Mammoth Cave, Slug Lake - Oct 2004
Aim: Initial purpose of this trip was to pursue the deeper lead of slug lake beyond the 96mtr point reached by Allum and O’Brien in 1999. To achieve this goal safely the use of closed circuit rebreathers were to be utilized. This would allow the diver more time to explore and document the cave. This would not be possible with conventional scuba due to the huge logistics and support necessary to move large amounts of Open circuit equipment.
Due to a current policy of the Jenolan Trust, rebreathers have, at this time been banned from being used in any of the sites under the trust’s jurisdiction. Our permit was approved about 4weeks before the proposed dates under the proviso that rebreathers weren’t to be used.
Our goals therefore changed to being a survey and reconnaissance trip to assess the ease and viability of conducting some deep exploration in Slug. Also, to survey the outer walls of the “Gargle chamber” as it had been said that some of these walls had not been seen. We felt that confirmation of the extent of this area be gained before proceeding.
Sat 2nd Oct:
After arriving the previous night into Jenolan camping ground we all commented on the fantastic setting of this site, nestled in the valley just before the Grand Arch of Jenolan, on the banks of the Jenolan River. Other than having to put up with incredibly tame wombats and possums rummaging through our food, the camping area is a credit to the Trust with amenities close by but still having the feel of being “ in the bush”.
We were abit slow off the mark today due to a misunderstanding with keys to the cave. Phil Maynard and the SUSS( Sydney Uni Speoleo Society) guys had grabbed them for mammoth, Spider and Jubilee Cave for their w/ends adventures.( I think in hindsight they must’ve thought a through trip all the way from Jubilee to Mammoth was on the cards!! J)
So with 5 of us and 13packs of dive gear we set off. Just after the “Forty footer” ( called this as it’s a 40ft vertical climb or abseil) we ran into Dan Cove and company on their way out from being to Slug lake.( Jenolan Caves Trust run adventure tours in the “wild” caves of Jenolan). Us and 13 packs may have been an obstacle in other parts of the cave but luckily we met at “Home Sweet Home” thus utilizing the two passages at this point to by pass each other.
We arrived at lower river in reasonable time and as Tony was in a wetsuit already( must’ve left his caving overalls at home) he simply walked all our packs across, therefore making this transition easier. I had contemplated using a flying fox as we had in the past but decided it quicker, and easier to simply walk them across.
From here, the trip to slug is a mere hop step and a fall(if your not careful). The closer you get to Slug the more mud and slush seems to appear. We arrived with our 13 packs 3hrs after commencing the cave.
Visibility is always atrocious for the first few mtrs. Paul descended first and as I followed I noticed huge amounts of silt that had accumulated on the roof, being disturbed by Paul’s bubbles. Visibility for me was zero and once Paul met the restriction the silt had caught up and reduced his to the same. As I descended the big concern was the state of the guideline. Approx five yrs previously I had laid a thick 6mm “Parramatta” rope down to approx 20mtrs. This line had somehow become entangled in the original line, making it very confusing in the bad vis. I made a mental note to tidy this up.
At the restriction I swam into Paul’s fins. Realizing he was working his way through slowly I sat and waited. I soon received a tactile signal on my hand to say that he was o.k. but returning as he wanted me to have a go at passing the restriction. Communication in this sort of vis is difficult however diving with people who understand good “tactile” signals is advantageous. I jumped around Paul and proceeded into the lowest point. It seemed a lot lower than I remembered from a previous trip and ascertained that it had obviously silted up quite severely in recent yrs ( reasons for this explained later). I wiggled and dug a bit to work my way through and emerged on the other side to find that after about 3mtrs the visibility went from zero to 6+ mtrs ( probably was better than that but that was as far as my torch could see). I sat and waited for Paul. A few minutes past and no sign so I began to think he may have had trouble in the restriction. I returned to find him waiting patiently on the other side (outside). His reasons were explained later, when we exited. This was an unfortunate breakdown in communication which meant we didn’t achieve our goals for this dive, but I must say that due to the fact that Paul had not been able to read either contents gauge or his decompression computer for over 50mins of the dive and I had seen mine once, it was time to get out and reassess tomorrow. Decompression from this dive was interesting. I must say that having been diving caves for approx 12yrs I had never had consistently zero vis for the whole of a decompression dive. Not knowing your depth and your decompression obligation and only being able to rely on the audible alarm in the computer to know when you had gone too shallow is an interesting experience to say the least. Using an open circuit gas supply in these conditions is unnerving as having to manually calculate in your head how much gas you’ve used, approximately how long you’ve been underwater, and how much decompression you probably have is challenging.
