Editing Cenote (section)

==Geology and hydrology==
[[File:Cenote in valladolid mexico (21362599476).jpg|thumb|upright|The [[Samulá]] Cenote in [[Valladolid Municipality, Yucatán|Valladolid]], Yucatán, Mexico]]

Cenotes are formed by the dissolution of rock and the resulting subsurface void, which may or may not be linked to an active [[cave system]],{{clarify|active cave system|date=January 2021}} and the subsequent structural collapse. Rock that falls into the water below is slowly removed by further dissolution, creating space for more collapse blocks. Likely, 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 overhanging above the water. The stereotypical cenotes often resemble small circular [[pond]]s, measuring some tens of meters in diameter with sheer rock walls. Most cenotes, however, require some degree of stooping or crawling to access the water.

===Penetration and extent===

[[File:Bolonchen Cenote Catherwood.jpg|thumb|upright|Cenote at [[Bolonchén, Campeche|Bolonchén]], Mexico, used as a source of water, painting of 1842 by [[Frederick Catherwood]]]]

In the north and northwest of the [[Yucatán Peninsula]] in Mexico, the cenotes generally overlie vertical voids penetrating {{convert|50|to|100|m|abbr=on}} 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.<ref name="Beddows, P.A. 2003"/>

In contrast, the cenotes along the Caribbean coast of the Yucatán Peninsula (within the state of [[Quintana Roo]]) often provide access to extensive underwater cave systems, such as [[Sistema Ox Bel Ha]], [[Sistema Sac Actun]]/[[Sistema Nohoch Nah Chich]] and [[Sistema Dos Ojos]].

===Freshwater/seawater interface===
The Yucatán Peninsula contains a vast coastal [[aquifer]] system, which is typically density-stratified.<ref name="Beddows, P.A. 2003"/> The 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 pool|anchialine system]] (one that is land-locked but connected to an ocean). Where a cenote, or the flooded cave to which it is an opening, provides deep enough access into the aquifer, 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 caused by [[refraction]] between the different densities of 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 further from the coast, and in the Yucatán Peninsula this depth is {{convert|10|to|20|m|abbr=on}} below the [[water table]] at the coast, and {{convert|50|to|100|m|abbr=on}} below the water table in the middle of the peninsula, with saline water underlying the whole of the peninsula.<ref name="Beddows, P.A. 2003"/>
[[File:Cenote IK KIL map.png|alt=cutaway of cenote ik kil, at the bottom there is a pile of debris|thumb|upright=1.25|Geological cutaway of [[Ik Kil|Cenote Ik Kil]]]]

===Types===
In 1936, a simple morphometry-based classification system for cenotes was presented.<ref name="Hall1936"/>
* '''''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 later with the initiation of cave diving exploration.{{citation needed|date=February 2020}}