Conversations with Bill Stone: The joys and perils of exploring the deepest cave on Earth.

It’s hard to believe that there is any stretch of terrestrial land on this planet that has not been explore. Explorer: The Deepest Cave which premieres tonight, May 30 at 10/9c and stream this summer exclusively on Disney+, handily dispels this notion. The one-hour special follows renowned cave explorer Bill Stone as he and his team push the boundaries of what has ever been done before as they attempt one of the greatest achievements of modern exploration — to set a new world record by venturing into the bottom of what is thought to be the deepest cave in the world.

Deep in the uncharted depths of Cheve Cave in Mexico, the expedition team navigates through over 12 miles of unexplored tight, twisting passages, sometimes in complete darkness, where one mistake can be deadly. 

During the dangerous and highly technical adventure, not only is Bill and the team trying to break the world record for venturing deeper than any other person on Earth, the expedition’s other goal is to map everything the team sees to create both traditional 2D maps as well as CGI 3D models relative to the surface topography so others can study the cave and discover what its future holds.

Bill Stone discussed cave diving in Cheve cave as well as Explorer: The Deepest Cave.

How did you first get interested in the shepherd cave?

We were working for about 15 years in an area very close to there, and we had been exploring a very deep cave system. You could walk from the highest entrances in that cave system to the South and see that there were mountain ranges extending down there and none of us ever put one on one together. We went over there to see if there’s any other similar caves there because we have this gigantic system on the north side of the river called the Santa Domingo. 

Somebody finally did in 1986 and the entrance that they found out was at an elevation of over 10,000 feet, which put it at almost 3500 feet higher than anything that we had on the wild side of the river, which meant that there might be a possibility for the world’s deepest cave over there. 

I went over there in 1988 and anybody that was with us, were just stunned by what we saw, to have an entrance that you could fly a 747 into, sitting above 10,000 feet elevation, with the air blowing into it. It was obvious that a major discovery had been made in hydrogeology and caving that it was going somewhere big. That was 37 years ago. I’ve spent over forty years of my life on that. 

How does air flow tell you that there’s potentially a big cave there?

To give you an idea of the entrance to Cheve is over 80 meters wide and 40 meters tall. This is enormous and yet within that you can feel hurricane-level cold air being sucked into that cave, enough to wave a flag horizontal. The only way that that is created is by the presence of an extraordinarily long, extraordinarily deep, open void below you. We have, for all those years, followed where that wind leads. 

In fact, 2017 was probably the biggest revelation. We had been stopped for almost 30 years at the deepest sections of the cave. One of the groups hauling equipment out from a diving effort took a wrong turn, and they ended up climbing up into this tunnel and when they got there, they discovered this vortex of wind going into this tiny tunnel. They called up and said, “You know there’s something strange going on down here. You guys better get down here and look at this.” When we did and it was kind of like the magic key to the doorway to the beyond. When we got another 10 kilometers beyond that, the wind was still roaring through with hurricane force, which means that the air, even down there, even that far in, is going somewhere big. 

Cavers walk into the entrance of Cheve Cave. (National Geographic/Pablo Durana)
Bill Stone, caver and expedition leader, checks in on a cave radio to take notes on the days’ happenings at Cheve Cave. (National Geographic/Kasia Biernacka)

You know the film showed a lot of stressful moments going into the caves. But there must be something about it that you love, some glorious moments. What keeps you going back?

It’s funny that you asked that because a lot of people think, Oh, well yeah, you go for the record or something. No, those things are super ephemeral. There have been times when we’ve had the second deepest cave in the world, we’ve had the third deepest cave in the world twice, and you go home and you party. But basically what keeps you coming back are two things. 

Number one, when you do this, with the very small number of people on this planet who are technically versed – these are all multidisciplinary hands who are on a level above astronauts – and know all these techniques, they are all psychologically comfortable with being in a no-rescue situation at a place where you are five-and-a-half days one way travel from the entrance. A typical trip last year was 30 days round trip from the entrance and back. 

When you get down there, if you’re not really into it, and comfortable with it, and trusting your teammates, you’re on the verge of panic thinking that you got to get out. You filter those people out over time. What’s left are the superstars. It is a privilege to be in these places with these people. 

Nobody who has been there in a remote place like that, depending on those people for their lives ever forgets it ever. It’s one of these things where you want to go back and do it again, partially because of that, but secondarily – and this is the second reason – is because this is the last terrestrial frontier. It is gloves off exploration, where we don’t know where it’s going, but we do know it’s going and it is going to go remote like nobody’s business.

The view of the clear night sky outside of the Cheve Cave entrance. (National Geographic/Kasia Biernacka)
Tea member Katie Graham looks on as a caver navigates through ropes over large passage in Cheve Cave. (National Geographic/Pablo Durana)
Cavers Sean Lewis and Witek Hoffman admire a fresh new area of the cave that they discovered. (National Geographic/Pablo Durana)

Explorer: The Deepest Cave shows a lot of the physical prep. How do you get mentally prepared for a trip like this?

