Here is an article in todays (May 22, 2002) NYTimes:
http://www.nytimes.com/2002/05/21/science/21MAYA.html
Nearly 100 feet beneath the Yucatán Peninsula in southern Mexico, cave divers are mapping the world's longest underground river. More important, they are unraveling the mysteries of a fragile ecosystem that may be destroyed before it is fully understood.
That the peninsula is rich in human history is attested by the temples and pyramids built by the Maya during the first millennium. Underground runs a common thread that has woven the fabric of life and directed the distribution of human settlement for the past 10,000 years: a complex system of rivers and natural wells whose formation began more than 100 million years ago, when the peninsula lay beneath a shallow seas.
Over a succession of ice ages, sea levels dropped some 300 feet, exposing the limestone platform that makes up the peninsula. Over time, rivulets of carbonic acid (a byproduct of rainwater bonding with carbon dioxide in the atmosphere) carved out the caverns. When sea levels began to rise with the last ice age 18,000 years ago, the once dry caves began to fill with water, a process that continued until about 1,000 years ago. Collectively, these submerged river systems provide all of the peninsula's fresh water. . . .
http://www.nytimes.com/2002/05/21/science/21MAYA.html
Nearly 100 feet beneath the Yucatán Peninsula in southern Mexico, cave divers are mapping the world's longest underground river. More important, they are unraveling the mysteries of a fragile ecosystem that may be destroyed before it is fully understood.
That the peninsula is rich in human history is attested by the temples and pyramids built by the Maya during the first millennium. Underground runs a common thread that has woven the fabric of life and directed the distribution of human settlement for the past 10,000 years: a complex system of rivers and natural wells whose formation began more than 100 million years ago, when the peninsula lay beneath a shallow seas.
Over a succession of ice ages, sea levels dropped some 300 feet, exposing the limestone platform that makes up the peninsula. Over time, rivulets of carbonic acid (a byproduct of rainwater bonding with carbon dioxide in the atmosphere) carved out the caverns. When sea levels began to rise with the last ice age 18,000 years ago, the once dry caves began to fill with water, a process that continued until about 1,000 years ago. Collectively, these submerged river systems provide all of the peninsula's fresh water. . . .