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On Sat, 8 Jan 2005 22:18:03 +0000 (UTC), "Franz Heymann"
wrote: 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. In the links I posted earlier (see below) and which seemed authoritative, tsunamis were described as shallow water waves, despite propagating in deep water. I assumed this meant their characteristics place them in the 'shallow water wave' category, and didn't mean they only appear in shallow water. I am now confused. http://www.fluidmech.net/tutorials/ocean/tsunami.htm http://www.es.flinders.edu.au/%7Emat...lecture10.html 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. That would certainly fit the descriptions coming from survivors, who talked about the tide going right out very rapidly, before the crest of the wave arrived. But I also heard that it doesn't always happen this way, depending on whether a crest or a trough hits the shore first. And wouldn't this also occur with any type of wave? They all presumably have peaks and troughs. Solitons are peculiar beasts in which certain specifically-shaped transient surface disturbances can move unchanged in shape. Franz -- Chris E-mail: christopher[dot]hogg[at]virgin[dot]net |
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