Cave
SUMP POTION #9
Located high in the Sierra Mazateca mountains in Oaxaca, Mexico, Sistema Huautla has captured the imagination of elite cave explorers for more than 50 years. Join photographer SJ Alice Bennett and cave/tech instructor Jon Kieren on Beyond The Sump’s recent March/April 2022 expedition to Sump 9.
Text by Jon Kieren. Images by SJ Alice Bennett.
🎶🎶 Pre-dive Clicklist: 붐바야 (BOOMBAYAH) by BLACKPINK curated by Steve Lambert
Sistema Huautla, in Oaxaca, Mexico, one of the most iconic and expansive cave systems in the world with over 30 entrances, more than 100.7 kilometers/62.5 miles of known passage, and reaching a depth of over 1500 meters/5000 feet, has been an obsession for cavers around the world for over 50 years. Every year, several groups such as Beyond the Sump (BtS) and Proyecto Espeleológico Sistema Huautla (PESH) mount expeditions to the region to explore. Surrounded by karst topography with several other gigantic systems, such as Chevé and Kijahe Xontjo are close by, there is surprisingly only one main exit point for the water flow (based on several dye trace studies), the Huautla Resurgence. Huautla is still being actively explored from the plateau to find the allusive connection with its resurgence. Terminating in a 9th sump at 81 m/264 ft depth, it is logistically extremely difficult to push the end of the line from there. This leaves exploration from the resurgence as the most likely tactic to make the connection.
Nestled deep in a canyon 1200 m/4000 feet below the sleepy little town of Santa Ana Cuauhtémoc in the Sierra Madre de Oaxaca mountains in Oaxaca, Mexico, is the Santo Domingo River. The Santo Domingo is fed by multiple water sources from various cave systems in the area including the Peña Colorada, Agua Frio Resurgence, HR Resurgence, and the Huautla Resurgence. The Huautla Resurgence was first explored in 1982, followed by expeditions in 1984 and 1995 led by Bill Stone. In 2001, Jason Mallinson and Rick Stanton pushed the cave to a maximum depth of 65m/215 ft and reached a sump pool where a dry cave passage heading off could be seen 10m/30 ft above, but with vertical muddy walls stopping the divers from being able to exit the water. Beyond the Sump, expeditions began exploring the resurgence in 2016 and 2017 where they found an exit from Sump 2 into a dry section, named “Passage of the Cheeky Monkey”, which was thoroughly explored and mapped, with several sumps found along the way. When time ran out for the 2017 expedition, several questions remained unanswered. Primarily, “where the hell does all the water come from?”, as the only source of water seemed to come from a small flowstone restriction affectionately named the “Squirty Hole”. A question that would need to wait five years to be answered.
In late March, 2022, Beyond the Sump set off on another expedition to Santa Ana to find the way on to “Sump 9”. The team consisted of Andreas Klocker (AUT/AUS), Zeb Lilly (USA), Steve Lambert (USA), SJ Alice Bennett (UK/GER), Ben Wright (UK), Rob Thomas (UK) and myself, Jon Kieren (USA), with logistical support happening remotely by Alejandra “Alex” Mendoza (MEX). Bios on the team can be found at: Beyond The Sump-Team. This is a log of our experiences and discoveries.
28 March, 2022
The entire group met for the first time in Tehuacán. Andreas, Zeb, and Steve had driven down from the US, while SJ and I had driven over from Tulum, and Ben and Rob had flown in from the UK. Everyone’s travel up to this point was relatively uneventful, except for SJ. She had managed to badly sprain her ankle the night before, leaving us questioning how the first couple of weeks of the expedition would pan out for her. Both trucks were packed tight, but room was made for the Brits and SJ’s swollen ankle for the remaining four-hour drive up through the Sierra Madre mountains to Santa Ana. The drive is spectacular, beginning on the north western side of the mountains where it is an arid desert filled with giant cactus and ending at an elevation of about 5200 ft in a lush green mountain forest.
After a quick stop for tacos and to grab a “few” bottles of mezcal, we arrived at our field house after dark. We quickly scrambled to unload the trucks into the concrete box we would call home for the next four weeks. We hastily set up our beds, and a bottle of whisky and mezcal made a few quick passes around the room to con- gratulate our arrival before lights out.
29 March 2022
Church bells rang at 5:30 am which woke both us and the surrounding livestock as the sun began to rise through the canyon below us, a truly remarkable sight that I highly doubted I would ever grow tired of. First order of business was to dig out the coffee pot and tea kettle. Once adequately caffeinated, we started organizing all of the equipment for base camp and diving. We set up a makeshift kitchen with two small camping stoves and a fold-out table. After a batch of scrambled eggs were devoured, everyone started tearing into the dive equipment and getting personal kit and team resources organized. We assembled a boosting station in the field house and set the compressor up outside. Regulators, cylinders, and rebreathers were scattered everywhere, and SJ was busy with camera equipment. Morale was high as everyone made predictions for what the cave was going to do.
Steve, Zeb, and Andreas were supposed to have a meeting with the town council to finalize permission to use the road leading down the canyon and set up operations in the cave. We had no doubts we would gain permission, but it was important to play the local politics and stay friendly with the community. The meeting didn’t happen, but we were assured “mañana” (which often means “later” as opposed to the direct translation of “tomorrow”). Instead of holding the meeting, Steve, Zeb, and Andreas were handed a bottle of moonshine made from sugar cane, called aguardiente. In an effort to be diplomatic, they graciously accepted a drink, and then another. Soon they were hooked into a few hours of hilarity trying to socialize in broken Spanish while the rest of us waited patiently for word on what our plan would be for the next day. We would need to wait until 5:30 am when the church bells rang to assess everyone’s energy levels and see what we thought about the “beg for forgiveness” tactic for finalizing permission before deciding to head down into the canyon or not.
