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Pozo Azul Exploration 2019


Covanera, Burgos, Spain

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Simon Halliday & Emma Heron at the resurgence of Pozo Azul

The Team

Jason Mallinson, Simon Halliday, Emma Heron, Pedro González, David Perez, Kev Gannon & Alan Purcell

Not quite sure when the phone rang but sometime in July, Kev Gannon (CDG and Craven) rang with an invite to support Jason Mallinson on his Pozo trip 2019. Thought about this for a nano second before jumping at the opportunity. The fact that Mrs H had her 50th in the middle of the trip was only a minor hindrance. Preparation seemed to take an age but eventually I was as ready as I was going to be and the time for departure had arrived.

Feeling a lot like a schoolboy I waited for Alan Purcell (CDG and Bradford) to arrive. We duly loaded the van and set off for the tunnel. Late night and the very early hours showed Britain’s motorways off and we soon enough landed at the tunnel terminal.

Continental Motorways as always making ours look appalling, a relatively easy but long drive eventually saw the intrepid duo arrive in Covanera in one piece if a little tired.

Pitched the tent and out like a light, we woke the following morning and straight to it. Had a walk up to the resurgence with KG to help with kit and get a feel for the place. The cave is easiest reached by driving the short distance to the parking area and then it’s a 300m carry to pool. Made significantly easier by the use of Pallet trucks; luckily, I was pre warned on this one.

Day 1: 29th August

Back to the camp site and prep the gear for the first dive. Deciding to keep things simple I opt to dive the new chest mounted re-breather, RB(CM). Alan and I are soon ready and in blazing sun we kit up and set off into Sump 1. First time in this magnificent cave and first time on a scooter underground I take it nice and steady.

Sump 1 is 700m long followed by a 300m long deep water canal. For our first dive its all about familiarisation, and a steady dive through to the end of Sump 1 in about 25min. I dekit and have a brief look up to la burbuja, the bubble, back to the gear, rekit and it’s a swift fly back through to daylight.

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Pedro Gonzalez in la burbuja "The Bubble"

Day 2: 30th August

We’re setting up for the coming dives. The aim of the expedition is to radio locate Tipperary, the end of Sump 2, this requires a monster 5km+ dive and the prep for this is what we’re here to support. JM has asked us to tow a few bits through to the end of Sump 1, in preparation for his forthcoming dive. Jason plans to dive to 2km to stage some bailouts. There’s a small leak on the habitat and we are tasked with attempting to fix it. Alan and I drop into Sump 2 and with Alan cleaning the inside I spend a few minutes looking for the leak. The habitat is an upside down waste skip, approximately 1500 X 900 X 900mm and it's holding about a foot of air space in the top. By the time Alan has finished cleaning, his exhaust gas has almost filled the habitat making reaching the top difficult and we struggle to affix anything to stem the leak. It really is a micro leak so not great shakes. I can’t resist a quick look into the sump and briefly drop to about -30m, this is truly an awe inspiring sump. Return to Sump 1 and make our way out.

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Simon Halliday, Pegasus C.C.


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Kevin Gannon Craven P.C.


Pedro González


Alan Purcell, Bradford P.C.

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Jason Mallinson

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Emma Heron

Day 3: 31st August

Jason is to dive to 2km, Myself, Kev, Alan and Pedro (one of the Spanish divers) enter Sump 1. JM dives the big Zepp through and it’s our job to get the unit up the cascades and into Sump 2. JM explains that without this piece of kit the whole expedition is off, so care is required. Steady away and we soon enough have the scooter moved. JM kits up and sets off to 2km. He expects to return in approximately 80mins and it’s my job to dive support, on time we see JM’s lights and I dive to meet him and recover the scooter, I’ve already staged the habitat floor and a couple of cylinders at -7.5m.

As soon as I reach Jason, I know something is wrong, He’s a little deeper than expected and on open circuit. At this point I have no idea what the problem is. We communicate with slates and luckily, I have a cylinder of Nitrox with me. At this point JM is on his mix. I retrieve a bottle of 31% for him and he can start to accelerate the deco. JM is feeling the cold, so I return to the surface and Alan has the stove going. Also, again by luck Kev is using 34% as a bailout so Pedro returns to Sump 1 to fetch that.

I return to the water to assist JM to put the floor in the habitat. Once installed I return to the surface to get him some noodles. These I take back and JM can eat them in the habitat. I start to get an idea of how he must feel cos there’s blood in his phlegm, can’t be good. There’s little else I can do other than be there and support as best I can, but with Jason’s re-breather dead for the time being its going to be a long hang. We slowly get through it and JM can eventually return to surface. Struggling to speak he explains that his RB has flooded on the way back but still nearly 2km into the sump!!! I’ve done this myself; not a pleasant experience but to experience it that far into a penetration is testament to JM’s experience that he manages to sort it out.

JM strips and sorts the re-breather and we all dive out through Sump 1.

