Scuba Diving

Cenotes are natural formations that occur when a connection is made between the surface of a region and a below-ground space or void. These voids often fill with ground- or rain-water, and in Latin America, the Yucatan region of Mexico is noted for being particularly plentiful with these unusual and important geological structures. Since the dawn of human civilization in the region, they have been sought out and made use of for a variety of purposes.

Cenote Classification

Since 1936, scientists have classified cenotes into several distinct categories. Pit cenotes (sometimes called jug cenotes) are openings that are smaller than the underground body of water they provide an entrance to. These are differentiated from cylinder cenotes, which have strictly vertical walls, and basin cenotes, which have very shallow water basins at their lowest point. The last class of cenote is the cave cenote, which unlike the other kinds, has a horizontal entrance that is largely free of water.

Cenote Creation

The formation of cenotes is due mainly to processes of dissolution and weathering (or erosion). Water, aided by wind, rain, and gravity, gradually degrades the surface strata until an opening forms, revealing the subterranean caverns below. Often, this is followed by a partial or complete collapse of the roof structure, leaving a circular portal from the surface to the underground.

Saltwater tends to form cenotes more quickly than fresh water, as it is more abrasive. Also, a developing cenote which is not yet completely filled will generally degrated the surface rock faster, as the sloshing action of the pooled water is a powerful abrasive force.

Cenotes whose roofs do not completely collapse usually leave a ledge or platform of rock, obligating any who wish to enter to crawl or slouch in order to gain entrance to the water source beneath.

Cenote Systems

The Yucatan is also the location of a huge, partially submerged crater, called the Chicxulub crater, which was created by an asteroid strike about 65 million years ago, and is suspected to be one of the major events that resulted in the extinction of the dinosaurs. A ring of cenotes is arranged on the circular rim of the section of crater which lies on land.

These cenotes can extend to a depth of greater than 100 meters below the surface, where fresh groundwater and rainwater accumulates; thus, the water contained within the underground caves is remarkably clear and pure. Many of these cenotes are interconnected, making for passageways that support an underground river which can be used (and historically has been important) for transportation or recreation. This is especially significant in the Yucatan, which suffers from a dearth of natural lakes and rivers, the only major water source (the Gulf) being saltwater and unsuitable for supporting human or plant life. The currents that carry these subterranean natural canals from cenote to cenote can be quite rapid, usually more so when the roof of the cenote above has not completely collapsed.

Though there are few rivers or lakes that run anywhere through the Yucatan peninsula, the currents that run through the water in these subterranean caves are often quite fast, and usually faster below cenotes with collapsed roofs than those who still retain a portion of their strata. Because they provide a natural source of fresh water in an environment where it's otherwise in short supply, the Yucatan cenotes were instrumental in helping the first urban centers develop. They were just as crucial to the first irrigation works built by the Maya, who ruled the region beginning over 2000 years ago.

Even today, the cenotes of the Yucatan are pivotal in the maintenance of the region's environmental health, and fascinating reminders of the wondrous complexity that interweaves geology and ecology on the surface of planet earth. Their continued exploration and enjoyment by tourists and spelunkers alike is a testament to the age-old and undoubtedly important role they continue to play in human habitation.