What is a Tsunami?

 The term "tsunami" describes a series of long oceanic waves that is created in after a large volume of water has been displaced.  “Tsunami” is derived from the Japanese language, and when transcribed to English, it means “Harbor (“tsu”) Wave (“nami”).  The term was first coined by Japanese fisherman to describe the destruction caused by large waves that would wipe out entire areas surrounding the harbor.  The strange thing was that they would experience little to no effects of the tsunami on their boats in their sea.    

Tsunamis are waves characterized by moving at fast speeds, sometimes having a high amplitude (wave height), and long wavelength – thus tsunamis are essentially giant waves.  In the deep ocean, tsunamis are barely felt since they are masked by the sheer vastness of the rest of the ocean.  This is the reason why those aforementioned Japanese fishermen were not affected.  However, tsunamis can be absolutely devastating as ocean’s depth decreases with approaching land.    

The speed at which a tsunami travels is another impressive characteristic.  Tsunamis can travel at great speeds across an ocean, usually from 500 to 1000 kilometers per hour, with hardly any energy losses and are barely noticeable out at sea.  This is the reason why tsunami’s generated from one region can affect other regions thousands of kilometers away.  With the recent tsunami is South Asia, the epicenter of the tsunami was just of the coast of Indonesia, and yet the tsunami struck with the same amount of force in Eastern Africa – some 14 hours after Southeast Asia was hit.     

Wavelengths (the distance between wave crests) of tsunami can be in excess of 100 kilometers or more.  This means that once a tsunami initially hits the coast, the second wave might not occur for up to an hour afterwards.  That is part of the inherent dangers of tsunamis.  With the recent tsunami in South Asia, many individuals were killed with the initial wave.  However, more tragedy struck when a second tsunami claimed just as many people about an hour after the first tsunami, who had rushed back onto the beach after to help out survivors.       

As a tsunami leaves the deep water of the ocean and travels into the shallower water near the coast, it behaves like a normal wave, only that it travels significantly faster and packs more power with its long wavelength.  The tsunami slows down because of the shallow water, but that also makes the water “pile up” to increase the tsunami’s height.  By the time it reaches land, the tsunami’s height can be horrifically imposing (some have been known to be as high as 30 meters), and their effects can be equally devastating as they batter the coast with tremendous amounts of energy.  Tsunamis can strip sand from beaches, tear up trees, and even obliterate whole towns as seen with the latest South Asian tsunami disaster. 

A more familiar term that is often used to describe tsunamis is “tidal wave”.  This was used since the violent onrushing of tsunamis can be seen as being similar to a very large and fast tide.  Oceanographers are quick to point out that tidal wave is a misleading term that is incorrect in use because tsunamis are not connected with tides in any way.  Tides are the periodic movement of water produced by the gravitational pull of the sun and moon, whose entrance and exit can be accurately predicted.  Tsunamis are a rare phenomenon that is caused by the displacement of massive amounts of water and manifest itself as a series of massive waves.