Otter Hole - 25th September 2021
Following our previous two trips, I met up with David Hardwick, who has published a paper on the hydrology of Otter Hole
. Dave quizzed me on what we'd seen upstream and presented me with various theories about where the water comes from, with intriguing possibilities for further exploration.
Interestingly the cave is fed by at least 4 different streams and it is not yet known where in the system they all join. Further to this, Peter Bolt had perceived a lower flow in sump 6 than coming out of sump 5; this suggested an inlet part way through sump 5.
Studying the survey, I reasoned that any inlet was most likely to be on the right hand side and it was proposed for two divers to return, with one scouring the right hand wall of sump 5, while the 2nd made an attempt on sump 6, 7 and onwards.
Meanwhile, two others would go to the far end if the fossil cave, up a passage known as Tunnels Left, where a series of sumps was last attempted in the 80's. The purpose of this trip would be to place a dye detector and assess the route for carrying diving and camping equipment for a push next year.
With four cylinders in the cave already, we'd be bringing in three more bags of diving kit, plus food and sustenance for a long day underground. On the way out, there would be less food to carry, but four extra bags of diving kit, so a large team of porters would be required. Jann Padley of GSS did a sterling job pulling together a team if volunteers to help and with a week to go, all looked to be set...
But as with all the best laid plans, that wasn't to be. One of the divers pulled out to help with the Three Counties trip, one of the Tunnels Left team got stranded overseas with work, one of the porters injured themselves and another also had to pull out.
After a rethink, I managed to rope in Dave Hardwick to join the Tunnels Left trip (to be fair, he offered to go) in my place. Craig Holdstock would carry on as planned on this aspect of the trip.
Jann found a replacement porter and after a call for help around my club Rob Thomas also offered to help porter; we were back on.
Until the day before when the second diver phoned me after a skydiving accident, now unable to cave...
Another rethink was in order.
Since the streamway between Sump 4 and Sump 5 is quite mobile underfoot on various boulder slopes, I was keen to have two divers beyond Sump 4 in case of an accident. Fortunately, Rob, who was staying at the Wessex, was able to cobble together enough kit to dive, but we were now down a porter.
In the end, we settled on taking in a 2 litre cylinder to supplement the kit in the cave. This would be enough to get Rob through Sump 4 and assist with my kit in the streamway up to Sump 5. I would carry on as planned, scouring the right hand wall of Sump 5 for an inlet, and place a dye detector in the start of Sump 6, but we'd save a push dive for another day. This would mean that most of the cylinders would still be full and could stay in the cave for next time, as we were short on porters.
Tide times meant an early start and seven of us met in the car park at 05.30 on Saturday 25th. After a bit of faffing with gear, we were packed and on our way down the hill and into the cave at 06.30, bang on schedule.
Craig and Dave set off first as they had the furthest to go, with the rest of us following, with a bag of kit each. By 08.00 we had arrived at Sump 2, where Rob and I kitted up and were off by 08.30, with an estimated two hours before we'd be back.
Since Rob had not been before, I let him dive first to get some visibility in the low wide sumps; I followed, with about six inches of visibility...
Dumping Rob's kit, we carried a cylinder each up to Sump 5, where I kitted up again, for a slow dive through, to look for any possible inlet. I was expecting another low wide silty sump, with poor visibility. I was expecting to be groping about trying to feel for any widening as the bedding pinched off to the side, so imagine my surprise, to find myself standing upright (I was overweighted and not wearing fins) in a huge passage full of crystal clear water!
It must have been 6m high in places and over 3m wide. The whole place completely illuminated, I could see every detail!
If only I'd known it was going to be like this, I'd have brought the fins we had stashed at Sump 2, I'd even have ditched some lead and taken a more neutrally buoyant approach. In a passage that size, even I could have avoided stirring up the silt!
Anyway, that was not to be, I stirred up great clouds of muck as I walked along, before climbing on ledges to follow the line to surface beyond the sump.
Regardless of my silt-stirring, I got a really good look at the whole passage and was able to confirm that there is categorically no inlet along the length of the sump, and I didn't have to resort to a fingertip search!
Beyond the sump, instead of the streamway I'd expected, I found myself in a large air bell, with no dry land and 6m of water under me and I was still well overweighted...
I managed to remove my weight belt and popped it on a narrow ledge; now able to float, I was able to inspect my surroundings a little better.
To the left, a virgin passage headed off above water. This had been noted by previous divers, but never entered. To get into it would involve removing diving kit and digging over a mud bank and right now, this didn't appeal. It would have been criminal to dump all that silt into such clear water!
Opposite this, to the right, the dive line was tied off to a flake of rock and disappeared off diagonally down a narrow rift into Sump 6, however, by descending straight down at this point, a wide tunnel could be seen heading off, with the line pulled into the rift above. With such clear visibility, it was easy to see what was going on, but I can imagine in more typical conditions (our trip came after a very dry period with unprecedented low water levels) this area could be pretty confusing. I made a mental note to fix the the dive line back to the left hand wall, half way down, to give a better route into the passage below, before attempting this next sump.
Back in the air bell, I shot a small bit of video, before finding the pre-tagged dye detector destined for Sump 6 and fixed it securely to the line.
After this, I put my weight belt back on and returned to Rob, with reasonable visibility, as the water had cleared a bit while I was faffing in the air bell.
On my return, Rob borrowed my kit and popped through to the air-bell for a look, while I fixed the next dye detector downstream of Sump 5. On his return, Rob and I split the kit to carry and set off out.
While I was gone, Rob had taken a short wonder downstream and had noted a couple of interesting holes that might be worth a look some time.
Back at Sump 4, we both put our own kit on again and dived back out, reaching the dive base at Sump 2, just 5 minutes after the porters had returned.
Rob hadn't used much air off the 2 litre cylinder and hadn't used the 3 he was carrying at all, so both these could stay in the cave.
I'd also not touched one of my cylinders, but the other was now down to about 100 bar, having been used on two previous trips and by both of us for Sump 5, so the full one could stay in and the other come out.
After repacking kit, we had a bite to eat and a cup of coffee before setting off out, with more or less, the same amount of kit we'd brought in, fixing the final dye detector a short distance downstream.
Wandering along the passage, I stepped off a rock into what had been ankle deep water and disappeared up to my chest. We'd reached the tidal zone and for the first time, I was seeing it at high tide!
As we were wearing wetsuits Rob and I decided to swim on, taking two bags each. The logic being, we'd plod slowly on and the others would catch up quicker without bags and we'd all get out sooner.
At about 1pm, we reached the tidal sump.
At about 1.45 the others arrived.
At about 2pm (bang on schedule) the tidal sump opened.
Again, Rob and I opted to push on ahead with the bags, while the others waited for the tide to drop, so they'd stay dry.
Rob and I eventually emerged at 3pm, with Jann, Ross and Paddy surfacing half an hour later, for the long slog back up the hill.
By 5pm, we were starting to wonder where the Tunnels Left team had got to and agreed we'd need dinner before going back to look for them, but eventually we decided to walk back down the hill and were very happy to find them at the kit washing point only 15 minutes from the car park.
They too had had a successful trip, reaching the end of Tunnels Left and finding water lower than it had been seen before were able to duck through into a considerable distance of passage that is usually blocked by a sump, before eventually arriving at the beautiful blue pool marking the end of their trip and our objective for next year.