GS Paper I 2025 · Q7
10 marks · 150 words Geophysical phenomena & changing features X-Ray · Core #45What are Tsunamis? How and where are they formed? What are their consequences? Explain with examples.
Approach · directive: “what / how / explain”
What it asks · Define tsunamis, explain their causes and the regions where they occur, and describe their effects, with examples.
It asks 4 things — answer each
- What: define tsunamis
- How: explain the triggers and mechanism by which tsunamis form
- Where: identify the zones where tsunamis form, including those threatening India
- Explain: their consequences, with examples
Open with · A tsunami is a train of very long sea waves set off when a large mass of ocean water is suddenly displaced; NCERT stresses that it is a wave generated by tremors, not an earthquake itself.
Cover
- Formation flowchart: undersea quake at a subduction zone → sea floor displaced → water column pushed → fast, low waves → shoaling near shore.
- NCERT: a tsunami follows only when the epicentre is under the sea and the magnitude is high enough.
- 2004 Sumatra–Andaman earthquake (Mw 9.3): mainly vertical displacement of the seafloor (NDMA); other triggers: submarine landslides, volcanoes (Krakatoa 1883, Hunga Tonga 2022).
- Where: Pacific Ring of Fire; Sunda trench (east coast) and Makran zone (west coast) threaten India.
- Consequences: 10,749 dead and 5,640 missing in India in 2004; salinised farms, wrecked boats, damaged mangroves; Tohoku 2011 led to Fukushima.
- Response: INCOIS early warning detects tsunamigenic quakes within 10 minutes; Tsunami Ready, mock drills, mangrove belts.
Close with · Tsunamis cannot be prevented, but the two hours the 2004 waves took to reach India's east coast are now enough warning, if alerts reach every fishing hamlet.
Add value (verified)
- India's Tsunami Early Warning Centre at INCOIS, Hyderabad, set up after the 2004 tsunami, has been operational since 15 October 2007.PARLIAMENT QUESTION: Performance of early warning systems — PIB (Ministry of Earth Sciences), 12 Feb 2026 ↗“Operational since 15 October 2007, the centre uses advanced real-time seismic and sea level monitoring, computing and communication systems to detect tsunamigenic earthquakes within 10 minutes and issues tsunami advisories as per SOPs.”
- The 2004 Sumatra–Andaman earthquake (Mw 9.3) caused its tsunami mainly through vertical displacement of the seafloor.Tsunami — National Disaster Management Authority ↗“The tsunami that occurred during 2004 Sumatra-Andaman earthquake of Mw 9.3 was primarily caused by vertical displacement of the seafloor, in response to slip on the inter-plate thrust fault”
- In 2004 about 10,749 people died in India and 5,640 were reported missing.Protection from Tsunami — PIB, December 2016 ↗“In India, an estimated 10,749 persons lost their life and 5,640 people were reported missing”
- Coastal communities in Tamil Nadu, Puducherry, Andhra Pradesh, Kerala and the Andaman and Nicobar Islands were devastated in 2004.Protection from Tsunami — PIB, December 2016 ↗“the coastal communities in Tamil Nadu, Puducherry, Andhra Pradesh, Kerala, and Andaman and Nicobar Islands were devastated”
- India's east coast was hit about two hours after the 2004 earthquake.Protection from Tsunami — PIB, December 2016 ↗“east coast of India was affected two hours later”
- INCOIS's early warning centre detects tsunamigenic earthquakes within 10 minutes.Indian Tsunami Early Warning Centre — PIB (MoES), 12 February 2026 ↗“detect tsunamigenic earthquakes within 10 minutes and issues tsunami advisories as per SOPs”
Question: UPSC's CS (Main) 2025, GS Paper I — paper ↗. Approach: Minimalist IAS, checked 16 Oct 2026 (how we verify) — UPSC publishes no model answers. ·
Model answer· 218words · Minimalist IAS
A tsunami is a train of very long sea waves set off when ocean water is suddenly displaced; NCERT calls it a wave generated by tremors, not an earthquake itself.
How they are formed
- Undersea quake
- sea floor displaced
- water column lifted
- fast, low waves cross ocean
- waves slow and pile up near shore
- The trigger: only a strong quake with an undersea epicentre raises one (NCERT).
- Case: the 2004 Sumatra–Andaman quake (Mw 9.3) acted mainly through vertical seafloor displacement (NDMA).
- Other causes: submarine landslides and volcanic eruptions (Krakatoa 1883, Hunga Tonga 2022).
Where they form
- Pacific Ring of Fire generates most; in the Indian Ocean the Sunda trench threatens India's east coast and the Makran zone its west coast.
Consequences
- Human toll: in 2004 about 10,749 died in India and 5,640 went missing, devastating Tamil Nadu, Puducherry and the Andamans.
- Livelihood and ecology: boats and harbours wrecked, farmland and aquifers salinised, mangroves and reefs damaged.
- Cascading hazards: the 2011 Tohoku tsunami caused the Fukushima nuclear accident.
Reducing losses
- Early warning: INCOIS's centre, set up after 2004, detects tsunamigenic quakes within 10 minutes; Tsunami Ready villages and drills follow.
Tsunamis cannot be prevented, but deaths can: the two hours the 2004 waves took to reach India's east coast are now ample warning, if alerts reach every fishing hamlet.
Prepared by Minimalist IAS to the answer standard of Shivam Singh (mentor, 7 years) · facts checked against official sources (how we verify) · updated 16 Oct 2026. UPSC publishes no model answers: compare your structure and coverage with this, then write your own.
