We stumbled through the dark forest on our way to Hang Dai Cao. The idea was to camp at Hang Dai Cao and then to cave through three further caves in order to reach the upstream Hang Ho entrance, where on a previous expedition, in 1997, two lads had followed a dry riverbed to a new entrance while the rest of the team finished the survey. There had been no time to explore the new entrance then, and so we were returning now to complete the work they had started.
Hang Dai Cao, our camp-site-to-be, is a link in the >30 km chain of caves that form the Hang Vom hydrological system, originally found in 1992. Hang Vom, the cave that lends its name to the system, is a 15 km long cave of truly enormous proportions. Its sink, Ruc Caroong lies near the border with Laos, far away from civilisation, about 44km up the Ho Chi Minh trail from the nearest sizeable village (Son Trach), our base.
The water of the Ruc Caroong sink disappears in a downstream sump after only 2.8 km of passage. The main water then re-emerges 10 km further downstream in an inlet of Hang Vom itself, and finally resurges into the Chay river having crossed Hang Vom for a further 15 km.
Apart from this massive 10 km question mark, downstream Ruc Caroong also continues in two semi-circular dot-to-dot-caving series of flood overflow caves, some completely fossil, others semi-active, separated by stretches of jungle. These two hydrological prongs unite at Hang Ho (Tiger cave, named for the tiger footprints found at the sandy beach at its upstream limit), hence making Hang Ho a keystone in the flood overflow part of the system. Downstream of Hang Ho, the two flood overflow branches unite and are channeled towards Hang Vom, via Hang Pitch, the complex Hang Duat, and finally Hang Dai Cao. All of the caves below Hang Ho are wet and have impressive proportions.
One of the two flood overflow branches passes through two caves (Hang Pygmy and Hang Over) and is completely explored. The other branch still carries a question mark of maximally 2 km between Ruc Caroong and Hang Ho. In all probability, the entrance seen by the two lads in 1997 would provide this missing link. More tantalisingly, this final piece in the overflow puzzle might also provide a way into the completely unknown missing10 km branch that takes the main water from Ruc Caroong to Hang Vom.
Our aim was to camp in Hang Dai Cao and to then cave through Hang Duat and Hang Pitch to Hang Ho, where we would swim to the upstream end, exit across the sandy beach through a dry river bed to find the connection with Ruc Caroong and perhaps a way into the unexplored 10 km. Worth a go, and even the more so for me, as it involved camping in the jungle in the vast Khe Bang Massif, a great treat for me.
So we were stumbling down a small dry river bed in the dark and our guide appeared to be lost. It was raining and the sharp limestone boulders in the riverbed were slippery and the leeches were coming out in force. Howard kept insisting we had gone wrong, that we should have climbed two steep hills by now. He was worried with good reason, as he had got lost in the jungle for two days off the self-same track, in 1999. Déjà vu? This should be a 3 hour walk and we were coming up to about 3 hours, with Hang Dai Cao nowhere in sight and the terrain unfamiliar. Our guide was arguing about the direction to Hang Dai Cao with every team of woodcutters we encountered. The fact that they invariably shouted Hang Dai Cao in a surprised tone and then wildly pointed back to where we had just come from did little to reassure us. Nevertheless I took heart, as our guide confidently insisted that he knew the way, ignoring the woodcutter’s gesticulations.
After another quarter of an hour in the dark (well, with LED torches), I could hear frogs ahead and shouted to the rest of the team that we must be nearing water. The path suddenly dipped very steeply down a sandy bank among tall grasses. I was first to stumble to the bottom, watching the guide turn round triumphantly to show me what he thought was Hang Dai Cao entrance. Except I had camped there in 1999, and this didn’t look anything like it…
We were clearly in a dry stream bed. About 6 m wide, the ground at the upstream end was punctuated with fetid green pools and boulders on a basically sandy floor. Raising my eyes, everything was shrouded in vegetation, tall trees interpsersed with bushy jungle. The downstream end terminated in a large arched cave entrance above a sandy beach and further downstream a deep looking sump pool. Several, no doubt tiny, frogs had chosen the pool as their home and resonance chamber, producing stentorian echoing calls audible a considerable distance away.
Howard and the others soon arrived and agreed this was definitely not Hang Dai Cao. While we sorted out the camp and got food and water on, Martin, Duncan and Sweeny got kitted up in wet suits to swim into the cave and see if Martin would recognise it. Martin had caved in the area several times before, Duncan and Sweeny had never been to the area, but were desperate to get underground and to lend moral support. We stood on the sandy beach, listening to the frogs calling and watched the three lights slowly disappear in the dark. Our slightly miffed guide still insisted this was Hang Dai Cao, despite Howard’s attempts at explanation. About an hour later Martin was able to report that we were encamped at the upstream entrance of Hang Ho. Delighted with the good news, we thanked our bemused guide. By insisting on taking us to the entrance he knew as Hang Dai Cao, he had saved us several hours of caving through Hang Duat, Hang Pitch and Hang Ho, and had taken us precisely to the one spot from where the remaining lead could be accessed by a mere 20 minute stroll up a river bed.
Next morning, we split into two teams. Howard, Martin, Sweeny and Snablet caved back through Hang Ho into PitchCave to follow a lead there. Duncan, John, Dan and I went up the river bed to hopefully find a way into the Hang Vom system.
