Bernard; Thank you for the info. I was not aware of some of this.

I don't know the minimum depth at which cold water geysers can form
but this water which forms (and formed) most of the water table at
Giza is (was) coming from far to the south. If it was upwelling from
very deep aquifers, it's not difficult to imagine it coming up with
lots of CO2.

Everything that I've read agrees that all or most such geysers are
man-made. With the Egyptians' penchant for digging, tunneling, and
drilling it's within the scope of their ability to have done this. All
it would take is to see a little water coming up where it was needed
and they might start operations to see if the flow might be increased.

The primary and initial reason for even mentioning Lake Kivu is that
this was within the Nile drainage basin and is now carbonated. This
is ongoing and there was an eruption this century.

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Man fears the pyramid, time fears man.