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Jason Mallinson setting off for the two kilometre dive into sump 2

Day 4: 1st September

After Yesterday’s drama’s JM’s throat is not good so the decision is taken to abandon any attempt at Tipperary. That leaves 2 20L cylinders at 2km which need retrieving and I volunteer for the dive. So today I want to test the scooter duration and do several runs through Sump 1 totaling 6km.

Day 5: 2nd September 

Its my turn for the support. Alan, Pedro and Emma Heron all come along and without any fuss we get my gear to Sump 2. Today I’m diving a duel RB set up, a pair of 300bar 7’s one with trimix and a further AL OC Bailout. There’s the 2 20’s to use if I need them but that's plenty of bailout; I set the gear up and a minor issue with a passing flowstop is an annoyance but no Biggy (This I later regret, don’t set off with a problem!!).

I set off on what turns out to be my longest ever dive. Using my silent sub scooter, I’m towing JM’s bailout and an additional bailout tank and can immediately feel the drag, this is my inexperience showing; I haven’t configured the setup very well and its slowing me down. JM’s backup scooter is slightly negative unlike mine which is the opposite and I’m not used to this; I find it an annoyance but not worth bothering about. Sump 2 is lined with a very thin, approximately 1mm line and I’m having to concentrate to keep the line. Even so I lose it a few times and it takes time to relocate. I know I’m traveling slowly but with little to tell me the distance I carry on. The dive itself is stunning. A huge and beautiful tunnel slowly descends until I’m at around -50m. I’m an hour into the dive and am expecting to be somewhere near the cylinders by now but know I’m not yet deep enough. There are no issues with any of the kit and I feel fine, so I set a limit of 90min and continue into the sump. Again, losing the line a couple of times the final one at 86min and I decide I’m far enough from home at -60m. I’m accumulating a lot of deco so turn the dive feeling somewhat disappointed I failed to get the cylinders. It’s a long way back but I recognise a couple of landmarks on the way heading home. Deco starts at -22m and I’ve not been there long when Alan descends to see where I’ve been. We communicate via slate and I let him know I’m OK. My O2 is running low so watching the levels I prepare my Chest mount for bailing into. This is when the issue with the flowstop causes a problem. On pressurising the CM (Chest Mounted Re-breather) I get a high pressure leak, not an easy fix underwater but the habitat is only a few minutes away so I bailout to Open circuit and finish the next couple of stops like this, Alan takes the CM and leaves in the habitat. Not long and I can get into the habitat and now on 34% nitrox I quickly resolve the CM issue and swap to O2. This will massively accelerate deco but after 3hrs at depth I’ve still nearly 2hrs total hang. Luckily the team look after me and a couple of soups and the odd swim round the habitat passes the time. Exiting the water after a total dive of 5:10.

Whilst I was diving the support team setup the Spanish radio Beacon, this unfortunately proved unsuccessful.

Out to the air bell and I reconfigure my gear and we all exit together into brilliant sunshine. 

I’m disappointed That I failed to get the cylinders and it now falls to JM to retrieve them. I volunteer to have another crack but can’t guarantee I’ll do any better.


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Simon Halliday setting off into Sump 2

Day 6: 3rd September

A rest day for me. I get up at the usual time and help Kev carry his gear to the pool but generally hang round the camp and fettle gear. Find time for a run for a couple of hours but a very pleasant day sorting kit. Kev Dives to the air bell and to up the British Radio Beacon. This the team manage to detect but not precisely. David has a long dive to test gear and retrieve the beacon. SH fussing about David almost sets off to look for him as he returns to camp all smiles. 

Day 7: 4th September

Quick dive to the habitat to tidy up. 

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Simon Halliday setting off in Dual Re-Breather setup

Day 8: 5th September

Jason is diving to 2km to get the 20’s. Easy dive through S1, almost taking for granted now, and great teamwork gets the big Zepp to S2. JM kits up and departs. I’m again diving support. Alan mans the stove and Pedro and David (Perez) are also assisting. Kev feeling a little under the weather joins us shortly after I’ve borrowed his scooter and Kev returns to camp for my spare. No issues this time and JM reappears on time (38mins to get to 2km, easy when you know how) and I descend to start bringing his gear up. Really couldn’t go smoother I bob up and down several times with kit and bring JM a hot drink and he disassembles the habitat. Deco soon burns off; Alan has already started his exit with some kit and I soon follow. As I reach the surface Emma is ready to leave and she enters the cave to bring the last of the gear out. Surface support is in abundance and all the kit is soon at the vans. 

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Emma Heron & Alan Purcell with the Spanish radio beacon in the bubble

We return to the camp site and start to sort the gear out. Alan and I have a natter about train times, and we make the decision to try and get an early train. It’s a mammoth drive back to the UK but tag teaming we make it home in about 24hrs, tired but very satisfied after a great trip.

Personally, a great success, some new kit configurations worked out as hoped. Came away with a boat load of enthusiasm and a lot to learn. Great days.

My thanks to Pedro for allowing me to use his photos and to whoever took the one of Jason, I hope they don't mind.

Simon Halliday   September 2019

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