There are many unique geological features: mountains, deserts, glaciers - but unless you’ve been to Mexico, you’ve probably never seen a “cenote.” The Yucatan Peninsula is pockmarked with natural, freshwater filled sinkholes. Cenotes vary in size from tiny openings to vast caves.
But how are they made? The bedrock of the Yucatán is porous, sedimentary limestone. This stone is mostly calcium carbonate, made from the compacted remains of bones and shells of Marine animals. This buildup occurred 65 million years ago when the peninsula was completely submerged. Because of changes in tectonic plates and climate, the Yucatan Peninsula is now above sea level.
This section of Mexico is relatively flat, with few rivers. During the rainy season, rainwater percolates through the soil, seeps below the limestone and is stored underground. These cenotes are places where the cap limestone has collapsed, revealing the groundwater below.
What’s more amazing is that these cenotes are all connected, forming the world’s largest underground river network. Indigenous communities, such as the Maya, relied on them for freshwater, fishing and farming. Cenotes were also believed to be entrances to the Mayan underworld, so offerings of carved jade, human skeletons and even gold have been found in their depths.
This underground system is fascinating, but it is also fragile. Geologists, divers, spelunkers and day-trippers are drawn to cenotes. To achieve sustainable use, we need a comprehensive understanding of the entire hydrogeological system and how it’s connected. It is also necessary to evaluate the impact of urban areas, livestock farms and pollution, as groundwater is the only source of fresh water in the area.
You can investigate cenotes yourself, as many in Mexico are open to tourists.
Special thanks to this episode's reviewer, Dr. Emiliano Monroy Ríos, an independent environmental consultant in geologic hazards associated with Karst.
Learn more
Sources
Speleogenesis: How were caves and cenotes formed? Northwestern University
The Secret Underwater World of Mexico's Cenotes, Much Better Adventures Magazine
