The tsunami's energy is so great, it travels around the world three times. Earthquakes at sea cause water to be displaced, creating a fast-moving wave that spreads out in all directions.

A huge impact into water – like a large landslide or meteor – can also cause tsunamis ... of the best ways to spot an incoming tsunami is a sudden retreat of coastal water.

Preliminary reports from the U.S. Tsunami Warning System said tsunami waves were possible for coastlines within about 190 miles of the earthquake’s epicenter, including those on Tonga. The system ...