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original document: PlayaInfo Cenote Overview

Cenotes - Overview

A long time ago, dinosaurs roamed the planet and topped the food chain. Humans had not yet come into existence. The form of the continents and the composition of the earth was very different from that of today. Everything was about to change. Many experts feel that the end of the dinosaurs' reign came about as the result of a major astronomical event.

Deep Impact

Using imagery collected from NASA shuttle missions, scientists have been studying a large, multi-ringed crater centered near the town of Puerto Chicxulub on the Yucatan peninsula. It is believed that the crater was formed by an asteroid or comet which slammed into the Earth more than 65 million years ago. It is this impact crater that has been linked to a major biological catastrophe where more than 50 percent of the Earth's species, including the dinosaurs, became extinct. The 180 to 300 kilometer diameter (110 to 180 mile) crater is buried by 300 to 1,000 meters (1,000 to 3,000 feet) of limestone.

Big Changes

After the impact, incredible global changes occurred including a significant drop in sea level which exposed land masses. The Yucatan's limestone rock bed, which had been formed from millions of years of sea life and reef growth now overlooked the sea with great cliffs in place of today's white sandy beaches. At some point it is believed that the sea dropped as much as 100m from its present level. Falling precipitation mixed with carbon dioxide from plant life to form a weak carbonic acid which slowly dissolved the cement-like binding of this great slab of limestone. Over millions of years, this intensely slow process formed subterranean channels as the groundwater flowed in search of it's own level.

Speleothems and Collapses

The mineral rich seeping water dripped and flowed reforming the rock in its path. Intricate, delicate and sometimes massive formations called speleothems resulted after millions of years. During this time, the sea level crept back to its present level. In some areas, the overhead rock of certain larger channels became thin to the point of collapsing by its own weight. These openings at first provided entrance to this natural shelter to animals and, later, for a brief moment in geological history, to man, until the caves were finally filled again by the rising sea level.

Sacred Water Source

The Mayans consider these 'sinkholes' sacred and gifted by the gods. Their name for them is dzonot. To the Spanish ear, this word was registered as cenote. Many ancient ceramic and precious stone pieces have been found in cenotes, suggesting that ceremonial offerings were made to them. It is common to find skeletal remains of animals and humans in the water-filled underground cave systems of the area. Some are found great distances away from cenote openings, hinting of the subterranean world that existed before the passageways flooded as the sea settled near its present level some 16,000 years ago.

How may cenotes are there?

It seems that cenotes are normally found near trails or where people live. In other words, cenotes are all over the place in this region of the Yucatan. It is believed that fewer than 10% of cenotes have been explored by modern man. The jungle is vast and protective of its secrets. Most of the easily accessed ones have been explored by cave divers, but each year more and more systems of underground passageway are put on the map as explorations penetrate deeper. Many reach thousands of meters in length, often connecting multiple cenotes.

Big Deal

There are water-filled caves in many parts of the world. Those found in the Riviera Maya area of Mexico's state of Quintana Roo are considered by many to be the finest for diving. Compared to other water-filled cave systems in the world they are shallower, warmer, more decorated with speleothems, more easily accessed, and more complex with the greatest water clarity one could expect anywhere in any dive situation worldwide. Added to the mix is the fantastic beauty of the jungle oasis-like setting of many cenotes. You don't need to be a diver to become enchanted with these miracles of nature. Beautiful exotic birds frequent the cenotes' lush flora. They define the perfect summer swimming hole.

Caves and Caverns

There's a difference. At least as far as diving is considered. Most technical diving agencies consider the cavern zone to be that area of an overhead environment limited to:

• within visible range of direct sunlight
• within 67m/140' of combined linear distance of the open water area
• less than 33m/100' of depth
• area sufficiently large for two divers to pass side by side
• minimum starting water visibility of 13m/40'
• always maintaining a continuous guideline to the surface.

Cave Diving

To dive in water-filled caves, a diver must utilize specialized equipment and specialized training. Improperly trained divers, including open water instructors, have a very poor safety record in caves. If you are interested in cave diving, be sure to receive the proper training from a well-respected instructor. There is nothing worth dying for in the caves.

Cavern Tour

Purpose

Confident and relaxed Open Water certified divers can safely participate in a guided cavern tour at one of many local cenotes with an adequately large cavern zone.

Pre-requisites

Confident, certified Open Water diver with good buoyancy control
Not claustrophobic
Recently logged dive or refresher course

Limits

a. Natural Daylight
b. Max linear distance from surface: 65m/200ft
c. Maximum depth: 30m/100ft
d. No restrictions where two divers cannot pass side by side
e. No planned decompression
f. Minimum starting visibility 10m/30'
g. Maximum ratio of one guide to 4 divers
h. Minimum tank pressure to begin cavern dive: 135BAR/2000 psi (AL80 tank)
i. Continuous guideline to the surface

Guide Qualifications

This is a hotly contested issue in the local diving community, and presently under review. Guides have been seen exceeding the limits, taking more than four customers, leaving the guideline, passing through restrictions, etc. Normally the customers have no idea that they are exceeding limits. A dangerous situation could result. Your guide should have logged at least 50 cave dives before leading customers in the cavern zone. Each guide should cover the major points of this article in a briefing before the dive, review signals and special equipment configurations and swim techniques, and debrief each dive with comments and recommendations for improvement. Full cave equipment, including double tanks, large primary light with a minimum of two backup lights, redundant regulators, and safety reels should be used.

The majority of guides are competent and thorough. Choose yours with care and enjoy this one of a kind dive experience. You will be very glad that you did.