Despite the regions rich in Mayan history, the Yucatan peninsula is considered very young, formed during the Cenozoic era - 65,000,000 years ago. This flat land was once an ancient reef but as the sea level dropped the Yucatan emerged. The peninsula is a huge porous shelf of sedimentary rocks consisting of dead coral, shells and the break down of lime left behind from decomposition. The limestone that makes up deposits near the coasts range in age from the Pleistocene and Holocene periods.

The peninsula encompasses 73,000 square miles (190,000 square kilometers) of limestone lowlands perforated with underground caves and tunnels, a majority filled with water. There are no surface rivers or streams (except the far southern portions). The limestone is so soft that rain
percolates easily through the ground. Cenotes are natural wells that evolve when the limestone weakens and collapses forming “windows” to the underground aquifer. The land surface is virtually dotted with these cenotes.

The Yucatan is made up of three states; Campeche, Yucatan and Quintana Roo. The peninsula divides the Gulf of Mexico from the Caribbean Sea. Fed into the Caribbean basin by the Atlantic currents, these massive ocean rivers flow north along the peninsula’s eastern shore, producing a steady, strong flow of water that touches every channel and offshore island. The warm, water temperature and the water clarity makes it ideal for the growth of coral. Wetlands and estuaries combine to create the best conditions for food sources feeding the corals, sponges and other reef-building organisms.

These coral reefs and a multitude of ancient life forms have been in existence for 500 million years. These coral polyps range in size from a mere particle to as large as grapefruit. The water temperatures range from 75 degrees F - 85 degrees F.

UNDERSTANDING THE CENOTE ENVIRONMENT

The word “cenote” is derived from a Mayan term - D’zonot - and represents a subterranean cavity that contains permanent water. While diving the cenotes of the Riviera Maya, you can actually witness the geological calendar. Through your mask you will see spectacular formations formed during the last ice age
and appreciate the archaeological discoveries. As visitors, cave and cavern divers learn to be safe and carefully become part of this unique and beautiful cave environment.

There are five categories of underwater caves; sea caves, coral caves, lava flow caves, glacier caves and solution caves. All share similarities in composition, general location, shapes and genesis mechanisms. Solution caves represent the majority of all caves found throughout the world and make up all the cenotes and underground cave systems along the eastern Yucatan peninsula.

Limestone is a large grouping of similar minerals made up of calcium carbonate (CACO3). The shallow tropical oceans help to produce an abundance of these sediments called lime. Most of the lime derives from the calcium skeletons of marine animals and some types of algae. These
sediments accumulate over geological time and form into layers. Time, pressure and temperature actually solidify these sediments into a rock material. This metamorphous is accomplished by the compacting, cement bonding and the recrystalization of the limy sediments. The dissolution is the breakdown and removal of rock formation as a result of acids facilitated by the circulation of fresh water within the pores that make up part of the rock volume.

The landscape is known as the ideal karst terrain that is characterized by a tremendous presence of limestone collapses. A steady movement of underground water through vast network of passages flows where it finds the least resistance. The volume of water drainage is so great that it cannot exist on the surface. All water is highly filtered through the soft, porous limestone and flows underground.

The evolution of cave passageways, which forms or exists below the water table, is known as the phreatic zone. The water moves through the passageways (pores) vertically and horizontally from higher pressure to lower pressure. The vadose zone is any chamber, passage or air space that forms above the aquifer. Many vadose passages and rooms exist in both the local cavern areas and cave systems. The Riviera Maya is typical with thick limestone, low relief and a high water table. The water table has risen and
fallen during the last ice age, causing rapid cave development and creating the best surroundings for cave diving.

The complete understanding of the hydrological purpose is very important as the Riviera Maya coast continues to develop and grow. Recognizing the special needs of a very sensitive karst terrain and preventing problems from surface contamination can preserve the environment and make good use of the
natural resources. Sewage runoff into the aquifer can slowly choke the life out of the cenotes and the fringing reefs along the Riviera Maya coast. Hotel and resort communities must incorporate their own self-contained sewage treatment plants. Smaller dwellings such as condominiums, villas and private homes must
find alternative solutions and stop this contamination.

