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Home » El Zacatón Cenote, Mexico

How Low Can Geologists Go?

A Visit to El Zacatón Cenote - The World's Deepest Water-Filled Sinkhole
Featuring: Marc Airhart, Science Writer, University of Texas at Austin

El Zacatón Cenote

Marc Airhart's
Updates from the Field
Wrap-up - June 20, 2007
Fourth Report - May 22, 2007
Third Report - May 19, 2007
Second Report - May 18, 2007
First Report - May 17, 2007
Pre Trip Report - May 11, 2007
El Zacatón Location Map / Satellite Image

At Last, Back in the Water
From: Marc Airhart, June 20, 2007

I had the good pleasure of sitting down with Marcus Gary, a doctoral candidate at the University of Texas of Austin and one of the primary members of the DepthX team, to talk about what happened after I left Mexico on Monday, May 21.

After several days out of commission, the DepthX crew was finally able to return to work on Friday, May 25. In the last three frenzied days of the mission, the robot returned to the bottom of Cenote Zacatón to investigate a mysterious feature in the deepest corner. It turned out to be only an alcove, not the entrance to some exotic new tunnel. I asked Marcus if he was disappointed. He replied zen-like, "No. That's science. It just is what it is."

The team also took the robot to two other cenotes in the system -- Caracol and Verde -- and mapped them. Gary, who has explored these cenotes as a scuba diver for over 10 years and more recently as a hydrologist, was pleased to find that cartoon cross sections he had drawn of the cenotes several years ago based on limited data turned out to be essentially correct. Zacatón is a deep, cylindrical shaft, while Caracol and Verde are shallower and more bowl shaped.

In a way, Gary seems relieved the project is over. There was a deluge of media interest while the scientists were working. Reporters and photographers from Reuters, Discovery Channel, Astrobiology, and Mexican newspapers and television news stations all visited the ranch. There was also a steady stream of high school and university students, local officials and townspeople vying for a glimpse of the robot in action. He acknowledged the importance of getting the word out about his research, but in the future hopes to have the media visit the site at the end of the project, when most of the science is done.

What's next for Gary? He's taking a break from Mexico field work for a while and hoping to stay out of the media spotlight. He has a doctoral dissertation to write, projects to work on for the U.S. Geological Survey (his day job), and a new house to finish building.

As for me, it's on to the next big science story. Thanks for sharing this journey with me.

Marc Airhart
Science Writer
Jackson School of Geosciences
University of Texas at Austin

The Hits Just Keep on Coming
From: Marc Airhart, May 22, 2007

Ask any scientist who does international field research and you’ll find that delays and unforeseen technical issues are the norm. DEPTHX, a NASA funded project, is no different. The good news is that after a few days out of the water, the team is now preparing to send the DEPTHX robot back into Zacatón.

Now that I’ve returned home to Austin, it’s amazing to think how much the team has already accomplished. By any measure, it’s been a smashing success.

The robot reached the bottom of El Zacatón, revealing for the first time ever its internal geometry, while still leaving the intriguing possibility of a small side cave in one corner. The robot created the first 3D maps of Zacatón and La Pilita, a smaller water-filled sinkhole nearby. An understanding of the internal structures of these sinkholes will be of tremendous help to people like Marcus Gary and Jack Sharp of the University of Texas at Austin, who are trying to better understand how they formed and how they evolve over time.

The robot successfully demonstrated co-called SLAM technology in three dimensions. In other words, it’s the first robot with the ability to simultaneously create maps of unexplored places and use the maps to determine where it is in the world, not just in two dimensions, but in every direction. The robotics and software experts at Carnegie Mellon University have truly pushed the envelope in robotic mapping and navigation.

Members of the DEPTHX team and the media take a break to explore Cuarteles, a dry cave nearby.
Photo by J.A. Soriano.

