Science
What is Tsunami?
A tsunami is a series of huge ocean waves caused by a sudden disturbance of the sea floor — usually a large undersea earthquake. In deep water the waves are low and fast; as they reach shallow coastlines they slow down and pile up into towering, destructive walls of water.
See it, don’t just read it.
Watch a 2-minute lesson with voice + animation that explains tsunami.
Key things to understand
- 1Most tsunamis are triggered by undersea earthquakes that abruptly shift the ocean floor, displacing a vast volume of water.
- 2In the open ocean a tsunami may be only a metre high but travels as fast as a jet plane (~800 km/h).
- 3Near shore it slows and its energy compresses, so the wave height grows dramatically.
- 4A tsunami is a series of waves, not one — and a later wave is often bigger than the first.
- 5A common warning sign is the sea suddenly drawing far back from the shore before the wave arrives.
Frequently asked questions
- What's the difference between a tsunami and a normal wave?
- Normal waves are made by wind and move only surface water. A tsunami displaces the whole water column (often by an earthquake), so it carries enormous energy from the sea floor to the surface.
- What causes most tsunamis?
- Large undersea earthquakes are the most common cause. Underwater landslides, volcanic eruptions, and rarely meteorite impacts can also cause them.
- What should you do if the sea suddenly recedes?
- Treat it as a tsunami warning — move quickly to high ground or inland, away from the coast, and don't return until officials say it's safe.