A tsunami (pronounced /tsuːˈnɑːmi/) is a series of waves created when a body of water, such as an ocean, is rapidly displaced. Earthquakes, mass movements above or below water, some volcanic eruptions and other underwater explosions, landslides, underwater earthquakes, large asteroid impacts and testing with nuclear weapons at sea all have the potential to generate a tsunami. The effects of a tsunami are always devastating due to the immense volumes of water and energy involved. Since meteors are small they will not generate a tsunami.
A tsunami can be generated when converging or destructive plate boundaries abruptly move and vertically displace the overlying water. Such large vertical movements of the Earth's crust can occur at destructive plate boundaries. It is very unlikely that they can form at divergent (constructive) or conservative plate boundaries. This is because constructive or conservative boundaries do not generally disturb the vertical displacement of the water column. Subduction zone related earthquakes generate the majority of all tsunamis.
There is often no advance warning of an approaching tsunami. However, since earthquakes are often a cause of tsunami, any earthquake occurring near a body of water may generate a tsunami if it occurs at shallow depth, is of moderate or high magnitude, and the water volume and depth is sufficient. In Japan moderate - 4.2 Magnitude earthquakes can generate tsunami which can inundate the area within 15 minutes.
A tsunami cannot be prevented or precisely predicted - even if the right magnitude of an earthquake occurs in the right location. Geologists, Oceanographers and Seismologist analyse each earthquake and based upon many factors may or may not issue a tsunami warning. However, there are some warning signs of an impending tsunami, and there are many systems being developed and in use to reduce the damage from tsunami. One of the most important systems that is used and constantly monitored are bottom pressure sensors. These are anchored and attached to buoys. Sensors on the equipment constantly monitor the pressure of the overlying water column - this can be deduced by the simple calculation of:
F = Gdh
where F = the overlying force or pressure in Newtons per metre square, G is the acceleration due to gravity, d = the density of the water and h = the height of the water column.
G = 9.8 m s2, d = 1.1 x 103 kg m3 and h is the depth of water in metres
Hence for a water column of 5,000 m depth the overlying pressure is equal to 9.8 x 1.1 x 103 x 5 x 103 or about 5.4 x 10 7 N m2 or about 5.7 Million tonnes per metre square.
Recently we saw a great tsunami efect on south east asia on coasts of countries like India, Indonasia,Srilanka etc.