PHYSICAL FEATURES OF THE CENOTE

Any time a cave diver plans to explore a new cenote, it is important to understand the physical features and the water flow. Cave openings provide information about the movement of water, its point of the compass, clearness and the general characteristics. By understanding these clues, the cave diver can explore the potential cave system with the best results.

Cenotes can be any shape or size. They can appear as a pond, such as the Cenote Carwash, a tiny shaft such as Cenote Mundo Escondido (Hidden World), a crack, hole or a lagoon. Any form of collapse can represent a cenote. Cenotes can also be mostly dry with the jungle continuing to survive down inside
the basin and water flowing around the edges. Good examples include the Grand Cenote, Cenote Chac Mool and Cenote Taj Mahal. Cenotes can also be filled with water. Distances from the normal land surface down to the water can vary from a few feet up to thirty feet/10 meters. Consider the difference in distance at Cenote Naharon (Cristal) which drops only one foot compared to Cenote Dos Ojos that falls over twenty five feet/7.6 meters from the top to bottom. Surface and topography of the land and the underground water table play important roles in a cenote formation.

Water that flows into the cenote is called the spring side or upstream area. It is also known as the outlet. Water that flows from the cenote back underground is known as the siphon side or downstream area.

Hazards exist when diving downstream because of the minimal water flow. Water in the cenote basin is called the pool. The water volume and flow will vary but because most water drainage originates from a horizontal source and not depth, the flow of water is minimal. Cenotes close to the coast, such as
Tankah, may be affected by water flow or reverse direction due to the tides. These cenotes are known as anchialine pools, a term coined by Holthuis (1973) to denote; “pools with no surface connection to the sea, containing salt or brackish water, which fluctuates with the tides”. Water levels will fluctuate by
12 inches or more in the Cenote Eden between a high and low tide. In cave passages, you can actually view saltwater moving upstream while the freshwater continues to drain downstream.

How Solution Caves Form

Several conditions are necessary to form solution caves. These items are:

1. Host rock.

2. Groundwater.

3. Structural setting.

4. Time

Host Rock involves the limestone found in the Yucatan. Between this bond of limestone cement and these granules are spaces called porosity. Add the ability for the rock material to be able to transmit fluids and the limestone becomes permeable.

A constant flow of fresh water is needed to dissolve away the calcium carbonate. Fresh water is more acidic because it has higher levels of dissolved carbon dioxide (CO2) and humic acids. Acidity allows aggressive dissolution of calcium carbonate to break down the cement that bonds the original particles together. The naturally occurring mixture of CO2 and water creates carbonic acid (H2CO3).

Groundwater must be continually flowing with fresh, chemically unsaturated water and be able to pass through the rock pores to flush the newly dissolved cement away from the particles. Fresh water flow is an important process in the formation of solution caves.

The structural setting is an integral process in the formations of caves. Most cave formations take place when the cave passageways are submerged in the fresh flow of the aquifer allowing the maximum exposure for the calcium carbonate glue to break down and dissolve away.

Time is the overall factor in forming caves. Thousands of years worth of constant reactions and movement of water are necessary for cave development. This geological calendar allows the opportunity for the cave to evolve and make its shape and form the decorations and characteristics it contains.

SPELEOTHEMS.

Picture yourself floating through some of the most decorated caves in the world. You only need to drive one kilometer south of Aventuras Akumal to a commercial dry cave called AKTUN CHEN - the wood cave. This cave adventure is very popular because it will dazzle your imagination and answer the most commonly asked questions; why cavern dive and what do you people see in caves? Aktun Chen is an archaeological gallery of cave formations produced by mineral deposits known as speleothems. The name is taken from the
Greek spelaion meaning cave and thema meaning deposit. Speleothems are mineral deposits that formed when the environmental conditions were just right. This occurrence in the cenotes took place during the last Ice Age.

