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
- Tectonic Activity: Movement of plates at divergent, convergent, or transform boundaries.
- Volcanic Activity: Magma movement triggers minor quakes near volcanoes.
- Human-Induced: Mining, reservoir-induced seismicity (e.g., dams), fracking.
- Faulting: Normal, reverse, or strike-slip faults release energy.
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
- Ground shaking: Damages buildings, infrastructure.
- Surface rupture: Cracks in land along fault lines.
Secondary Effects
- Tsunamis: Submarine quakes displace ocean water (e.g., 2004 Indian Ocean tsunami).
- Lake Seiche: Earthquake-induced waves in enclosed bodies of water.
- Landslides: Triggered in hilly areas, blocking roads, rivers.
- Fires: Ruptured gas lines or electrical faults ignite fires.
- Liquefaction: Saturated soil loses strength, causing structures to sink.
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:
- Circum-Pacific Belt (Ring of Fire): 80% of quakes, around Pacific, e.g., Japan, Chile.
- Mediterranean-Himalayan Belt: 15% of quakes, includes Alps, Himalayas, Iran.
- Mid-Oceanic Ridges: Minor quakes at divergent boundaries.
- Intra-Plate Regions: Rare but significant, e.g., Peninsular India (Latur, 1993).
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
- Plate Tectonics:
- Convergent Boundaries: Subduction melts crust, forming stratovolcanoes (e.g., Mount Fuji).
- Divergent Boundaries: Magma wells up at mid-ocean ridges (e.g., Iceland).
- Hotspots: Mantle plumes create volcanoes away from plate boundaries (e.g., Hawaiian Islands).
- Rift Zones: Continental rifting allows magma to surface (e.g., East African Rift).
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
- Lava flows: Destroy infrastructure, reshape landscapes.
- Pyroclastic flows: Hot gas and ash clouds, highly destructive.
- Volcanic ash: Disrupts air travel, damages crops.
- Volcanic gases: CO₂, SO₂ affect health, climate.
Secondary Effects
- Lahars: Mudflows from ash and water, devastate valleys.
- Climate Change: Ash and SO₂ block sunlight, causing cooling (e.g., 1815 Tambora eruption).
- Tsunamis: Volcanic collapse or explosions displace water.
Positive Effects
- Fertile soils from ash (e.g., Java).
- Geothermal energy potential.
- Mineral deposits (e.g., sulfur, gold).
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:
- Ring of Fire: 75% of active volcanoes, e.g., Mount Vesuvius, Popocatépetl.
- Mid-Ocean Ridges: Submarine volcanoes, e.g., Mid-Atlantic Ridge.
- Hotspots: Hawaiian Islands, Yellowstone, Réunion.
- Rift Zones: East African Rift, e.g., Mount Kilimanjaro.
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
- Richter Scale: Measures magnitude (energy released), logarithmic.
- Mercalli Scale: Measures intensity (surface effects), I–XII.
- Seismographs: Detect and record seismic waves.
- Monitoring: GPS, tiltmeters track crustal movements.
Volcanoes
- Volcanic Explosivity Index (VEI): Measures eruption size (0–8).
- Monitoring Tools: Seismometers, gas sensors, satellite imagery.
- Warning Systems: Alert levels based on activity (e.g., dormant, active, eruptive).
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:
- Seismic Zones: II (low risk) to V (high risk).
- High-Risk Areas: Himalayas, Northeast, Kutch, Andaman & Nicobar.
- Major Quakes: 2001 Bhuj (7.7), 2005 Kashmir (7.6), 2015 Nepal (7.8, affected India).
Volcanoes
India has few active volcanoes, but notable ones include:
- Barren Island: Andaman & Nicobar, India’s only active volcano (last erupted 2020).
- Deccan Traps: Extinct volcanic activity (65 million years ago), formed basalt plateaus.
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
- Memorize causes (tectonic, volcanic, human-induced) and effects (primary, secondary).
- Focus on global and Indian distribution (Ring of Fire, Himalayas, Barren Island).
- Understand measurement scales (Richter, Mercalli, VEI) and monitoring techniques.
- Link earthquakes and volcanoes to plate tectonics and Earth’s structure.
- Practice map-based questions on seismic zones and volcanic regions.
- Revise key events (2001 Bhuj, 1883 Krakatoa) and terms (focus, epicenter, lahar).