Peggy,

<sigh> Well, I suppose you could say we're both right. Most of the world's
shorelines have two high tides and two low tides per day ("semidiurnal
tides"). But some nearly enclosed bodies of water resonate in such a way as
to result in one set of tides while the other ends up subdued or absent,
just a couple of blips on the curve most of the month ("diurnal tides").
See:

NOAA website
http://www.nos.noaa.gov/education/tides/tides07_cycles.html

Also
http://www.du.edu/~jcalvert/geol/tides.htm#Gulf

In the Gulf of Mexico, most shores have diurnal tides, and the total tidal
range is also low (only 1 m in Alabama at maximum).

Cheers,
Andy

Andrew K. Rindsberg
Geological Survey of Alabama

-----Original Message-----
From: Conchologists of America List [mailto:[log in to unmask]] On
Behalf Of Peggy Williams
Sent: Friday, February 06, 2004 9:58 AM
To: [log in to unmask]
Subject: Re: San Francisco Bay (Donax)


> Donax doesn't have to be quite as alert on the Gulf of Mexico, with
> only one high and one low tide per day. But I do wonder where they go
> during hurricanes. It must be exhausting.
Actually, we have usually two highs and two lows, but occasionally three
tides, or two, or even one per 24 hours.

Peggy

>           Peggy Williams: shell collecting trips
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