Zacatón

Zacatón: A Deep Thermal Sinkhole

Zacatón is a remarkable thermal water-filled sinkhole located in Aldama Municipality, near the Sierra de Tamaulipas in the northeastern state of Tamaulipas, Mexico. It is part of the Zacatón system, a group of unusual karst features. Zacatón is recognized globally for its extreme depth, with a total depth of 339 meters (1,112 ft), making it one of the deepest known water-filled sinkholes in the world. The underwater portion alone extends to 319 meters (1,047 ft).

Hydrogeology and Formation

The formation of Zacatón and other sinkholes in the region is theorized to be linked to volcanic activity during the Pleistocene epoch. This activity is believed to have made deep groundwater slightly acidic by introducing dissolved carbon dioxide and hydrogen sulfide. This acidic water then slowly dissolved the overlying limestone, creating porous karst formations. Subsequent collapses of rock into these subterranean voids formed the deep shafts, a process known as hypogenic karstification. This differs from classical cave formation theories and suggests Zacatón shares more in common with features like Mammoth Hot Springs in Yellowstone.

Scientific Exploration and Discoveries

Zacatón's significant depth has made it a crucial site for scientific research and technological development. It served as a testbed for NASA's Deep Phreatic Thermal Explorer (DEPTHX) project, which utilized an autonomous robot to explore the sinkhole's deepest regions. This exploration led to significant biological discoveries, with researchers identifying at least 100 different microbes in the water, including three entirely new phyla of bacteria. Scrapings from the rock walls beneath the surface also yielded new bacterial phyla.

Diving Significance

The sinkhole's depth has also positioned it as an important site for extreme diving. In 1993, Dr. Ann Kristovich set the women's world depth record by diving to 169 meters (554 ft). The following year, on April 6, 1994, explorer diver Jim Bowden achieved a men's world record depth of 282 meters (925 ft) within Zacatón. Tragically, pioneering cave diver Sheck Exley died during this expedition, likely succumbing to high-pressure nervous syndrome at a depth between 268 and 276 meters (879 to 906 ft).

Naming and Features

The name "Zacatón" is derived from the free-floating islands of zacate grass that drift on the surface of the sinkhole, propelled by the wind. The Zacatón system encompasses more than 15 sinkholes and other karst features, some of which exhibit unique characteristics such as travertine lids forming over isolated water bodies below. Some sinkholes, like Poza Seca, appear to be closing over time as travertine crusts form, potentially sealing off underwater lakes and perhaps unique life forms adapted to an oxygen-free and sunless environment.