:
- "Ring of Fire" → Pacific Ocean belt (most active volcanic region on Earth)
- Mediterranean Belt
- Mid-Atlantic Ridge
Key Facts:
Most volcanoes occur in specific zones due to plate movements
Exam Trick: "Pacific = Fire Ring Zone"
6. Effects of Volcanoes
Positive Effects:
New fertile soil (lava ash contains minerals)
Geothermal energy source
New land formation (e.g., Hawaii Islands)
Negative Effects:
Destruction of life & property
Air pollution from gases
Tsunamis (if undersea eruption)
7. What Is an Earthquake?
Definition:
An earthquake is a sudden shaking or vibration of the Earth's surface caused by the release of energy in the Earth's crust.
Memory Trick: "Slip → Shock → Shake"
Causes of Earthquakes:
- Plate movements (main cause)
- Volcanic eruptions
- Faulting and folding
- Human activities (dams, mining, nuclear tests)
8. Key Earthquake Terms
| Term | Meaning |
|---|---|
| Focus (Hypocenter) | Point inside Earth where earthquake originates |
| Epicenter | Point directly above the focus on Earth's surface |
| Seismograph | Instrument that records earthquake waves |
| Richter Scale | Measures earthquake magnitude (0–9+) |
| Seismic Waves | Waves generated during an earthquake |
9. Major Earthquake Zones in India
| Zone | Risk Level | Example Areas |
|---|---|---|
| Zone V | Very High | NE states, Kashmir, Himachal, Bihar |
| Zone IV | High | Delhi, Gujarat, Uttarakhand |
| Zone III | Moderate | Maharashtra, MP |
| Zone II | Low | Karnataka, TN |
Important: India's most earthquake-prone region: Himalayan belt
10. Effects of Earthquakes
Positive Effects:
Changes Earth's surface (uplift, new landforms)
Discovery of underground minerals
Negative Effects:
Building collapse, loss of life
Tsunamis and landslides
Fire & infrastructure damage
11. Safety Measures During an Earthquake
Do's:
Stay away from windows and heavy objects
Take shelter under a sturdy table
Move to open space if possible
Don'ts:
Do not use elevators
Do not run during shaking
Do not stand near buildings or trees
Exam Trick: "DROP – COVER – HOLD"
12. Quick Comparison – Volcano vs Earthquake
| Feature | Volcano | Earthquake |
|---|---|---|
| Origin | Magma eruption | Sudden crust movement |
| Occurrence | At weak crustal points | Along faults & plate boundaries |
| Measurement | VEI (Volcanic Explosivity Index) | Richter Scale |
| Predictability | Sometimes possible | Difficult |
| Effect | Lava flow, ash | Shaking, tsunamis |
PYQs (Delhi Police, SSC & State Exams)
Which of the following is the main cause of earthquakes?
Options: (a) Rainfall (b) Tectonic movement (c) Wind (d) Ocean currents
Category: Earthquake Causes
Show Answer
b) Tectonic movement
The point inside the Earth where an earthquake originates is called —
Options: (a) Epicenter (b) Focus (c) Seismic point (d) Richter point
Category: Earthquake Terminology
Show Answer
b) Focus
The instrument used to measure earthquakes is —
Options: (a) Thermometer (b) Seismograph (c) Barometer (d) Anemometer
Category: Earthquake Instruments
Show Answer
b) Seismograph
The magnitude of earthquakes is measured on which scale?
Options: (a) Celsius Scale (b) Richter Scale (c) Kelvin Scale (d) Centigrade Scale
Category: Earthquake Measurement
Show Answer
b) Richter Scale
The "Ring of Fire" is located around —
Options: (a) Atlantic Ocean (b) Indian Ocean (c) Pacific Ocean (d) Arctic Ocean
Category: Volcanic Zones
Show Answer
c) Pacific Ocean
Which of the following is not a type of volcano?
Options: (a) Active (b) Dormant (c) Extinct (d) Magnetic
Category: Volcano Types
Show Answer
d) Magnetic
Which region of India is most prone to earthquakes?
Options: (a) Indo-Gangetic Plain (b) Peninsular Plateau (c) Himalayan Region (d) Coastal Plains
Category: Indian Geography
Show Answer
c) Himalayan Region
Which of the following pairs is correctly matched?
Options: (a) Earthquake – Richter Scale (b) Temperature – Seismograph (c) Pressure – Barometer (d) Both (a) and (c)
Category: Instruments & Measurement
Show Answer
d) Both (a) and (c)
Final Exam Tips
Volcano = lava, gases, cone
Earthquake = focus, epicenter, seismic waves
Richter Scale & Seismograph = guaranteed 1 mark question
"Ring of Fire" → Pacific Ocean
India's major earthquake zone = Himalayas (Zone V)
Trick to remember Earthquake Sequence: "Stress → Break → Shock → Waves → Damage"
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