cladking Wrote:
-------------------------------------------------------

>
> At leaSst some of the CO2 in a lake will be
> released to the air or to plant life.
>
> If the volcanic magma can carbonate a lake then it
> surely can carbonate and aquifer. Since the magma
> and the rising mountain are continually tipping
> the aquifer basin then at some point it can be
> essentially emptied so there is no more flow of
> CO2 into the aquifer.

I think you are mixing up two different things. One is the process of creating lakes with large CO2 concentrations at the bottom (a rare thing-- 3 lakes in Africa) lakes are formed both by groundwater and by rainfall. The CO2 accumulates and ocassionally the lake overturns with tragic consequences and the cycle begins anew. Cold geysers (which apparently do not occur naturally) by definition would not involve contact with magma (otherwise you get a normal geyser.

>
> > "There are three lakes in the world which
> exist
> > under a very unusual and dangerous set of
> > conditions. They are all in areas of
> volcanic
> > activity. Springs feed into the bottom of
> these
> > lakes, containing huge amounts of dissolved
> carbon
> > dioxide, released by magma below the earth's
> > surface. When triggered the lower waters of
> these
> > lakes can release huge clouds of carbon
> dioxide
> > gas in an eruption from the lake caused by
> gas
> > bubbles rising rapidly through the water.
> This is
> > known as "lake overturn" as the lake is
> literally
> > overturned as carbon dioxide from the bottom
> of
> > the lake is released pushing water up with
> it. The
> > only three lakes which contain such high
> amounts
> > of CO2 are lakes Monoun, Nyos and Kivu in
> > Africa."
> >
> > Even if there were a CO2 laden aquifer in
> Egypt,
> > the Egyptians did not have the technology to
> drill
> > down far enough to reach such an aquifer.
> >
> > Bernard
>
> There would be very high water tables during the
> inundation. There was apparently a river flowing
> west to east just north of Giza and if large
> amounts of water were coming up in this region
> there would be a more minor tributary flowing
> north nearly from Lake Moeris.
>
> The Nile once flowed a little west of Giza. When
> the "Great Green" was cut off from the world's
> oceans the level dropped hundreds of feet which
> caused the Nile to carve a deep canyon all the way
> to Aswan. Eventually the connection was
> reestablished and the canyon flooded becoming a
> fiord. This took many tens of thousands of years
> to fill in but it would have created numerous
> caverns and caves in the surrounding area as it
> did. About the time it completely filled the
> river switched to the east side of Giza.
>
> Since the water came from higher areas there's no
> reason that it can't be very high on the Giza
> Plateau. Even today there are trees in the area
> with their roots extending deep to the water
> table.
>
> There was a great deal more water in antiquity.
> Horapollo claimed that the ancients believed water
> came from the ground.


all this is irrelevant to the question at hand. Even if there were a CO2 rich aquifer under the Nile Valley, the Egyptians did not have the technology to drill deep enough to get to such an aquifer. To get the kind of pressure in an aquifer to cause a cold geyser the aquifer would have to be pretty deep. At water table level what would happen is you get a well or, naturally, a spring. If there were CO2 it would just bubble out because it would not be under high pressure.
Here is a description of a cold water geyser in Utah. Notice 1) that the aquifer is 225 meters deep and 2) the CO2 does not come from magma so that the African lake analogy is even farther from reality.

[www.blackwell-synergy.com.ezproxy.lib.utexas.edu]



The immediate source of both the water and the carbon dioxide in Crystal Geyser is almost certainly the Navajo Sandstone, reached at a depth of about 215 m in the well. Along with the Wingate Sandstone, and with impermeable shales both above and below, this constitutes a major aquifer fed from outcrops on the San Rafael Swell 25 km to the west. The fountaining water contains over 12 000 ppm of dissolved salts, largely derived from the Navajo Sandstone, but possibly also by saturated seepage from evaporites deeper down in the Carboniferous sequence. The main source of the carbon dioxide is thought to be a reaction between acidic groundwater and the carbonate fractions within the Navajo sandstone. The contribution of meteoric and soil gas is likely to be small in the desert climate, and there is debate over the role of deeper warm waters in the carbonate breakdown.

Whatever its source, the carbon dioxide content of the groundwater is high under the hydrostatic pressure induced by depth. As more is generated, the water becomes saturated with the gas, which therefore starts to exsolve. The column of water in the well conduit therefore starts to effervesce, and pushes water out of the top of the well. Less water in the well conduit causes a reduction of hydrostatic pressure in the aquifer, and in turn causes more carbon dioxide to be exsolved. This is a chain reaction, very similar to the flashing of steam due to reduced pressure in a conventional hot geyser. But in the case of Crystal Geyser, the process is more akin to an effervescing bottle of champagne. The rapidly generated gas drives the eruption, until gas and water achieve a new equilibrium under lower pressure. Then all is quiet, while dissolved gas accumulates until the cycle can repeat.


Bernard



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>
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> tempus fugit