Physics behing Tsunami

The principal generation mechanism of a tsunami is the displacement of the volume of water of the sea. This displacement of water is usually attributed to either earthquakes, landslides, volcanic eruptions, or more rarely by meteorites and nuclear tests. The waves formed in this way are then sustained by gravitational force. There is a misconception that tides cause tsunamis, however this is untrue

Tsunamis cause damage by two mechanisms: the smashing force of a wall of water travelling at high velocity, and the destructive power of a large volume of water draining off the land and carrying all with it, even if the wave did not look large, back draft of water.

While everyday waves are about 100 meters wide and 2 meters high, a tsunami in the deep ocean has a spread of about 200 kilometres. Such huge wave travels at well over 800 kilometres per hour(about the speed of jet fighter), but owing to the enormous wavelength the wave oscillation at any given point takes 20 or 30 minutes to complete a cycle and has an amplitude of only about 1 metre. This makes tsunamis difficult to detect over deep water. Ships rarely notice their passage. This is also a problem faced by geologist.

As the tsunami approaches the coast and the waters become shallow, wave are compressed against each other, which slows its speed to below 80 kilometres per hour. However, this causes the waves to get taller each time and the waves grow to enourmous heights.

When the tsunami's wave peak reaches the shore, the resulting temporary rise in sea level is termed run up. Run up is measured in metres above a reference sea level. A large tsunami may feature multiple waves arriving over a period of hours, with significant time between the wave crests. The first wave to reach the shore may not have the highest run up.