Most speleothems are made up of crystallized calcium carbonate. The deposits can evolve into any shape or form. The most common and familiar speleothems are stalactites and stalagmites. When it rains, this groundwater seeps through the porous limestone and into the cave where the carbon dioxide
can be absorbed into the cave atmosphere. This out gassing of carbon dioxide from the groundwater makes calcium carbonate and precipitates calcite.

The first step in the formation of these beautiful cave features begins with soda straws. They are hollow, tubular stalactites of calcite usually no bigger in diameter than the water droplet that formed it. If the water droplets are able to flow down outside the soda straw, it becomes thicker and forms a stalactite. The following descriptions explain the various names of speleothems.

Draperies - calcium carbonate that forms as layers or drapes from water droplets flowing down walls or from ceilings.

Helictites - calcium carbonate that forms twisting, irregular shaped branches or twig-like rods extruding from the walls or ceiling. The water oozes through the central core of the formation defying gravity. They can evolve into very odd designs and form in random directions.

Columns - when stalactites and stalagmites join together.

Flowstone - a thin film of calcium carbonate from water flowing down a wall.

Dripstone - dripping water forming speleothems such as stalactites and stalagmites.

Rim stone dam - a calcium carbonate deposit which forms around a cave pool or tends to obstruct a cave stream

The appearance of underwater speleothems that form only in air is a clear indication that the underwater caves of the Riviera Maya were once dry and now are immersed by rising water levels.

UNDERWATER HAZARDS OF THE CENOTES

Scuba diving in underwater caves presents a variety of hazards that can make it a very dangerous activity. Understanding the environment and being prepared for the risks are crucial to a safe dive. Creating specialized equipment and applying specific techniques increases the safety and psychological comfort for the cave diver. If not appropriately prepared it becomes unsafe to participate. Hazards of the cenote environment present a technical challenge but your dive can be very successful if suitably trained and equipped.

GENERAL HAZARDS

Water is a general hazard simply because we are air breathing mammals not adapted to survive underwater. Scuba allows us to experience the underwater world, therefore, it becomes imperative to know how not to misuse or abuse these valuable tools.

The temperature of water can be a substantial factor for survival or being comfortable. A diver’s environmental suit makes a tremendous difference between a fun and enjoyable dive or a miserable one; even a life threatening situation.

Natural daylight cannot penetrate cave systems making it necessary to carry adequate lights. A minimum of 3 powerful lights should be taken with each cave diver. Research, locate and use the best lights for your diving. Remember, these lights do more than illuminate a cave - they are safety tools.

SPECIFIC HAZARDS

Most caves around the world present water flow that can be a specific hazard in cavern and cave diving. The current can affect the diver’s air consumption, stamina and underwater rate of swimming. Fortunately, almost all of the caves of the Riviera Maya offer no “high flow” that can be considered treacherous. Only Sistema Ox Bel Ha located south of Tulum beach has a challenging
flow of water as it approaches the Caribbean Sea. That flow may make divers think twice about the dive.

Silt is the most dangerous natural hazard of the cave environment and can greatly affect visibility. Poor visibility is due to the particles suspended in the water. These particles are arranged into three simple categories:

1. Sand and gravel

2. Mud or mung

3. Clay

Sand and gravel are large sized particles that pose no threat to the diver. The weight and size of these types of silt keep them from suspending in the water and harming visibility. Most of the cenotes in the Riviera Maya lack this type of silt.

Mud is an organic material resulting from surface intrusion. Leaves, dirt, and decomposing aquatic plant life are examples of the accumulation of mud in the cenote basin or pool. These types of silt are usually found on the siphon or downstream area of cenotes. Once stirred visibility is reduced but not to the point of being dangerous unless in huge amounts in small areas. It will quickly settle but can be annoying or make your dive very unpleasant. Mung is an organic material that exists in marine caves that can vary in size. It is light-weight and tends to cling to everything like a fine dust.

