Cave Diver Risks All To Explore Places 'Where Nobody Has Ever Been'

DAVE DAVIES, HOST:

This is FRESH AIR. I'm Dave Davies, in for Terry Gross, who's off this week. Our guest Jill Heinerth. has one of the most fascinating and dangerous jobs on earth. She's one of a rare breed of technical divers who explore underground waterways and submerged caves deep beneath the earth's surface or sometimes, as you'll soon hear, inside an iceberg.

"So many cave divers drown in these underwater catacombs," Heinerth writes, "yet they can't buy life insurance at any price." She writes about her explorations, some harrowing escapes and the challenges she's faced as a woman in the cave diving community in a new memoir. Jill Heinerth is also a writer, photographer and filmmaker who's starred in TV series for PBS, National Geographic Channel and the BBC. Her new book is called "Into The Planet: My Life As A Cave Diver."

Jill Heinerth, welcome to FRESH AIR. I'd like to start with a reading from the very beginning of your book, on a pretty gripping experience you had in Antarctica.

JILL HEINERTH: Sure. This is from the prologue.

(Reading) If I die, it will be in the most glorious place that nobody has ever seen. I can no longer feel the fingers in my left hand. The glacial Antarctic water has seeped through a tiny puncture in my formerly waterproof glove. If this water were 1/10 of a degree colder, the ocean would become solid. Fighting the knife-edged freeze is depleting my strength, my blood vessels throbbing in a futile attempt to deliver warmth to my extremities. The archway above our heads is furrowed like a surface of a golf ball, carved by the hand of the sea.

Iridescent blue, Wedgwood, azure, cerulean, cobalt and pastel robin's egg meld with chalk and silvery alabaster. The ice is vibrant, bright and, at the same time, ghostly, shadowy. The beauty contradicts the danger. We are the first people to cave dive inside an iceberg, and we may not live to tell the story. It's February, in the middle of what passes for summer in Antarctica.

My job for National Geographic is to lead an advanced technical diving team in search of underwater caves deep within the largest moving object on Earth, the B-15 Iceberg. I had known that diving into tunnels inside this giant piece of ice would be difficult, but I hadn't calculated that getting out would be nearly impossible. The tidal currents accelerated so quickly that they've caged us inside the ice. We're trapped in this frozen fortress, and I have to figure out how to escape.

DAVIES: And that is our guest Jill Heinerth, from her new book "Into The Planet: My Life As A Cave Diver." Now, in the case of this dive into this iceberg in Antarctica, the (laughter) largest moving object on Earth, the B-15 Iceberg. What was making the water move so fast that it trapped you and your fellow divers inside this cave in the ice?

HEINERTH: Well, in the ocean, you have significant tidal exchanges, but there's a lot of things that are happening around an iceberg. As it's melting, you get freshwater dropping into saltwater, and that actually also creates really weird up currents and down currents. So there's a lot of environmental factors at play, none of which we could have predicted because nobody had written a handbook for something that hadn't been done before.

DAVIES: So literally, nobody had dived into the pockets, the spaces in an iceberg before?

HEINERTH: Yeah, nobody had ever attempted to cave dive inside an iceberg. And this iceberg was not just the largest moving object on the planet, but it was the size of Jamaica. So when this broke away from the Ross Ice Shelf in Antarctica and started to make its journey north, it started breaking into pieces along fractures and crevasses that we were able to exploit and swim inside of to find tunnels within the ice and tunnels beneath the iceberg where it had sort of tripped up on the seafloor.

DAVIES: Right. And I have to say, I mean, this chapter of the book, even if you had never made it into the iceberg itself, just the voyage on this boat to get there was really scary. I mean, you had some huge rogue waves.

HEINERTH: Yeah.

DAVIES: You finally get there, and there's a big opening, a big crevasse in the iceberg, and you dive into it. And on one of the earlier dives, before this one that you were describing, where you become trapped, there was a big groaning noise above you, right? What was that?

