Tsunamis are ocean waves caused by large earthquakes and landslides that occur near or under the ocean. Scientists do not use the term "tidal wave" because these waves are not caused by tides. Tsunami waves are unlike typical ocean waves generated by wind and storms. When tsunamis approach shore, the behave like a very fast moving tide that extends far inland. A rule of thumb is that if you see the tsunami, it is too late to out run it. Most tsunamis do not "break" like the curling, wind-generated waves popular with surfers. Even "small" tsunamis (for example, 6 feet in height) are associated with extremely strong currents, capable of knocking someone off their feet. Because of complex interactions with the coast, tsunami waves can persist for many hours.
 

As with many natural phenomena, tsunamis can range in size from micro-tsunamis detectable only by sensitive instruments on the ocean floor to mega-tsunamis that can affect the coastlines of entire oceans, as with the Indian Ocean tsunami of 2004. If you hear a tsunami warning or if you feel strong shaking at the coast or very unusual wave activity (e.g., the sea withdrawing far from shore), it is important to move to high ground and stay away from the coast until wave activity has subsided (usually several hours to days). For more general information on tsunamis and what to do during a tsunami warning, please visit sites sponsored by FEMA, the National Weather Service, state agencies, NOAA, and the USGS.

There are many causes of tsunamis but the most prevalent is earthquakes. In addition, landslides, volcanic eruptions, explosions, and even the impact of cosmic bodies, such as meteorites, can generate tsunamis. Seismic disturbances causing Earthquakes, volcanic activities, submarine faulting are the main reasons for occurrence of Tsunami. A seismic disturbance can move the seawater to form huge waves by creating a rise or fall in the level of the ocean. The seismic activity takes place mainly due to the movement of earth's tectonic plates.  To learn more about Plate tectonics  Click here. This rise or fall in sea water level is the early formation of a tsunami wave. The wall of this water can be more than 100 feet or several story high. The earthquakes that take place on the seafloor or in coastal areas usually cause tsunamis. To learn more about Earthquakes click here.

Science behind Tsunamis
Tsunamis are mainly caused by  high intensity under sea earthquakes, volcanic activity,  landslides, or even the meteorites falling in the oceans. Any of these activities inside the ocean can releases large amount of energy and as a result this energy starts traveling outward in all directions. This causes the ocean level of that region to either rise or fall temporarily thereby creating a large waves which starts spreading in all direction. The amount of time between consecutive waves is called as the wave period. Wave period is only a few minutes to an hour long. As the tsunami waves crosses the ocean, its length from crest to crest could be around hundred of miles, and its  height can be from few feet to  several hundred feet. The speed of the waves can go up to 750 miles per hour. When they reach shoreline they can be as high as 30-40 meters. The tsunami waves after reaching the shore line looses all its energy but by doing so wherever they strike they engulfs the coastal regions few meters to several hundred meters inside the land and creates widespread havoc which usually results in widespread damage of property and loss of life.

Tsunami Warming Systems:

Various methods and instruments have been developed and deployed for Tsunami warmings. Pacific tsunami warning system (PTWS) is one of them. PTWS was established in 1948 for watching US territories,  but it soon became an international system after 1965. Now PTWS has  26 nations as its members.
After a tectonic activity is recorded in a particular region satellites are the first to monitor and send the information of warning to Pacific tsunami warning system. When information from tidal station reveals that a potentially destructive tsunami exists then an alert signal is passed on to all stations. This message is then passed on to the member nations which then warns the residents via TV, radio or other local media to inform the public of that region.

 NOAA and Tsunami warning system:

NOAA participates in the Tsunami Warning System, and is operating two Tsunami Warning Centers. The Alaska/West Coast Tsunami Warning Center (ATWC) in Palmer, Alaska, serves as the regional Tsunami Warning Center for Alaska, British Columbia, Washington, Oregon, and California. The Pacific Tsunami Warning Center in Ewa Beach, Hawaii, serves as the regional Tsunami Warning Center for Hawaii and as a national/international warning center for tsunamis that pose a Pacific-wide threat. Fol

Click on the picture to see how NOAA system works

(Figure1: Courtesy : NOAA)

Tsunami Survival Tips:

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