By Sushant Agarwal
Published on | Jul 30, 2025
Tsunamis are massive ocean waves triggered by sudden underwater disturbances. They can cross oceans in hours and devastate coastlines.
Tectonic plates shifting under the sea can violently push or drop the seabed, displacing vast amounts of water and unleashing tsunami waves.
Volcanic eruptions, landslides, massive storms, or even meteorite impacts can generate tsunami waves powerful enough to destroy coastal areas.
The Krakatoa volcano exploded with such force that it created a deadly tsunami killing 30,000 people—heard 4,500 km away.
“Tsunami” means “harbour wave” in Japanese. It’s more accurate than “tidal wave,” which wrongly links it to tides.
In deep ocean, tsunami waves are small and spread out. But as they near shore, they compress and rise into towering, destructive waves.
In 365 AD, Roman historian Ammianus Marcellinus described the sea vanishing—followed by giant waves swallowing ships and people.
The sudden retreat of the ocean is often the first visible sign. It can be followed by several large waves over hours—or even days.
The quake’s magnitude, sea floor shape, water displacement, and coastal barriers all affect how deadly the resulting tsunami is.
A 9.1 quake off Sumatra triggered one of the deadliest tsunamis in history, killing over 220,000 people across 11 nations.