Push [Poŏ SH] - by Rich Walker
Updated: Feb 16, 2020
It sounds a bit silly really. To push a cave. A cave is an empty void, and difficult to push in the conventional sense like you would push a car that won’t start. Pushing a cave means, to the cool kids, to extend the limit of exploration. To go further in that cave than anyone has been before. You have to be careful here as it is very easy to sound like you are lost up your own arse. I suppose that would need some sort of pushing to rectify as well.
The Perdreau Formi is a bit of everything in a cave sense. It starts with an awkward boulder choke at the entrance. For the uninitiated, a boulder choke is a pile of rocks, stuck and hopefully wedged in the passage of a cave. We are fortunate that this choke is normally dry, so we can get through it without dive gear. This often involves some pushing as well, but more like what you would do with a car. Or a turd.
Once you have got past the choke, you arrive in a large chamber at the top of a 45degree slope. The slope is slippery, but manageable. We put a rope on it though and descend down the slope well protected as at the end of the slope is a vertical drop, 20m high. If you were to loose your footing on the slope and fall off, you might be lucky to land in the sump with a splash, but you would probably bang on a few rocks on the way down, and more likely splatter somewhere in the boulder strewn area at the bottom. You might survive, but then you’d be faced with being pulled up the 20m pitch, up the slope and pushed (there’s that word again) through the boulder choke again.
Tim Webber and Jarvist Frost had done a fantastic job sorting out the vertical section of this cave. They had built a system of tensioned lines, pulleys, hauling lines and brakes that would have looked good on a Spanish galleon. Moving the equipment up and down the pitch was considerably easier than the brute force methods we’d employed last year, and made the trip run significantly faster.
The sump at the bottom of the pitch is well lined, and normally clear. We dived it last year and it was a short, but very pretty trip. The walls are white and the water has a blue tinge to it. The passage twists around, through an easy restriction to a maximum depth of 19m, where it comes up steeply into a large airbell.
It takes about 5 minutes to cross this sump, whereby you are faced with a steep wall 3m tall, at about a 70degree incline. The way on is this way. Climbing the wall is precarious, but manageable with small cylinders. The second sump is found on the other side of this wall at the bottom of a couple of round pots.
Tim and Jarvist had been hard at work in the airbell too. They had installed for us a wire ladder to climb the wall, a gear line to clip off bigger cylinders and similar assistance on the descent into sump 2. This was to be critical when we returned later in the week.
Diving in the second sump, the line is not so good. It is often loose, and many belays have come free, so the first dive this year was to check the state of this line, effect some repairs and to have a quick look to the end of the line laid by Joe Hesketh and Osama Gobara on last years project. Their line was excellent and the reel was there waiting for our return. The line ended at a depth of 29m. The passage had dropped down 20m from the tie-in on the main line and we had been concerned about the cave heading into deep water. Spending a few minutes looking at the way on was time well spent, as it seemed that the passage levelled off, at least for as far as we could see. This was good news to us - shallow means more time exploring and less decompression.
Christine and I had a chat back at the surface about our decompression strategy. We had expected the cave to head deeper much more quickly than would now appear, which would require a more significant decompression strategy - this in simple terms meant a lot of decompression gas was needed. Given our look at the end of the line, we decided not to pull in the big decompression cylinders, and stick with a smaller volume of oxygen, for use at 6m, rather than the big cylinder of 50% nitrox for 21m decompression. This was a gamble, but would make the logistics significantly easier. For our return dive to “push” the cave, we had mixed gas for a maximum of 60m in two large 15 & 12L cylinders each, and a small 5L cylinder filled with oxygen for decompression. We were diving in wetsuits, which in 11C water would be a push on a longer dive, but as long as we limited the dive time to an hour, we figured we’d be OK.
On the day of the dive, the gear went in very smoothly with assistance from Jean Tarrit and friends from the CLPA. These people have been so good to us in our efforts here, and never fail to turn up to help out. It’s not always the same people though, so maybe word is getting out ;-) All we needed to haul in was the cylinders, the deco gas and the wetsuits, as we’d left all of the other gear in after the first dive.
Chris and I dived through sump 1 and were ably assisted by Tim and Jarvist, and we pushed and they pulled our heavy cylinders up the rope to the start of sump 2. Kitting up in sump 2 was a bit more awkward, but again our helpers did a sterling job of pushing us into the water ready to dive. The oxygen was handed down, and we set off.
After depositing the oxygen at a suitable place to do the deco, we headed off down the line. This had come loose again and floated into the ceiling (I hate blue polyprop). We missed the junction as it had itself floated into and behind a crack in the ceiling, and we arrived at the old end of the line. Very puzzled, we backtracked, and this time spotted the junction, more visible from the other angle. We still weren’t pushed for time, so we headed off to the end of the line. Pushing on through a patch of low visibility left from our dive 3 days previously, we soon came across the start of Joe and Osama’s line. Junction marked, and away we went, soon reaching the reel that had been waiting a year for our return.
I picked it up, and looked at Chris. She had her survey gear out, and we exchanged an OK and we started to swim. I like to keep the number of tie offs to a minimum, and if possible to have spotted the next one before I leave the current one. This makes the surveyors job much easier, as the line doesn’t wave around, and tying off takes time, slowing down the act of pushing. The cave made this pretty easy, as it soon turned from large open passage into a narrow rift, 2m across at an angle of about 45degrees.
It was probably 20m high in places, pale walls with delicate mineral veins extending from the rock. It was pretty silty, and as usual in places less well travelled, percolation from your bubbles traveling up the walls quickly reduced the visibility, meaning that constant motion is preferable. I put in 6 tie-offs before the reel was empty, a total distance of around 50m. Looking ahead, the rift appeared to get narrower, although probably passable. My gut tells me that there is something else though. Maybe it surfaces at the top of the rift, or perhaps there is another connection we have missed along the new line.
I glance at Christine and push my thumb up (quiet at the back). She returns the compliment and we head for home, 25 minutes after leaving the airbell. Now it was time to see how well my line was laid and whether it was easy to follow in low visibility. My ability to write the blog says that it was good enough, I suppose.
We got back to the oxygen and given that the dive had not gone anywhere near as deep as expected, decided to not bother with any decompression and get back to the warm. We surfaced at around 40 minutes, with an empty line reel, my knife that I had found after loosing it on the first dive and a full survey of the line we’d just laid. A proper good day out!