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Subject: Re: Tsunami fishes
From: "Trevor J. Kenchington" <[log in to unmask]>
Reply-To:Scientific forum on fish and fisheries <[log in to unmask]>
Date:Sat, 12 Feb 2005 20:59:54 -0400

text/plain (65 lines)

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Water motion is only circular if the wave is a deep water wave (meaning
that the water is deep relative to wavelength), which tsunamis never
are. Their periods are just too long. However, I would agree with you
that the major axis of the near-elliptical orbit of each water particle
would be insignificant at depths of several hundred metres, where the
seabed is thousands of metres below. After all, a typical tsunami has a
height of only a metre or so when in open ocean and the amplitude of the
motion must decrease with depth.

However, the issue is not a wave passing over deep ocean but rather a
wave passing from deep ocean, across the shelf break and into shoal
water. Under (at least) some circumstances, the sudden shoaling can very
greatly magnify the velocities and amplitudes of the flow up and down
the slope.

We are left with a question of whether a tsunami could produce flows of
sufficient velocity that they would carry fish with them, into depth
zones where the species in question do not live. I don't know the
answer. But pointing to what happens as the wave crosses deep ocean
won't provide it.

Trevor Kenchington

You wrote:

> Hello All,
>     As my major prof. reminded me when we first saw these pictures, a
> tsunami is a wave, not a current. The physics of a water particle in a
> wave is a circular motion, not directional. Displacement of a deepwater
> fish in such a condition would have probably been on the order of
> millimeters at most. Besides, if you're looking at the same photos we
> saw, if you look closely at some (i.e., coffin fish) you'll see a date
> with the year '03.
> None the less, cool pictures.
> Michael Cooperman
> Dept. Fisheries and Wildlife
> Oregon State University

Trevor J. Kenchington PhD                         [log in to unmask]
Gadus Associates,                                 Office(902) 889-9250
R.R.#1, Musquodoboit Harbour,                     Fax   (902) 889-9251
Nova Scotia  B0J 2L0, CANADA                      Home  (902) 889-3555

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