A few years ago if you had searched any encyclopedia (remember those?) it would have told you that the longest cave in the world was the Mammoth Cave System in the United States, with the length of the combined passages dependent on the year the reference book was published.
Today, that system is 685.6 kilometers (426 miles) long. But all of us cave explorers—the worldwide community of speleologists (as we call ourselves)—know that the longest cave in the world is actually found, not in the United States, but in Mexico.
Cave divers have been exploring and mapping Mexico’s cenotes (natural pits exposing groundwater) for years, discovering kilometers of underwater passages and linking them together. Meanwhile, other explorers were mapping the dry caves in the same areas. When the various groups got together, they discovered that all these pieces were interconnected.
“There’s only one cave in (the state of) Quintana Roo,” says speleologist Peter Sprouse, who has been studying the area for years. “It’s just a case of connecting all the pieces.”
The biggest of those pieces is the Sistema Ox Bel Ha, 436 kilometers long, followed by Sac Actún at 386 kilometers. To these, you can probably add 29 other systems already mapped in Quintana Roo. By my reckoning, all of the above, when totaled, add up to a mega cave of 6,898 kilometers (4,286 miles) in length.
So there it is, Mexico houses the unofficial longest cave in the world. SO what are they building right on top of it?
Ah yes, we all know: the Mayan Train track. But what only a few of us know, is what the consequences are of building a train line on top of karst.
Karst is the magic word here. To me it means “that lovely kind of rock where caves are likely to be found,” and it typically looks like Swiss cheese, full of interconnected holes and topped with sharp, pointy prickles.
This means that anything accumulated on the surface of karst, like fertilizers and pesticides or anything leaked from a cesspool or spilled from a tanker, will be washed directly into the aquifer within seconds after a rainfall.
In Europe, complex laws govern the construction of roads on top of karst. For example, a trench plus holding tanks must be built on both sides of a highway in a karst area, to collect the kind of hazardous materials that recently caused havoc in East Palestine, Ohio, where 100,000 gallons of dangerous liquids were spilled from a derailed train.
Geologist and speleologist Chris Lloyd has explored and surveyed caves in Quintana Roo over many years and gave me his opinion on the Mayan train and its effect on the cave system.
“Obviously, it’s affecting all of the caves that it goes over,” he told me. “There’s already been one collapse along the corridor where the train is going and there will undoubtedly be more collapses of existing caves. One of the caves I surveyed in that area has a 30-meter-wide entrance and the train goes over it, right over the open space.”
Another problem that Lloyd mentioned is related to that huge aquifer housed inside the cave system.
The problem, says the geologist, is that the new train track is going over the higher part of the aquifer, while the existing roads and population centers are close to the coast, at the lower end of the aquifer. “So, water goes into the aquifer through the jungle and it leaves the aquifer near the coast.”
That water, Lloyd pointed out, is unpolluted because no one lives in the jungle. But the Mayan Train project has created new access points and in many places there will be a road next to the railroad tracks.
“Whatever purpose it may have, it is still a road and people will use it, and they will be building on properties out in the jungle,” says Lloyd. “Eventually, whatever is built above the aquifer will pollute it.”
Another speleologist, Peter Sprouse, told me that this aquifer is more accessible to humans than any on the planet: “Near inhabited areas you can dive in this system and see a pipe coming down through the ceiling of the cave with feces and toilet paper coming out. So anything encouraging more development without waste management is going to have a negative impact.”
The Yucatán aquifer, explained geologist-speleologist Ramón Espinasa, is Mexico’s biggest aquifer and one of the largest in the world, hosted in one of the widest stretches of karst in the world. “The train is not the last problem of this aquifer,” he said. “We are just at the beginning of the problem. Once you have that train working, it’s going to attract more population. You are going to have more growth, more towns and more pollution of the aquifer that they are drinking from.”
Espinasa continued: “It’s sad that they are going to harm the world’s largest cave, but it will survive. However, contamination of the aquifer is the real problem. The aquifer only needs one contamination point to foul up the whole thing, and remember—because this is karst—that there is nothing between the surface and the water to filter the contaminants.”
Because the railroad is located right on top of the nation’s most precious aquifer, a karst aquifer that will be extraordinarily difficult to protect, Mexico will require the strictest regulations the world has ever seen!
This is the message that Mexico’s speleologists and geologists would like to place before the eyes of the country’s president.
Over to you, Señor Presidente!