What are Tsunamis? How and where are they formed? What are their consequences? Explain with examples.

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Ghissu Editorial · Accepted Answer

Tsunamis are long, fast ocean waves formed when seawater is suddenly displaced, mostly by shallow subduction earthquakes on the Pacific Ring of Fire and the Sunda trench, and also by volcanoes and landslides. The 2004 Indian Ocean tsunami killed about 2.3 lakh people in 14 countries.

**Introduction**

A tsunami, Japanese for "harbour wave", is a series of very long waves set off when a large column of seawater is suddenly displaced. In deep water they race at 700-800 km/h yet stand under a metre high; near the shore they slow and pile up into walls of water.

**How and Where Tsunamis Are Formed**

SKETCH: flow | Formation of a Tsunami
- Megathrust slip
- Seafloor uplift
- Water column displaced
- Long waves radiate
- Shoaling near coast
- Run-up and inundation

1. **Subduction earthquakes**: Most follow shallow undersea quakes above about magnitude 7.5 where one plate snaps upward, as in Sumatra-Andaman (2004) and Tohoku (2011).
2. **Volcanoes and landslides**: Krakatoa (1883), Hunga Tonga (2022) and the Lituya Bay slide in Alaska (1958) also displaced water violently.
3. **Where they occur**: About 80% arise on the Pacific Ring of Fire; India faces the Sunda trench and the Makran zone, whose 1945 tsunami reached Mumbai.

**Consequences of Tsunamis, with Examples**

1. **Loss of life**: The 2004 Indian Ocean tsunami killed about 2.3 lakh people in 14 countries, over 10,000 of them in India, worst in Nagapattinam and Car Nicobar.
2. **Cascading disaster**: In 2011 the waves overtopped Fukushima Daiichi's sea wall and caused a nuclear meltdown.
3. **Land and livelihoods**: Salt water spoiled Tamil Nadu's coastal farms and wells, and fishing communities lost boats and homes, though villages behind the Pichavaram mangroves suffered far less.

**Conclusion**

Tsunamis are rare but inevitable along subduction margins. INCOIS's Indian Tsunami Early Warning Centre (2007) and UNESCO's "Tsunami Ready" tag for two Odisha villages (2020) show that warning, mangroves and drilled communities make them survivable.

What are Tsunamis? How and where are they formed? What are their consequences? Explain with examples.

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