HEINERTH: Yeah. We were, you know, diving beneath this iceberg, and we were sort of well into these passages when I was hearing, you know, cracks and pops and groans and all sorts of sound from the ice.

And in the moment, I didn't realize what it was, but when we turned around to retrace our footsteps and come back out, we got to a point where we could swim towards the surface, towards daylight. And I realized that the doorway, the very opening that we had gone into to get into the iceberg had closed. There'd been a calving, and a massive piece of ice had blocked the doorway out.

DAVIES: So what happened?

HEINERTH: Well, you know, the pit of my stomach first (laughter) was just like, oh, no, what are we going to do? And we, you know, worked our way around and in between blocks of ice and found a new route back to the surface.

And I remember sitting there about 20 feet below the surface, just doing a hang for what we called decompression time at the end of the dive, just to allow my body to reacclimate to the pressure. And I looked up, and I could see my colleagues on a Zodiac boat waiting for us, and they were, like, high-fiving and dancing. And apparently, it was much more dramatic from their viewpoint than from mine. When that piece of ice calved and blocked the doorway, it nearly threw them out of the boat, and they were sitting up there assuming that we were dead.

DAVIES: Right. It had created, like, an eight-foot swell which nearly capsized the boat. They assumed you were dead.

HEINERTH: Yeah, yeah.

DAVIES: So returning to this dive where - that you begin the book with, where you and - was it one other diver or two, in this case?

HEINERTH: Yeah. On that dive, two. Yeah.

DAVIES: OK, two. The - right, the photographer was there from National Geographic.

HEINERTH: Yeah.

DAVIES: You go underneath hundreds of tons of ice above you and then suddenly discover the current is sweeping you away from the opening, and you can't get back. One of the things you could try and do was wait until the current abated, right? But there was time pressure. Why couldn't you just wait it out?

HEINERTH: Well, we were already deep. So we were 130 feet deep, and we're accumulating inert gases in our bodies that will mean that the longer we stay, the longer it's going to take for us to slowly stage our way back to the surface and do our decompression time, otherwise we can get bent. And...

DAVIES: That's the bends that divers know about.

HEINERTH: Yeah, the bends.

DAVIES: You want to just take a moment and explain what that is?

HEINERTH: Sure. Decompression sickness is - I guess the closest analogy is a soda pop bottle. You know, when you're down under the water, you're under pressure, much like a soda pop bottle with the cap screwed on tight. So there are gases that get sort of pressed into your tissues. And when you slowly ascend back to the surface, you have to do that in stages in order to slowly relieve that pressure. Otherwise, you're just like that soda pop bottle if somebody shook it up and took the cap off, and that can cause, you know, injuries. It can cause paralysis. It could even cause death.

So every minute that we spend on the bottom, trapped inside an iceberg, we have to account for that time and some to come slowly back to the surface. And when you're in water that's 28 degrees Fahrenheit, you don't have that much time before hypothermia kicks in. So we're struggling for our lives to get out of the iceberg. We're trying to get out quickly so we don't amass too much decompression time, and, you know, we're worried about freezing to death.

DAVIES: Just that, wow.

HEINERTH: Yeah.

DAVIES: So what goes through your head that allows you to focus at a moment like that?

HEINERTH: You know, when something terrible happens, it's really easy for your mind to just explode into these, like, chattering monkeys. It's like your emotions want to take over. You start to breathe fast. Your heartbeat starts to race. And you have to turn that all off. So I take a really deep breath and try and slow my heart, slow my breathing, and then just focus on pragmatic, small steps.

Like, the big picture of survival is sometimes so hard to see, but we always know what we can do to make the next best step towards survival. So it's really all about controlling emotions and controlling your breathing.

DAVIES: OK, so you and your other two divers are trapped by a current that's really too hard for you to swim against. How do you make it out?

HEINERTH: Well, I dove my hand into the doughy sea floor that was covered with this really, you know, beautiful marine life, filter-feeding organisms that were just like, you know, gobbling up all the nutrients that were being delivered to them into the current. And every time I drove my hand in my, you know, my muscles were shaking just to pull myself forward an inch at a time, an inch at time.