We didn’t actually show this in the movie, but something that happens every once in a while is where you hit a flooded tunnel at great depth. It’s an underwater tunnel and you have to get past that. You have to have diving equipment. During filming, we ended up in a situation like that. 

We’ll start rehearsing a year in advance and the candidates for the diving team will actually come down here to Texas – sometimes we’ll go over to Florida – and we will rehearse the exact maneuvers that we’re going to do underwater, because if you know anything about cave diving, it is exceedingly dangerous. We’re doing it in spades. Not only are we cave diving, we are carrying all the equipment that we have to have to do everything we do in a dry cave beyond there – all of your camping equipment, your food, your climbing equipment, your rope, your drills, all the technical equipment that comes with high end cave exploration. You’ve got to take all that through, and then get on the other side, fix your diving gear and then go on as if nothing happened. That psychology weighs on you. You’re out there thinking, “Okay, I need to be kind of careful here. Because if I sprained my ankle, am I going to be able to swim back through the underwater tunnel and the five days of travel you’ve got to cover when you get back from the entrance side of it. The second you cross an underwater tunnel underground, that is a demarcation of psychological pressure that you’re dealing with. The people who do that they’ve got my highest level of respect. 

Where it’s super technical, we train. We simulate and go through all the possible failure modes. Otherwise, what we do for everyone is when you arrive in base camp, there is a rope course setup that simulates every single type of rigging that exists underground. We have over 12,000 meters of rope in Cheve right now. It’s all there and you’re doing it with all your gear on in the dark under the spray of a waterfall with a 20 kilogram pack, hanging below you. This is the kind of stuff that Everest climbers don’t do. Yosemite climbers don’t do – well maybe maybe Yosemite climbers do, but they don’t do it the way we do there. We’re always in the dark and usually there’s water. Those are the kinds of things that you have to have training in advance. 

As far as psychology, when new people wake up in the morning, they’re sitting there very pensive. Their mind is a million miles away, their eyes are staring a million miles away, and you know what’s going through their mind. “Can I get out of here?” In the back of their head, they’re remembering every drop and every obstacle that they had trouble with coming down and it starts to add up. 

A Cheve caving team member lights up the cavern in front of him deep beneath the cave’s entrance. (National Geographic/Pablo Durana)
A Cheve caving team member lights up the cavern in front of him deep beneath the cave’s entrance. (National Geographic/Pablo Durana)
Team member Katie Graham looks at an illuminated crystal formation inside Cheve Cave. (National Geographic/Pablo Durana)

From what I gathered, supplies played a significant role in the expedition’s ultimate outcome. How difficult would it have been to get supplies replenished? Does that happen on missions? Is it a possibility or is that too logistically difficult at this point?

That is the critical issue. We’re using siege tactics because that’s the only way we know. There are certain things that we try to reduce the weight of, but food is important. You have to have energy to explore. We have tried over the years to compress that food weight as much as we can. 

This conversation is happening while we are getting ready for a telecon with 24 of the best team members, best cavers in the world, coming up here in a week to decide how and when is the return? How are we going to do it? Part of the biggest problem that we have is that it is so far out there during a 30 day round trip. How do you supply these people? Because last year we did an experiment, and we called in an emergency – it wasn’t really an experiment but it became an experiment because we all learned a lot – we phoned in emergency requests for a couple of items that were critical to try to continue right there at the end of April. Well, the April crew that came in, they had a month on site. They were support personnel. 

Basically, time was wasted because it took them time to acclimate, a few people got injured. By the time it was all over their gear never made it to Camp Six, so those people at the end were done. They had to leave, they were out of food, they were out of gear. That was that was the wake up call to everybody that we were playing an entirely different game right now. So going back, what we’re trying to do is figure out what we can cut out of that supply line. 

One of them that has come up as something that we might actually be able to tackle is energy. We’re designing our own micro-generator. This is something that’s about the size of a football, that puts out about 200 Watts and runs off gasoline. It does not exist. You can’t find it anywhere. We’ve got our engineers working on it, and the idea is that we use that to recharge our drills, our batteries, all of our surveying tablets, our survey instruments. Anything that runs off electricity, we recharged on site. By doing that, we are saving roughly 30% of our logistics load from what we do right now. 

But food is still an issue. Rigging gear is also an issue .Everybody is now having discussions about using titanium hardware, going to seven millimeter spectra, or Dyneema rope instead of nylon. These are all kinds of things that we would never ever have considered in the past but now do because we’re being forced to go so far.

Explorer: The Deepest Cave premieres tonight, May 30 at 10/9c and will stream this summer exclusively on Disney+.

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