Clay silt is the most dangerous type of particle because it is light or dark in color and is very light weight. It can easily be disturbed and will reduce visibility to zero. This visibility loss, due to clay turgidity, is a cave or cavern diver’s worst fear. In the fresh water zones of the cenotes, clay silt is usually not present and poses no immediate threat. In the salt water areas, the break down of the limestone produces a very fine power or dust that can amass in thick drifts. The size of the passageways will determine the severity of low visibility if this kind of silt is agitated. Another threat is percolation, clay particles clinging to the ceilings, particularly where few or no cave divers have explored. When cave divers swim into new cave or cavern passageways that lie in saltwater, it is common for the exhaust bubbles from the scuba to dislodge these tiny particles causing zero or low visibility. The dive in may be crystal clear but swimming out can be a pure nightmare. An experienced and safe cave diver will use good buoyancy and propulsion techniques and have complete confidence in his or her ability to psychologically deal with this type of predicament.

Statistically, many cave fatalities involve diving too deep on air. Fortunately, this specific hazard is not a factor in the cenotes and cave systems of the Riviera Maya. The consistent, shallow depths minimize decompression and do not pose the typical problems associated with nitrogen narcosis or oxygen toxicity. With the exception of a few places, all the cave systems are eighty feet/24 meters or less. This is a major reason why cavern and cave diving in the Riviera Maya are so popular and safe.

The configuration of every cenote and cave system varies. As with fingerprints, not one is alike. Each has its own personality and distinctive features. The structural components of restrictions are potentially dangerous. A minor restriction is where the cave passage or cenote entrance narrows down
to a size small enough for one diver to squeeze or swim through. This is why long hoses are necessary for a cave diving team in case of the emergency to share air single file through a minor restriction. A major restriction is where the diver must remove or manipulate his or her equipment. Cave divers, wearing double tanks on their backs, will not fit through. Major restrictions usually require the side-mount technique. Low visibility because of silt or organic debris, poor guideline management where entanglements can occur,
buoyancy deviations, separation from your buddy or air supply and any combination of all these factors can cause disaster. A safe cave diver knows the limitations, experience level, and uses good judgment and common sense to avoid problems while approaching restrictions.

Large passages and mazes are very common in the cave systems. Many gigantic rooms exist such as the “Hall of Giants” and the “Coliseum Room” in the Cenote Calavera, the “Jumna River” and the City of Agre” room in Sistema Taj Mahal, the “Pool Hall” on your way to “The Chapel” downstream Sistema PonDeRosa, “Chac’s Room” upstream Cenote Cristal (Naharon) are just a few examples of huge passageways or rooms that can potentially be a hazard. Losing reference with the walls, floor or ceiling is possible. Luckily, visibility is always exceptional and does not create such a perilous threat unless the cave diver technique becomes very sloppy. Confusion in direction can cause mental anguish if not careful.

Several cave systems almost look like Swiss cheese. Examples are Sistema Minotauro, Sistema Chac Mool, parts of Sistema PonDeRosa, and Cenote Abejas. Passages can look completely different when you are returning from the other direction. Maintaining that continuous guideline and remaining within easy reach are important parts of safe cave diving.

Line traps are another unique, specific hazard of the cenotes. Though rare, laying your guideline around bends or areas where the line can move into a low clearance can invite an ugly challenge. If visibility is reduced, forcing the cave diver to follow the string by feel, you may find yourself feeling trapped or your exit hampered to the point where you have jeopardized your air supply. By moving the guideline sideways and carefully feeling your way through, the larger passageway will be found. To avoid such a hazard always recognizes a potential line trap and anchors your guideline in the easiest portion of the passageway to swim out.

Cave-ins are very rare! All caves are formed over thousands of years. Geologically, the cave structure is very stable and the water acts as its own natural support. However, ceiling collapses and breakdowns are a natural part of the evolution of caves. The rubble piles and the breakdown of boulders and rocks that are encountered on a dive are the results of cave collapses. No one really knows when they occurred. Several instances have taken place with evidence of noticeable changes in the cave. But, from a geological time stand point, the odds of any form of collapse while cave diving would be the same as a giant meteor hitting the earth. It is possible but unlikely. As pointed out in the dedication of this web site, only one fatality has occurred involving a form of geological disturbance which was a freak event in itself.

