A tsunami is caused by a large and sudden displacement of the ocean. Large earthquakes below or near the ocean floor are the most common cause. But landslides, volcanic activity, near earth objects (e.g., asteroids, comets), certain meteorological conditions and nuclear tests can also cause tsunamis.
- Tsunami can be generated when the sea floor ruptures abruptly due to tectonic earthquakes, causing vertical displacement of the overlying water. Most of the earthquakes which generate tsunamis occur on thrust faults. These earthquakes occur mainly in the areas where tectonic plates move toward each other in subduction zones.
- As per data, ten to fifteen percent of the most damaging tsunamis are generated by strike-slip earthquakes involving a horizontal movement of the earth.
- Example – 2004 Indian Ocean Tsunami was an earthquake-induced Tsunami, caused by an earthquake (Mw 9.2) in the Indian Ocean.
- landslide is a general term that involves the ground movement of different types, including rock slide, block slide, debris flows, avalanches, and glacial calving (referring to the breaking off of large pieces of ice from a glacier).
- Tsunamis can be generated when a landslide enters the water and displaces it. Such generation of Tsunami depends on the amount of rock material that displaces the water, the speed with which it is moving, and the depth it moves to.
- Landslide-generated tsunamis may be larger than seismic tsunamis near their source, but they usually lose energy quickly and rarely affect distant coastlines. A landslide big enough to cause a transoceanic tsunami has not occurred in the recorded history.
- Example – 1998 Papua New Guinea Tsunami was generated by a landslide cause by an earthquake.
III) Volcanoes –
- volcanoes generated Tsunamis are very infrequent, both above and below water. However, different types of volcanic activity can displace enough water to generate tsunamis e.g. submarine explosions, caldera formations etc.
- Like other non-seismic tsunamis, such as those generated by landslides, volcanic tsunamis usually lose energy quickly and rarely affect distant coastlines.
- Example – 1883 Indonesia Tsunami was caused by the explosion of Krakatau volcano.
IV) Near Earth Objects
- It is very rare for a near earth object like an asteroid or comet to reach the earth and its potential to generate Tsunami is still uncertain, as there are no records of a Tsunami caused by near earth objects, in recent human history. However, scientists are of the opinion there are two ways near earth objects could generate a tsunami.
- Large objects (more than 1,000 meters in diameter) that make it through Earth s atmosphere without burning up could hit the ocean, displacing water and generating an impact tsunami.
- If this happens above the ocean, the explosion could release energy into the ocean and generate an airburst tsunami.
- Some meteorological conditions, for example, air pressure disturbances often associated with fast moving weather systems, can displace bodies of water enough to generate Tsunamis. These meteotsunamis are similar to tsunamis generated by earthquakes, but usually with lower energies.
- The development of these Meteotsunamis depends largely on the direction, intensity of air pressure and ocean depth. Meteotsunamis are regional, and it is found in some part of the world frequently due to regional factors such as topography of earth’s surface both below and above the ocean.
- Example 2013 New Jersey, USA Tsunami caused by a high-speed windstorm associated with thunderstorms.
VI) Nuclear Weapon or tests–
- it is an example of man-made disaster. Massive explosions created by a nuclear weapon of nuclear tests have the potential to cause Tsunami. There have been dangers of using this as a tectonic weapon.
- There has been considerable speculation on the possibility of using nuclear weapons to cause tsunamis near an enemy coastline. In fact, In World War II, the New Zealand Military Forces, in a failed attempt, tried to create small tsunamis with explosives.
So a strike slip fault earthquake never cause a Tsunami . Animation of strike slip fault is as below: