"Tsunami" is a Japanese word that literally translates to “harbor wave”. It is the internationally accepted term to describe waves generated by major earthquakes (caused by a vertical shift of the earths crust along a zone of fracture), undersea or coastal landslides, volcanic activity, meteor impacts, or other large scale disturbance of the surface of a body of water.
Tsunamis caused by landslides or volcanic activity are less powerful and usually have only local effects (within a few miles), whereas, tsunami’s caused by major earthquakes can travel thousands of kilometers across oceans at speeds of 500 to 800 kph and be very devastating. Local tsunamis (within a few miles of the disturbance) occur within a few minutes and, therefore, does not allow time for ample warning. Other tsunamis can take four hours or longer to traverse oceans. For estimated travel times for various locations see the following: Tsunami Travel Time Maps
Tidal waves are those generated by predictable periodic changes in gravitational attraction by the moon and sun. Waves can also be caused by winds where their size may range from a few feet under normal conditions to heights of 15 meters or more, depending on wind speed and strength of the storm. Wave speeds typically range from a few miles per hour up to about 100 kph. Typical wind generated wave heights may range from a few feet up to 15 meters or more and with a distance between waves of a few to about 300 meters.
Tsunami waves traveling across an ocean or other deep body of water can be less than 30 to 60 cm in height. But, once generated, wave height, speed, and strength are influenced by the depth and topography of the sea floor and the shape of the shoreline. The distance between successive waves, referred to as wavelength, can range from a few hundred meters to a few hundred kilometers, depending on the cause of disturbance. Tsunamis are usually not the large, shore-breaking waves that most people think of but a large surge of water without a well defined face. These large and powerful surges are usually preceded by an unusual and noticeable receding of the water. Tsunamis usually consist of a series of waves ranging from a few minutes apart to over an hour apart. Many have lost their lives returning to low-lying coastal areas after the first wave, thinking that the tsunami is over. For a introductory lecture on tsunamis, go to the following superlecture site: http://www.pitt.edu/~super1/lecture/lec18071/index.htm
Tsunamis are among the most devastating natural disasters in terms of property damage and loss of life. Most tsunamis occur in and along the perimeter of the Pacific and Indian Oceans, (world map of tsunami occurrence) but they can occur along any large body of water. See "Tsunamis and Tsunami-Like Waves of the Eastern United States" and "A Brief History of Tsunamis in the Caribbean Sea" for discussion and information on tsunamis in the Atlantic and Caribbean regions, respectively. For photos, videos and animation of tsunamis and their effects, see the following: http://cwis.usc.edu/dept/tsunamis/video/.
The Pacific Tsunami Warning System was established in 1948 following the April 1, 1946 tsunami that was triggered by an earthquake in the Aleutian Islands that resulted in 159 tsunami related deaths in Hawaii. Following the great Alaskan earthquake that occurred in Prince William Sound on March 27, 1964, the system was expanded in 1967 by the creation of the West Coast and Alaska Tsunami Warning Center in 1967.