Cenote

A cenote is a natural pit or sinkhole formed when limestone bedrock collapses, exposing groundwater. Cenotes have been generally used for water sources by the ancient Maya, and sometimes for sacrificial sacrifices, in the Yucatán Peninsula of Mexico. Similar rock-sided sinkholes, such as cenotes, being common geological types in low-altitude areas, especially on coastlines, islands, and platforms with young post-Paleozoic limestones with less soil growth. Similar karst characteristics in several other countries, including Cuba and Australia, have been referred to as cenotes.

Here is the List of Notable Cenotes: 

• Gran Cenote, 

• Cenote Suytun, 

• Cenote Zaci, 

• Cenote Angelita, 

• Cenote Hubiku, 

• Cenote Oxman, 

• Cenote Maya And 

• Cenote Samula.

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Geology and Hydrology

Cenotes are created by rock dissolution and also the subsequent structural collapse of a subsurface void, that might or might not be connected to an active cave system. Additional dissolution slowly removes rock that drops into the water underneath, making room for even more collapse blocks.

Because the rock ceiling is no more buoyantly protected by the water in the void, the level of collapse is able to intensify whenever the water table is under the void's ceiling. Cenotes can be completely collapsed, resulting in an open water pool, or severely damaged, with certain rocks overhanging well above water. Cenotes are frequently compared to small circular ponds with sheer rock walls, stretching tens of metres in diameter. Many cenotes, on the other hand, need some stooping or crawling to get to the water.

Penetration and Extent

The gran cenote in Mexico's Yucatán Peninsula's north and northwest overlie vertical voids that reach 50 to 100 metres (160 to 330 feet) below the modern water table. Nevertheless, several of these cenotes tend to be related to horizontally vast underground river systems, with aquifer matrix and fracture streams possibly dominating water flow via them. 

Cenotes across the Yucatán Peninsula's Caribbean coast (throughout the state of Quintana Roo) frequently provide access to vast underwater cave systems, including Sistema Ox Bel Ha, Sistema Dos Ojos and Sistema Sac Actun/Sistema Nohoch Nah Chich.

Freshwater/Seawater Interface

The Yucatán Peninsula has a large coastal aquifer system that is usually stratified by density. The infiltrating meteoric water (that is, rainwater) floats on the surface of the saline water intruding from the coastal margins, which has a greater density. As a result, the entire aquifer seems to be an anchialine system (one of which is land-locked, however, is connected to an ocean).

The interface between fresh and saltwater can be achieved where a cenote, or the submerged cave to which this is an opening, offers shallow enough entry into the aquifer. A halocline seems to be a sharp change in salt concentration beyond a slight change in depth there at the density interface amongst fresh and salty waters. The refraction between the various densities of fresh and salty waters causes a distorted swirling effect when fresh and saline water are mixed.

Climate, precisely how much meteoric water charges up the aquifer, hydraulic conductivity of the host rock, accessibility and distribution of established cave systems, as well as how efficient these are at draining water to the shore, as well as the distance from the coast, all influence the extent of the halocline.

The halocline is lower farther away from the shore, and in the Yucatán Peninsula, such depth is 10 to 20 m (33 to 66 ft) underneath the water table at the coast, as well as 50 to 100 m (160 to 330 ft) far below the water table in the centre, with saltwater covering the entire peninsula.

Types: Cenotes were first classified using a basic morphometry-based classification scheme in 1936.

• Cenotes-cántaro (Jug or pit cenotes) have a surface relation that is narrower than the water body's diameter.

• Cenotes-cilndricos (Cylinder cenotes) have walls that are completely vertical.

• Cenotes-aguadas (Basin cenotes) have shallow water basins, and 

• Grutas (Cave cenotes) have a horizontal gateway and dry areas.

Since the classification scheme is dependent on morphometric observations well above the water table, it only partially represents the mechanisms by which cenotes evolved and also the inherent hydrogeochemical relationship with the corresponding flooded cave networks, that were only identified in the 1980s and subsequently with the start of cave diving exploration.

Flora and Fauna

Although flora and fauna are usually scarcer throughout caves than those in the open ocean, marine animals still thrive there. Mojarras, guppies, mollies, small eels, catfish, and frogs could all be found in caverns. The fauna has developed to mimic that of several Cave-Dwelling animals in the most secluded and deeper cenotes.

Numerous animals, for particular, lack pigmentation and are sometimes blind, thus they have large feelers to locate food and navigate in the dark.

Chicxulub Crater

While cenote suytun can be found all over the Yucatán Peninsula, the estimated rim of the Chicxulub crater is overlain by a higher-density circular alignment of cenotes.

This crater formation, which was discovered by the alignment of cenotes but later mapped utilizing geophysical methods (such as gravity mapping) and drilled into this with core recovery, has also been dated to the 66 million-year-old Cretaceous-Paleogene geologic boundary. As a result of the meteorite impact at the Cretaceous–Paleogene boundary, the mass extinction of dinosaurs is regarded as the Cretaceous–Paleogene extinction event.

Scuba Diving

Cenotes frequently attracted cavern and cave divers, and attempts to investigate and map such underwater structures have been coordinated. They are either public or private, and are occasionally referred to as "National Natural Parks." When swimming, extreme caution should be exercised to avoid destroying this delicate ecosystem.

The Quintana Roo Speleological Survey in Mexico keeps a record of the state's deepest and longest water-filled and dry caves. When caving, one ought to be enabled to see natural light for the duration of the cavern exploration (for example, Kukulkan cenote near Tulum, Mexico). Throughout a cave dive, one crosses the point whereby daylight will enter the cave and exits by following a protection guideline. When you transition from a cavern dive to a cave dive, things change drastically. So many more divers, including the most seasoned, have died as a result of disregarding safety precautions. 

Cenote cave diving, unlike cenote cavern diving, necessitates specialised equipment and preparation (certification for cave diving). Both cavern and cave diving, on the other hand, necessitate thorough briefings, prior diving experience, and weight adjustment to freshwater buoyancy. Typically, the cenotes are loaded with cold, freshwater. Cenote divers have to be cautious of the potential halocline, which causes vision to blur until they enter a much more homogeneous region.

Conclusion

A cenote is a natural pit or sinkhole created by the collapse of limestone bedrock, exposing groundwater. Cenotes were used by the ancient Maya in the Yucatán Peninsula of Mexico as water sources and sometimes for sacrificial sacrifices. Cenotes are formed by the dissolution of rock and the resulting structural collapse of a subsurface void, which may or may not be linked to an active cave system. Additional dissolution gradually eliminates rock that falls into the water underneath, allowing further collapse blocks to be added.