Pozo Azul in northern Spain is the Everest of caves. A 55-year-old from Huddersfield just went deeper inside than anyone has before — almost all of his journey fully under water.
Late in the morning of August 31, Jason Mallinson slid beneath the surface of a dark forbidding pool. Having already spent most of a week inside Pozo Azul, a cave system in northern Spain, he was about to enter a deep, water-filled tunnel, an underwater passage with no air space whatsoever. Since passing the cave’s first bend he had been navigating through total darkness, entirely dependent on the lithium-powered lamps mounted on his helmet. Now, having checked his equipment one final time, he was ready to advance still further. If all went to plan he would create a new world record. He hoped to make the remotest dive in history, becoming the first person to reach a point underground where to return to daylight would require a total diving distance of more than 10km.
At the edge of the pool a white nylon cord attached to the cave wall dipped into the water — the lifeline he and others had installed on previous dives to guide them home. Mallinson knew that the line stopped several hundred metres into the tunnel: the limit of exploration. He intended to swim on further, into the unknown.
Mallinson, 55, who lives in Huddersfield with his partner, Emma Heron, a fellow cave diver, and Joe, their seven-year-old son, played a key role in rescuing the members of the Wild Boars football team trapped by floodwater in Tham Luang cave in Thailand in 2018. Once Mallinson’s friends Rick Stanton and John Volanthen had reached the 12 boys and their coach deep in the cave system, he had flown in with other divers from Britain and Australia to get them out. For three days he’d had to carry the heavily sedated boys a distance of 1,500m underwater, but exploring Pozo Azul was a challenge of a different order of magnitude.
On previous ventures into Pozo Azul Mallinson had twice experienced equipment failures and had been lucky to survive. The day before his record dive his companion Craig Challen, also a Thailand rescue veteran, had almost drowned in an underground lake. Exploring Pozo Azul requires a mountain of high-tech equipment, a large support team to help carry it through the initial, awkward parts of the cave and an acceptance that rescue is impossible.
“Some people have this fretful mentality, constantly asking themselves, ‘What if this happens or that happens?’ " says Challen, a 58-year-old retired vet who lives south of Perth in Western Australia and who had never dived Pozo Azul before. “Our principle was, don’t have an accident. You know that if anything goes seriously wrong when you’re that far in, you’re f***ed. You’re not going to get out alive. You just have to be very confident of your ability and go as far as you can without being stupid.”
No one has ever been killed in Pozo Azul, but cave diving carries a high risk. There have been 18 fatalities in the UK since the 1940s. America’s record is worse — 161 cave divers perished there between 1985 and 2015. Safety is improving, but some of Britain’s leading exponents have come to grief. The most recent fatality was Simon Halliday, 49, a father of two from Clitheroe in Lancashire, who drowned in Lancaster Hole, beneath the Pennines, in January 2020. He was a Pozo Azul veteran, having been a member of Mallinson’s support team in 2019.
Pozo Azul has been an obsession for Mallinson for 22 years. At the time of his first trip the size of the known, mapped cave was relatively modest. Since then he has mounted expedition after expedition, methodically extending it. Driving him, like all exploratory cavers, is the buzz of new discovery: “When you get into virgin passage, it’s the best feeling in the world. You can surface in a big, air-filled river passage that no one has seen before, with waterfalls, huge caverns and stalactites. To put yourself into the position where you can do that is the ultimate goal.”
Challen agrees. “To go somewhere no one has seen is the biggest thrill you can get and you never get tired of it,” he says. “The big mountains have all been climbed and pretty much everything else has been explored. You have to try a bit harder underground, but the unknown is still there. But let’s face it, it’s also a bloody good adventure. The general public has this idea we’re all members of some adrenaline-fuelled death cult, but it’s not like that at all. Everyone has to strive for self-fulfilment in one way or another. This just happens to be ours.”
Terra incognita
The entrance to Pozo Azul is a submerged hole in a turquoise pool in scrubland near the village of Covanera, a two-hour drive southwest of Bilbao. Like most caves the system was formed in limestone, eroded by water flowing through cracks and fissures over many thousands of years. Spanish geologists believe that Pozo Azul dates back at least a million years.