The walk up the river bed was more of a scramble, as it had rained overnight and the large, algae covered boulders were treacherous and slippery. In between climbing boulders we waded through fetid, green, swampy puddles, left over from the last floods and now reduced to slime and sediment towards the end of this dry season. After about 30 mins, the riverbed just stopped at a high limestone cliff. To the left of the cliff we saw a gravelly ramp that looked very much as if it might carry a stream in the wet season. To the right, behind several bus-sized boulders, we could just glimpse a tantalising black hole. We had found the entrance.
Dan and John climbed into the entrance to check out whether the cave was a going concern. I got the GPS out to get a fix on the entrance, and Duncan had a look for our beautiful interpreter, Miss Hoan. Even though she was very much under equipped for the cave, having just a pair of canvas trainers for footwear and no wetsuit to speak of, and even though she had not really enjoyed our nocturnal walk to the cave, she had insisted on joining us (accompanied by the guide), but had been left behind after the first few metres. We thought it wise to have a last attempt at dissuading her from coming along. By now Dan and John were hooting loudly with delight as they established that there was passage to survey. I could no longer wait for the GPS satellites to appear and climbed over the boulders to join them. And then the three of us waited for Duncan. And waited. And outside, behind the huge boulders, Duncan waited for Miss Hoan. And waited. And then Duncan went back to the camp to make sure Hoan hadn’t drowned in one of the puddles, or broken her legs on the slippery boulders. After what seemed like hours, Duncan finally re-appeared, having found Hoan safely snuggled up in her hammock, reading her Vietnamese-English dictionary. We were finally done hanging about and ready to reel out survey tape.
The passage started off with boulders and sand in the entrance, then lead into an imperceptibly slowly flowing stream. To begin with, we walked and waded. The cave was very bare in character, like other active parts of the caves I had seen in this area. The walls were completely smooth and grey, not a decoration in sight; obviously it would be blasted in the wet season.
Soon the stream became deeper, and before long we had to survey while treading water - at least that made the clinometer readings easy. After two hundred meters of bleak, clean washed, dripping passage, we reached a second entrance with a steep green ramp. Beyond this, the river continued at swimming depth. Looking behind her towards the alternative entrance, Dan noticed the water had an eerie, greenish phosphorescent glow. On closer inspection, this turned out to be due to a hanging wall, just low enough in the water to appear solid when nearby, but letting the sunlight filter through underneath. One of the few pretty features of this no-nonsense cave. Further along, we reached a boulder collapse. Climbing down the other side, we found a third entrance. This was preceded by an ornamental elliptic eyehole into the green rainforest outside our cave. John named this the ‘Jade Splinter’. Here, the river stopped, allowing us to briefly leave the cold, deep water to find the way on at the other side. Back into the water to swim into the black distance. As the passage dimensions increased, we stuck to the left hand wall. After the second survey station, we entered a large, very misty chamber with a magnificent echo that I timed at 14 seconds. This made understanding the survey readings quite difficult, especially as we were reeling out 50 metre lengths. We reached a small rock island. Blackness all around, and even our best spot searchlights could not see an end to the swim. Was this a lake, a terminal sump or just very large passage?
We fettled our lights and had a snack to decide on how to progress. We had been going for a few hours, but had only surveyed about 650m so far, what with all the waiting for Hoan. Duncan was feeling very cold and got his survival bag out. He was in a semi-furry suit, not at all appropriate for a full on swimming cave. John had been feeling unwell and was keen to call it a day. Dan was happy to go on, but was without a life jacket. Although a very confident swimmer, she understandably did not fancy a long swim on her own without buoyancy aid. And so all eyes turned to me, in my full wetsuit and bright yellow life jacket.
I lowered myself into the water and swam towards what we thought was most likely the passage continuation. I started off with a survey tape and reeled out 36m to the nearest wall. I then let go of the tape and carried on swimming, always along the left hand wall. The passage was actually much less wide than we had believed, and I could see the other wall quite easily, about 20m away. As I progressed, I turned round every once in a while to see the three lights on Duncan’s island grow dimmer and dimmer. Every movement I made created waves that filled large scallops and air pockets in the walls near the surface of the stream, producing unnervingly loud booms with full 14 second echoes.
Was this lake not likely the perfect habitat for large, predatory catfish - and just how big would these catfish get? Best to keep swimming vigorously, to discourage any wildlife from being too inquisitive and to stave off the cold.
After what seemed like several hundred meters, I began to feel a draught. The draught steadily increased, and I saw the roof lowered right down in the distance. The air whistled around my head, causing my carbide light to hiss alarmingly. I sure hoped it would not blow out, as I was not at all confident that my LED backup would still work in these conditions. As soon as I popped out behind the low arch, the draught stopped as if someone had turned it off. A few more meters round a rocky protrusion and - I had found the fourth entrance. With this reported to the marooned on Duncan’s Island, they agreed to survey to this last entrance and to return the next day. We had about 800m in the bag.
The next day, the entire team came to Hang About. We were meant to leapfrog survey, and there was also a photography team - all expecting to find a way into the giant Hang Vom system. In the end, our team was caught up by the keen second team in the last entrance; where we were still busy trying to find the way on. Ironically, given that there were now eight of us rearing to go, there was no way on. Not only were we not going to break into the Hang Vom system, we hadn’t even managed to realise the cave’s full 2 km potential. Just to make sure there was not a way on at the other end of the last entrance doline, Martin, Dan and Sweeny thrashed through the leech-infested jungle, but found nothing.
We took a few photos of the rather unassuming passage and then we went out the second, rather than the original entrance to connect this with the gravelly slope at the end of the riverbed and get a GPS fix. Back to camp for a last day in the rainforest, to prepare for the return to Son Trach’s committee politics.