And when I finally got to the point where I would be able to ascend, there was this terrible current that was just pouring down these cliffs of ice. And I couldn't move upwards. And I noticed something that I had seen on previous dives, these tiny little fish about the size of my thumb. And they were transparent. Like, I could see their insides. And every time the current got strong, they would hide in these little burrows inside the ice walls.

And when I saw that, I thought OK, it's a handhold. And I ended up jamming my fingers into these holes to try and pull myself up and get some traction. And at this point, my hands were so cold, especially my left hand. It felt dead. But I just slammed it into these holes and pulled myself up until I could get free of the current.

DAVIES: Wow. And every time you went into a hole, a little fish darted out saying hey...

HEINERTH: Yeah, he...

DAVIES: ...What happened to my home?

HEINERTH: ...Made the ultimate - yeah, the ultimate sacrifice for me (laughter).

DAVIES: You managed to climb and decompress on the way up, and the three of you got out.

HEINERTH: Yeah, yeah. I remember swimming back to the boat. And when I got to the swim ladder, you know, everybody was hanging over the side of the boat because we were so late. We'd turned a one-hour dive into a three-hour dive. And our chief science officer bent over the railing and said wow, what happened? And I remember looking up to him and just saying the cave tried to keep us today.

DAVIES: That was your last dive on the trip, wasn't it?

HEINERTH: It was. We had planned to get back in the water. We felt like we needed a little bit more footage for the film that we were making called "Ice Island." And so we prepped our gear, and we sat down to have a meal. And we set someone on deck to let us know when the current, when the tidal currents, finally slowed down and would give us a chance to do one more dive.

And as we sat there eating our meal, suddenly I heard a scream on deck. And we went running up the companion way and onto the deck to see the very iceberg we had just been inside of cracking and dissolving and breaking up into just slush ice on the surface of the ocean as far as the eye could see. So the cave we had just been inside was now gone.

DAVIES: Had you been there, what would have been your fate?

HEINERTH: Oh, my gosh. If we'd been in there, we would have been killed. There's no doubt.

DAVIES: How dangerous is cave diving?

HEINERTH: Boy, well, some people call it one of the, you know, most dangerous occupations or even recreational activities. I've lost, you know, more than 100 friends and colleagues throughout my career in underwater caves and technical diving.

DAVIES: You know, when I heard the term cave diving, I pictured people going out into the ocean in a boat and then, you know, going over the side and finding caves near the shore or along the ocean floor. But what you do often involves dives that are, you know, miles, sometimes hundreds of miles, from the ocean, to really serious depths inside the earth - a couple hundred feet or more. What kinds of bodies of water are you exploring in these dives?

HEINERTH: Well, underwater caves are really abstract. It's hard for people to grasp that the earth is like a giant sponge. And so far inland, far away from the ocean, I can climb down into a sinkhole and go into a cave passage that's filled with water that branches out like a tree fingering through the planet.

DAVIES: Right, and up and down hills and cliffs - right? - through great elevations.

HEINERTH: Absolutely.

DAVIES: Yeah.

HEINERTH: Yeah, sometimes inside mountains, where you're climbing down in a cave, traveling through a waterfall and then reaching a body of water within the earth.

DAVIES: Right, and when you're down there, does this water have movements, currents?

HEINERTH: Yeah, sometimes the currents are so hard that we can't even make headway against them. It's kind of like trying to walk against a hurricane-strength wind. And you're pulling yourself along the rocks against the flow.

DAVIES: And what's propelling the water?

HEINERTH: Well, water moves through the planet from higher elevations to lower. You know, just like you have a waterfall on the surface, the same thing can happen underground, making the water move with great velocity.

DAVIES: Jill Heinerth's book is "Into The Planet: My Life As A Cave Diver." We'll talk some more after a short break. This is FRESH AIR.

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DAVIES: This is FRESH AIR. And we're speaking with Jill Heinerth. She is a veteran cave diver exploring underground bodies of water. She's also a writer, photographer and filmmaker. Her new memoir about cave diving is called "Into The Planet."

