Cenote
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A cenote (pronounced in Mexican Spanish [seˈnoˌte] and in English [səˈnəʊˌteɪ], plural: cenotes; from Yucatec Maya dzonot) is a type of sinkhole containing groundwater typically found in the Yucatán Peninsula and some nearby Caribbean islands. The term is derived from a word used by the low-land Maya to refer to any location where groundwater is accessible.
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[edit] Definition and description
Cenotes are surface connections to subterranean water bodies [1]. While the most well-known cenotes are large open water pools measuring tens of metres in diameter, such as those at Chichén Itzá, the greatest number of cenotes are smaller sheltered sites and do not necessarily have any surface exposed water. The term cenote has also been used to describe similar karst features in other countries such as Cuba and Australia, in addition to the more generic term of sinkholes.
Cenote water is often very clear, as the water comes from rain water infiltrating slowly through the ground, and therefore contains very little suspended particulate matter. The groundwater flow rate within a cenote may be very slow at velocities ranging from 1 to 1000 meters per year. In many cases, cenotes are areas where sections of cave roof have collapsed revealing an underlying cave system and the water flow rates here may be much faster: up to 10,000 meters per day[2]. Cenotes around the world attract cave divers who have documented extensive flooded cave systems through them, some of which have been explored for lengths of 100 kilometers or more.
[edit] Geology and hydrology
[edit] Formation
Cenotes are formed by dissolution of rock which creates a subsurface void, which may or may not be linked to an active cave system, and the subsequent structural collapse of the rock ceiling above the void. The rock that falls into the water below will then be slowly removed by further dissolution, creating space for more collapse blocks. The rate of collapse increases during periods when the water table is below the ceiling of the void, since the rock ceiling is no longer buoyantly supported by the water in the void. Cenotes may be fully collapsed creating an open water pool, or partially collapsed with some portion of a rock overhang above the water. The stereotypical cenotes often resemble small circular ponds, measuring some tens of meters in diameter with sheer drops at the edges. Most cenotes however require some degree of stooping if not crawling to access the water.
[edit] Penetration and extent
In the north and north-west of the Yucatan Peninsula, the cenotes generally overlie vertically extensive voids penetrating 50 - 100 m below the modern water table. However, very few of these cenotes appear to be connected with horizontally extensive underground river systems, with water flow through them being more likely dominated by aquifer matrix and fracture flows. In contrast, the cenotes along the Caribbean coast of the Yucatan Peninsula (within the state of Quintana Roo) often provide access to extensive underwater cave systems, such as Ox Bel Ha, Sac Actun, Nohoch Nah Chich and Dos Ojos.
[edit] Freshwater/seawater interface
The Yucatan Peninsula contains a vast density-stratified coastal aquifer where infiltrating meteoric water (i.e., rainwater) floats on top of higher density saline water intruding from the coastal margins. The whole aquifer is therefore an anchialine system (i.e., one that is land-locked, but connected to an ocean). Where a cenote, or the flooded cave it is an opening to, provides deep enough access into the aquifer then the interface between the fresh and saline water may be reached. The density interface between the fresh and saline waters is a halocline, which means a sharp change in salt concentration over a small change in depth. Mixing of the fresh and saline water results in a blurry swirling effect due to refraction between the different density fresh and saline waters. The depth of the halocline is a function of several factors: climate and specifically how much meteoric water recharges the aquifer, hydraulic conductivity of the host rock, distribution and connectivity of existing cave systems and how effective these are at draining water to the coast, and the distance from the coast. In general, the halocline is deeper the further from the coast. In the Yucatan Peninsula this depth is 10 to 20 meters below the water table at the coast, and 50 to 100 meters below the water table in the middle of the peninsula, with saline water underlying the whole of the peninsula.
[edit] Types of cenotes
In 1936, a simple morphometry based classification system for cenotes was presented [3]. Cenotes-cántaro (Jug, or Pit cenotes) are those with a surface connection narrower than the diameter of the water body; Cenotes-cilíndricos (Cylinder cenotes) are those with strictly vertical walls; Cenotes-aguadas (Basin cenotes) are those with shallow water basins; and grutas (Cave cenotes) are those having a horizontal entrance with dry sections. The classification scheme was based on morphometric observations above the water table, and therefore incompletely reflects the processes by which the cenotes formed and the inherent hydrogeochemical relationship with the underlying flooded cave networks, which were only discovered in the 1980s and onwards with the initiation of cave diving exploration.
[edit] Association with the Chicxulub structure
Although cenotes are found widely throughout much of the Yucatan Peninsula, a ringlike arrangement of cenotes coincides with the theorized rim of the Chicxulub Crater. This crater structure, suggested by gravity mapping, may be the result of the meteorite that is theorized to be responsible for the K-T Boundary and the mass dinosaur extinction that occurred 65 million years ago known as the Cretaceous–Tertiary extinction event.[citation needed]
[edit] Cenotes and the Maya
Cenotes have long been the principal sources of water in much of the Yucatán Peninsula. The region has almost no rivers and only a few lakes, and those often marshy. Cenotes are widely distributed, and supply better-quality water year-round. Major Maya settlements required access to adequate water supplies, and therefore cities, including the famous Chichén Itzá, were built around these natural wells. Some cenotes like the Cenote of Sacrifice in Chichén Itzá played an important role in Maya rites. Believing that these pools were gateways to the afterlife, the Maya sometimes threw valuable items into them. The discovery of golden sacrificial artifacts in some cenotes led to the archaeological exploration of most cenotes in the first part of the 20th century. Edward Herbert Thompson, an American diplomat who had bought the Chichén Itzá site, began dredging the Sacred Cenote there in 1904. He discovered human skeletons and sacrificial objects confirming a local legend, the Cult of the Cenote, involving human sacrifice to the rain gods (Chaacs) by ritual casting of victims and objects into the cenote.
[edit] Cenotes and cave diving
Cenotes have attracted cave divers and there are organised efforts to explore and map the underwater systems. The Quintana Roo Speleological Survey maintains a list of the longest and deepest water filled and dry caves within the state boundaries.
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[edit] Notable cenotes
[edit] Mexico
Yucatan Peninsula:
- Dos Ojos, near Tulum, Mexico
- Dzibilchaltun, Yucatan, Mexico
- Sacred Cenote, Chichen Itza, Mexico
- Xtacunbilxunan, Bolonchen , Mexico
Central and Northern Region:
- Zacatón, Tamaulipas, Mexico
[edit] Canada
- Devil's Bath, northern Vancouver Island, Canada
[edit] United States
[edit] References
- ^ Gaona-Vizcayno, S., T. Gordillo de Anda and M. Villasuso-Pino (1980), Cenotes, karst característico: Mecanismo de formacíon, Instituto de Geología, v. 4; pp 32-36.
- ^ Beddows, P.A. (2003) Yucatan Phreas, Mexico , In J.Gunn (ed) Encyclopaedia of Cave and Karst Science, Routledge Taylor & Francis Group, New York, USA. 794-796
- ^ Hall, F.G. (1936), Physical and chemical survey of cenotes of Yucatán, Carnegie Institution of Washington Publication 457, pp 5-16.
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