A tsunami (pronounced /(t)suːˈnɑːmi/) 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 can be devastating due to the immense volumes of water and energy involved. Since meteorites are small, they will not generate a tsunami.
The Greek historian Thucydides was the first to relate tsunamis to submarine quakes,[1] [2] but understanding of the nature of tsunamis remained slim until the 20th century and is the subject of ongoing research.
Many early geological, geographic, oceanographic etc; texts refer to "Seismic sea waves" - these are now referred to as "tsunami."
The Greek historian Thucydides was the first to relate tsunamis to submarine quakes,[1] [2] but understanding of the nature of tsunamis remained slim until the 20th century and is the subject of ongoing research.
Many early geological, geographic, oceanographic etc; texts refer to "Seismic sea waves" - these are now referred to as "tsunami."
causes
A tsunami can be generated when converging or destructive plate boundaries 
abruptly move and vertically displace the overlying water. 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.
On 1 April 1946 a Magnitude 7.8 (Richter Scale) earthquake occurred near the Aleutian Islands, Alaska. It generated a tsunami which inundated Hilo on the island of Hawai'i with a 14 m high surge. The area where the earthquake occurred is where the Pacific Ocean floor is subducting (or being pushed downwards) under Alaska
abruptly move and vertically displace the overlying water. 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.On 1 April 1946 a Magnitude 7.8 (Richter Scale) earthquake occurred near the Aleutian Islands, Alaska. It generated a tsunami which inundated Hilo on the island of Hawai'i with a 14 m high surge. The area where the earthquake occurred is where the Pacific Ocean floor is subducting (or being pushed downwards) under Alaska
Signs of an approaching tsunami
The monument to the victims of tsunami at Laupahoehoe, Hawaii.
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.
If the first part of a tsunami to reach land is a trough (draw back) rather than a crest of the wave, the water along the shoreline may recede dramatically, exposing areas that are normally always submerged. This can serve as an advance warning of the approaching tsunami which will rush in faster than it is possible to run. If a person is in a coastal area where the sea suddenly draws back (many survivors report an accompanying sucking sound), their only real chance of survival is to run for high ground or seek the high floors of high rise buildings.
In the 2004 tsunami that occurred in the Indian Ocean drawback was not reported
on the African coast or any other western coasts it inundated, when the tsunami approached from the east. This was because of the nature of the wave - it moved downwards on the eastern side of the fault line and upwards on the western side. It was the western pulse that inundated coastal areas of Africa and other western areas.
80% of all tsunamis occur in the Pacific Ocean, but are possible wherever large bodies of water are found, including inland lakes. They may be caused by landslides, volcanic explosions, bolides and seismic activity.
Indian Ocean Tsunami According to an article in "Geographical" magazine (April 2008), the Indian Ocean tsunami of 26th December 2004 was not the worst that the region could expect. Professor Costas Synolakis of the Tsunami Research Center at the University of Southern California co-authored a paper in "Geophysical Journal International" which suggests that a future tsunami in the Indian Ocean basin could affect locations such as Madagascar, Singapore, Somalia, Western Australia and many others. The Boxing Day tsunami killed over 300,000 people with many bodies either being lost to the sea or unidentified. Some unofficial estimates have claimed that approximately 1 million people may have died directly or indirectly solely as a result of the tsunami.
The monument to the victims of tsunami at Laupahoehoe, Hawaii.
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.
If the first part of a tsunami to reach land is a trough (draw back) rather than a crest of the wave, the water along the shoreline may recede dramatically, exposing areas that are normally always submerged. This can serve as an advance warning of the approaching tsunami which will rush in faster than it is possible to run. If a person is in a coastal area where the sea suddenly draws back (many survivors report an accompanying sucking sound), their only real chance of survival is to run for high ground or seek the high floors of high rise buildings.
In the 2004 tsunami that occurred in the Indian Ocean drawback was not reported
on the African coast or any other western coasts it inundated, when the tsunami approached from the east. This was because of the nature of the wave - it moved downwards on the eastern side of the fault line and upwards on the western side. It was the western pulse that inundated coastal areas of Africa and other western areas.80% of all tsunamis occur in the Pacific Ocean, but are possible wherever large bodies of water are found, including inland lakes. They may be caused by landslides, volcanic explosions, bolides and seismic activity.
Indian Ocean Tsunami According to an article in "Geographical" magazine (April 2008), the Indian Ocean tsunami of 26th December 2004 was not the worst that the region could expect. Professor Costas Synolakis of the Tsunami Research Center at the University of Southern California co-authored a paper in "Geophysical Journal International" which suggests that a future tsunami in the Indian Ocean basin could affect locations such as Madagascar, Singapore, Somalia, Western Australia and many others. The Boxing Day tsunami killed over 300,000 people with many bodies either being lost to the sea or unidentified. Some unofficial estimates have claimed that approximately 1 million people may have died directly or indirectly solely as a result of the tsunami.
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