In 1979, after 15 years of attempts by Spanish cave divers, Carmen Portilla and Fernando Fuentes managed to pass the first underwater passage, known as a sump. Having dived through a spacious tunnel for 700m, they surfaced in an open, air-filled passage that they named La Burbuja — the bubble. It continued for more than 300m, the stream surging through pools, around potholes in the floor and down a powerful waterfall. Eventually it led to sump 2.
By the time Mallinson first visited it in September 2001 with another British cave diver, Rupert Skorupka, it was already apparent that sump 2 was a monster. The Spanish had explored it for 780m, but the tunnel was heading down, not up.
Mallinson can’t remember exactly how many trips he has made to Pozo Azul — he thinks close to 20 — but he won’t forget the date he entered the cave for the first time in 2001: “I did a short push into sump 2. We came out and went to a bar and saw the burning buildings on TV — it was 9/11.”
Mallinson was experienced: he had made pioneering explorations in long, deep sumps in Britain, Florida, Mexico and France. He was accustomed to riding an AquaZepp scooter, a 2m-long torpedo-like device that enables divers to move much faster through the water. He was also adept at using a rebreather, a device that recycles exhaled air by “scrubbing” the carbon dioxide from it before feeding it back to the diver, therefore reducing the number of cumbersome gas cylinders required. Instead of a neoprene wetsuit to ward off the chill of the 11C water, he took to wearing a heavy-duty waterproof drysuit over thermal underwear and an electrically heated jacket.
By the end of 2007 his explorations had taken him more than 3.5km into sump 2, at a depth of 70m. This meant he had to breathe a specialised deep-dive gas mix containing helium and make lengthy decompression stops on the way out to ward off the bends — the painful, potentially fatal condition caused by nitrogen bubbles forming in the blood.
Mallinson says his explorations would not have been possible without his many Spanish friends, both other cave divers and the people of Covanera, who have always welcomed and supported him. “We used to base our expeditions in the field behind the village bar,” he says. “One of my greatest wishes is that one of the Spanish guys will come to the far end with me one day.”
In August 2009 he came to Pozo Azul with a team that included Volanthen and Stanton. “Team pushes make it much easier,” Mallinson says, not least to help carry equipment along the “dry” passages.
Volanthen and a Dutch cave diver, René Houben, ventured a further 375m through the sump. At last the tunnel seemed to be heading up. Next came Mallinson, who advanced another 625m in an epic solo dive that lasted more than 12 hours. Finally came Stanton, who became the first person to escape sump 2, finding air space 140m beyond the line laid by Mallinson. Electronic surveying equipment showed that sump 2 was 5,160m long — over three miles. It remains the world’s longest navigated sump. Beyond it lay a dry chamber, which the team named Tipperary, after the First World War marching song, because it was a long way to get there. And then came another sump.
In 2010 Mallinson and his friends were back. They took waterproof “dry tube” containers filled with food, stoves, sleeping mats, sleeping bags and dry clothes through sump 2 and camped in Tipperary. “It’s peaceful there,” Mallinson says. “With a warm sleeping bag and plenty of hot food, you can get a decent sleep.” His go-to meals include porridge, curry and rice, and tinned fabada, a Spanish stew of white beans, pork belly, chorizo and morcilla black pudding — all prepared by the light of a headlamp in otherwise pitch darkness.
Sump 3, Mallinson says, is of “vast dimensions — we’ve never had enough light to see both walls at the same time”. Passed for the first time in 2011, it is 3,275m long and 40m deep.
On the far side of sump 3 the cave totally changed. It consisted of a narrow, steeply ascending canyon, down which a foaming stream thundered, forcing the team to clamber along the walls. The rock was spiky and friable, putting their drysuits at risk of ripping — the consequences of which would be dire. They called it Razor Passage.
Sump 4 was a shallow, easy dive, just 150m long. That was followed by Razor 2, a canyon as strenuous as Razor 1, and then the 150m sump 5. Still more open river passage lay beyond, leading to sump 6.
Near death
Mallinson first entered sump 6 in 2015. “I was desperate to keep on exploring the cave but I couldn’t get anyone else to come that year.” It was on his way out that he suffered what he calls his first “near-death experience” in Pozo Azul. “Everything was going really well. I got back to Tipperary after 22 hours on the go and stopped for a meal and a sleep, then set off into sump 2.”
