Earthquakes and Volcanoes for UPSC – Complete Notes with PYQs (भूकंप और ज्वालामुखी)

🔥 What is an Earthquake?

An earthquake is the sudden release of energy in the Earth’s lithosphere that creates seismic waves. These are recorded by a seismograph.

🔸 Causes of Earthquakes

• Tectonic movements (major cause)
• Volcanic activity
• Anthropogenic causes (like mining, reservoir-induced)
• Fault slippage

🔸 Types of Earthquakes

1. Tectonic Earthquakes – due to movement of plates
2. Volcanic Earthquakes – associated with volcanic activity
3. Collapse Earthquakes – due to land subsidence or mines
4. Explosion Earthquakes – nuclear or chemical explosions

🔸 Seismic Waves

• P-Waves (Primary Waves): Fastest, travel through solids and liquids
• S-Waves (Secondary Waves): Slower, travel through solids only
• Surface Waves: Cause most destruction

🌋 What is a Volcano?

A volcano is a vent or opening in the Earth’s crust from which molten magma, ash, and gases are ejected.

🔸 Types of Volcanoes

1. Shield Volcanoes – gentle slopes, basaltic lava (e.g., Mauna Loa)
2. Composite Volcanoes – layered lava and ash (e.g., Mount Fuji)
3. Cinder Cone Volcanoes – steep and explosive
4. Caldera – large depression after a major eruption

🔸 Distribution of Volcanoes

Most volcanoes are located in:

• Ring of Fire (Pacific Ocean)
• Mid-Atlantic Ridge
• African Rift Valley

🌍 Plate Tectonics and Their Role

Both earthquakes and volcanoes are directly linked to plate tectonics.

• Convergent Boundaries – subduction causes earthquakes & volcanoes
• Divergent Boundaries – magma rises, causes volcanoes
• Transform Boundaries – intense earthquakes (e.g., San Andreas Fault)

🇮🇳 Earthquakes and Volcanoes in India

Earthquake Zones in India (Zonation)

• India is divided into Zone II to Zone V.
• Zone V is the most seismically active (e.g., Northeast India, Himalayan belt).

Active Volcanic Sites in India

• Barren Island (Andaman & Nicobar) – India’s only active volcano
• Narcondam Island – dormant

🔍 UPSC Previous Year Questions (PYQs)

Prelims PYQs:

1. Q. Consider the following phenomena:
   • Earthquake
   • Lightning
   • Volcanic eruption
   • Cyclone
     Which of the above can be caused by the movement of tectonic plates?
     [UPSC Prelims 2011]
     👉 Correct Answer: 1 and 3
2. Q. Consider the following statements:
   • S-waves can travel through both solids and liquids.
   • The epicentre of an earthquake is the point on the surface directly above the focus.
     Which of the above is correct?
     [UPSC Prelims 2020]
     👉 Correct Answer: Only 2

Mains PYQ (GS-1):

3. Q. Why are the world’s fold mountain systems located along the margins of continents? Bring out the association between mountain building and plate tectonics.
   [UPSC Mains 2014]
4. Q. Bring out the causes for more frequent landslides in the Himalayas than in the Western Ghats.
   (Links tectonics and earthquakes)
   [UPSC Mains 2013]

📘 How to Prepare Earthquakes & Volcanoes for UPSC?

📖 Recommended Sources:

1. NCERT Geography Class 11 – Fundamentals of Physical Geography
   🔗 NCERT Link
2. G.C. Leong – Certificate Physical Geography
3. Majid Husain – Geography of India
4. PMF IAS Notes – https://store.pmfias.com

🧠 Tips for Answer Writing in Mains

• Use diagrams and maps – like Plate boundaries, Ring of Fire, Earthquake zones of India
• Add recent examples (e.g., Turkey-Syria Earthquake 2023)
• Quote statistics from NDMA or IMD

✅ Conclusion

Understanding earthquakes and volcanoes is not only important for static geography but also useful for environment and disaster management. For UPSC, always integrate current affairs with core concepts.