Decompression however was completed without incident and upon surfacing I was pleased to note that my rough “on the fly” gas consumption calcs had been correct and I‘d exited with plenty of reserve.
We packed out 6 packs that afternoon, and hit open air at a bit before 7.00p.m.
The night was spent sitting around the campfire, next to the river, discussing the best tactics to tackle the Gargle chamber tomorrow.( I should point out here that Jenolan camp area is very sparse when it comes to firewood and we had stocked up Simo’s car full of good eucalypt before leaving “the playing fields” located close to Mammoth cave entrance.)
Sun 3rd Oct
The plan for this dive was to descend to the 30mtr restriction, pass it, and begin to survey the Gargle chamber. Reports from Rod Obrien and co. gave me the impression that after the restriction the floor just dropped away down to approx the 45-50mtr mark. With this in mind we thought, once through the restriction we would instantly drop down the western wall to a depth of 45mtrs and commence a circular survey of the room. I tied off to the original line at the 24mtr mark and commenced a descent. Within seconds I could see the floor on this side of the room commence it’s gentle slope to the East(NE??)at approx 30mtrs. I followed the right hand wall(Southern) around further and paused when it disappeared off to my right. There seems to be two small fissures as you venture around this wall that peter out into nothing after only 3-4mtrs.
Apon tying off near the second one I caught a glimpse of something green out of the corner of my eye. I turned and instantly had my heart in my throat!! Emerging from the silt was a green fin with a leg attached to it!! Having been involved in body recoveries before I heart rate raced for a few seconds as questions of “ who is missing?? ….. no-one is ….. where’s Paul??( my dive buddy)….. behind me(phew!!). This all happened in about 2 seconds and as my eyes followed the leg up it stopped. Turned out it was a fin with a Gumboot still stuck in it!! I laughed out loud as I remembered reading Al Warilds report of a recent previous dive where his drysuit had managed to blow off both his boots and fins as he tried to regain composure. My breathing rate back to normal, I made a mental note to pick up the fin on a subsequent dive. Still proceeding in a anticlockwise direction around the room we crossed the vertical descent line of Ron Allum’s that leads to the deeper sections of the cave. Proceeding along this wall lead us into another fissure that terminated quickly. I tied off and cut the line and left it ,so to survey later. On the return we reached the intersection of ours and Ron’s line and decided to follow his line into the deeper section. We proceeded down to approx 40mtrs where I tied off and followed the wall back to our right to ensure we knew where the walls of the cave were. As I followed this wall it kept forcing my back to the direction I’d come and I quickly realized it was curving back around to the restriction area up a gentle silt slope.( no leads there!) We returned and decided it was time to go home. Following Ron’s line back to our intersection and then past it we saw it rise vertically to a large protrusion where it was tied off, then straight back horizontally across the passage to the restriction. I only conducted a grade 1 survey on this leg as knew it had been done before but interestingly noted that this line really runs across the northern wall of the room, it’s maximum distance away from the wall being about 2mtrs. After negotiating the restriction Paul and I had accumulated 1hrs worth of decompression!! We weren’t used to getting such as short dive time for such a large decompression penalty. Oh well, we just sat it out, we’d certainly all had to do longer deco’s before.
