While diving the Riviera Maya cenotes, you can witness the geological calendar. You will see spectacular formations formed during the last Ice Age and appreciate the archaeological discoveries through your mask. As visitors, cave and cavern divers learn to be safe and care to observe and preserve this unique and beautiful cave environment.
The word “cenote” is derived from a Mayan term D’zonot and represents a subterranean cave that contains permanent water.
Types of underwater cenotes and caves
There are five categories of underwater caves:
- Sea caves
- Coral caves
- Lava flow caves
- Glacier caves
- Solution caves
All share similarities in composition, general location, shapes, and tools of origin. Solution caves represent most of all caves found worldwide and makeup 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. The compacting, cement bonding, and recrystallization of the limy sediments accomplish this metamorphosis. 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.
Evolution of cenotes
The tremendous presence of limestone collapses characterizes the landscape as the ideal karst terrain. A steady movement of underground water through a vast network of passage flows where it finds the least resistance. The volume of water drainage is so great that it cannot exist on the surface. The soft, porous limestone highly filters all water, causing it to flow underground.
We know the evolution of cave passageways that form or exist below the water table 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 a thick limestone and has a low relief and a high water table. The water table has risen and fell during the last Ice Age, causing rapid cave development and creating the best surroundings for cave diving.
Physical features of the cenotes
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, the point of the compass, clarity, and 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 Tajma Ha. Cenotes can also be filled with water.
Water in the cenotes
Distances from the normal land surface down to the water can vary from a few feet up to thirty feet (ten meters). Consider the difference in distance at Cenote Naharon (Cristal), which drops only one foot compared to Cenote Dos Ojos which falls over twenty-five feet (7.6 meters) from the top to bottom. The surface and topography of the land and the underground water table play important roles in the 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 Cenote Manati (Casa cenote), may be affected by water flow or reverse direction due to the tides. Water levels will fluctuate by 12 in or more in the Cenote El Eden between a high and low tide. In cave passages, you can actually view saltwater moving upstream while the freshwater continues to drain downstream.
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.”
How Solution Cenotes and Caves Form
Several conditions are necessary to form solution caves. These items are:
- host rock,
- groundwater,
- structural setting,
- and 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 dissolves away the calcium carbonate. Fresh water is more acidic because it has higher levels of dissolved carbon dioxide (CO2) and humic acids. Acidity allows the 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. Freshwater flow is an important process in the formation of solution caves.
The structural setting is an integral process in the formation of caves. Most caves form when the cave passages are immersed in the freshwater flow of the aquifer so that the calcium carbonate glue is exposed to maximum decomposition and dissolution.
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 2.5 km south of 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 spelling 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.
Various speleothems
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 – form 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.
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