Posted by Mike Field on 12/18/99 from 203.87.22.78 via proxy cache.net2000.com.au:
In Reply to: Peter Duck and Winter Holiday posted by Tom on December 18, 1999 at 09:47:20:
Tsunamis (tsunamii?) only build to any height in shoal water. Deep-sea tsunamis might be only a couple of feet high, but of course very fast-moving. So, like a tidal bore, once they reach the shallows the mass of water can pile up very high and very quickly. Hence the havoc they can wreak.
Near the (small) Crab Island the effect would not be great (unless one were in an additionally-confining river channel or some such,) since the great part of the wave would simply divide itself and pass each side of the island.
As with all waves, in deep water the body of water comprising a tsunami doesn't move laterally -- it simply oscillates up and down as the wave passes. However, the wave breaks in the presence of shoals, and then the body of water does indeed move laterally, potentially causing a great deal of damage. So a tsunami at sea in fact isn't all that different from the tidal wave (ie the wave that circles the earth twice a day to produce the tides.) Hence it's common name. But isn't it unfortunate that the term "tidal wave" is applied in common speech to a volcanically-originated and completely NON-tidal event?
This is not a particularly erudite analysis, but it may clear up the point for a few people.