While working our way up through the deco stops from the 20mtr mark I took the opportunity to tidy the guidelines and remove one, so to simplify the rigging of this cave. As previously mentioned the 3mm original line and the 6mm “Parramatta rope” had managed to become entangled in them selves making it extremely difficult to follow in bad visibility( the time you need guideline most). I removed the 3mm rope as the 6mm seemed very secure and would be more robust in yrs to come.
After packing all spent tanks in bags we proceeded out, taking 2hrs to exit. Due to the late start it was just turning 7.00p.m.
Mon 4th Oct
Today we had big plans, we wanted to survey an area around the 40-45mtr mark, as this was really one of the original goals but we still hadn’t achieved it. Due to limitations on gas supply it was decided that I would accurately survey the wall where I’d laid the line previously( 25-30mtr area) and Pauls would quickly drop to 45mtrs and attempt to find a wall off to the left of where we’d been yesterday.( the right as you remember curves back to the restriction). After the restriction, Paul signaled that he would be back at the 30mtr mark in ten minutes. I proceeded to record distance and direction along the southern wall. Paul returned as planned and we exited the cave back to entrance chamber. Obviously Paul had slightly different deco obligations than I did so I twiddled my thumbs for the extra 20mins that he had accumulated. Upon surfacing Paul relayed an account of what he saw. Unfortunately the brief time that he had at this depth did not enable him to find the left hand wall we had been looking for.( We were REALLY now remembering the limits of conventional scuba).
After exiting, I made the decision that we would use the rest of our permit time that we had applied for and return next week to hopefully achieve the goals we had set out to. With this in mind we left all my dive gear (Paul wasn’t sure whether he could make it) minus the spent cylinders and exited the cave at approx5.00p.m In our three trips we had ascertained that the Pack to Person to time ratio of traveling to Slug was almost proportional. I.E: 1pack per person equaled 1hr trip, 2 packs per person equaled 2hrs and so on. This was definitely worth recording for future large trips.
A quick pack up was required in order to get the key back to the guides office and discuss our accomplishments( or lack of) with the guides.
A big weekend caving, but we were all “keyed” up for next week!!
Sat 8th Nov
Slightly down on numbers this week, we only had four people( three from last week). Samir had joined us as he had no excuse this week as the Bulldogs had won their premiership and he had celebrated all week. Time he received his initiation to Mammoth and Slug lake.
The purpose of this dive was to once again dive to the 45mtr level of the cave and find the left hand wall. Samir and myself entered on Sat lunchtime with this in mind. Visibility down to the restriction was about 2mtrs. This was expected due to the amount of diving from the previous week. What was not expected was the lack of visibility after the restriction and in gargle chamber. We proceeded down to approx 37mtrs depth and decided that with the vis still restricted that very little would be accomplished in the way of surveying this area.( Maybe I need to practice my surveying skills in limited vis) Due to the size of this passage so much more can be accomplished in clear water. So we turned the dive and proceeded back to the tie off point at 25mtrs. From here we decided we might as well have a look at the shallow sections of gargle chamber. No matter how this cave is described it always seems to be different than what you envisaged. My picture of the top section was that it ascended straight up to an air bell, however on following the line ( still in 2mtr vis) I found myself swimming up on about a 60-70deg angle for most of it. This intrigued me ,however Paul later commented that he’d seen a map of Slug that put the air bell close to or above the 30mtr restriction that we had already past. This certainly made sense and as I surfaced in the air bell my original thoughts of using this area as a “starting point” for a big dive quickly changed. We had envisaged being able to rest in this chamber after a big dive before proceeding to exit through the restriction. While this is still the best option, we would have to rethink as the bottom composition from approix 6mtrs up is thick muddy ooze( which once again reinforces why this place is called “slug lake”) We dekitted on a fantastically muddy slope that a person sinks about six inches into with every step.
