How Fast Is Tsunami Wave?

Tsunamis race across deep ocean at 220 m/s — 800 km/h, the speed of a jet airliner. They are nearly invisible at sea, just a metre tall over thousands of kilometres of wavelength, but they slow and tower upward into walls of water as they approach shore.

The Hilo, Hawaii tsunami warning system uses deep-ocean pressure sensors that detect tsunamis in open water — long before they reach any coast.

• Faster than airliners cruise
• Crosses an ocean in under a day