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How does a tsunami happen?
Quick answer
A tsunami happens when a large, sudden movement of the seafloor — usually from an undersea earthquake — pushes a huge volume of water upward. That energy spreads as fast, low waves that grow into towering walls of water as they reach shallow coasts.
Step by step
- Most tsunamis start with an undersea earthquake that shifts the seafloor.
- The displaced water spreads outward as a series of long, fast waves.
- In the deep ocean the waves are low and can travel as fast as a jet plane.
- As they reach shallow water near shore, they slow and pile up into great heights.
- Underwater landslides and volcanic eruptions can also trigger them.
People also ask
Why is a tsunami so different from a normal wave?
Normal waves are driven by wind at the surface; a tsunami moves the entire column of water from seafloor to surface, carrying vastly more energy.
What's the warning sign of a tsunami?
Often the sea suddenly draws far back from the shore before the wave arrives. Strong coastal shaking or an official alert means move to high ground immediately.
How fast does a tsunami travel?
In the open ocean it can race at 700–800 km/h — as fast as a jet — then slow dramatically as it nears the coast and grows in height.
What causes a tsunami?
Usually an undersea earthquake, but landslides, volcanic eruptions, or impacts can also displace enough water.
Why are tsunamis so dangerous near the coast?
As waves enter shallow water they slow and grow taller, surging far inland with immense force.
How fast do tsunamis travel?
In the open ocean they can race at hundreds of kilometers per hour — as fast as a jet plane.
Part of the guide: Water & Weather Phenomena →