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

What are tsunamis?

Tsunamis (Japanese for 'harbour waves') are a series of very long-wavelength sea waves generated by the sudden displacement of the ocean's water column. In deep water they travel at 500–800 km/h with heights under a metre; nearing shallow coasts, shoaling compresses their energy into walls of water that can exceed 10–30 metres.

How and where they form

• Undersea megathrust earthquakes at subduction zones — the dominant cause (2004 Sumatra-Andaman, magnitude 9.1; 2011 Tohoku, Japan).
• Volcanic eruptions — Krakatoa (1883) and Hunga Tonga (2022).
• Submarine or coastal landslides, and, very rarely, meteorite impacts.
• Principal zones: the Pacific Ring of Fire (about 80% of events); for India, the Sunda-Andaman trench and the Makran coast are the key sources.

Consequences

• Mass casualties: the 2004 Indian Ocean tsunami killed about 2.3 lakh people across 14 countries, including in Tamil Nadu and the Andaman and Nicobar Islands.
• Destruction of ports, housing and coastal infrastructure; salinization of farmland and aquifers.
• Cascading technological disasters — the Fukushima nuclear accident (2011).
• Ecological damage to mangroves, coral reefs and coastal wetlands.

Conclusion

Early-warning systems such as the INCOIS Tsunami Early Warning Centre, Hyderabad (2007), coastal zoning and mangrove bio-shields have converted this rare but catastrophic hazard into a risk that preparedness can manage.