Spanish Cave Diving


A team of British cave divers travelled to northern Spain to explore the unknown submerged tunnels of Pozo Azul in a perilous expedition that pushed the discipline to its very limits 

I am alone now and I’m heading out. My scooter is running well and I have plenty of gas. More than six hours ago, when I entered, there was good visibility and I could appreciate the magnificence of the tunnel. Now the water is murky, I’m tired, and I need to concentrate; there is simply no room for error at this level of diving. 

The line follows the roof and the floor lies 10–15m below. Ahead of me is a 700m stretch of tunnel that leads back to the sun-drenched entrance of this incredible cave. 

For hours, I have been holding the darkest thoughts that run through a diver’s head at bay, but now my colleagues are safe and everything is running to plan once more. The lead divers – John Volanthen and René Houben – are ensconced in their underwater habitats in Sump 2, and I have been relieved of my long vigil by a small team of Spanish divers. 

Few people have heard of Pozo Azul (pronounced ‘po-tho a-thool’), but for the past few summers, it has become the focus of attention of Europe’s foremost cave-diving explorers. Some 30 miles north of Burgos lies the small village of Covanera, high among the headwaters of the Ebro Valley in northern Spain. It’s a beautiful spot on the busy main road between Burgos and Santander, nestling beneath spectacularly sculpted cliffs at an altitude of about 700m. But unless you stop at the tiny Bar Muñecas – a staging post for explorers of Pozo Azul – beside the road, you’d never know that you were just a few hundred metres away from one of the longest cave dives in the world. 



Pozo Azul is the most audacious exploratory cave-diving project of recent times and pushes the absolute limits of what is possible: it’s serious stuff for all involved. I am on this trip as a support diver, lending what assistance I can to the guys doing the real business and playing a very small part in the ongoing exploration of this flooded cave. As this project’s ‘fly on the wall’, I am fortunate indeed. I can scarcely believe the immensity of what the lead divers are doing – it is far off the scale by normal diving standards. While I feel privileged to be here, I find myself constantly worrying about all the things that could go wrong. 

Cave explorations progress slowly, depending on the location, the conditions, and the equipment, time and money available. The Spanish pioneered this cave, passing the spectacular first sump in 1979 and establishing Pozo Azul as the longest cave dive in the country. In 1991, another progression, by Spain’s GE Gaia team, took the cave’s known length to a total of 1,780m. This comprised 700m of diving in Sump 1, a deep-water canal and awkward length of cave streamway totalling almost 300m, followed by Sump 2, which was pushed out to a termination at 780m. 

Then, in the summer of 2001, British cave diver Jason Mallinson made a visit to the area. He had come to Spain shortly after his epic dives with Rick Stanton at the Emergence du Ressel in Lot, southwest France. Here, they had taken open-circuit diving – indeed, underground exploratory techniques in general – to a whole new frontier. They used a ridiculous number of stage cylinders, camped beyond one of the longest sumps in the world, became proficient in the use of scooters – propulsion units that are heavier, sturdier and with far longer duration than regular sea scooters, which are like toys in comparison – and learned to cope with hideously long periods of decompression in cold water. 

Jason knew from the outset what was required to explore (or ‘push’) the cave further. Well used to working alone and a highly skilled rope-access technician, he installed wire hawsers along the streamway between sumps so that the heavy scooters could be transported to the front line with less risk of damage. Unlike the one-day operations that typified the majority of cave diving operations, this one employed tactics akin to a siege. An advance base was set beyond Sump 1, and in 2003, the first of several underwater decompression habitats (see Underwater habitats) was transported and installed a short distance into Sump 2. The villagers took Jason to heart, and as word spread, he gained the confidence and support of leading Spanish amateur divers, who have taken their holiday time to assist with the project. 

Jason had invested seven years to gain a point 3,530m in Sump 2 when, in May 2008, a rival team of divers from Germany recognised the potential and mounted their own push on the cave. While they quickly proved their calibre by progressing a further 490m, their incursion to an ongoing project flew in the face of accepted protocol and soured relations within the diving community.