HYDROLOGICAL CIRCUMSTANCES

The quality of water in cenotes and underwater caves can be directly influenced by clarity, color, salinity and temperature. A cavern or cave diver’s ability to navigate, his or her comfort and ability to perform safely are very important in managing these conditions.

Chemicals.

Tannic acid results from the decaying vegetation from the jungle that becomes flushed into the cenotes from a large volume of rain. Usually, this occurs during the rainy season that begins mid-June and runs through to early October. When this tea color substance enters the water it can cause reduced visibility. Fortunately, the constant flow of water and warmer water temperatures
keep tannic acid at the surface and does not impose any problems with visibility. Tannic acid will, over time, stain the calcium carbonate surface of all cave features, walls, ceiling and floor. An excellent example is the cavern and cave system of Cenote Cristal (Naharon) - Sistema Najanral. In the freshwater sections of the cave everything is stained a very dark brown absorbing any light that strikes the exterior, minimizing the light output. According to topographical maps, a huge swamp exists several kilometers inland from this cenote. Theory is that surface intrusion from this swamp places a lot of tannic acid into the fresh groundwater.

Another chemical factor that acts upon visibility is called hydrogen sulfide. This chemical appears as a layer and usually is a thick cloud of gas. No reports of toxicity have occurred but hydrogen sulfide can make a diver nauseous. Hydrogen sulfide has a pungent odor of rotten eggs that you can smell and taste as you swim through it. It turns any brass or bronze surface, such as clips, into an ugly black coated mess. The Cenote Angelita located south of Tulum has a layer of this hydrogen sulfide at 100 Feet/30 meters that is about three feet/one meter thick. It is an exciting experience to dive and disappear through the cloud as if a ghost. The Cenote Siete Boca (Seven Mouths) or known as Deep Blue is located eleven kilometers west of Puerto Morelos. This cenote is 175 feet/53 meters deep. From 99 feet/30 meters there is an unusual concentration of hydrogen sulfide. So strong that it burns your skin, causes physical tension in the facial muscles and nausea. This cenote is regarded as very dangerous for divers.

HALOCLINES

Imagine yourself diving with your vision blurred. That is what a halocline does. Halo means density and cline means change. When fresh water meets salt water, they cannot mix because of the higher density of dissolved minerals and/or differences in temperature. Because the cenotes are located close to the Caribbean Sea, salt water seeps inland while fresh water drains to the ocean. This interface between these two density-stratified layers of water is very sharp and visually distinct. The visual disturbance is caused by refraction. The sunlight rays bend at a slower rate, moving from the freshwater into the saltwater, causing the blurring. The refracted rays deform the images. The halocline can actually reflect, appearing as a surface, and create the illusion of a false bottom. The best example of a halocline is the “River Run” passage going west from the Connote Eden basin. As you swim upstream you vividly see the fresh water moving rapidly over the saltwater. By moving yourself up into the freshwater you can actually feel a 2 degree F difference in water temperature. By dangling an object, such as a primary light head from the freshwater into the saltwater, you can easily demonstrate the two completely different types of water. The depths of the halocline vary from each cenote and cave system depending on the distance from the ocean. The halocline at the Sistema PonDeRosa is situated at approximately 33 feet/10 meters because it is about 5 kilometers from the ocean. At the Sistema Carwash, the halocline occurs at 70 feet/21 meters because it is further inland, roughly 13 kilometers from the
Caribbean Sea. Haloclines can be a thrill to experience but you must be careful when it blinds your vision. The best way to minimize the impact while diving with a team is to swim side by side thus not being forced behind the wake of another swimming cave diver. The “halocline room” in the Sistema Najanral (upstream Cenote Naharon/Cristal) has a permanent line located smack in the middle of the halocline so divers have no choice but to follow each other. Try to be the first one in cave diving team.