30 March 2022
We decided to go for it and started to set up in the canyon. The 1219 m/4000 ft descent down to the canyon took about an hour by 4×4 truck and was absolutely breathtaking, second only to the hike to the resurgence. The hike was a fairly easy- going 1.2 miles, but took about 40 minutes each way with heavy loads and several river crossings. Luckily, we were able to keep most of the heavy kit in the cave for the majority of the expedition with only CCR bottles, the “cave cascade” (a few lightweight high pressure carbon cylinders we had set up in the cave to refill cylinders), and other little bits and bobs of personal kit needing to be transported in and out each day.
Andreas, Steve, and I did the first dive to reline and survey the first sump and rig the waterfall. Upon surfacing at the waterfall, a wave of “holy shit, this is remote” hit me quite hard, and the smile would not come off my face. While we dove, the rest of the group (minus poor gimpy SJ, who was stuck at the field house knotting line) did two more gear hauls from the truck. Everyone was pretty beat, but nothing a couple Victoria beers and a few liters of gatorade wouldn’t fix.
In the evening, we were able to meet with the local officials for formal permission to use the road and access the cave. We donated some pesos to fund their annual celebration of the anniversary of Emiliano Zapata, which we also had to promise to attend.
Despite Steve’s insistence on K-pop for our daily soundtrack, morale was high.
31 March 2022
Day 2 of diving was productive. Zeb, Rob, and Ben were able to set up the gear line for the far side of the waterfall to hang the deep bailouts, run line to 140 feet, and set the deep bailouts. Andreas, Steve, and I did a few gear hauls through the canyon. The next day, Steve and I planned to reline and survey the second sump out another 1200 feet or so at a max depth of about 215 ft. I was excited for the “real” diving to begin.
1 April 2022
Instead of the fiery red sunrise through the canyon, we were suddenly in the clouds and surrounded by cold mist, chugging coffee and tea but still struggling to wake up. The group appeared tired from the few days of intense hiking in the canyon, but moods lightened as the coffee hit, and we started to think about today’s dive. After today, we would likely begin pushing the leads left over from 2017 and searching for the way on to Sump 9. I was a bit apprehensive about making it over the waterfall with my Fathom CCR on, and felt a bit jealous of the side mount and chest mount units other team members were using. The waterfall was only about a meter high, but had high flow and razor sharp jagged rocks protecting it. I figured if it was a big hassle, I’d switch out my Flex2 side mount unit for future dives to make getting to sump 2 a bit easier.
On our drive down to the canyon, we were stopped by a group of enthusiastic locals. With big smiles on their faces, they insisted we get out of the truck and follow them up a small trail in the mountainside. As we followed, we could see smoke coming from a pit, and a strong scent of something sweet in the air. The group wanted to show us how they were processing sugar cane to produce piloncillo, an unrefined sugar commonly used in Mexican cooking. We were given a block of the piloncillo, which we later used to make syrup for pancakes and French toast when we started getting tired of scrambled eggs.
Steve and I had a great dive. We crossed the waterfall to sump 2. I made it over with my Fathom on, but it took a bit of effort. I was thinking that switching to the Flex for the next dive would make life easier, especially if we would be hauling more cylinders and scooters over the waterfall. Sump 2 was just a truly stunning, big passage with rolling hills all covered in silt. Our max depth was 56 m/183 ft on this dive, with about an hour of deco to do upstream of the waterfall. We laid another 365 m/1200 ft of line while swimming, setting up the next team to re-line all the way to camp 1 in the Passage of the Cheeky Monkey, and check what was thought to be the most promising lead discovered in 2017, referred to as the “11 meter lead”.
2 April 2022
SJ came down into the canyon for the first time today. Her ankle was still in pretty rough shape, but life in the box on the mountainside had become dull. She had been as productive as she could be by knotting line and photographing the town. She also managed to make no less than four new boyfriends, led by a 6-year-old who kept bringing his siblings and friends into the field house and proudly exclaiming “gringa!” while pointing at SJ. He then would lead them around the field house showing off all of the strange equipment we had scattered about.
On our way into the canyon, we were hailed by another group of farmers just a little down the road from the piloncillo farm. As they enthusiastically led us to their farm, we could smell the pungent aroma of fermenting sugarcane before we could see the still. They first showed us how they crushed the sugarcane plants to extract the juice, which we sampled. Rich, sweet, and syrupy, it was hard to get down with the thought of the hard hike through the canyon ahead. Next, they showed us where the fermentation was taking place in large tubs next to the still. We were offered a sample straight from the still, which we had to decline, as there was much work and diving to be done yet. So we promised to stop back at the end of the day to have a drink.
The diving for the day proved to be less productive. SJ was able to take some photos of the canyon and divers prepping to enter the cave, but the dive was called early due to a rebreather failure. The line was still extended a few hundred feet, so all was not lost. But the line still did not reach the Passage of the Cheeky Monkey nor had any leads been investigated. Morale was a bit low.
At the end of the day, we stopped back at the aguardiente distillery and were poured a fresh bottle to be passed around. Before taking a drink, Steve asked how much alcohol was in it. The man proudly proclaimed “22 grado,” which Steve interpreted as 22% and took a chug. His eyes went big, he handed it to me, and I took a big swig for myself and quickly realized that “22 grado” does NOT equal 22% as I handed the bottle on to the next person. Realizing we needed to leave ASAP or it would be unlikely any of us could drive the truck home, Rob (who seemed quite pleased with the aguardiente) offered to buy the bottle to take home with us. With the transaction complete, we headed back up the mountain to get to the bottom of this “22 grado” business.