One of the things that you write about is that mud and silt, when you're diving in various underground bodies, can really create a hazard, right? You can't see.

HEINERTH: Oh, sure. Yeah. When you swim into a cave, especially when you're the first person to go into a place that nobody's ever explored, there's silt on not just the floor but on the walls and ceiling. And your very passage through that space and the bubbles that you make from your scuba equipment can knock that silt off the walls, the floors, the ceiling and obscure your visibility so that you can't even see when you're coming out.

DAVIES: You talk about diving in a Florida spring called Devil's Eye, where you go down to a certain depth, and there is an underwater sign featuring an image of the Grim Reaper. What was this doing under the water?

HEINERTH: Well, we put signs in springs, especially at popular locations like the ones in North Florida, to warn untrained scuba divers from going into these environments because when they get into these environments, the doorway can be very alluring. The water may look clear, and the room may look spacious, but when they go in, if they haven't been trained properly, they may kick up the silt and be suddenly blind and unable to find their way out. They could get lost in the mazelike passages.

So there's a lot of things that can go wrong. They also don't have a sense of how much of their gas supply they need to reserve to get out. And so it's very, very dangerous without proper training to go into a cave, and we hope that these signs will scare people off.

DAVIES: So this is difficult and dangerous. What's the appeal of it to you?

HEINERTH: Wow. You know, since I was the smallest child, I always wanted to be an explorer, to have an opportunity to go someplace where nobody has ever been before. And as an artist, with my camera, it's an incredible opportunity to document these places and bring back images to share with others.

DAVIES: Have you seen some pretty strange lifeforms down there?

HEINERTH: Oh, caves are filled with remarkable life forms that we barely understand. We're barely even beginning to document these new species. There were animals living inside the earth that don't live by photosynthesis. And many of these animals have no eyes, no pigment, but they have remarkable sensory capabilities. And all of these animals with these unique characteristics may be able to teach us an awful lot about evolution, about survival, maybe even about new chemical and drug compounds that are of use to humanity.

DAVIES: Can you expand on that a bit? Are there particular insights that we've gotten from some of what's been discovered in caves?

HEINERTH: Sure. Yeah. The longevity of some of these animals within the cave diving environment is remarkable. I mean, we can look at the blind albino crayfish that can live for 200 years inside a cave, when its closest relative in the river outside only lives two to three years. Now, that crayfish is living in an incredibly food-scarce environment where he has to conserve energy. So that's kind of an interesting strategy to look at. You know, what's he feeding on and how often and why does that make him live longer?

And then these animals that have been sort of stuck in evolution and haven't evolved in over 65 million years, you know, did they reach some sort of a perfection in the environment, or does that represent something about the environment that hasn't changed? We don't even know yet. So those animals are really special and interesting. And since we're only beginning to identify them and record them as a new species, there's a lot of work left to do.

DAVIES: What's a remipede?

HEINERTH: A remipede is a cool little animal. It's, you know, less than 2 inches long, kind of a centipedelike, white, blind animal, again. But it has venomous fangs and pincers, and it can attack something 40 times its size, immobilize it and then turn the insides of that prey into jello so that it can suck the life out of it over time. And if this animal was the size of a cat, it would be the deadliest thing on the earth. And it's also been unchanged for over 65 million years, so it's like a living, swimming dinosaur.

DAVIES: Jill Heinerth's new memoir is "Into The Planet: My Life As A Cave Diver." After a break, she'll talk more about the dangers involved in cave exploration, about how her thinking about fear and risk were shaped by a terrifying experience aboveground and about being a woman in the male-dominated world of cave diving. Also, Maureen Corrigan recommends two mystery novels by women whose titles evoke classic suspense novels by men. I'm Dave Davies, and this is FRESH AIR.

