Re: dry Meditteranean

chornedsnorkack_at_hushmail.com
Date: 01/17/05 

Date: 17 Jan 2005 08:42:41 -0800

Paul Ciszek wrote:
> In article <1105793550.000353.151430@z14g2000cwz.googlegroups.com>,
> <chornedsnorkack@hushmail.com> wrote:
> >
> >In geologically short time, but not historically short time.
> >
> >IIRC, Mediterranean now receives about 30 000 cubic metres per
second
> >of fresh water by rain on the water surface, 8000 -"- by all rivers
> >directly entering and 5000 -"- from the Black Sea. The evaporation
is
> >around 150 000 cubic metres per second, so 100 000 cubic metres per
> >second is a shortfall.
>
> Water flows from the Black Sea to the Mediterranean? How salty is
the
> Black Sea?
>
> I ask because there is evidence that the Black Sea was once isolated,
> then when sea level everywhere else rose at the end of the Ice Age,
> the Black Sea suddenly filled from the Mediterranean through the
> straight. If the Black Sea had had a surplus of water flow at that
> time, it would have filled up the straight and flowed into the
> Mediterranean on its own. I suppose that amounts of rainfall have
> changed a lot since then, though.
>

Yes. There seems to have been a dry period - drier than now - in late
Ice Age. As mentioned, the current surface salinity is around 18 per
mill.

> >The shortfall is compensated by water entering from the Atlantic by
> >Gibraltar Strait.
>
> I guess I had assumed that the Black Sea was in the same situation
> WRT the Mediterranean.
>
> >Were the Gibraltar Strait suddenly closed again, the level of
>
> Closed, or if the sea level of the rest of the ocean dropped below
> the bottom of the straight of Gibraltar. How deep is it, and what
> is the lowest sea level has dropped during glaciations?
>
I think around 330 m. The lowest sea level is quoted as about 150 m.

> >Mediterranean would start falling at about 1 metre per year. Which
is
> >about what happens to salt lakes, like Aral Sea or Mono Lake or Dead
> >Sea if the rivers flowing in are suddenly diverted.
> >
> >And at 1 metre per year, well, the Mediterranean is about 5000
metres
> >deep, so it cannot dry up faster than 5000 years. Which is why Mono
> >Lake, Aral Sea and Dead Sea also still exist.
>
> But how deep is it over most of its area?

Well, the average is about 1500 m.

Within decades, all the
> existing seaports will be out of business or will have had to make
> radical adjustments.

I think more like in years. Sea transport could only go on using easily
movable port installations, with the level falling a metre per year.

I expect that it would not take long for the
> Mediterranean to shrink laterally. How long before Sicily becomes
> part of the mainland again?
>
I think the sill depth at Messina Strait is about 115 m - marginal for
Ice Age landbridges.

Shrinking would probably start at places like Adriatic and Gulf of
Gabes.

At about 430 metres, there would form a landbridge between Sicily and
Tunisia. Thereafter, the western and eastern basin would each shrink at
the rate determined by local climate and inflow.

But I wonder about another thing...

Suppose Gibraltar were closed right now - but no one shut the Suez
Canal?

Right now, the Suez Canal has depth of about 20 m and cross-section of
IIRC something like 3000 square metres. There is a weak northward
current - not much.

Is the Suez Canal dug in rock or in loose sand?

In a few years, the level of the Mediterranean would sink so much that
there should be a strong and steady northerly current in the Canal. And
this current would begin to erode the canal, starting from Port Said
and continuing with knickzone migration. It has to achieve something.
The Mediterranean requires about 100 000 cubic metres per second of
water. The existing cross-section cannot support this. Were the
northern mouth of the Canal built of solid rock or masonry, it might
form a waterfall with water speeds of 10-20 metres per second above the
lip - but I expect that in soft sand, rivers generally support flow
speeds of around 1 metre per second, because this is the speed where
sand erodes or settles. And an eroded channelbed 100 000 square metres
in cross-section... Hm. The water volume would be more than for Congo,
slightly less than Amazon. Of course, there should be a transient as
the Mediterranean is filled back to nearly Red Sea levels. So,
depending on the character of rock, one might expect the Suez Channel
to erode to widths of 1...5 km and depths of 30...150 m. Or
something... That is, for the beginning. Which would mean removing, hm,
170 km... something like 20 cubic km rock and dumping it as a delta or
down submarine canyons.

How fast do you think would the matters go this far - i. e. one-way
flow keeping Mediterranean on the Red Sea levels?

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