Science
How do tsunamis form?
A tsunami forms when a sudden event — usually an undersea earthquake — abruptly displaces a huge volume of ocean water. That energy spreads outward as fast, low waves that grow enormous and destructive as they reach shallow coastlines.
See it in motion.
Watch a 2-minute animated lesson that shows exactly how tsunamis works.
Step by step
- 1Most are triggered by undersea earthquakes shifting the sea floor.
- 2The displaced water sends energy racing across the ocean.
- 3In deep water the waves are low but extremely fast.
- 4Near shore they slow down and pile up into towering, destructive waves.
Frequently asked questions
- 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.