Yax Chen Survey Map

Marcus and I headed back to Mexico in June 2010 to take part in the Mexico Cave Exploration Project (MCEP) Science Week with Dr Chris Werner, Dr Eduard Reinhardt and  hosted by Zero Gravity – it seemed as good an excuse as any to head west again! Our objectives were primarily to produce an accurate and detailed map of the Yax Chen section of Ox Bel Ha, the world’s longest underwater cave system and deploy an array of temperature sensors that will help inform scientists modelling water flow through the caves. Dr Reinhardt and his team would take sediment samples that reveal records of paleoclimatic change in layered deposits of formainifera. A little further exploration would also be undertaken in Ox Bel Ha if the chance arose. The surveys were hugely successful and it was a great opportunity for us to see part of a world famous cave. Marcus and I totalled 8 dives for the project, the longest of which was just under 4.5 hours.

More details can be found here: MCEP Science Week

The beautiful setting for the pool at Glavas. Photo courtesy of and copyright Dražen Gorički.

Day two saw us at Glavas, a stunning pool set below a wonderful stone church. The relatively small pool belies an open shaft that heads down pretty much vertically to approximately 80m. From here the onwards passage descends at a more moderate 45 degrees to the maximum explored depth of 115m where the passage levels out and ends in a pinch shortly after. The CSS researchers were interested in generating a relatively high resolution cave map including passage dimensions that could be used for hydrological modelling. We split the cave into sections for survey according to our available gas. The RB80 team would lay the survey line to a depth of approximately 100m and survey from this maximum depth back up to 65m. Florian and I would survey from 65m up to the side passage that branched off horizontally at around 35m and then put in the jump reel connecting the main vertical line to the side passage for the third team to  survey. Unfortunately problems with the RB80s meant the entrance into the cave was delayed significantly. The way we’d planned the dive, with successive efforts making use of the previous teams lines meant this delay filtered through all the teams and we spent a lot of time twiddling thumbs and gazing into the pool.

Deco bottles on the line. Photo courtesy of and copyright Dražen Gorički.

With the time for our effort finally arriving, we dropped our O2 and 50% bottles on the line laid by the RB80 team and met them ascending from the shaft below at 21m. Following a quick confirmation that everything was in place below we continued down into the shaft. After a minor kink at 30m the cave becomes entirely vertical and just drops away below. The visibility here allowed us to see about 15m below us as the walls faded into the black void below. The shaft is approximately 6m in diameter and we were able to go into seemingly relentless free fall whilst the walls expanded and contracted around us. Finally, as we approached our maximum depth of 70m, we could just make out the break in the shaft below. Looking up, it was also possible to make out the glow from the opening way above. With nowhere else to go here we ascended slowly, investigating the passage walls as we went which were rocky, jagged and irregular. In places this gave way to sheets of erosion worn stone.

Reaching the arch that separates the side passage at around 37m we spooled off from the mainline, beneath the base of a narrow chimney that ascends vertically parallel to the main shaft and into the side passage. We had plenty of gas to press on so had a bit of a poke along the line here but, having agreed a rendezvous with the third team at the 21m stop after 45mins, we were forced to head back all to soon. The forty minutes of deco was pretty chilly but passed without event and we surfaced with big smiles on our faces (possibly because they were frozen in place).

The RB80 team checking in with support divers. Photo courtesy of and copyright Dražen Gorički.

Part three of the Croatia Cave Exploration Blog can be found here: Croatia Cave Exploration Day 3 – Radovjića

The pool at Vucovjića. Photo courtesy of and copyright Dražen Gorički.

After the previous year’s spectacular wreck trip with Maurizio at Krnica Dive in the Northern Adriatic, Florian and I were drawn back to Croatia in April 2011 by the lure of unexplored caves. Maurizio had teamed up with some researchers from the Croatian Speleological Society (CSS) to gain us access to some of the freshwater caves in the area around Knin. We set up our fill station in the pump house at Vucovjića which would also be the location for the first dives. Vucovjića is a relatively well known cave, for the first sump at least, however the spring melt in the surrounding mountains generates sufficient flow that any line laid in previous years is inevitably ripped out. The  CSS researchers had a number of studies planned in this cave for this season so the first job was relining sump 1.

From the surface this cave looks absolutely stunning and the azure blue easily rivals the cenotes of Mexico for tranquil and inviting beauty although the 6 degree water temperature makes it a little bracing by comparison! Crystal clear water gives way to inky blue as the rocky walls drop precipitously into the gloom below. Florian and I were first in and descended to the bottom of the outer pit, leaving our O2 bottles on a convenient ledge on the way down. A low archway leads into the cave proper with a strong flow exiting the cave. This is the narrowest part of the cave and consequently where the flow coming out of the cave is the strongest but once past we emerged into a reasonably large room. The whole of sump 1 is relatively shallow and this first room is actually the deepest point at just shy of 30m whilst the ongoing passage trends gradually upwards towards the airspace at the end.  The cave itself is very clean with white stone walls and a pebbly/rocky bottom. Again the flow has banished any silt and percolation is minor.

Sculpted Walls. Photo courtesy of and copyright Dražen Gorički.

We pressed on through large rooms connected by low arches or longer sections of conduit. Every now and then we reached points where it appeared we could tie in to an old segment of line but, invariably, this would only continue to the next tie off before the old line would end and we’d need to restart our own line again. In the end it proved quicker to simply keep going with the new line and mark the old sections for removal later. After 50 mins we hit turn pressure so tied off the reel ready for the next team before heading out. Riding with the flow in this direction we were back at the arch restriction and exiting the cave in no time. The quick exit meant we escaped having to do any deco as well – bonus!

In the afternoon two more teams took the line further into the cave and on into sump 2. Florian and I headed back in later that afternoon in order to do a bit of housekeeping and pull some of the old line from sump 1 whilst the RB80 guys were off ahead in sump 2. Not having to lay line against the flow we reached the end of sump 1 pretty quickly where there was a real mess of birds nested old line and loops floating up mid passage. We managed to clear the worst of it before hitting turn pressure and heading out again. This dive was slightly longer so we enjoyed a short stint on O2 in beautiful surroundings whilst the sun set on the world above. The beauty of the surroundings was put into stark context by the presence of the grenades observable in the outer pool, disposed of in the ‘bottomless pools’ by local militias during the fighting that ravaged this area during the mid-90s.

Decompressing as the sun goes down. Photo courtesy of and copyright Dražen Gorički.

Part 2 of the Croatia Cave Exploration Blog can be found here: Croatia Cave Exploration Day 2 – Glavas