CAVE DIVING CONTRIBUTIONS

With the discovery and exploration of the cenotes and underwater cave systems of the Riviera Maya, cave divers have made generous and significant contributions in many different ways. Maps have been drawn, outlining the profiles and features of the cave passageways, documenting the location and the morphology of the water drainage. This helps tremendously in educating people about where the water comes from and where it is going. Wise and sensible decisions and policies can be made with the environment of the Riviera Maya just from the maps produced by cave divers. Water flow, chemical
composition, water color, temperature, depth of haloclines all can be measured, data and samples collected and resourceful observations noted by cave divers for government agencies, private companies, and scientists. Water-tracing studies which involves releasing dyes in the underwater cave systems by cave
divers, can help discover where the water flows.

CENOTES AND UNDERWATER CAVE FAUNA

The cenotes of the Riviera Maya contain a wealth of biological animals that are fascinating to find and observe. The abundance of interesting animal species found in and around the cenote is incredible. Birds, reptiles, amphibians, fish and mammals all exist around and depend on the cenotes for one important factor - source of water. Without it animals and humans cannot survive. Water is our most precious commodity!

You begin to explore underwater in the cenote and beyond into the cave system you will discover an entire new and incredible world lives and thrives. These cave animals survive without sunlight and green plants. These creatures are categorized into two groups. The first collection includes all animals that live in the twilight or dark region but can survive outside the cave environment. They are called troglophiles which comes from the Greek words troglos meaning cave and phileo which means love. The second collection of animals consists of species that have no eyes or pigmentation. These are called troglobites which uses bios, meaning life.

Twenty species of aquatic, troglobitic organisms are presently known in the cenotes and underwater cave systems in the Riviera Maya. These include 18 species of crustaceans from 7 orders and 2 fish species from two orders. Twelve species inhabit anchialine (coastal, brackish water) caves, while the remainder is limited to the freshwater caves. Almost all are marine based organisms.

Cave diving explorations, which began in the mid-1980’s, are now documenting the rich fauna that inhabit the cenotes of the Riviera Maya. When you swim in the underwater caves; you are actually witnessing an exceptional ecosystem. The evolution of these creatures represents some of the oldest living biological life forms on earth. For animals that live in a perpetual world of total darkness their behavior and survival are amazing sights to behold.

SUMMARY

The cenotes of the Riviera Maya provide a precious and unique environment to study, play and enjoy. Their fragile existence must be recognized and respected. They are the “windows” to the most important assets - the water. In the next thirty years, you may see wars in other parts of the world because of the lack of and demand for water. The hazards of the cenote and cave environment will require education, training, special equipment and experience to safely explore and learn. The supreme challenge for the future will be how we manage, protect and preserve this very special environment.

BIBLIOGRAPHY

Iliffe, Thomas M., 1992 An Annotated List Of The Troglobitic Anchialine And Freshwater Fauna Of Quintana Roo, Texas A & M University at Galveston, Galveston, Texas, p. 197- 198.

Tyson, Robert, 1994. “The Cave Diving Environment.” In Saltzman, Dayton. The Art of Safe Cave Diving. p. 15 - 23. The National Association for Cave Diving.

Wilson, William L., 1988 “Cave Formation and Terminology”. In Zumrick Jr. M.D., John L., Prosser, Joseph, and Grey, H.V.. NSS Cavern Diving Manual. p. 3 - 16. The National Speleological Society - Cave Diving Section.

Wilson, William L., 1988 “Cave Hazards.” In Zumrick, Jr. M.D., Prosser, Joseph, and Grey, H.V.. NSS Cavern Diving Manual. p. 17 - 21. The National Speleological Society – Cave Diving Section.

Wilson, William L.,1992. “Hydrogeology For Cave Divers.” In Prosser, Joe & Grey, H.V.. NSS Cave Diving Manual. p. 218 - 251. The National Speleological Society – Cave Diving Section.

Yager, Ph.D., Jill, 1992 “Underwater Cave Fauna” In Prosser, Joe & Grey, H.V.. NSS Cave Diving Manual. p. 210 - 217. The National Speleogical Society - Cave Diving Section.