There the trouble began. “I wasn’t quite balanced in the water. Then I felt some resistance in my rebreather mouthpiece when I tried to inhale. It started to get worse and I realised water must have got into the system. Suddenly I took in a mouthful of it, contaminated by the caustic chemical that rebreathers use to scrub the carbon dioxide. I had to find my back-up regulator [scuba mouthpiece] and switch to using my bailout, open-circuit gas.”
This meant no more recycling, forcing him to depend on the emergency supply he was carrying. Thankfully he had stashed two cylinders ahead of him and a spare rebreather near the end of the sump, but there was still a very long way to go. “At this point I’m 3.5km from base and I’ve got to do my decompression before I can get out,” he says. “I honestly didn’t think I had enough gas to get back.” It was, he suddenly realised, Emma’s 39th birthday.
To speed his passage he unclipped some of his equipment from his harness and abandoned it, “but in my haste I jettisoned my spare scooter — only realising afterwards that if anything went wrong with the one I was using I was finished”. He was “skip breathing, holding each breath for several seconds, in the hope my gas would last”. And somehow, to limit his oxygen consumption, he had to keep his pulse rate down.
Needless to say, he made it. “Some would say, why the hell would I go back after an experience like that? But I did, because I knew what had caused the rebreather to flood” — a modification he had made that had caused a valve to open on a part of the system where a hose passed behind his neck.
Cave divers who don’t die young swiftly learn that, when things go wrong, “if you panic you’re not going to survive. But you’ll only be able to do that if you’ve experienced such incidents, so that when a problem occurs your brain knows how to go into survival mode rather than panic mode.”
Between expeditions Mallinson paid his bills by working as a rope access specialist, dangling high above the ground at power stations, football stadiums and telecoms masts. Then in 2018 came an unexpected job: the Thailand rescue. “The great thing about the rescue is that it has shown us what’s possible — until we got the boys out, no one knew if we could succeed.” It was not without tragedy, however. Saman Kuman, a former diver in the Thai navy, drowned in the cave while ferrying equipment, and another Thai navy diver, Beiret Bureerak, later died from a blood infection he may have caught in the cave. Earlier this year Duangphet Phromthep, one of the rescued boys, who had moved to Britain, took his own life, an inquest heard in October. He had been a pupil at the football academy at Brooke House College in Leicestershire.
In deep
A year after the Thai rescue Mallinson took a break from the media frenzy and returned to Pozo Azul. He thought he had fixed the cause of the leaky rebreather valve, but in 2019 it failed once more. This time it was even more serious. Again, he was alone, on a set-up dive before his planned big push, hauling equipment through sump 2. There, 2km from the nearest air space, “again I felt that resistance. The rebreather flooded completely about ten seconds later. On this occasion it took me much longer to find my spare regulator, and all the while the caustic liquid was burning my mouth and throat. Even when I found it, I could hardly breathe.”
The liquid had caused his windpipe to constrict, so that even when he managed to get out of the water, he was “wheezing, really struggling. The lining of my throat was shredded. I was still losing bits of it for a full week afterwards. I was really lucky to get out of that one — if my throat had constricted any further I’d be dead.” In the wake of this incident, Mallinson admits, “Emma does get worried about me”.
The Covid 19 pandemic put paid to Pozo Azul expeditions until this year — and Mallinson planned a bumper return. He mustered a big support team, with at least 15 divers on hand for most of the month-long trip beginning on August 13. For three months before setting off he trained intensely, testing and modifying equipment at Capernwray quarry, a popular diving site on the edge of the Lake District.
His first objective at Pozo Azul was to continue exploring sump 6; his second objective was to investigate a complex of dry tunnels he had found leading off from Tipperary. He was able to communicate with support team members on the surface with Cave-Link, a device that enables text messaging through hundreds of metres of solid rock. Having done so, they deployed a radio-location “pinger” to pinpoint the exact spot on the hillside above Tipperary in the hope of finding a second entrance that would bypass sump 2.
