Cenotes are natural sinkholes formed when limestone bedrock collapses, exposing the groundwater below. They are most famously concentrated in the Yucatán Peninsula of Mexico, where they connect to a vast subterranean water system. Cenote depth varies significantly, ranging from shallow, basin-like pools to deep, vertical shafts that plunge hundreds of feet. Understanding their depth requires looking at both their geological history and their physical classification, as the age and structure of the sinkhole directly influence how far down the water extends.
Geological Origins and Structure
The existence of cenotes is rooted in the unique geology of the Yucatán Peninsula, which is characterized by extensive karst topography. This landscape is primarily composed of porous limestone, a sedimentary rock easily dissolved by water. Rainwater absorbs carbon dioxide from the atmosphere and soil, forming a weak carbonic acid solution as it filters through the ground.
This slightly acidic water slowly dissolves the calcium carbonate in the limestone, a process called chemical weathering. Over thousands of years, this dissolution enlarges existing fissures and cracks, creating expansive networks of underground caves and tunnels. These subterranean voids are filled by the region’s aquifer, forming interconnected underground rivers.
The formation of the cenote occurs when the limestone ceiling of an underground cave can no longer support its own weight and collapses. This structural failure creates a sinkhole, exposing the water table below. The ultimate depth is determined by the height of the cave ceiling before the collapse and the current elevation of the aquifer, which can extend far below the surface.
Categorizing Cenote Depth by Type
Cenotes are commonly categorized into three structural types, reflecting different stages of the collapse process. These classifications serve as an indicator of their typical depth profiles. Depth generally increases as the cenote becomes more enclosed.
Open Cenotes
The least deep, and often the oldest, are the open cenotes, where the roof has fully collapsed, leaving a wide, open pool exposed to the sky. These open or cylinder-type cenotes often resemble natural, flooded quarries and are typically shallower than other types. Depths commonly range from 15 to 30 meters (approximately 50 to 100 feet). Since they are the oldest, the surrounding rock walls have had the most time to erode.
Semi-Open Cenotes
Next are the semi-open cenotes, characterized by a partial collapse, leaving a significant portion of the roof intact to form a cavern. These are younger than the open type and often feature large overhangs with clear water visible from the surface. The depth profile tends to be greater, often reaching 30 to 45 meters (about 100 to 150 feet) in the submerged cavern area.
Cavern or Cave Cenotes
The deepest and youngest cenotes are the cavern or cave cenotes, which are almost entirely enclosed with only a small surface opening or entrance. These formations represent the most recently collapsed sections of the cave system and grant access to the most intact portions of the underground river network. The water in these cenotes frequently plunges well over 45 meters (150 feet), sometimes reaching depths exceeding 100 meters (330 feet).
Record-Holding Cenotes and Underwater Cave Systems
While typical tourist cenotes offer a glimpse into the aquifer, extreme depths are found in cenotes that serve as entry points to the region’s massive, interconnected underwater cave systems. The largest of these systems, like Sistema Sac Actun, is a vast network of submerged passages stretching over 378 kilometers (235 miles) in length. Cenotes are the vertical access shafts to these horizontally extensive underwater labyrinths.
The deepest explored cenote passage in Quintana Roo is known as “The Pit,” an access point to the Sistema Dos Ojos cave system. Technical divers have mapped this vertical shaft to a depth of 119.1 meters (391 feet), demonstrating the deep connection to the subterranean water table. These depths often require specialized technical diving equipment and decompression procedures.
In the neighboring state of Yucatán, the open cenote Sabakha is officially recorded as plunging more than 150 meters (492 feet) deep. Explorations have reached at least 140 meters (460 feet) in this single, massive sinkhole.