3 April 2022
Another cold and cloudy day. I was tired, and my back felt broken when heading down the mountain. I needed a day of rest but knew we needed to push on. I switched to the Flex and headed in with Steve on DPVs to line the cave to camp 1 and check the 11 meter lead. I immediately realized I was overweighted with the Flex, steel side mounted bailout cylinders, and extra safeties and deco gas that were to be installed in sump 2.
Crossing the waterfall, I tore the right ankle of my drysuit, which I noticed as soon as I got back in the water on the other side. Knowing I had heated undergarments on and plenty of battery power for the couple hours of deco we might end up with, I decided I would be fine to continue the dive.
With each stage drop, I hoped my stability would improve, but it didn’t. I struggled on, Steve and I making it to the far side of sump 2 to search for the way on to Cheeky Monkey. We made our way up what we believed to be the correct path, doing our deco as we circled up towards an air bell. We did not find the 11 meter lead where we thought it would be, and realized we were in an area known as “Jason’s Eyes,” a dry section first discovered in 2001 by Jason Mallinson which had no way on. Steve asked if I wanted to surface to look around and chat about where to look next, and I reluctantly raised my thumb and pointed back toward the exit. I was super uncomfortable being overweighted as well as needing to dive back to 65 m/215 ft and have an hour or so of deco before the waterfall with a flooded drysuit. Plus, I knew that if we dragged this dive on much longer, I was going to start making mistakes. So we re-descended from our 3 m/10 ft stop and headed back toward Sump 1, when I was abruptly stopped at 9 m/30 ft as I could no longer inflate my wing or drysuit.
Grabbing the cave wall, I realized that the two liter cylinder I had dedicated for wing and suit inflation was dead, clearly a result of struggling with being overweighted and unstable. I got Steve’s attention and communicated the problem, and we started to inventory resources with an LPI connection. We had an O2 bottle, which would not be great for suit inflation considering I was already shivering in the 18º C/65º F water and would desperately need to use my heat during deco. The 50% bottle we were to drop at the deco station heading to camp 1 only had a QC6 connection, which would be no help to me. And that left only my side mounted bailout, which was 15/55 trimix. Certainly not ideal for suit inflation, but better than starting myself on fire. I plugged in and filled my suit with the icy trimix as we started to exit. I had to constantly switch the hose from my suit to wing as we scootered out but managed to make it back to the waterfall with only an hour of deco, which was manageable with my heated vest on full blast.
We were unsuccessful in completing our tasks for the day, and I was in a world of self-pity from my poor decision to change configurations without a shakedown dive. We went back to the field house to conduct some experiments regarding the actual alcohol content of the Aguar. Tomorrow we would rest and re-group. Morale was low.
8 April 2022
The past few days had been challenging. Several attempts at exploration in Sump 2 had proven unsuccessful. We had scoured the deep section, and the fabled 11 meter lead, and others like it, which all pinched off quickly. While there was significant flow coming out of these tight passages, they were simply Swiss cheese that was not passible by humans. Maybe after a few hundred thousand years or so, they would be big enough so we could jam Steve in there to take a look, but for now, we were going to have to focus our search in the Passage of the Cheeky Monkey and the sumps within it to find the way on.
Logistically, this would mean exploring from camp 1 to avoid having to pass a waterfall and do a 65 m/215 ft dive prior to surfacing and hiking gear a couple thousand feet through dry cave to the Sump each day. We would be using the next day as an opportunity to rest and get the first camp team, Rob and Andreas, ready to set off for a couple of days in the Cheeky Monkey.
SJ’s ankle was feeling well enough for her to dive, so we’d done a couple of shakedown dives to test the ankle and get a feel for the cave before starting to shoot the next day.
9 April 2022
SJ and I entered the water for a photo dive shortly after Andreas and Rob pushed off for camp 1. About 30 minutes into shooting, we noticed lights and the sound of scooters buzzing toward us. It was Andreas and Rob, obviously having had some sort of problem and aborting early. We decided to exit with them to see if we could assist somehow. Turned out they had a dry tube failure when they made it to the end of Sump 1, drowning most of the camping equipment.
With only 9 days of diving left, and time starting to run out, we couldn’t afford any more mishaps if we were going to figure this cave out. A serious team discussion was had to decide on the schedule for the next few days to prioritize exploration, as well as to ensure that we would have opportunities for documentation. We planned to prep and re-group again the next day, then Steve, Zeb, and I would head into camp 1 for a very long day of poking around in the Cheeky Monkey to determine what the objectives should be for the first camping team.
In the evening, we had a chance to meet up with Bill Stone and his team who were exploring a nearby dry cave. It was pretty surreal to be in Oaxaca with Bill, hearing him tell stories of exploration in the area, as well as to discuss what we had found and what we thought the cave might do. Bill was convinced the Swiss cheese we had found could not be the only water source, as it was rumored that during the rainy season the resurgence produced a geyser several meters tall. We discussed what our plans were moving forward, and Bill seemed to agree that the sumps in the Cheeky Monkey must be hiding something.
10 April 2022
A day of rest and prep for a long day tomorrow. There was a celebration in town for Emiliano Zapata with parades, fireworks, and lots of mescal and aguardiente. It began last night and never really ended. We were supposed to attend the festivities that evening, but hopefully only for a short while as we were planning to leave the field house at daybreak to be in the water early morning.
The music and festivities in town added a joyful feel to the somewhat mixed emotions in the field house. Excitement, stress, and anxiety. Morale was pretty high considering the pressure we were under.
