What are Tsunamis ? How and where are they formed ? What are their consequences ? Explain with examples. (Answer in 150 words)

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सुनामी क्या हैं ? वे कैसे और कहाँ बनती हैं ? उनके परिणाम क्या हैं ? उदाहरणों सहित समझाइए । (उत्तर 150 शब्दों में दीजिए) 10 अंक

The question as printed in the 2025 General Studies paper

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Model answer

Drafted with AI by UPSC Answer Check against this question's marking rubric, to the 150-word length. UPSC does not publish answers for Mains — this is one way to score well, not an official key. How we build rubrics and answers.

Tsunamis are long-period ocean waves generated by sudden vertical displacement of a large water body, not by tides. They form mainly when submarine earthquakes, especially at convergent plate boundaries and subduction zones, uplift or drop the seafloor; other triggers include coastal landslides, volcanic eruptions and rare meteorite impacts. Geographically, they are most common around the Pacific Ring of Fire, where plate margins are active, and also in the Indian Ocean, such as the Sunda Trench in the eastern Indian Ocean. Consequences include coastal inundation, loss of life, destruction of housing, ports, agriculture and industry, ecological damage to mangroves and fisheries, and industrial disasters, as when Japan’s 2011 tsunami struck Sendai and caused the Fukushima meltdown. The 2004 Indian Ocean tsunami, triggered by a Sumatra earthquake, killed about 2.3 lakh people. Hence, early warning systems, evacuation plans and coastal preparedness are essential.

Diagram: Tsunami generation at a subduction zone: megathrust rupture lifts the seafloor and the water column, waves spread out and rise near the coas

How this answer will be evaluated

Framework: GS1 Geography: Mechanism, Location, Consequence

What earns full marks: Mechanism explained, location linked to tectonics, consequences detailed with specific examples.

Evaluation rubric

Each sub-part is marked on its own, against the marks and word limit printed on the paper.

The answer Define tsunami, explain how and where they form, and detail their consequences with examples. 10 marks · 150 words

explain— definition/context → points in order → small example → short close
Must cover
- Define tsunami as a series of long-wavelength waves from sudden displacement of water
- Explain mechanism: undersea earthquakes at subduction zones, vertical seafloor displacement; also landslides, volcanic eruptions
- Identify location: Pacific Ring of Fire, Sunda Trench, other subduction zones
- Detail consequences: coastal inundation, loss of life, infrastructure and ecological damage
Loses marks
- Narrating events without explaining mechanism
- Location without cause
- Confusing tsunamis with storm surges or tides
Earns more
- Specific examples (e.g., 2004 Indian Ocean, 2011 Tohoku–Fukushima)
- Wave behaviour: low height and high speed (about 700–800 km/h) in deep ocean, shoaling and run-up near coast
- Link physical geography to human outcome (mangroves as buffers, coastal density)
- Distinguish from storm surge; mention early warning (INCOIS, Indian Tsunami Early Warning Centre)
Extra mark
- Sketch of a subduction zone generating a tsunami
- One robust statistic (e.g., 2004 death toll about 2.3 lakh)

What "Explain" is asking you to do

Make the working of something clear — what sets it off, what follows from what, and what it produces. Explain is the Commission's mechanism word: it dominates the technical papers and the “explain why” stems, where the marks sit in the causal chain and not in the label.

Structure that answers it

State what it is → the initiating condition → the chain of cause, step by step → an instance where it plays out → what the chain produces

Where marks are lost

Describing what something looks like instead of why it works that way. Naming the stages without linking them reads as description too.

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