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"Stuart" wrote in message k... When did everybody start calling a tidal wave a tsunami and why? When they learnt the difference. A tidal wave is something completely different to a tsunami, but a lot of people don't seem to realise this. If you were to crack a book on hydrodynamics you will find that there are essentially four different types of wave in an ideal non-viscous liquid Capillary waves Surface waves Deep water waves Solitons (actually, there are also linear combinations of the first two) Capillary waves are what you get if you induce a wave by vibrating a tuning fork witih one tine just touching the liquid Surface waves are what you normally see on the surface of the ocean before they break near the shore. That includes the so-called "Giant waves". These are simply distinguished by having a very large amplitude of oscillation. In both those types of wave any "piece" of water moves vertically up and down. In the case of a deep water wave, any *piece" of water executes a circular motion, with the diameter of the circle equal to the depth of the water. Both tidal waves and tsunamis are synonyms for deep water waves. In the open ocean with a constant depth, a deep water wave is essentially harmless and may pass practically unnoticed. It only becomes dangerous when it meets a sloping ocean floor, so that the nornal circular motion can no longer be accomodated. It is at that stage that it begins to "suck" in water ahead of it and begins to pile up in height. Solitons are peculiar beasts in which certain specifically-shaped transient surface disturbances can move unchanged in shape. Franz |
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