Tsunamis are huge waves of water that are usually caused by earthquakes or volcanic eruptions.
As a tsunami approaches the shore, water may recede from the coast, if it is shallow enough the water may be pulled back hundreds of metres. If you are in the area, observing this is a good indication that a tsunami is on the way.
Regions in tsunami danger zones often have warning systems in place to give people as much time to evacuate as possible.
When tsunamis hit shallow water (often near the coast) they slow down but increase in height.
An earthquake in the Indian Ocean off Indonesia in December 2004 caused a tsunami that killed over 200000 people in 14 countries. More earthquake facts.
In March 2011, the Tohoku earthquake off the eastern coast of Japan caused a tsunami that was a major factor in the death of over 15000 people.
The tsunami waves created by the Tohoku earthquake reached heights of over 40 metres (131 feet) in some areas, wiping out coastal towns and causing a number of nuclear accidents.
The Japanese word tsunami literally means ‘harbor wave’.
Tsunamis are sometimes referred to as tidal waves but this term has fallen out of favour because tsunamis are not related to tides.