11 April 2022
A long but successful day. Steve, Zeb, and I pushed off early in the morning and spent the majority of the day in Cheeky Monkey. From the beach where we surfaced, it was about a 30-minute hike through fairly rough terrain, but no serious climbing required. Hauling dive gear did create some challenges, though. We checked Surprise Sump first, which had not been dived before, and it turned out to be the biggest discovery we’d had the whole month. Immediately upon descending, Steve noticed darkness beyond the duck under in front of him. As he shouted for joy through his loop and descended with a line peeling off the reel, hearts started pounding as we realized what might have been right under the team’s noses during the 2017 expedition.
After a hundred feet or so, it surfaced, followed by a short hike and another sump which had an upstream and a downstream, and then another waterfall on the upstream side. Not the borehole we were hoping for, but there was more cave here than we knew about the day before, so that was a huge plus, and it seemed to be heading in the right direction–toward Sump 9. Logistics would definitely get more interesting, but we had a good idea of what resources would be needed for the first camping trip. We exited the water a little after 6 pm with rejuvenated spirits and confidence that we were on the brink of breaking this thing open.
13 April 2022
SJ, Andreas, and I were supposed to do a photo dive today. On our way down the mountain, Zeb’s truck’s suspension started making some terrible noises. When we inspected it, we noticed the leaf spring hanger bracket had torn in half, leaving the leaf spring pressing up into the bed. With no option, we slowly drove the truck back up to the field house to start the process of finding parts and tools. After a quick team meeting, we made new plans based on best and worst case scenarios. Best case would be that the truck was fixed today or early tomorrow morning, and we could get a camping team in to push from Surprise Sump for a few days while SJ and I got as many photos as possible. Worst case, we wouldn’t have time left for camping and would have to do the best we could with a couple of day trips.
SJ and I drove down to Tehuacan to pick up a new bracket while the team tried to get the old one off. At the suspension shop, I was struggling to communicate with the woman at the parts counter. She seemed to know what we needed, I was just trying to verify the part number to be sure we weren’t about to make a 7-hour round trip and return with the wrong part. A kind man waiting in line asked us in decent English what we needed, and I explained. He said, with a sly grin and a wink pointing at the woman behind the counter “she knows”. The woman looked at me and smiled. I shrugged and nodded as she grabbed the bracket and darted off while saying something to our new friend. He told us she took it in back so the shop could press the bushing into the bracket for us. While we waited, we chatted with the man about what we were doing there. He seemed intrigued, was enjoying the stories of our adventure, and I was showing him some photos of caves in Tulum on my phone, when the woman returned with the bracket. As I was paying her, two young men were trying to give SJ a couple sandwiches and pepsis. When she tried to refuse, the woman behind the counter got very excited, gesturing for us to take them. Apparently, when we said we had come 3.5 hours down the mountain to get the part, they were empathetic to our situation. And based on my ragged clothes, matted hair, tired face, and sand-fly covered body (SJ looked great as always), they must have assumed it was quite the journey and refused to let us go away hungry and thirsty.
When we got back to Santa Ana, the team let us know they were unable to pull the old bracket, and that we’d have to take the truck to the nearest town with a mechanic first thing in the morning to try to repair it.
14 April 2022
It took until about 2 pm to get the truck fixed, but determined to get some work done, Steve, Zeb, and Andreas decided to push off for camp 1. They were in the water by 6pm, planning to reemerge on the 18th at 4pm.
While driving the truck back up the mountain, I noticed the brakes seemed a bit soft and the steering a bit stiff. However, this was my first time driving Zeb’s truck, and without much other choice, I kept making our way back up to the field house. When we arrived at the house, it was noticed that power steering fluid was leaking below the truck. By then it was after 8 pm, and there really wasn’t much we could do about it at the moment anyway, so we all promptly crashed out so we could get up early and try to sort out the problem in time for SJ and I to finally get in a proper photo dive.
15 April 2022
We topped off the hydraulic fluid but were unable to determine the source of the leak. Ben and I drove the truck around on the more benign roads at the top of the mountain with no noticeable leaks or ill effects on the steering or brakes. So we made the decision to head down the canyon and take some pictures. SJ on the camera, me on lights, and Ben as a model. All went off without a hitch, and the truck made it back up the mountain with still no signs of a leak. I was happy about that, but quite wary. As my dad says, “Problems don’t usually just fix themselves…”
16 April 2022
A day for surface photos. SJ had plans to photograph the canyon as well as take some simple shots in the cave entrance. It was a light and easy day that should have wrapped up quite early. However, as we started to pack up and leave the cave for the day, two by two, our entire host family, all 13 of them, started coming around the corner walking toward the cave. It was surreal, we hadn’t seen a single other human in the canyon for weeks, and there out of the blue, was the whole family. Dragging half sleeping children, the happy and excited adults hastily climbed the rocks up to the cave entrance. They were amused to hear that our friends were several kilometers underground and wouldn’t return for a few days yet. After a bit of climbing around, we all started to make our way back down the canyon toward the truck. After the first river crossing, SJ noticed one of the young mothers struggling to carry Liam, the two-year-old. She gave me a nudge, and I turned and offered to carry the little guy. At the next river crossing, we noticed they had a whole camp set up at the edge of the river. As we approached, the young mother offered us a drink, took Liam back from me, and before we knew what was happening, they had reignited the campfire stove and were preparing a late lunch for us. We ate some of the most amazing refried beans on the planet while the kids played in the river until the abuela (grandmother) started packing up a few things. I looked at her and asked “vamos?” (We go?), to which she loudly exclaimed “VAMANOS!” (Let’s go!) With a smile on her face, as everyone scrambled and had camp packed up and were hiking again within moments.