Ethics are very difficult in a case such as this: there is no way that the British team could argue over a Spanish cave. But at the same time, it served to spur Jason into action. Adding further insult, the German team refused to supply details of the trend of the cave. Did it continue at depth or might the tunnel finally be surfacing? Such information is crucial in dive planning. 

Jason’s last dive, in August 2007, had run to ten hours – two getting in, two out, getting to the end and back, and six on decompression. He had pushed his Kiss rebreather well beyond its accepted duration and was approaching a similar position with his scooters. Given the distance and depth of the dive, every aspect of the operation was reappraised for this latest assault in July this year. Now he felt that it was time to draw on the full expertise of his peers. 

Jason, Rick and the aforementioned John Volanthen are the lead divers on this project (see The team, page 62). These guys are the best there is, and I count myself privileged to share such company. My fellow support divers are Brian ‘Scoff’ Scofield, chairman of the Cave Diving Group, and Rob Dalby – both highly respected and capable figures in UK circles. Our ‘sump donkey’ role is simple: we carry gear and assist in any way possible. 

Sharing our camp is erstwhile supporter René Houben, 36, from the Netherlands, a professional diver who, having arrived a week earlier than the main group, has done much of the setup work and has aspirations of joining the lead men. Alongside this motley crew are the Spanish divers, who are instrumental in some of the more difficult tasks and whose camaraderie and support is second to none. The team dynamics are spot on: there is one goal – to push out the line – and everyone works toward it. 


Back when I started cave diving 20 years ago, the orthodoxy was that you would need to set aside three or four times the duration of the dive for preparation of gear. Today, that figure is multiplied tenfold due to the complexities involved in developing and trialling the ever more sophisticated equipment. For example, a number of divers now use undersuit heating, and thus have unimaginably large and heavy battery packs that require long periods of charging and tinkering. 

One look at Jason’s rebreather setup reveals the huge investment in time and experimentation it takes to fine-tune such gear. It may appear to be a ramshackle, untidy assemblage, but every strap and cord plays an important part; it may be complex, but given the array of hardware that needs to be coupled and unclipped over the course of a dive, it is supremely practical. These men are skilled engineers – Jason has personally modified his rebreather in recent months to enhance its duration by 50 per cent. John’s Inspiration is substantially modified to the same end, and all three lead divers have at least one other custom-built rebreather ready to press into service at a moment’s notice. 

The level of preparation cannot be overstated. Even the smallest setback – a bump, a malfunction, a leak – will make the difference between success and failure, life and death. When we discuss the possible ramifications of a mistake or breakdown, time after time, John wryly retorts: ‘What can possibly go wrong?’ 

Attention to detail and maintaining focus is essential. In the moments before the dive, checklists are set aside and each diver begins his vital mental preparation. John may take ten or more minutes in solitude visualising the dive; none of these guys will be distracted at this stage. 

After six days of setup operations, a vast array of equipment lies assembled at the start of Sump 2 and the habitats bristle with the accoutrement hanging from their sides. Scooters and cylinders are staged along the route to the 2,000m mark. All equipment has been trialled, the habitats are filled with air… all systems are go. 

Two days later, a rolling series of assaults begins. Rick’s appearance at the site is delayed due to an equipment malfunction (his Land Rover broke down in Dover), so Rob accompanies lead divers Jason, John and René to the start of Sump 2. He alone will tend to the final preparations here while the rest of the manpower waits at the Covanera campsite to take their turns hours later. As Rob exits, we know the schedule we will work to: Jason, John and René will take about five hours scootering and laying new line in Sump 2, while the deco will probably run to seven hours or more. 

In 11°C water deep within the cave, everything simply must work to plan; the word ‘emergency’ does not figure at any point. The gear the divers carry provides for every eventuality, as long as they remain calm. It is taken as read that each diver is independent. Consequently, when Jason has a problem with his rebreather’s oxygen sensors about 1,000m into Sump 2, he aborts, leaving John and René to continue down the line. He’s markedly upset, but determined to have another shot later on. 

John and René reach the end of the German team’s line at 4,020m to find that the cave has shallowed significantly, from 70m to about 25m. The Germans had tied their line off in a dead end, and John quickly identifies the true continuation. Some 375m of new line is laid at similar depths, suggesting that the cave may well be rising. 