(SOUNDBITE OF ALBERTO IGLESIAS' "LA TELA ROJA")

DAVIES: This is FRESH AIR. I'm Dave Davies in for Terry Gross, who's off this week. We're listening to my interview with Jill Heinerth, who belongs to an elite group of divers who explore underground waterways and submerged caves deep beneath the earth's surface. It's an undertaking that requires enormous technical skill and special equipment and comes with serious risks. Her new memoir is called "Into The Planet: My Life As A Cave Diver."

When you're diving, you're not just gawking or taking pictures, right? You're surveying unexplored territory. How do you do it?

HEINERTH: We used to use very traditional techniques to survey underwater caves. We would run a spool, like a reel of nylon guideline through the system and then meticulously count the distances in between each turn and corner and measure the compass bearings and then draw a traditional map.

But today, we're using some really exciting new technologies that allow us to make three-dimensional maps. So now we're driving scanning systems, like sonar wrappers, through cave systems. And they're pinging the walls and allowing us to make 3D models that are more like something that you could drive through with a joystick or experience in a VR or augmented reality set of glasses.

Today we're were making these incredibly detailed maps down to sub-centimeter accuracy in three dimensions. And now we're collaborating with scientists and engineers in making these maps. And they're finally, you know, of interest and use for urban planning and understanding what's beneath the surface of the earth and even understanding what we may find in places beyond our earth. Some of these mapping devices are being tested in caves so that they can go to space.

DAVIES: You know, you describe a lot of pretty harrowing experiences in the book. And you write that some people must think cave divers have a death wish. How do you regard personal danger? What has shaped your thinking about it?

HEINERTH: You know, people usually laugh when I tell them that I'm actually risk averse. I'm not fearless. I think that it's important to be scared. When you approach anything new - and for me, that's often - I certainly get that fear in the pit of my stomach. But the problem-solving to do something new that's never been done before allows me to plan through all the potential risks. And then when I get in the water, I'm actually sort of free in my mind and totally focused on what's ahead.

But I don't want to go diving with people that are fearless. I want to go diving with people that are scared because to me, that tells me that they care about the outcome and that they're not going to be foolish if we encounter something underwater.

DAVIES: You grew up in Canada, a suburb of Toronto. And when you were in college, you had a really scary experience with a burglar. Tell us about that.

HEINERTH: Yeah, when I was in college, I had just moved off campus into a house. And I was alone on the very first night in the house. And I heard something downstairs. And I woke up in the middle of the night knowing that somebody else was in the house, and I was the only person with a key. And my heart was racing, and my first reaction was just to pull the covers over my head and hide.

And then I realized that whoever was in the house was now, like, rifling through things downstairs. And I had to let them know that somebody was home. And I got out of bed, and I started stamping around and thinking that, you know, if they hurt me that they'd leave. And the person didn't leave. They just kept rifling through the closets and moving things around downstairs. And I didn't want to scream out because I didn't want them to know that I was a female.

And one thing led to another, and as time passed, I heard the steps coming up the stairs towards my bedroom. And I realized that I was going to have to defend myself. I didn't have a phone hooked up. There was no way for me to jump out the window of the second story. I would have landed into a busy street. And so there I was, like, 2 o'clock in the morning just, like, pawing for X-ACTO knives from my drafting table in my bedroom and clenching them into my fists while somebody was coming up the stairs.

And after a wait, he finally basically - practically ripped the bedroom door off the hinges and came into the room. And I turned on a light and flashed it in his eyes and screamed at him, and he still came after me. And in the end, I lunged and slashed across his chest with one of these art knives for my drafting table. And only at that point did he finally step back and look at me. And he laughed. And he turned around, and he slowly walked down the stairs and out of the house.

And it was only after sort of, you know, getting up and kicking the door open and going through the bathroom and making sure he wasn't in the closet that I ran through the stairs and was down the stairs and was able to run out of the house and get help. And it was terrifying. I was unable to speak when finally the police arrived.

DAVIES: That's a really traumatic experience.

HEINERTH: It was. It was totally traumatic. I was awake for days.

DAVIES: Do you think that connects at all to the way you handle the danger of what you do now?

