Precipitation, already slightly acidic due to atmospheric carbon dioxide, upon contact with the ground also absorbs tannic acid from vegetation before percolating through the porous surface, irresistibly seeking its way back to the sea through fractures and cracks. On its course, the acidified rainwater reacts with the limestone, dissolving it and, over time, creating ever larger conduits and longer passages.
Ever so slowly, amazing tunnels and caves were hollowed out from the underground, giving dripping water and howling wind unimaginable artistic freedom to lazily form speleothems of wonderful beauty.
Then, about eighteen thousand years ago, as the last glacial period declined, sea levels began to rise again, thereby also lifting the freshwater table and causing Yucatan's fabulous underworld to flood.
Cenotes refer to locations where the groundwater is accessible from the surface, typically where a section of cave has collapsed under its own weight during a period of drought. Having been filtered on its way down through the porous limestone, cenote water is usually crystal clear and, being sheltered, has a relatively constant temperature of about 24-25°C (up to 26 below the halocline).
The word cenote is derived from the Mayan word "dzonot" meaning "sacred well", as these waterholes were of life sustaining importance to them, there being next to no open waterways on the peninsula.
For the Maya, these mysterious water filled sinkholes were also believed to be gateways to the other world, which explains why some of them were offered valuable objects and even human sacrifices, in order to appease the gods, e.g. the rain deity Chaac.
Besides the natural cave decorations, prehistory can still be observed today in many cenotes in the form of petrified layers containing bits of corals and fossilized shells, traces of charcoal fires, ancient bones of long dead animals and humans, and even intact pottery.
→ Quintana Roo Speleological Survey
→ Wikipedia: Cenotes