The reel is left at the limit of penetration ready for the next operation. ‘The moment you turn the dive, all you have to do is survive,’ John says. 

At a depth of 60m on the way out, his adage takes on new resonance, as René accidentally gets line wrapped around his scooter’s propeller – it’s a critical situation. It takes him ten minutes to rectify it; he is cold and greatly relieved when he finally reaches the safety of the habitats. 

By early afternoon, Scoff and I reach the Sump 2 base and confirm that John and René are well. With the deco schedule established, Scoff then departs to notify the remainder of the team on the surface. 

I feel strangely alone and vulnerable as I maintain the surface cover. I make half-hourly visits to the pair, transporting hot chocolate drinks to them and checking that they are okay, as well as shooting a couple of photos of ‘life’ in the cramped habitats. It is a real struggle just to insert my head into the structures, and at water level the CO2 inside them makes me pant dangerously. Yes, the lads can talk, eat, drink, take oxygen and shed all their cumbersome gear here, but it’s claustrophobic, dank and cold. Later, John and René complete their longest-ever dive – 15 hours – and emerge from the cave late at night to a blitz of strobes and a barrage of questions from the rest of the team. 

Three days later, Jason makes a solo penetration. With all his staging equipment untouched from his premature retirement, and fired up at the prospect of pushing the cave further after his earlier disappointment, he reaches 5,020m before running out of line. At a depth of just 6m, he has made 1,000m of progress over two push dives and only has 45 minutes of deco remaining on his computer. The trend is now absolutely clear: the tunnel is rising. Pleased with having laid an astonishing 625m of new line, Jason completes a smooth dive of 12 hours and 20 minutes, leaving the place wide open for a final assault by Rick, who, after his delayed arrival, is keen to make his mark. 

On his solo push, Rick surfaces to air just 140m beyond Jason’s limit. At 5,160m, there’s a 70m passage to the newly discovered Sump 3, which he dives for 160m. He ties off the line 6,020m from the cave entrance, establishing the site as the longest cave-diving penetration in Europe, before emerging at 3.30am after 19 hours underground. With the cave descending once more into a large ongoing tunnel, Sump 3 presents the ultimate challenge. Pozo Azul could well be the longest cave-diving penetration in the world. 

Pozo Azul has been an outstanding expedition, and the strategy of multiple rolling assaults has been wholly vindicated. Next time the team comes here – perhaps next summer – the approach will be similar, but the divers will camp beyond Sump 2. 

With training, experience and the right kit, anyone can follow a line, but laying one into unknown territory at depths in excess of 60m takes a steely nerve, and maintaining this composure over a protracted period is a rare attribute. In my opinion, these guys are simply the best. 

• The team wishes to thank Carlos and Tere Rodrigues of Bar Muñecas, as well as all the people of Covanera for their unwavering generosity and support. Thanks also to our Spanish diving friends, who, coordinated by Xesus Manteca, struggled under heavy loads, singing ‘It’s a long way to Tipperary’


the team

  • A Jasons suit heating optA cave diver since 1988, Jason, 41, has made several multi-day explorations in the deep cave systems of France, Mexico and northern Spain. He partnered Rick Stanton on the Emergence du Ressel explorations, extending the cave from 2km to 5km in overall length. At Cueva Cheve, Mexico, in 2003, with Stanton, he reached 1,484m.
  • Ric Stanton in gear optSince first becoming a cave diver in 1981, Rick, 48, has made many of the longest and deepest penetrations in European cave systems. Among his most impressive projects are the Emergence du Ressel between 1998 and 2001 (together with Jason Mallinson), the St George connection with the Gouffre de Padirac in 2003, and the 220m depth attained in the Goul de Tannerie, Ardèche, in 2008.
  • A modified rebreather optAn explorer of many technically demanding cave systems across Europe, John, 38, has also had notable British successes including partnering Rick Stanton at Wookey Hole in Somerset in 2004–05. In France, he made major headway at the Emergence du Bourne and at the Source de Marnarde. He began cave diving in 1998.




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