Tsunami is a Japanese word meaning "harbor wave". It is unlike a tidal wave, in that it can start after an earthquake, building momentum under the water as it moved inland, so that a boat out on the water may continue on without occupants realizing the force moving under it towards the shore. It can also be caused by volcano eruptions and landslides. The people on the coast would be quickly experiencing the effects once the tsunami reaches land. A tsunami is many waves coming in, moving in several hundreds of kilometers or miles per hour under the surface of the ocean. When they reach shallow water they break into very powerful and sometimes gigantic waves, which can occur over a series of hours. You may think the worst is over, when really it is yet to come. This is why leaving the coastal area for inland and higher ground is crucial and going to the shore to keep an eye out could be a mortal decision. You should seek ground 15 metres or 100 feet higher than sea level. The most dangerous of areas is the land one mile within the shore and less then 25 feet above sea level.

When an earthquake in December 2004 resulted in a tsunami in the Indian Ocean, the waves that came onto the coastal land were up to 60 feet in some areas. Eleven countries by the Indian Ocean were hit, but the impact of the tsunami was felt around various parts of the world, even as far as Peru. Over 200,000 people lost their lives.

Countries and coastal areas have their own set of emergency notification responses from tsunami warnings. They can range from warnings and watches to letting the public know all is clear and the tsunami advisory is now cancelled. Sirens or telephone relays, broadcasts over radio and television are all ways different communities handle tsunami warnings.

If you are on a boat when the tsunami warning comes in, plan to leave the inland area of the harbor and head out towards deeper water. If there has been a strong earthquake in the area you are in, it is safer to travel by foot unless you are disabled, as roads could be damaged, trees and bridges could have collapsed, etc.

If you have time, take your hopefully prepared emergency survival kit with enough supplies for at least 3 days. Return home or to your original location only when the tsunami warning has been lifted and people have been advised they can return to the coastal area.