page_title: Cenote
section_title: Freshwater/seawater interface
hierarchical_section_title: Cenote / Geology and hydrology / Freshwater/seawater interface
caption_attribution_description: English: geological cutaway of cenote IK KIL
context_page_description: A cenote is a natural pit, or sinkhole, resulting from the collapse of limestone bedrock that exposes groundwater underneath. Especially associated with the Yucatán Peninsula of Mexico, cenotes were sometimes used by the ancient Maya for sacrificial offerings.
  The term derives from a word used by the low-land Yucatec Maya—tsʼonot—to refer to any location with accessible groundwater. Cenotes are common geological forms in low altitude regions, particularly on islands, coastlines, and platforms with young post-Paleozoic limestones that have little soil development.
context_section_description: The Yucatán Peninsula contains a vast coastal aquifer system, which is typically density-stratified. 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 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 10 to 20 m (33 to 66 ft) below the water table at the coast, and 50 to 100 m (160 to 330 ft) below the water table in the middle of the peninsula, with saline water underlying the whole of the peninsula.
caption: Geological cutaway of Cenote Ik Kil
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