One of the Deepest Caves in the World is Even Bigger Than We Thought

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While trapped inside Mexico’s Sistema Huautla by torrential flooding, cavers and scientists discovered new connections—expanding the map of the Western Hemisphere’s deepest cave.

Katie Graham was trying to escape the cave she’d been trapped inside with her teammates for the past three days. She held her breath and cautiously swam underwater through the turbid flood that was all but completely filling an underground corridor, ominously dubbed Skeleton Canyon, in Sistema Huautla, the deepest cave in the Western Hemisphere.

Only a few inches of air existed between the water’s surface and the roof of the cave. When she emerged, she did so face first, her head tilted all the way back to put herself in the best breathing position.

With her nose and mouth pressed to the slimy limestone roof, she calmly inhaled and made a deliberate effort to move forward slowly so as not to create any waves that would disrupt the bell jar of air surrounding her face. When the air pocket ran out, Graham used her legs as antennae, probing her feet around the pitch-black sump to feel for the next pocket of buoyancy ahead of her. Upon locating one, she’d dive under, swim forward, and again come up face first, her head tilted back.

MAPPING MEXICO’S DEEPEST CAVE

“On the third time, I came up into something really low,” says Graham. “I couldn’t see anything. I thought, ‘this situation isn’t OK; I should backtrack back to camp.’”

For the past three days, Katie Graham, Stephen Gladieux, Tiffany Nardico, Elliot Guerra-Blackmor, and Chase Varner had been trapped 2,199 feet (670 meters) underground, at a low camp in Sistema Huautla. Located in Oaxaca, Mexico, Sistema Huautla is one of the deepest, longest, and, some say, greatest caves in the world.

The team had known a light rain was in the forecast prior to entering La Grieta, one of the many distinct caverns connected to the greater Huautla system. However, the team had assumed the portion of La Grieta in which they were traveling would be relatively dry, even in a flood.

On the first evening of their trip, a “high-water event” knocked Graham off her feet and swept her nearly 328 feet (100 meters) downstream. The force of the flood pinned her down by her backpack, and she struggled to stand up in the torrent.

“It took quite a bit of effort to get out of the water,” she says, modestly. “We got back to camp, traumatized. That’s when we knew something big was happening. Our water source was increasing.”

“I tried to look for areas to bypass and shouted to see if I could hear them without any luck,” says Hernandez. “I thought I heard them once, but maybe it was just the cave playing a trick.”

Hernandez returned to the surface to inform the rest of the expedition about the situation.

For three days, the five cavers rationed a small bag of Clif Bar protein bars and continued to do their work in the farthest depths of La Grieta. They completed several new aid climbs, conducted surveys, and discovered a new passage they dubbed “Powered by Bars,” which led to a chamber with a dome estimated to be 492 feet (150 meters) tall, or perhaps larger.

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At about 479 feet (146 meters) high, the “TAG Shaft” is one of largest chambers in Sistema Huautla. TAG stands for “Tennessee/Alabama/Georgia,” where several different surface entrances meet. During the 2018 expedition, cavers pushed through a tight crack at the bottom of the shaft in a successful attempt to connect it to Sistema Huautla. To capture this image of the illuminated cave, the photographer overlayed multiple photographs taken with different exposures.

PHOTOGRAPH BY JOSHUA HYDEMAN, NATIONAL GEOGRAPHIC

“There were a lot of new discoveries,” says Stephen Gladieux. “A lot of excitement down there.”

At five in the morning of the fourth day, Katie Graham made a second effort to escape in order to catch her flight home. She returned to the water-choked Skeleton Canyon and once again found herself traversing the passage with her head tilted back, her nose and lips pressed to the ceiling, drawing from the pancake of air.

The water levels had gone down, but not by much. Still, it was just enough for Graham, considered one of the best cavers in the world, to make it out.

The following day, with the water even lower, the remaining team members took the opportunity to exit through the watery Skeleton Canyon and up thousands and thousands of feet of rope. Eventually, they all crawled out of an utterly indistinct hole in the ground and into the blinding sunlight.

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Scott Trescott, from Costa Rica, climbs over falling rocks while working his way through a canyon passage in Sotano de Agua de Carrizo.