After encountering the family, our day suddenly became much longer than we had anticipated. We got home after dark, exhausted from another hot day hiking in the canyon, yet rejuvenated from the experience we had just had. It had been hard to keep morale up with the never ending issues we encountered, as well as less than stellar productivity, but to be able to share a bit of what we were doing there with our caring and supportive host family was truly an experience. They thought what we were doing was truly remarkable, which it really was; it was just hard to remember that when facing failures and adversity. So, a little reminder by way of the smiles on the faces of our new friends gave us quite a boost. We ate dinner quickly and settled in as early as we could. One more shot at cave photos the next day. Before Steve, Zeb and Andreas come out and mess up the vis hauling all of their camping gear out.
17 April 2022
SJ and I were able to get in a nice long photo dive. As we were packing up to head out, we saw lights flicker below the surface. Steve, Zeb and Andreas were back a day early, not necessarily a good thing…
As they emerged, one by one, there were no high fives or cheers of joy. Just a content look on Zeb’s face as he calmly stated in his mild southern drawl, “she doesn’t go”.
Arriving at camp 1 after 8 pm on the 14th, they had set up camp and prepared for the following day’s explorations. Over the next two days, they scoured the Passage of the Cheeky Monkey and the sumps within.
They dived Surprise Sump, the newly discovered Gold Star Sump, as well as checked the stream way beyond the new waterfall, and searched every corner of the dry cave. The downstream section of Gold Star Sump pinched off into swiss cheese where there was a significant amount of flow. The stream way beyond the waterfall also pinched off into another flowstone restriction, similar to the Squirty Hole. No new sections of dry cave were discovered. Based on observation of the amount and direction of flow exiting downstream Gold Star Sump and the small restrictions in Sump 2, the team estimated it is approximately equal to the flow coming over the waterfall in Sump 1 as well as exiting the resurgence. Concluding that all water sources have been discovered, none of which will allow a human to pass, and no passable dry cave is accessible.
Disappointed, but content that every corner of the Huautla Resurgence had been checked, they decided to close the book on the project and head out a day early.
The next few days were dedicated to more photos and cleanup. With 12 safety and deep bailout cylinders remaining in Sump 2, scooters staged at the waterfall, several safeties in Sump 1, six shallow bailout cylinders, rebreathers, and personal gear for seven divers left in the cave entrance, there was a lot of work to do. However, with teamwork, we managed to get everything out of the canyon in just three days. Our backs a bit sore, and our dreams of big going borehole passage beyond Sump 2 unrealized, moods were a mix of relief to be finished and a reluctance to leave, knowing we would likely never have a reason to return to this truly remarkable site.
Completing a project is a bittersweet feeling, of course. While sad there’s no more cave, there’s also a feeling of content completion. We did everything possible to find the way to connect the resurgence to Sump 9 of Sistema Huautla, and we are probably the last team to ever see the inside of the resurgence for the foreseeable future (or ever), which is pretty damn cool. We also had the opportunity to spend time with new friends in a truly remarkable place with extraordinarily gracious hosts. So, in all, I would certainly call this year’s Beyond The Sump expedition a success.
Dive Deeper
Wikipedia: Sistema Huautla
Explorers Club: Sistema Huautla, Mexico – the 50-year original exploration and study of the deepest cave in the world
NatGeo: One of the Deepest Caves in the World is Even Bigger Than We Thought
Exploration groups involved with Sistema Huautla:
| Beyond The Sump | www.facebook.com/CaveDive |
| Proyecto Espeleológico Sistema Huautla (PESH) |
| United States Deep Caving Team |
SJ Alice Bennett has been photographically documenting the world around her since she was a kid. After completing a diploma in Graphic & Communication and a B.A. in Visual & Motion Design and moving to Quintana Roo, Mexico in 2017 she’s turned her focus on the underground rivers of the area. Her documentary style of shooting is well known for capturing the emotions of the moment and creating a sense of being there with her. She has a passion for documenting exploration and has worked as a freelance photographer and graphic designer around the globe and just joined the InDepth team. Watch this space.
Jon Kieren is a cave, technical, and CCR instructor/instructor trainer who has dedicated his career over the past 13 years to improving dive training. As an active TDI/IANTD/NSS-CDS and GUE Instructor, and former training director and training advisory panel member for TDI, he has vast experience working with divers and instructors at all levels, but his main professional focus resides in the caves. In his own personal diving, Jon’s true passions are deep extended range cave dives (the more deco the better), as well as working with photographers to bring back images of his favourite places to share with the world.
Cave
N=1: The Inside Story of the First-Ever Hydrogen CCR dive
This Valentine’s Day, Dr. Richard Harris, aka ‘Dr. Harry,’ and the Wetmules made the first reported hydrogen (H2) rebreather dive to a depth of 230m/751 ft, in The Pearse Resurgence, New Zealand. The 13 hour dive, which was nearly two years in planning, was a field test to determine the efficacy of using hydrogen to improve safety and performance on über-deep tech dives. Harris’s dive was the deepest “bounce” dive in approximately 54 experimental H2 dives—the majority SAT dives—that have been conducted over the last 80 years by military, commercial and, yes, a group of technical divers. Now in this first published account, InDEPTH editor Ashley Stewart details the inside story behind the dive, a dive that will arguably be remembered 100 years from now!
By Ashley Stewart. Images courtesy of Simon Mitchell unless noted.
On March 11, a little more than three weeks after completing what is believed to be the first-ever rebreather dive with hydrogen as a diluent gas, Dr. Richard “Harry” Harris convened the group of scientists and researchers who had spent years helping to plan the attempt.
He started with an apology. “All of you had the sense that you were party to this crime, either knowingly or suspecting that you were complicit in this criminal activity,” Harris, an Australian anesthesiologist and diver known for his role in the Tham Luang Cave rescue, told the group.