I was extremely paranoid of my cylinders sliding back into the water and down to “who knows where” even though they were clipped to the guideline. Samir dutifully stayed with the tanks while I climbed up to the beginning of where Al Warild and Rod O’brien have spent many an hour slowly “bolting” up a wall to check out prospective leads. I must say ,even as a caver with limited vertical experience the potential here looks promising. I can see why they have preservered .
On our return down I strained to see the other walls of this area but could not and still have a hard time grasping what the cave is doing at this point. Another dive will be needed to this area to ascertain it’s 100% suitability for our future dives.
Decompression was minimal after this dive and we exited a little disappointed, realizing that any surveying or more familiarity with the cave this weekend would be difficult.
We decided to pack out half the gear today and leave the rest until tomorrow as no diving would be conducted from here.
Once again a fantastic night a Jenolan Camping area was had, with all the team commenting that this was the best way to enjoy “caving at Jenolan”
Sun 9th Nov
A whirlwind trip was planned today, with Samir setting up some shots with his video camera in the dry sections to show the effort involved in moving dive gear to Slug. Unfortunately, when we were picking up the key Dan advised us that Jenolan rd would be closed later that afternoon and if we weren’t out of the camping area by that time then we may well have to stay until 10.00a.m the following day. This meant the trip was now exclusively a recovery of equipment one. We managed to get to Slug in 35mins and return in 50mins with the remaining 4 packs. By this stage we certainly had moving through the cave down to a refined art.
I did however, survey the last dry restriction about 30mtrs short of Slug. This area posed a problem on the 99 trip that we did with a rebreather , so I was interested to measure it accurately to use for possible future reference.
We managed to return to the campsite with 30mins to spare( much to the relieve of our spouses who thought we would not be back until 4.00p.m). A customary debrief was held at Hampton pub, a chance for all divers to sketch their perception of the cave.
Conclusions:
It would seem a possible explanation for the increased amount of silt in all cave areas may be due to lack of decent heavy rainfall over the past few yrs. On previous trips in Slug we have not seen the collection of silt on walls and roof. Also the floor at the restriction used to be smooth, small pebbles whereas now these pebbles have a deep layer of silt covering them. A decent flood in here would flush out the silt periodically.
A dive trip of more than 4-5days of consecutive diving will possibly find limitations as silt from entrance chamber will progress well into the rest of the cave and make exploration of this area difficult. A 4day dive trip followed by an approx 3week break to allow clear water to flush through the cave would possibly be ideal.
The Gargle chamber is not as wide as first thought, with the only way on being down to the deeper sections of the cave(50mtrs +)
The shallow section and air bell of gargle chamber does not give direct access to surface from deeper sections of cave as first envisaged. This area will need more attention to ascertain it’s suitability for decompression stages of a push dive.
Diving with open circuit scuba significantly inhibits good visibility due to diver’s bubbles disturbing silt on roof and walls.
Diving with open circuit scuba to depths of 40mtrs and beyond is limiting and only a few small tasks can be achieved on any one dive.
Diving on air on open circuit scuba gives large decompression penalties for very little bottom time. The use of nitrox mixtures for decompression would help reduce this however the extra effort in gear transportation to the dive site does not make this the ideal choice.
The use of rebreathers( if allowed) would be limiting at this stage as fully redundant mixed gas rebreathers would have extreme difficulty passing the restriction at –30mtrs.
Use of small decompression rebreathers( if allowed) would allow significant increases in bottom times with minimal decompression penalty, thus creating more opportunity to achieve numerous tasks on each dive.
The Way Forward
The use of rebreathers, while not in the capacity we first pictured, will still offer a huge advantage to exploring the sections at 50mtrs and beyond. Dives that utilise a combination of open circuit scuba and a rebreather for decompression purposes from approx. 20mtrs up would mean good bottom times could be achieved with minimal equipment being transported into the cave. Also, there should be less disturbance of silt in the entrance chamber during these decompression phases, thus reducing the silting problems we have encountered.
Images from the Trip
