Tsunami is a Japanese word for “Harbour wave”. They are also known as seismic sea waves. They are very long-wavelength water waves in oceans or seas. They are commonly referred to as tidal waves because of long wavelengths, although the attractions of the Moon and Sun play no role in their formation. They sometimes come ashore to great heights – tens of metres above mean tide level – and may be extremely destructive.
Causes of Tsunami:
- A tsunami can be caused by any disturbance that displaces a large water mass from its equilibrium position.
- The usual immediate cause of a tsunami is sudden displacement in a seabed due to submarine earthquakes sufficient to cause the sudden raising or lowering of a large body of water. The tsunami on December 26, 2004 was caused after an earthquake displaced the seabed off the coast of Sumatra, Indonesia.
- Large volcanic eruptions along shorelines, such as Krakatoa (1883 CE), have also produced notable tsunamis.
- A marine volcanic eruption can generate an impulsive force that displaces the water column and gives birth to a tsunami.
- During a submarine landslide, the equilibrium sea-level is altered by sediment moving along the floor of the sea. Gravitational forces then propagate a tsunami.
- Landslides along the coast, high intensity explosions can also cause tsunami.
- Most destructive tsunamis can be caused due to the fall of extra-terrestrial objects on to the earth.