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Earthquakes and Volcanoes for UPSC Prelims

1. Introduction to Earthquakes and Volcanoes

Earthquakes and volcanoes are dynamic geological phenomena driven by Earth’s internal processes, primarily plate tectonics. Earthquakes result from sudden energy release in the Earth’s crust, causing ground shaking, while volcanoes involve the eruption of magma, ash, and gases from beneath the surface. Both have significant impacts on human life, landscapes, and economies, making them critical topics for UPSC Prelims in physical geography.

Key Facts

  • Primary Cause: Plate tectonics and internal heat
  • Global Impact: Millions affected annually by seismic and volcanic events
  • Measurement Tools: Richter scale, Mercalli scale (earthquakes); Volcanic Explosivity Index (volcanoes)
  • Significance: Shapes topography, influences climate, poses hazards

Important Facts for UPSC

  • Most earthquakes and volcanoes occur along plate boundaries, e.g., Ring of Fire.
  • India lies in seismic zones II–V, with the Himalayas being highly prone to earthquakes.
  • Volcanic eruptions can cause global cooling by releasing ash into the stratosphere.

2. Causes of Earthquakes

Overview

Earthquakes occur due to the sudden release of energy along faults in the Earth’s crust, primarily caused by tectonic plate movements. Stress accumulates until it exceeds the strength of rocks, leading to a rupture.

Key Causes

Mechanism

The elastic rebound theory explains how rocks deform, snap back, and release energy, causing seismic waves (P, S, and surface waves).

Important Facts for UPSC

  • The focus (hypocenter) is the point of energy release; the epicenter is directly above on the surface.
  • Convergent boundaries (e.g., Himalayas) produce the most severe earthquakes.
  • Reservoir-induced seismicity, e.g., Koyna Dam (1967), is a human-induced quake.

3. Effects of Earthquakes

Primary Effects

Secondary Effects

Socioeconomic Impacts

Loss of life, property damage, economic disruption, and displacement of populations.

Important Facts for UPSC

  • The 2001 Bhuj earthquake (7.7 magnitude) killed over 20,000 in Gujarat.
  • Tsunamis can travel at 800 km/hr, causing widespread coastal devastation.
  • Liquefaction caused significant damage in the 2011 Japan earthquake.

4. Distribution of Earthquakes

Global Distribution

Earthquakes are concentrated along plate boundaries:

Factors Influencing Distribution

Plate boundaries, fault zones, and geological stability determine quake-prone areas.

Important Facts for UPSC

  • The Ring of Fire includes Japan, Indonesia, and the west coast of the Americas.
  • Himalayas are seismically active due to India’s collision with the Eurasian Plate.
  • Intra quakes occur in stable regions due to ancient faults.

5. Causes of Volcanoes

Overview

Volcanoes form where magma rises to the surface due to heat and pressure from Earth’s mantle, often at plate boundaries or hotspots.

Key Causes

Mechanism

Magma, less dense than surrounding rock, rises through cracks, erupting as lava, ash, or gases.

Important Facts for UPSC

  • Subduction zones produce explosive stratovolcanoes due to viscous magma.
  • Hotspot volcanoes form island chains as plates move over fixed plumes.
  • Magma composition (silica content) determines eruption style (explosive vs. effusive).

6. Effects of Volcanoes

Primary Effects

Secondary Effects

Positive Effects

Important Facts for UPSC

  • The 1883 Krakatoa eruption caused a global temperature drop of 1.2°C.
  • Lahars killed thousands during the 1985 Nevado del Ruiz eruption.
  • Volcanic soils support agriculture in regions like Indonesia.

7. Distribution of Volcanoes

Global Distribution

Volcanoes are primarily located along plate boundaries and hotspots:

Factors Influencing Distribution

Magma availability, tectonic activity, and crustal thickness determine volcanic zones.

Important Facts for UPSC

  • Over 1,500 active volcanoes exist globally, with 50–70 erupting annually.
  • Indonesia has the most volcanoes, including Krakatoa and Merapi.
  • Yellowstone is a supervolcano, with potential for catastrophic eruptions.

8. Measurement and Monitoring

Earthquakes

Volcanoes

Important Facts for UPSC

  • A magnitude 7 quake releases 32 times more energy than a magnitude 6.
  • VEI 8 eruptions (e.g., Toba, 74,000 years ago) can cause global climate shifts.
  • India’s NDMA uses seismic zoning maps for disaster planning.

9. Earthquakes and Volcanoes in India

Earthquakes

India is prone to earthquakes due to its position on the Indian Plate, colliding with the Eurasian Plate:

Volcanoes

India has few active volcanoes, but notable ones include:

Important Facts for UPSC

  • 60% of India’s landmass is earthquake-prone (Zones III–V).
  • Barren Island is part of a subduction zone in the Andaman Sea.
  • Deccan Traps volcanism is linked to dinosaur extinction.

10. Significance for Geography

Geological Significance

Earthquakes and volcanoes shape Earth’s surface, creating mountains, islands, and plateaus, and recycling crustal materials.

Environmental Significance

Volcanic eruptions influence climate, while earthquakes trigger tsunamis and landslides, impacting ecosystems.

Socioeconomic Significance

Both pose hazards, necessitating disaster preparedness, but also provide resources (fertile soils, minerals, geothermal energy).

UPSC Relevance

This topic connects to geomorphology, disaster management, and Indian geography, frequently tested in Prelims.

Important Facts for UPSC

  • India’s National Earthquake Risk Mitigation Project aims to reduce seismic vulnerability.
  • Volcanic ash improves soil fertility but disrupts aviation (e.g., 2010 Eyjafjallajökull).
  • Seismic zoning and building codes are critical for India’s urban planning.

UPSC Preparation Tips

  1. Memorize causes (tectonic, volcanic, human-induced) and effects (primary, secondary).
  2. Focus on global and Indian distribution (Ring of Fire, Himalayas, Barren Island).
  3. Understand measurement scales (Richter, Mercalli, VEI) and monitoring techniques.
  4. Link earthquakes and volcanoes to plate tectonics and Earth’s structure.
  5. Practice map-based questions on seismic zones and volcanic regions.
  6. Revise key events (2001 Bhuj, 1883 Krakatoa) and terms (focus, epicenter, lahar).