Bill Stone being interviewed by a film crew from NASA TV. Intense interest from the media kept team
members busy talking to reporters. Photo by Marc Airhart

The DEPTHX robot awaits its next mission. Photo by Marc Airhart

The microbiologists from Colorado School of Mines are ecstatic. They’ve collected samples of microbes from the water and rock walls at 115, 195 and 270 meters deep in Zacatón. They’ve already discovered nine entirely new classes of microbe (to add to the hundred or so known classes) and expect the total to rise to about 20 when the final DNA analyses are completed in a few months. It was possible to collect those samples because of the hard work of engineers at Southwest Research Institute who designed the robot’s sample arm and other scientific instruments.

The mere fact that the robot mostly does what it was intended to do is something of an engineering miracle. As Bill Stone, owner of Stone Aerospace (the company that designed and fabricated the robot) and principal investigator for DEPTHX, points out all of this was achieved for only $5 million. That might sound like a lot, but he says a large firm such as Lockheed Martin would have a hard time pulling off such a project for under $50 million. He credits the team’s success to being small, multidisciplinary, independent and flexible.

The DEPTHX project will wind down in a few days, but in some ways, this is just the beginning. Next year, a revamped version of the robot will go to Antarctica to explore Lake Bonney, an even closer analog to the ice-covered ocean of Europa.

Eventually, we may have the technology we need as a species to send a robot out in to space to help answer one of the biggest questions scientists have ever tackled: Are we alone in the universe?

Marc Airhart
Science Writer
Jackson School of Geosciences
University of Texas at Austin

Put a Lid On It
From: Marc Airhart, May 19, 2007

As I wrote in an earlier post, the sinkholes of Sistema Zacatón formed in a way similar to Mammoth Hot Springs in Yellowstone. Deep acidic water carved its way up through limestone, creating shafts to the surface. In other words, they formed from the bottom up.

There's a sequel to this geologic story. Some sinkholes appear to be in the process of closing up at the top as crusts of travertine (a form of calcium carbonate) form at their surfaces. It's a bit like the skin on a can of paint that has been left open in the sun. For the paint, it might take a day or two. In this case, the process probably takes thousands of years.

Without going into the chemistry, this is basically the sinkhole's way of taking a bunch of dissolved rock floating in the water and recycling it to form new rock at the surface.

At least one sinkhole (Poza Seca) appears to have closed up entirely, sealing off an underwater lake, possibly with unusual life forms.

Marcs Gary (UT Austin), standing on the travertine lid sealing off Poza Seca,
describes how the lids form.

A team from the University of Texas at Austin takes electrical resistivity measurements to map
the subsurface of Poza Seca in the summer of 2006. They found a thin cap of travertine covering
a body of water.

If such life forms exist, they're likely to be bacteria that can live without oxygen and sunlight. And assuming the lake has been sealed off from the outside world for thousands and thousands of years, they might have evolved to be different from anything scientists have ever discovered and characterized before.

In the summer of 2006, Marcus Gary (a hydrogeologist from the University of Texas at Austin and member of the DEPTHX team) conducted experiments at Poza Seca to try to determine the size and shape of the underwater lake. Walking across the flat, dry surface of travertine "felt like walking on the head of a drum," recalled Gary.

The researchers took electrical resistivity measurements to create an image of the subsurface. The research revealed a thin travertine cap two to four meters (six to twelve feet) thick. Beneath that lies a watery lake at least 25 meters (80 feet) deep.

Yesterday, Gary took a group of us out to stand on Poza Seca to explain the travertine story. He said he would like to study the water below Poza Seca's lid, but is concerned that such research might contaminate it with microbes from above. He envisioned someday drilling a small hole through the travertine to send instruments or perhaps even a small robot to study the environment and bring back samples. But he said a lot of thought and care should go into any such investigation.

Clearly, even after the DEPTHX team packs up and heads home in a few days, there will remain enough mysteries to keep Gary and others busy for a long time.