PHOTOGRAPH BY JOSHUA HYDEMAN, NATIONAL GEOGRAPHIC

ORIGINAL EXPLORATION

You can’t tell what lies beyond a cave’s entrance by looking at it. And that is one of caving’s great allures—exploring what cannot be easily seen from a safe distance or rendered in advance by technology. The thrill lies in the firsthand experience of making the unknown known, going not because “it’s there,” as the old mountaineering expression asserts, but because you ultimately don’t know what’s there, and can’t know until you take that first step into the dreadful abyss.

“Caving is original exploration. You gotta go to know,” says Bill Steele, one of the world’s foremost speleologists, expedition cavers, and co-founder of Proyecto Espeleologico Sistema Huautla (PESH).

Every year since 2013, PESH, an official project of the National Speleological Society and the United States Deep Caving Team, has been exploring, surveying, and studying the Huautla-area caves.

As an organization, PESH has committed to 10 consecutive years of expeditions to Sistema Huautla, always in April, reliably the driest month. This latest expedition concluded the fifth PESH trip—a halfway point for the ambitious project—and it was one of the most successful years yet, despite the uncharacteristically wet conditions.

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Sonia Meyer works her way through a canyon passage in Sistema Huautla, the deepest cave in the Western Hemisphere. This year, the system is being explored by two separate expedition teams, PESH (Proyecto Espeleologico Sistema Huautla) and Pena Colorada 2018.

PHOTOGRAPH BY JOSHUA HYDEMAN, NATIONAL GEOGRAPHIC

Following a “lead” discovered last year, the 2018 PESH expedition made a significant connection between a cave named Sotano de Agua de Carrizo and Sistema Huautla. This connection added 4.3 miles, or seven kilometers, to the system’s length, as well as five new entrances, making one of the longest, deepest caves in the world even longer and more complex.

Sistema Huautla is now known to be 53 miles long and has 25 distinct entrances. With a depth measurement of 5,118 feet (1,560 meters) from its highest known entrance to its lowest reached point, System Huautla is the deepest cave in the Western Hemisphere and the ninth deepest cave in the world.

For reference, most major caves have only one or maybe two entrances—and therefore only one or two routes through the cave system. For example, Veryovkina, in the country of Georgia, is the world’s deepest cave, at 7,231 feet (2,204 meters), but it’s a mere 7.9 miles long and has just one entrance.

“Carlsbad Caverns is known for one very big chamber called the Big Room,” says Steele. “We’ve got at least 12 of them in this cave area. One of them is twice the size of the Dallas Cowboys’ stadium.”

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A member of the expedition travels through a portion of Sistema Huautla that sits behind one of Skeleton Canyon’s water-filled passages. Traveling through the canyon requires stepping on thin scalpel-like blades, which can easily break under force. To capture this image of the illuminated cave, the photographer overlayed multiple photographs taken with different exposures.

PHOTOGRAPH BY JOSHUA HYDEMAN, NATIONAL GEOGRAPHIC

It’s the sheer complexity of Sistema Huautla that justifies its reputation as perhaps the world’s greatest cave. And, despite having been first explored by cavers in 1966, Sistema Huautla remains a frontier of science and adventure.

“After a lifetime of exploration, we have no way to predict how much of it we’ve explored,” says Steele. “My gut tells me that we’ve probably only reached two-thirds of it, if that—maybe only half!”

Steele, 69, made his first trip to Sistema Huautla in 1977. This year marks his 25th expedition to the region. He calls Sistema Huautla “the masterpiece of my contribution to speleology.”

A PERFECT STORM OF GEOLOGY

Caves become longer or deeper only through firsthand exploration—a physical connection must be made from one cave to the next. Sistema Huautla is the substructure of the Sierra Mazateca mountains, a jungle-covered range of limestone hiding a mind-boggling underworld of porous karst tunnels, waterfalls, and chambers.

“Leads” are places where one cave might connect to another. A lead could be the sound of water in the distance or the feeling of wind blowing through a faint crack in the wall. It could be an enormous tunnel or a crack so tiny a person could barely squeeze through.

Leads are identified, marked, and later explored by a team using state of the art tools for surveying. Modest excavation tactics may be used to remove mud, sediment, or rocks impeding travel. The goal is to make that connection in order to extend the cave’s depth or length. Ultimately, a more complete picture of the geology begins to take shape.

“Sistema Huautla is just the perfect storm of geology for cave development,” says Steele.

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