The apology came because the dive was dangerous—not just to Harris who was risking his life, but for the people who supported him were risking a hit to their reputations and worried their friend may not return home. Harris and his team put it all on the line to develop a new technology to enable exploration at greater depths.
A significant challenge to deep diving is an increased work of breathing and CO2 buildup as breathing gas becomes more dense at greater depths. This can not only culminate in fatal respiratory failure but also increases the risk of practically everything else divers want to avoid, like inert gas narcosis and oxygen toxicity. For this reason, helium is favored by divers for its low density and non-narcotic effect. However, at such great depths, helium increases the risk of tremors and seizures from High Pressure Nervous Syndrome (HPNS). This can be ameliorated by keeping a small amount of narcotic nitrogen in the mix. The problem is that even small amounts of nitrogen makes the mix too dense past 250 meters.
Harris’s experiment would determine if divers can turn to an even lighter gas: Hydrogen, the lightest in the universe. Hydrogen is about half the density of helium. It’s also slightly narcotic and hence thought to ameliorate HPNS, thus allowing elimination of nitrogen from the mix.
The addition of hydrogen into a breathing gas, however, comes with one small technical uncertainty—the extremely explosive nature of hydrogen. History confirmed this reality with the 1937 Hindenburg disaster in which the hydrogen-filled dirigible airship burst into flames. As Harris tells it, he set out to dive hydrogen in his diluent gas while avoiding the nickname “Hindenburg Harry.”
Hydrogen in the Mix
Why would anyone attempt to breathe hydrogen? Harris and his colleagues have spent more than a decade and a half exploring the Pearse Resurgence cave system in New Zealand. This extremely challenging, cold water cave system (water temperature is 6ºC/43ºF) has been explored by Harris and his team, who call themselves the Wetmules, to a maximum depth of 245 meters/803 feet in 2020. Their gas density at depth was 7.2 g/l, significantly above the recommended hard ceiling of less than 6.2 g/l.
Diving past this point introduces increased risks, not only of CO2 buildup, but narcosis, decompression sickness, HPNS, cold breathing gas, having adequate gas supply or bailout, and isobaric counter diffusion (ICD) in which different gasses diffuse into and out of tissues after a gas switch causing bubble formation and related symptoms, cold breathing gas, and having adequate gas supply or bailout.
Divers have been examining hydrogen as a breathing gas for decades. The Swedish Navy was the first to experiment with hydrogen as a possible deep diving gas during World War II. The U.S. Navy in a 1965 paper proposed replacing helium with hydrogen due to projected helium scarcity. Later, beginning in 1991, researchers at the Naval Medical Research Institute (NMRI) in Bethesda, Maryland spent a decade studying hydrogen’s potential physiological impacts and biochemical decompression. French commercial diving contractor Comex (Compagnie maritime d’expertises) launched its hydrogen program in 1982, and the Undersea Hyperbaric Medical Society (UHMS) held a workshop “Hydrogen as a Diving Gas,” in 1987.
Even technical divers considered hydrogen. Legendary cave explorer Sheck Exley considered hydrogen in the early 1990s to mitigate HPNS symptoms, which are ultimately believed to have contributed to Exley’s death at Zacatón in 1994. Nearly all of the experimental hydrogen work up until this point used surface-supplied systems and saturation diving versus self-contained diving, and none of it, as far as we know, has been done with a rebreather.
The primary objective of Harris’ hydrogen experiment was to address the issue of increased work of breathing. Harris’s team had previously encountered CO2 incidents at the Pearse Resurgence. In one incident, while at 194 meters/636 feet, explorer Craig Challen—Harris’s primary dive buddy since 2006—lost buoyancy but was unable to find his buoyancy compensating button quickly. He kicked up a couple of times to stop his descent and immediately got a CO2 hit. Challen was able to grab the wall, calm down, slow his breathing, and survive. Based on such incidents, it’s clear to the team that they have reached the limits of the gas. “I feel we are on the knife edge all the time,” Harris said, in terms of physiology and equipment.
While hydrogen in the diluent breathing mix was expected to address increased work of breathing, the rest of the issues associated with deep diving were “major unknowns,” and some (such as respiratory heat loss) were potentially even made worse by hydrogen.
“At what depth do the risks of introducing this new technology outweigh the risks of carrying on with trimix?” Harris said. “That’s a very difficult question to answer. At some point we are going to have to consider different technologies and, at this point, hydrogen is perhaps the only one available to us.”
H2 Working Group
In 2021, the year after Harris completed his deepest dive at the Pearse Resurgence, InDepth editor-in-chief Michael Menduno was taking a technical diving class and reading about the government looking at hydrogen as a diving gas again. “Technical divers should be at the table,” Menduno said he thought to himself at the time, “our divers are as good as anybody’s.” He called John Clarke, who had spent 27 years as scientific director of the U.S. Navy Experimental Diving Unit (NEDU), and discussed setting up a working group. Menduno’s next call was to Harris, who had shared his troubles with gas density at the Pearse Resurgence. Harris had also, separately, been thinking about hydrogen.
The so-called H2 working group met for the first time in May 2021 and included many of the top minds in diving medicine and research, including Clarke, NEDU’s David Doolette and Greg Murphy, research physiologist Susan Kayar who headed up the US Navy’s hydrogen research at the Naval Medical Research Institute (NAMRI), along with her former graduate student Andreas Fahlman. There was diving engineer Åke Larsson who had hydrogen diving experience, deep-diving legend Nuno Gomes, decompression engineer JP Imbert who had been involved in COMEX’s Hydrogen diving program, and anesthesiologist and diving physician Simon Mitchell. The group was later joined by Vince Ferris, a diving hardware specialist from the U.S. Navy, and explorer and engineer Dr. Bill Stone, founder of Stone Aerospace.
