The Zacaton Sinkhole 

The Zacaton sinkhole is located on El Rancho Azufrosa, near the town of Aldama in Tamaulipas in northeast Mexico. Zacaton is a thermal water-filled sinkhole belonging to the Zacaton system – a group of unusual Karst features. Several sinkholes have been observed in the same area, though studies have failed to demonstrate any underground connections between them. El Zacaton is about 100 meters wide and more than 339 meters deep. It is the deepest known water-filled sinkhole in the world.

World’s deepest Sinkhole

On April 6, 1994, two very experienced cave divers, Sheck Exley and Jim Bowden, dived into the sinkhole. Jim Bowden reached the world record of 282 m, but Sheck Exley died due to unexplained reasons at a depth of 268 – 276 m.

The El Zacatón was long considered to be bottomless, but in 1997, NASA solved the pit’s mystery when it sent an underwater robot mission and found the depth of El Zacatón to be 339 meters.

Situated near the Gulf coast of northeastern Mexico, the Zacaton has warm water, is highly mineralized, and has a sulfurous odor. The name El Zacaton comes from the floating islands of Zacate grass, which blows across this lake from one side to the other with the wind.

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Formation and Geology

The Zacaton sinkhole belongs to the unique Karst field Sistema Zacaton. These karst features have incredible characteristics elsewhere in the world. The area contains some 20 unusual sinkholes, caves, and springs created by volcanic processes. Karstification processes continue today as well, and acidic groundwater continues to erode away the limestone and deposits it in unusual travertine formations.

A geoscientist considers that the unusual Karst landscape of Zacaton has been formed by deep volcanic activity. Volcanism heats the deep groundwater and turns it into an acidic composition with some carbon dioxide and hydrogen sulfide.

When this water reaches limestone layers, it gradually dissolves, forming voids. Such a process is called “hypogenic karstification”. As the void becomes larger, the ceiling limestone layers collapse one after another and form a sinkhole. El Zacaton sinkhole is the most prominent and best-known feature in this karst field. Among the five unusual sinkholes, which are located close together but are not directly connected.

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How to reach The Zacaton Sinkhole

To reach the Zacatón Sinkhole, you need to travel to Rancho La Azufrosa near Aldama, Tamaulipas, Mexico, then follow signs to the sinkhole; it’s a scientific site, so access is generally free but rugged, requiring hiking to its rim, with diving restricted to highly experienced professionals via a connecting tunnel from a nearby spring, not direct cliff entry, due to extreme depth and unique hazards like sulfur layers.