Thai cave rescue diver Richard Harris devised an experiment. If he succeeds, he will be a hero. If not, it may explode Australian film

Deep in a valley in the New Zealand wilderness, cold, clear water rushes through moss-covered rocks.

In the morning the fog rises and extends across the valley. In the afternoon, the sun sparkles on the Pierce River, shafts of light filtering through the native tree canopy. It is a fertile, primitive place. The water flowed through tunnels at Mount Arthur, in the northwest of the South Island, to meet at its base at Pearce Resurgence. On the surface it appears to be a harmless, calm pond. But underneath lies one of the largest and deepest cave networks in the world; Unfathomable, unknown habitat, seemingly bottomless.

Its difficulty is legendary among cave divers. None more so than anesthesiologist and underwater explorer Dr. Richard Harris, who dived into dark recesses several times before attempting a dive like no one had done before. “It’s a very scary place,” Harris says in the documentary Deeper, released this week.

“You enter this cave that seems to swallow you up as you walk into it. It’s black. And you reach this deep drop that goes over the edge and drops down to a depth of 100 metres.”

And then it continues.

The primary fear of most people is being underground and Underwater has a limited amount of air, but for Harris, underwater caves contain great beauty. To him, these hostile places are mysterious hydrological mysteries waiting to be solved.

“Every cave is different and uniquely shaped,” he told The Guardian. “It’s an extraordinary world out there. That feeling of swimming down a new passage when you’re the first person to lay eyes on it is very addictive and exciting.”

“It’s very hard to describe, but it gets into your system…the more you do it, the more you need to do it.”

Diving into Pierce’s return became an obsession he couldn’t explain.

There, in 2007, while diving with the “gods” of cave diving, Rick Stanton and Dave Apperle, Harris’ suit flooded, he buckled and had to be treated with oxygen. It was hard to shake the feeling of failure. “I couldn’t stop thinking about that cave,” he says in the film.

In 2008, he dropped to 182 metres, farther than Stanton had reached in 2007. He desperately wanted to go further and deeper. He couldn’t let it go. But he was already close to doing it safely.

“We risk our lives every time we put our heads under the ground,” Harris says. He was moments away from death. He was stuck in very narrow caves. His biggest fear was entering the cave 1.7 kilometers away when the silt rose and he could not see the small crack through which he could return.

“I couldn’t really get myself back through it, so I had to start taking off the equipment and pushing it through the hole to get out.” But, he says, “If you panic you will die. And when you feel that deep fear starting to rise, you can actually talk to him and tell him: ‘This isn’t helping, I have to focus on the problem.'”

There’s one particular issue that would catapult Harris into the international spotlight: In 2018, he and his diving buddy Craig Challen became world champions and were named Australians of the Year for their role in rescuing 12 boys stuck in a flooded Thai cave. Despite this acclaim, Harris says he has never felt confident as a person and suffers from anxiety. But when he puts his head under water, anxiety and self-doubt disappear.

In February 2023, Harris assembled a team of his divers friends to attempt to go down in diving history. Harris wanted to be considered an elite diver. Pearce can provide this evidence.

TPearce Resurgence is so remote that people with the equipment have to be flown in by helicopter. Water 6C all year round. Divers will spend between 13 and 16 hours in these waters, much of it decompression. It’s a cold and wet place to camp. “Everything is wet,” says Jennifer Peedom, Dipper’s manager, who went on a later trip. “There was no phone signal, and there was only a 15-minute window of satellite signal.” There will be no help coming if the mission fails.

But, Harris says, “Being in that beautiful bush with a group of friends over a beer and a bonfire is a big part of it.” “They put their lives in each other’s hands,” says Peedum. “There’s a real sweetness that I found really unexpected.”

Challen was a “willing partner” in exploring Pierce’s return. But now, as Harris’ diving partner, their friendship will be tested to the limit. He will serve as Harris’ “backup and lookout” in the unplugged depths.

In 2020, Harris dived to a depth of 245 metres, but suffered from high pressure nervous syndrome, which left him with tremors in his hand. Not being able to operate his equipment with his hands was extremely dangerous.

Now, plan a radical new approach. Hydrogen will be provided as a breathing gas. It has never been used for deep diving. Its slight narcotic quality can cure Harris’ tremors, allowing him to move forward. But there will be helium in the mix because hydrogen and oxygen alone would be too dope. This will be known as the “hydrogen experiment.”

If successful, Harris will advance the science and technology of diving and future exploration. If not, Harris could explode.

It was a calculated risk. Or as Harris says, “informed risk acceptance.” He is a meticulous man. “I spent 18 months researching it, talking to international experts,” he says. But his team of scientists at the camp were not entirely convinced. They will literally be in uncharted waters.

“I don’t think any of us were sure,” says dive supervisor Professor Simon Mitchell, a leading academic in diving medicine. “There were too many risks.”

Deeper was filmed over three weeks on the countdown days of the Resurgence dive. It documents the mistakes that occur with more than 80 kilograms of equipment carried by drivers – dry suits, electrically heated underwear, cylinders, weight belts, and hoses. There were leaks, small failures. “The point of failure in a dry suit can be catastrophic,” says Mitchell.

One day before the big diving day, the film shows Chalene making the painful decision to quit. He doesn’t have a good feeling. He says he’s not in a “flaky” state of mind, he’s just been too busy to prepare properly. “You have to be in the right place and have a very positive attitude,” Harris understands.

But then Challen has a “change of attitude.” He decides to do so. If Harris explodes, he says with a smile, “I’ll pick up as many pieces as I can to take home.” They both say that if things go wrong neither of them wants anyone to risk their lives to collect their bodies.

The night before Harris had been obsessively checking his equipment. He lies awake imagining the dive, anticipating when things might go wrong and how he will react.

The day comes. At five in the morning, there is a distant glimmer of an apricot-shaped sunrise. As he always does, Harris wants to be left alone with his thoughts. “I like the peace and quiet while I get dressed slowly, so as not to break a sweat and raise my heart rate.”

It’s still dark as the men slide, like astronauts, into the cold water. The bluefin disappears under a rock ledge as it begins its descent.

Down, down, down they go. And he continued. At an altitude of 180 metres, Harris experiences tremors. At 200 metres, the moment comes. He presses the switch to stop breathing the helium mixture and start breathing the hydrogen mixture. It is, he says, “a scary moment.” There is a hiss in the bottle, a few careful sips and he is alive and the shudders subside. It doesn’t explode. “I felt incredibly comfortable and in control at this depth for the first time ever. I thought: ‘Great, I can keep going.'”

But it goes back to the agreed upon 230 metres.

And so began the 12-hour decompression climb. Decompression takes place in a series of waterproof chambers with breathable gas placed at depths of 40 meters (one hour), 28 meters (two hours), 16 meters (four hours), and seven meters (five hours). “By the time they got to the third room, we were just looking at each other with stupid smiles on our faces and not really talking because we were just thinking about the moment,” Harris says. “It was amazing, it was amazing.”

Darkness falls as they approach the surface, and a circle of faces and torches look at them.

Now, with the “pride and accomplishment” of making diving history, Harris says, it’s finally “enough.” He can’t keep doing this with his wife, Fiona, who has endured an agonizing wait at home without outreach at Pearce Resurgence. “I shouldn’t have to go to the bottom of a cave in New Zealand to come to terms with my identity,” he tells the camera.

He told Chalene he would not be returning to Pearce Resurgence.

“Okay, where are we going next?” Chaal asks.