how tsunami happens

                                      how tsunami happens

The term tsunami has its origins in the Japanese language; an English equivalent is "seismic sea waves." Tsunamis are often incorrectly interchanged with the term" tidal waves," which refer to high waves of water caused by changes in the flow and surge of the ocean. Tsunamis, on the other hand, can be caused by a few different means: 1) the down drop or upthurst of the Earth’s crust which results in an earthquake; 2) a large-scale undersea landslide; 3) a submarine volcanic eruption of a certain degree; or potentially, 4) a large meteor impact at sea. The vast majority of tsunamis result from earthquakes.

      

           

How Earthquakes Cause Tsunamis

The illustration below shows a subduction earthquake (one where a denser plates shifts below its neighboring plate, at left). Energy is transferred and the displaced water forms a wave. As the wave travels and enters shallower water in the coastal area, it begins to increase in amplitude.

Killer Wave! Tsuanmi--National Geographic Kids

Tsunamis are not always colossal waves when they come into the shore. In fact, "... most tsunamis do not result in giant breaking waves (like normal surf waves at the beach that curl over as they approach shore). Rather, they come in much like very strong and very fast tides (i.e., a rapid, local rise in sea level). Nevertheless, there is destruction of life and of property by floating debris and impact of water. The tsunami produces a series of rushing waves and also a series of withdrawals.

    

Tsuanamis and Earthquakes-Basics- USGS

If you think about throwing a rock in water, a ripple is formed. It is the same principle involving a meteor or an earthquake, except they form bigger ripples. If you think about that ripple, it seems to disappear as time goes on--but in actuality, it does not stop. In the picture below we can see that a tsunami is very fast (the speed often compared with that of a jet) and it has a height of 20 inches.

However, we need to take into consideration the effect of the tsunami reaching the shore. The speed is diminished but the wave height is increased drastically.

http://observe.arc.nasa.gov/nasa/exhibits/tsunami/tsun_physics.html

To view a QuickTime visualization: Tsunami Visualization

For more information about earthquake formation see Tectonics.

How Volcanoes Cause Tsunamis

There are two different ways that volcanoes can cause seismic waves. One possibility is for a land-based volcano to break down and collapse, forcing large amounts of ash and debris into the water. This sudden change and displacement of the water column transfers to kinetic energy and results in waves. More debris can create a bigger increase in wave amplitude and number.

Geosciene Australia

Tsunamis can also be induced by submarine volcanoes. These underwater volcanoes can collapse downwards or spew forth lava heating the surrounding water quickly.