Marc Airhart

Not all caves are created equal
From: Marc Airhart, May 18, 2007

A technical issue has again delayed more research in El Zacatón. So we took a field trip to Caverna Cuarteles, a large dry cave a short walk from the ranch.

Bats flitted above our heads and spider-like insects hid from the beams of our headlamps as we moved from room to room admiring the rocky daggers, veins and curtains decorating the ceiling. Here and there, massive tree roots thrust down through the rock seeking water.

It was once thought that all caves formed when slightly acidic water on the surface seeped down and dissolved rock, carving out majestic halls, underwater rivers and shafts. You can think of this as the top down theory.

There are also other ways to make caves, as scientists have been learning over the past 30 years. There is also a bottom up process.

Marc Airhart at the entrance to Caverna Cuarteles.

Skylights in one of the larger chambers of Cuarteles.

el zacatón cenote map
According to Marcus Gary, a hydrogeologist from the University of Texas at Austin and a member of the DEPTHX team, these caves (such as Cuarteles) and sinkholes (such as Zacatón) began to form during the Pleistocene as a result of volcanic activity from below. This is very different from the classical theory of how caves form and from how most of the other large caves in this part of Mexico likely formed.

Volcanism turned deep water slightly acidic by adding dissolved carbon dioxide and hydrogen sulfide. This water slowly nibbled away at the limestone above, creating porous karst. This is referred to as “hypogenic karstification.” From time to time, overlying rock collapsed into hollow chambers below, creating deep shafts.

Small formations on the Caverna Cuarteles ceiling.

An insect that resembles a spider, but apparently isn't.  It only has six legs.
The other two are antennae.

If his interpretation is correct, Sistema Zacatón has more in common with Mammoth Hot Springs in Yellowstone than with other deep sinkholes in this same region of Mexico.

Marc "I've got them subterranean homesick blues" Airhart

First Report from Mexico
From: Marc Airhart, May 17, 2007

When I arrived at Rancho La Azufrosa last night (Wednesday), the DEPTHX team was wrapping up a very successful day. The robot had just made the first ever map of the bottom of El Zacatón using its sonar sensors. Finally, a picture of the mysterious depths that eluded two divers 13 years ago was coming into focus.

As it turns out, the bottom of Zacatón is sloped, starting at about 290 meters at its shallowest, sloping down to over 300 meters. The exact depth is a little uncertain because where the floor should meet the vertical wall, there is a 15 meter high indentation which the sonar sensors didn't penetrate. Is it just a little bowl shaped hollow? Is it the entrance to a hidden passage? If so, where does it lead? Could the sinkhole actually be connected to much deeper chambers? The researchers are now interested in sending the robot back to this part of the sinkhole to explore this anomalous area.

Lowering DEPTHX into El Zacatón

Ironically, Jim Bowden, when he dived to 282 meters in 1994 was achingly close to the bottom. Had he dived just a few meters deeper, he would have stood on a muddy, sloping floor. His dive lights would surely have allowed him to see the ground around his feet. Because of the carefully choreographed dance that was required to make the world's deepest scuba dive, there wouldn't have been time to linger and conduct any scientific investigations. After dropping nearly 1,000 feet in just 11 minutes, he had to immediately begin a several hour return to the surface. Tanks were strategically positioned along a safety line to provide him with the appropriate mixture of oxygen, nitrogen and helium to avoid the painful and potentially deadly Bends.

Scientists communicate with the submerged DEPTHX robot from a platform floating
on the surface of El Zacaton.

This morning, the robot used its "sample arm" to take samples of the rock wall from three points - at 115, 195 and 270 meters depth. John Spear, a microbiologist from Colorado School of Mines will take these back to the lab and use DNA analysis to identify the microbes in them. This kind of work has already revealed several new classes of microbes unknown to science.

The team ran into some technical difficulties around the middle of the day today and had to postpone further investigations. They hope to be back at it tomorrow.