The working group met regularly with the goal of figuring out how one might possibly operationalize hydrogen for a deep technical dive using the Resurgence as an example. During one of their meetings, Clark used a breathing system simulator built for the Navy to predict how hydrogen would affect gas density in a closed circuit rebreather at depths to 300 meters/984 feet.
To Doolette, who has known Harris for decades and supervised his Diploma of Diving Medicine project in 2001, it was immediately clear this was not a hypothetical discussion. “Unlike some of the scientists, I was under no illusion that the question before the working group was fiction, I knew that Harry was likely to try a H2 technical dive in the Pearse Resurgence,” said Doolette, a cave explorer in his own right, who has laid line in the Resurgence.
By fall of 2022, it was clear to many in the group that Harris was going to attempt the dive. The group had mixed feelings ranging from cautious optimism to comments like, “My friend is going to die.”
Doolette was concerned Harris and Challen would not survive the dive due to either ignition of hydrogen—in the worst case, inside the rebreather at depth—or a serious adverse response to respiratory heat loss (the latter was especially if Harris attempted diving beyond 245 meters/803 feet as he had originally planned) he said. “I have known Harry for longer than most in the group. I encouraged him to take up cave diving, so I felt a personal responsibility toward him,” Doolette said. “I have a lot of experience in operationalizing new diving technology. My goal was, if unable to discourage him, to force him to focus on the important issues.”
Leading up to the dive, Menduno scheduled Harris to give the banquet talk about the expedition at the Rebreather Forum 4 industry meeting in April. The outcome of the dive, of course, was uncertain, and the two had to make an alternate plan in the event that Harris did not return. “We had to say we were going to talk about your dive one way or another,” Menduno said. “If you don’t make it back, Simon Mitchell is going to have to give a presentation about what went wrong. Harry made some typical Harry joke like, ‘Well, as long as you don’t stop talking about me.’” Harris’s lighthearted tone betrays how seriously he took the dive and its preparation, people close to him said.
While no one involved was taking as big a risk as Harris and Challen, they were risking a hit to their professional reputations by being associated with a controversial dive, especially in the event of a tragic outcome.
“At heart, I’m an explorer, and that was pure exploration,” Mitchell, who was the diving supervisor on Harry’s dive, said when asked why he would take such a risk. “Exploration in the sense that we were pioneering a technique that hadn’t been used for quite some time and never in technical diving, not deep technical diving.” He also emphatically added, “I was more worried about my mate dying than about my professional reputation.”
Later, in planning Harris’s trip to the RF4 event, Menduno had occasion to speak to Harris’s wife, Fiona who brought up the dive.
“She said to me ‘I hope Harry is going to be OK’,” Menduno said. “I had no idea how much Harry told her, what she knew and didn’t know. All I could say was he’s got the best people in the world on his team, and if anybody can do it, he can.”
“We all held our breath and waited,” Menduno said.
‘Hydrogen Trials’ at Harry’s House
Ahead of the dive, Harris was preparing at home. The first thing Harris said he had to get his head around was—no surprise—the risk of explosion, and how to manage the gas to mitigate that risk. The potential source of explosion that Harry was most concerned with was static ignition within the CCR itself, plus other potential ignition sources like electronics, the solenoid, and adiabatic heating. Industrial literature—or “sober reading” as Harris calls it—suggested that the tiny amount of static necessary to initiate a spark to ignite hydrogen is .017 mJ, 400 times less than the smallest static spark you can feel with your fingertips and several hundred times less than required to ignite gasoline. “It ain’t much, in other words,” Harris said, noting that counterlung fabric rubbing against itself could generate just such a spark.
Ultimately, Harris came across research that suggested that static decreases with humidity. “I started to feel like there was no source of ignition inside a rebreather, but then again I said to myself, ‘Harry you only need to be wrong once’.”
The other concern was whether he could actually fill hydrogen safely while decanting, or filling one tank from another at the same pressure, and boosting the gas to reach higher pressures.
“I decided there is only one way to actually resolve this and that is to retire to the shed, order a sneaky bottle of hydrogen, and without telling my wife what was going on down the back of the house, start to actually have a bit of a play with this,” Harris said.
First Harris had to make his own DIN fitting (though not out of the ordinary for the anesthesiologist who built and tested his own rebreather before buying a commercial one in 2002) to decant the gas. Next he took his dual Megalodon rebreather with 100% hydrogen in one diluent cylinder and 100% oxygen in the other to the “test bed” in his backyard—his pool—and started to introduce hydrogen into his rebreather.
“Putting an explosive device into water was perhaps not the most logical approach because it becomes more like a depth charge than a bomb, but I thought, ‘Well, at least it might contain the blast somehow into the pool.’ I knew if I broke the back windows in the house or worse, my life wouldn’t be at risk just from the hydrogen. There would be bigger trouble afoot,” Harris said. “I left the lid of the rebreather unclipped in the vain hope it would spare me and the pool and the dog, who was helping with this experiment.”
He pressed the button of the Automatic Diluent Valve (ADV) on his rebreather, introducing hydrogen to the loop, and finally activated the solenoid before he started breathing from it. The first breaths were pleasant, he said. “It did feel very light and very slippery, and the hydrogen voice is even sillier than the helium voice, as you would expect,” he said. “I don’t want people to rush away thinking this is a safe and sensible thing to do. I’m under no illusions I’ve produced any evidence for you to see, but this is an honest account of the hydrogen trials at my house.”
The unit had not exploded with a fill of oxygen from zero to 70%, and very low humidity. “Harry, dog, and CCR survive,” as Harry wrote in his report of the trials. “Nothing bad had happened, so it was reasonable to move to the next step,” he said.
