>
> From: Andy Rindsberg <[log in to unmask]>
> Date: 2004/12/09 Thu PM 02:49:03 GMT
> To: [log in to unmask]
> Subject: Re: FW: sand in the hourglass (2)
>
> Andrew Grebneff and Mike Gray both mentioned the shell-collecting
> possibilities after beach renourishment. Very interesting to hear what
> happens in the offshore pits, Mike. Anyone else have more information on
> that? It's hard to come by!
>
> OK, shell collecting. I've never managed to get to a beach right after the
> sand is pumped onto it, but I have visited Gulf Shores (Alabama) repeatedly
> after renourishment. On the first visit, there were a lot of sharp, broken
> shells, and they were oriented at all angles. There were complaints about
> tender young feet being cut by shells, so we decided to look into that as
> part of the beach renourishment project (that's called using a hammer
> because you have a hammer in your toolkit). I identified the main offenders
> as:
> 1. Bivalves with strongly ribbed shells that break along the ribs, e.g.,
> Argopecten and Dinocardium, yielding 4-sided fragments.
> 2. Bivalves with robust, convex shells, e.g., Crassostrea (exhumed from
> Pleistocene deposits offshore).
> 3. Bivalves with robust, flat shells, e.g., Dosinia, yielding triangular
> fragments.
> 4. Gastropods with robust shells, e.g., Oliva.
> As you can see, the fragile shells aren't really a problem despite the fact
> that they splinter. Dosinia was one of the worst, because it yielded the
> sharpest corners. But within a year, the problem had largely solved itself.
> Most of the sharp edges were a bit rounded by then, and the waves had
> reoriented the relatively flat bivalve fragments to horizontal instead of at
> all angles. The snails, not being flat, continued to act like caltrops. But
> all of this was pre-Ivan and a new round of renourishment is planned.
>
> If you live on a beach that has never been renourished but where plans to do
> so are in the air, why not make it your project to see what shells are there
> already? I found that every kilometer of Alabama shoreline has a different
> fauna, despite the fact that long stretches of it look much alike.
> Apparently this is because the mollusks live offshore and offshore
> conditions are not as homogeneous as beach conditions are. Some stretches of
> beach consistently yield fossil oysters and bay clams; pen shells; bivalves
> that bore in peat or clay; and other forms that are not otherwise common.
> Well, you could knock me over with a feather.
>
> So if you list the species of each stretch of beach separately, then you get
> some idea of what's going on offshore. But if you wait till after the beach
> is renourished, you'll never again see what would have been there naturally.
> The clock's ticking.
>
> Cheers,
> Andy
>
> Andrew K. Rindsberg
> Geological Survey of Alabama
>
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