HEINERTH: Having to confront a burglar in my own home was formative in my life experiences because my first reaction was to hide under the covers. And you can't do that if you're, you know, in a cave trapped. You've got to act. And I think that whole experience taught me not to hide, not to run, but to face danger and to know that I could succeed.

DAVIES: You were proving yourself in a very male-dominated world. What was that like?

HEINERTH: You know, sometimes it's extremely challenging. I've often been the lone woman on an expedition, the lone woman on a boat, the lone woman, you know, trying to get an opportunity in what is normally a predominantly, you know, male environment. And that has its challenges.

You know, as a young woman, I considered commercial diving. And I went to a workshop to be a commercial diver and was told I'm sorry, there's no room for women in commercial diving. You know, if you want to go train dolphins, go do that, I was told.

DAVIES: No room why, because someone wouldn't respect the authority or expertise of a woman or what? I mean...

HEINERTH: Well, this man that told me this seemed convinced that, you know, women weren't strong enough and that, in commercial diving settings, there wasn't an infrastructure that would allow for two genders to share the space on a ship or an oil platform or whatever else. And he just didn't think it was a job for women. I've had to fight that along the way, even, you know, through different levels of becoming a cave diving instructor as well.

DAVIES: What about the men that you, you know, really went through the trenches with, literally, I mean, had a lot of, you know, really intense experiences with? How did the sexism arise among you and these people who you'd really bonded with and should have respected that?

HEINERTH: Well, men - yeah. The men that I've been through the trenches with are are my brothers (laughter). And, you know, none of us on a tightknit expedition, you know, even has time to think about someone as one gender or another; they're just a teammate, and we have to bond. I mean, we're there covering for each other in a life-support sport. And all of us has to enter the water knowing we can take care of ourselves and that we're able and willing to take care of a buddy and bring them out in the worst-case-possible scenario.

DAVIES: Jill Heinerth's book is "Into The Planet: My Life As A Cave Diver." We'll talk some more after a short break. This is FRESH AIR.

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DAVIES: This is FRESH AIR, and we're speaking with Jill Heinerth. She's a veteran cave diver exploring underground bodies of water. She's also a writer, photographer and filmmaker. Her new memoir about cave diving is called "Into The Planet."

You say that you've known a hundred people who have died in cave diving incidents.

HEINERTH: You know, a few years ago, I actually thought, wow, how many people do I know have died? I mean, it was when my husband said to me, wow, I've known more deaths since I've been with you than I knew from my service in the military, that I sat down and I actually made this sort of macabre list of names of my friends and colleagues that have died from cave and technical diving, and it's well over a hundred people, some of whom were my very closest friends.

DAVIES: And the way it often happens is you're a community, and you know that somebody didn't come back from a dive. So you go to the point where you think they might have embarked, and if their vehicle is still there, you know what happened. But there's still a task to be done, right?

HEINERTH: Yeah, absolutely. I mean, there's been a number of times in my life when I either got the call from the police or from a loved one - you know, so-and-so didn't come home last night. And I know right away when so-and-so didn't come home last night and they're a cave diver and they were diving last night that it's going to be a body recovery.

But still, you know, we go and find the site, and when the car is sitting there alone with, you know, shoes neatly placed at the back of the pickup truck and everything put away nicely and this quiet body of water in the middle of a serene woods, we still know that we've got to gather together the tribe of friends and launch a body recovery.

DAVIES: Right. And this is because this is not something that EMTs or really anybody can handle, except for people with the technical diving experience that you have. So you've got to go bring your friend back.

HEINERTH: Absolutely. Oftentimes, when there's a cave diver that's missing, you know, the local police will be called in or even a local, you know, law enforcement dive team might come in, but it's extremely rare that law-enforcement divers are trained and experienced in cave diving to the degree that community experts are.

So we created our own team of people. It's like a phone tree. So if somebody is missing and we realize there's a body recovery to be done, a phone tree starts, and one person calls another until the group can be gathered together to go deal with this task.

DAVIES: How many times have you been in a situation on a dive where you felt there was a good chance you weren't going to make it back?