The Expedition
Harris, Challen, and other members of the Wetmules, arrived at the site of the Pearse Resurgence on New Zealand’s south island in February 2023. The cave system is so remote they needed around 10 helicopter trips to transport the team and all of its equipment. Mitchell, the diving physician, ran surface operations with “mixed feelings,” as Harris put it.
The group stayed for two weeks at a campsite, complete with a gas-mixing station, an electronics shelter for charging gear, and a “big green army tent where we meet and drink a lot of coffee and try and put off going back into the water each day,” Harris said.
The expedition was plagued with an unheard of number of problems, Harris said, “Every time we got in the water, something popped or blew up or failed.” The campsite is where Harris boosted hydrogen for the first time, from 100 to 150 bar. He flushed the booster and all the whips with hydrogen prior to boosting to make sure no oxygen was left in the system, but it was an anxious moment.
On dive day, Harris and Challen set out on what would be a 13 hour dive to 230 meters/754 feet—a “comfortable depth,” as Harris put it. Due to some problems during the expedition, it was decided that Harry would dive hydrogen, while Craig would dive trimix. At 200 meters/656 feet depth, Harris pivoted the switch block to introduce hydrogen into the loop. “The first cautious sip of hydrogen just to activate the ADV was satisfying,” he said. Gas density was not subjectively improved, but Harris noticed an obvious benefit—the HPNS-induced hand tremors he typically experienced after 180 meters/590 feet disappeared. Harris kept his setpoint at .7 during the descent and working portion of the dive, careful not to reach a fraction of oxygen above 4% which would make the mix explosive, and proceeded to the 230-meter test depth.
After completing their time at 230 meters, the team began their ascent. Harry shut off the hydrogen feed to the active loop of his dual Megalodon rebreather back at 200 meters, and then conducted a diluent flush every 10 meters/33 feet to remove the hydrogen from the loop until reaching 150 meters/492 feet. At that point, Harris boosted his PO2 to 1.3 from his set point of 0.7 (Challen remained at 1.3 throughout the dive), and they continued their ascent decompressing on a trimix (O2, He, N2) schedule, treating hydrogen as if it were helium. The complete technical details of the dive will be published in a forthcoming paper in the Diving and Hyperbaric Medicine Journal.
As soon as the team were helicoptered back to civilization, Harry called Michael from the road. “Michael, we did it!,” Harris said.
“Harry, you’re alive!,” Menduno responded.
N=1
At that March meeting with the H2 working group, Harris presented his findings from the dive. “I’m not sure what to conclude to a highly scientific, analytical, and evidence-based audience like yourselves,” he told the group. “Conclusions: N=1,” meaning it had been successful one time.
Doolette, who had been the most vocal in the group about his concerns, suggested Harris could add to his conclusions “the probability of survival is greater than zero.” Doolette, whom Mitchell contacted as soon as they reached civilization, said he “was relieved to hear that Harry survived this test dive” but remains disappointed with some aspects of the experiment, and concerned about possible future attempts. “For instance, I imagine among the engineers he consulted would have been someone with the ability and resources to do a computational fluid dynamic analysis of the Megalodon rebreather to establish the ignition risk, but instead Harry filled his rebreather up with hydrogen in his backyard.”
Overall, Harris said his findings are that hydrogen can be handled and boosted, hydrogen and CCR diving are compatible, a strategy to introduce hydrogen on descent was successful, a decompression dive was successful, a low setpoint at depth did not practically affect total dive time, strategy to reintroduce a high PO2 on ascent was successful, and HPNS and narcotic impacts were subjectively favorable.
“In introducing hydrogen we have addressed the issue of gas density, but we certainly have not established it is safe to use in terms of explosion risk, decompression of the thermal hazards,” Harris said.
Among his conclusions, Harris pointed out that he also managed to evade the nickname “Hindenburg Harry.” “Fortunately that was avoided,” he said, “but remains an ever-present risk.”
The Future of H2
Harris warns not to read too much into what his team achieved—a single data point that should in no way encourage others to repeat the dive. “David Doolette’s comment should be heeded,” Harris said. “All we have shown is that we got away with it on one occasion.”
Provided it can be safely proven and built upon, Harris said he thinks of his hydrogen dive as a window into the future that would enable tech divers to continue exploring into the 250 to 350 meter/820 to 1148 feet range. “Imagine the wrecks and caves that lay unvisited around the planet,” Harris said.
DIVE DEEPER
YouTube: Wetmules 245m Cave Dive in the Pearse Resurgence, New Zealand (2020)
InDEPTH: Hydrogen, At Last by Michael Menduno
InDEPTH: Density Discords: Understanding and Applying Gas Density Research by Reilly Fogarty
InDEPTH: Playing with Fire: Hydrogen as a Diving Gas by Reilly Fogarty
InDEPTH: High Pressure Problems on Über-Deep Dives: Dealing with HPNS by Reilly Fogarty
InDEPTH: The Case for Biochemical Decompression by Susan Kayar
John Clarke Online: Hydrogen Diving: The Good, The Bad, the Ugly (2021)
InDEPTH: Diving Beyond 250 Meters: The Deepest Cave Dives Today Compared to the Nineties by Michael Menduno and Nuno Gomes.
Undersea Hyperbaric Medical Society: Hydrogen as a Diving Gas: Proceedings of the 33rd UHMS Workshop Wilmington, North Carolina USA (February 1987)
InDepth Managing Editor Ashley Stewart is a Seattle-based journalist and tech diver. Ashley started diving with Global Underwater Explorers and writing for InDepth in 2021. She is a GUE Tech 2 and CCR1 diver and on her way to becoming an instructor. In her day job, Ashley is an investigative journalist reporting on technology companies. She can be reached at: ashley@gue.com.
