Volcanoes and Earthquakes

Volcanoes and Earthquakes (UPSC Geography Notes)

Overview: Volcanoes and earthquakes are among the most powerful natural processes on Earth. Both are caused by the movement of tectonic plates beneath the Earth's surface. Understanding their causes, types, and distribution is crucial for UPSC Geography as they help explain various landforms and natural hazards.

Table of Contents

• 1. Introduction
• 2. Volcanoes – Meaning and Causes
• 3. Structure of a Volcano
• 4. Types of Volcanoes
• 5. Distribution of Volcanoes
• 6. Earthquakes – Meaning and Causes
• 7. Measurement of Earthquakes
• 8. Effects of Earthquakes
• 9. Earthquake Zones of India
• 10. UPSC Quick Revision Notes
• 11. Previous Year Question

1. Introduction

Volcanoes and earthquakes are caused by internal (endogenic) forces acting within the Earth's crust. These forces originate due to heat, pressure, and movement of molten material inside the Earth. They continuously shape the Earth’s surface and influence human settlements and natural landscapes.

2. Volcanoes – Meaning and Causes

A volcano is an opening in the Earth’s crust through which molten material (magma), gases, and ash are ejected onto the surface.

Causes of Volcanic Activity:

• Movement of tectonic plates (especially at convergent and divergent boundaries).
• Melting of rocks due to high temperature and pressure.
• Weak zones in the Earth's crust allowing magma to escape.

3. Structure of a Volcano

• Magma Chamber: Underground pool of molten rock beneath the volcano.
• Vent: Passage through which magma rises to the surface.
• Crater: Opening at the top of the volcano where lava is ejected.
• Lava: Magma that reaches the surface and cools to form new landforms.

4. Types of Volcanoes

Volcanoes are classified based on the nature of eruption and shape:

• 1. Active Volcano: Erupts frequently. Example: Mount Etna (Italy), Mount Stromboli.
• 2. Dormant Volcano: Has not erupted for a long time but may erupt again. Example: Mount Vesuvius, Mount Fuji.
• 3. Extinct Volcano: No longer has the potential to erupt. Example: Mount Kilimanjaro, Aconcagua.

By Shape and Eruption Style:

• Shield Volcano: Gentle slopes, formed by low-viscosity lava. Example: Mauna Loa (Hawaii).
• Composite (Strato) Volcano: Alternating layers of lava and ash. Example: Mount Fuji, Mount St. Helens.
• Cinder Cone Volcano: Small, steep-sided, formed by explosive eruptions. Example: Parícutin (Mexico).
• Caldera: Large crater formed after collapse of the volcanic cone.

5. Distribution of Volcanoes

Volcanoes are mostly found along tectonic plate boundaries. The major volcanic zones are:

• 1. Pacific Ring of Fire: The most active volcanic belt encircling the Pacific Ocean.
• 2. Mid-Atlantic Ridge: Submarine volcanic zone between American and Eurasian/African plates.
• 3. Mediterranean Belt: Extends from the Alps through Iran to the Himalayas.

6. Earthquakes – Meaning and Causes

An earthquake is a sudden shaking or vibration of the Earth’s surface caused by the release of energy stored in rocks beneath the crust.

Causes of Earthquakes:

• Sudden movement along faults or fractures in the Earth's crust.
• Volcanic activity and magma movement.
• Human-induced causes (reservoir-induced, mining, nuclear tests).

7. Measurement of Earthquakes

• Seismograph: Instrument that records the vibrations of the Earth.
• Focus (Hypocenter): The point inside the Earth where the earthquake originates.
• Epicenter: The point on the surface directly above the focus.
• Richter Scale: Measures the magnitude (energy released).
• Mercalli Scale: Measures intensity (damage caused).

8. Effects of Earthquakes

• Primary Effects: Ground shaking, surface rupture, displacement of rocks.
• Secondary Effects: Landslides, tsunamis, fires, changes in groundwater.
• Human Impact: Loss of life, property damage, disruption of infrastructure.

9. Earthquake Zones of India

India is divided into four seismic zones (Zone II to Zone V) based on earthquake intensity:

Zone	Earthquake Risk Level	Example Regions
Zone V	Very High	North-East India, Kashmir, Himachal, parts of Bihar
Zone IV	High	Delhi, Uttarakhand, Punjab, Western Himalayas
Zone III	Moderate	Kerala, Goa, Gujarat, Maharashtra
Zone II	Low	Deccan Plateau, Central India

10. UPSC Quick Revision Notes

Volcano – Opening in Earth's crust emitting lava, gases, and ash.
Types – Active, Dormant, Extinct.
Earthquake – Sudden shaking due to energy release in Earth's crust.
Measured by – Richter Scale (magnitude), Mercalli Scale (intensity).
India’s Highest Risk Zone – Zone V (Northeast & Himalayan belt).
Volcano → Eruption; Earthquake → Shaking.

11. Previous Year Question

Q. The Pacific Ring of Fire is associated with —
(a) Volcanic eruptions and earthquakes
(b) Cyclones and tornadoes
(c) Glacial erosion
(d) Tsunami formation only
Answer: (a) Volcanic eruptions and earthquakes

Related Keywords

Volcanoes UPSC Notes, Earthquakes UPSC Notes, Tectonic Movements, Plate Boundaries, Seismic Zones of India, Ring of Fire, NCERT Geography Class 11 Simplified Notes.

---

Sources: NCERT – Physical Geography, Geological Survey of India, USGS, Britannica