HEINERTH: Well, there's been a few times (laughter) where I wasn't sure I was going to make it home. There was one dive where I was even dead for, you know, 73 minutes to my friends (laughter) because my diving partner made it out of the cave and sort of sounded the alarm and literally started that phone tree to bring in the recovery divers. And, you know, she said, she'd been stuck, and she'd broken the guideline. And I was still inside the cave, and so people were filling tanks and loading their cars with gear and rushing to the scene to try and help.

And meanwhile, I'm still in the cave searching for my diving partner because I didn't want to leave the cave if she was still there. So I had retreated all the way into the maximum penetration in this cave and was slowly working my way out on a methodical search to make sure I wasn't leaving her behind. And I remember the thoughts that were going through my head. You know, oh, my God, two women can't die in a cave; that'll be, like, world news, you know. And I even remember thinking crazy things like, I got to get out of here; my husband doesn't know how to do the taxes (laughter).

DAVIES: Yeah. This was with the marine biologist Ruth (ph), right? This is - you describe it.

HEINERTH: Yeah, yeah.

DAVIES: You know, what struck me about that episode which you describe in the book, that happened in 2011, I mean, long after Antarctica, long after other occasions in which you had skated to the edge of death. And I bring that up because you - I would imagine that with time and experience, you are ever more careful, ever more thoughtful about checking your equipment and making sure that there is a plan and that the communication is clear. And yet, you know, as recently as then, you almost didn't make it. Do you ever think it's time to let this go?

HEINERTH: Well, I don't think it's time to let it go. And you know, I have cave diving friends that cave dived into their 80s (laughter), if you can believe it.

But you know, from that particular incident, I survived that incident because of wise choices I made before I got in the water. I had a lot of gas. So by the time I got out of that cave, I still had half of my gas supply left. And that had given me time to make an extra 73 minutes of search within that cave. So yeah, the worst happened. But we both got out alive because we used our training. We went in with the right equipment, and we went in with lots of gas. So it's really scary, but we solved our problems.

I mean, my husband would love it if I just packed it in. He's said to me more than once - you know, how much more do you have to do in this career before we can just retire? You know, what I do scares him. But it is what makes me who I am. And so I'll continue to be vigilant with my training and equipment and currency and try to make the best choices each time I get in the water.

DAVIES: Is there an amazing, awe-inspiring moment from a dive that you would want to share with us - something that's been remarkable?

HEINERTH: Well, you know, I think these caves are like museums of natural history. They're beautiful. Like, in Abaco in the Bahamas are some of my favorite caves because they're so beautifully decorated. They were formed during times of lower sea levels, when there was no water in the cave. So the rain used to soak down through the ground and then drip from the ceiling to the floor. And with each drip, a tiny bit of calcite was deposited.

And so you end up with these crystal chandeliers hanging from the ceiling and then stalagmites rising up from the floor - you know, much like, you know, a pile of dripped candle wax would look like. But these things are crystalline, beautiful galleries that we get to swim through. And I am never tired of of being in that environment that we sometimes call frozen rain.

DAVIES: Do you - you go through very extensive safety checks before every dive. Are there any particular rituals that you have, any superstitions that you do before you go in?

HEINERTH: After all of my safety checks and checklists are done, I sit down, and I close my eyes. And I actually think about what could kill me today. So quite specifically, I work through a list in my head of all the horrible things that could happen. But I envision myself solving each one of those. And sometimes I'm actually, like, moving my hands and reaching for a valve or a button or whatever to solve each of those issues so that when I get in the water, my mind is really free. And then if something horrible happens, I've rehearsed it just a few minutes ago. And I kind of need to do that eyes-closed ritual before every dive.

DAVIES: Jill Heinerth, it's been fascinating. Take care of yourself. And thanks for speaking with us.

HEINERTH: Well, thank you so much.

DAVIES: Jill Heinerth's memoir is called "Into The Planet: My Life As A Cave Diver." Coming up, Maureen Corrigan recommends two mystery novels which she describes as stunning and breathless. This is FRESH AIR.

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