The third objective was to set a new world record for remote dive distance in an underwater cave. Houben, the Dutchman, held it, having dived for 9,635m in Pozo Azul in 2017. Mallinson wanted to surpass 10km. He and Challen carried two rebreathers each as far as the end of sump 3: “If one malfunctioned in the big sumps, I didn’t want to find myself again in a situation where I didn’t know if I had enough gas,” Mallinson says. Having stopped for a night in Tipperary, they camped again at the start of Razor Passage. “It was really noisy. You’re close to a waterfall. And it’s chillier — there’s a strong draught, laden with moisture. It’s not so easy to sleep there until you get used it.”
From there, at the apex of their logistical pyramid, they planned to make three exploratory dives — by Mallinson first, followed by Challen, then Mallinson again.
The first dive went smoothly. But on the second day Challen made his way alone through Razor 2 and came near disaster. Beyond the canyon lies a series of pools and lakes. One of them, Challen says, “is too deep to stand up in. I was carrying a bag of lead [to reduce his buoyancy underwater] and a gas cylinder in a backpack. I realised I was too heavy, but I wasn’t smart enough to turn back. I got to a spot where there was just a sheer, smooth wall with no handholds, and that’s when I started going down, submerging myself like a rat. I was flailing about, struggling to keep my head up. I wouldn’t say I was down to my last breath when I finally found something to hang on to, but it was close. Thankfully there were more handholds after that. In the end it came out all right. But after all those dives, to die that way would have been embarrassing.”
Astonishingly Challen pushed on and extended the sump 6 line by about 140m. Building on Mallinson’s work the previous day, that took the underwater distance from the entrance close to 10km, making him the world record holder — but only for 24 hours, for Mallinson snatched the record back the next day, clocking 10,095m. There was no feeling of resentment on Challen’s part. “I just felt privileged to be there,” he says. By the time Mallinson finally turned around, the sump was heading upwards and he sensed he was close to its end. “I wanted to continue but I didn’t,” he says. He was totally dependent on one rebreather: this far in he didn’t have enough emergency gas to get out if it failed.
It’s possible, he says, that fatherhood was also making him more cautious. “I thought to myself, this is really remote and I really would like to get out of here alive. I still had to decompress to get out of sump 6, go through the passage that leads to sump 5 and then the Razor passages, which are quite brutal — and all of that carrying gear. It was going to be hard. But then, if it were easy, everyone would go there.”
Mallinson dreams of what is beyond sump 6, of “wandering for miles up an open river passage. If we could go a long way without diving, that would be really great.” The open sections in the cave so far have been spectacular, washed clean and airy. There is also pristine beauty: between sumps 4 and 5 lies a complex of dry passages with white crystal floors. “We could find almost anything,” Mallinson says. “And of course that’s the attraction.”
For both men the journey out was arduous. But after nights at Razor Camp and Tipperary, they emerged from sump 2 to find a welcoming committee. “All my mates were there, beaming, offering me hot soup,” Mallinson says, “and we knew we had our record. It was fantastic.”
They still had to get down La Burbuja and through sump 1: “That last little bit, I just wanted it to be over,” Challen says. But then came daylight and the balmy air of a September afternoon in northern Spain. “It was so bright! And then I was able to get into dry clothes and sit around and do f*** all for the rest of the day. It was wonderful.”
The team had rented a large house with a garden, and celebrated there with drinks and dinner followed by a trip to the Covanera bar, where they were joined by their local friends. Mallinson admits that he felt fatigued the next day: “A trip like that does take it out of you. But after 48 hours I went back into the cave as far as the start of sump 2 to help retrieve equipment. The only other effect was welcome — I’d lost some flesh from around my stomach.”
At first both men vowed this would be their last expedition to Pozo Azul. There was still no second entrance and, Mallinson says, “when I got home I was adamant I’d never go back unless we found one. Then again I always say I’m never going back, but after a month or so I think to myself, it wasn’t so bad, and I start making plans.”
Geologists believe that the stream in Pozo Azul may originate in hills as far as 30km away from the entrance — which means the known cave system may one day be much, much longer. “The water has to come from somewhere,” Challen says. “And there’s only one way to find out.”
Written by: David Rose
© The Times of London