Until then,

Marc Airhart

From: Marc Airhart, May 11, 2007

I am heading to Mexico on Wednesday, May 16 to help document an amazing research project at the world's deepest known water-filled sinkhole, or cenote. The research will help scientists determine the physical and chemical processes that have formed a unique and immense cave system, better understand how microbes live in extreme environments and develop technology that might someday aid the search for life beyond Earth.

El Zacatón, a vertical cave about 100 meters (328 feet) wide and more than 300 meters (1,000 feet) deep, has been called an "upside down Mount Everest." It could easily swallow New York's Chrysler Building. No one has ever reached the bottom, so it's true depth is unknown.

Two scuba divers attempted to reach the bottom in April, 1994. In the process, Jim Bowden set the record for the world's deepest scuba dive by descending to 925 feet (282 meters). Sadly, his good friend and deep diving mentor Sheck Exley died making the same attempt. The tragic outcome caused Bowden and others to rethink the way they explore Zacatón.

Now a new probe - the world's only cave diving robot - is poised to unlock its mysteries.

The Deep Phreatic Thermal Explorer (DEPTHX) is a completely autonomous robotic probe designed as a prototype vehicle that might someday explore sub-ice oceans of Jupiter's moon Europa looking for extraterrestrial life. (More on that in a future post.)

In March, DEPTHX successfully explored La Pilita, the second deepest water-filled sinkhole in the system. It mapped the cave with sonar, navigated using its own maps, and sampled water and microbes, all without outside help. And I was there.

To read about my trip in March, 2007, go to: Dispatches from Zacatón.

DEPTHX exploring La Pilita

el zacatón cenote map
This time around, DEPTHX will dive three times deeper than it has ever gone before to explore the depths of Zacatón, where no human has ventured. What might it find? New forms of life? Hydrothermal vents like those in Yellowstone or deep on the sea floor? Side caves that connect Zacatón to other caves and sinkholes? Lost Aztec gold?

Okay, that last one isn't considered likely. But you never know!

And now for a little geology.

The caves and sinkholes of the Zacatón system are located on a ranch near the small town of Aldama in the state of Tamaulipas in northeastern Mexico.

According to Marcus Gary, a hydrogeologist from the University of Texas at Austin and a member of the DEPTHX team, these caves and sinkholes formed as a result of volcanic activity from below. This is very different from the classical theory of how caves form and from how most of the other large caves in this part of Mexico likely formed. (More on that in a future post.)

Today, the water in several of the sinkholes is fed by hydrothermal springs. Some are warm and smell faintly of rotten eggs, hence the name for the ranch - Rancho La Azufrosa - from the Spanish for sulfurous.

Marcus Gary with DEPTHX (photo by Marc Airhart)

The sinkholes also display another interesting characteristic. They appear to be in varying stages of closing up as crusts of travertine form at their surfaces. At least one appears to have already closed up entirely, sealing off an underwater lake, possibly with unusual life forms. (More on that in a future post.)

Gary first came to Zacatón in the early 1990s as a scuba diver. He assisted Jim Bowden in his attempt at breaking the world's deepest scuba dive record in 1994. The unique environment enchanted the young diver and inspired him to pursue a career in geology. For over 10 years, he has studied the system and is now on the verge of completing his Ph.D. in geology. The DEPTHX project will help cap off his dissertation on Zacatón.

Other major collaborators for DEPTHX include members of Carnegie Mellon University, Colorado School of Mines, Southwest Research Institute and Stone Aerospace. The DEPTHX project is funded by NASA.

For five days, starting May 17, I will trail the experts and post daily updates here at

Join me right here for the adventure!

Marc Airhart, Science Writer, Jackson School of Geosciences University of Texas at Austin

For more about Sistema Zacatón, Click Here.

** The photo of Marc Airhart and DEPTHX which appears in the navigation menu was taken by John Kerr. Art Palmer took the photo of El Zacatón that appears at the top of this page. The image of DEPTHX diving is by Stone Aerospace.

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