Cala Luna Exploration 2019

Cala Luna 2019: Cave Exploration in Europe is Alive and Well

I have often heard that exploration of flooded caves in Europe is over, and I smile. In fact, the reality is quite the opposite. Though it is true that easily accessible caves have been largely explored, more complex systems with challenging logistics remain to be explored by determined divers who are undaunted by the challenges involved. 

Sardinia is home to one of the most interesting caves in the region: Cala Luna. The aquifer beneath the eastern Supramonte Plateau (which includes the caves Su Palu, Su Spira, and Su Molente, which is connected to Blue Marino) discharges much of its water into the sea through multiple springs, with Cala Luna receiving a large volume of water during heavy rain and flooding. Dye trace experiments by local cavers have shown that inland cave systems connect to both the Bel Torrente cave system and Cala Luna, though these connections have not been confirmed by divers underground.

Over the last 10 years, concerted efforts have been made by local cave divers to explore the inland cave of Su Molente. This ongoing effort requires more than 20 Sherpas to carry equipment to the water’s edge, located in a dry and relatively narrow cave. Having helped in ferrying equipment on one occasion, I can attest to the daunting logistics and physical labor involved. Their efforts have resulted in an exploration total of 2,750 m (9,022 ft) of conduit and eight sumps. This includes both dry and flooded conduits with multiple sumps. The cave system continues to head towards the eastern coastline of Sardinia, in the direction of Cala Luna.

Cala Luna discharges by the sea and was explored and mapped 10 years ago; the survey, including a complete and detailed map, was made by the Czech team led by Daniel Hutnan. Unfortunately, despite sometimes presenting a strong flow that makes it impossible to dive, Cala Luna is characterized by increasingly smaller passages with complex navigation, multiple restrictions, and collapsed areas. As a result, explorers looking to connect to inland cave systems have failed to find the missing lead. The geology of the area is quite complex, as the Supramonte Plateau is characterized by multiple fractures and joints running both north to south and east to west. These elements combined make it difficult to find the connection between the inland aquifer and coastal springs.

In the summer of 2019, while cave diving recreationally in Sardinia with my friends Rob Neto, Olivier Bertieaux, and photographer Laurent Miroult, Rob accidentally discovered an interesting and unexplored passage by getting off the line on one of our dives in Cala Luna. Despite a tricky restriction, we found ourselves reconnecting to an existing line: a classic bypass tunnel. After the dive, we discussed the flow changes, specifically a section of the cave where the flow changed from upstream to downstream; we had reached the end of the mapped section of Cala Luna. 

The next day, with a plan in place, Rob quickly found a promising lead in a collapsed area at the end of the mapped section. However, we were unable to make our way through it; truthfully, I was relieved as I had concerns about the stability of the passage. About 30 m (100 ft) further and in shallower water, we approached the edge of the collapse where Rob found a vertical crack in the middle of two solid, sheer, white slabs of rock. Though the crack was far too tight to go through with our cylinders, this was an obvious continuation; we observed the flow and ripples of moving water a few meters into the restriction. My only disappointment was that Rob had to leave the next day.

In the following weeks, Stefano Gualtieri and I checked the lead again on a couple of dives to assess the feasibility of safely moving through the opening discovered by Rob. In the end, we realized the only option was to go no-mount, something I had sworn I would never do. However, considering the shallow depth, the crystal clear water, and the fact that the restriction was a simple and long corridor, I finally convinced myself to do it.

The first time we went through the restriction we ensured we were able to go back. Given the choice to use no-mount in a never-before-accessed restriction, safety for myself and my dive companion was of utmost priority. 

Continued exploration was facilitated by the fact that I was in Sardinia the entire summer and in possession of exceptional dive partners. After Stefano departed, I was joined by Mauro Bordignon, who had just arrived in Sardinia for the first time. As I knew Mauro and his sidemount experience, I was confident he would pass through the restriction without a problem. Once we were both on the other side, we could gear up in a relatively small room that lies between a pile of collapsed white boulders and a wall of light brown rock. 

I was still apprehensive about going through a restricted area decorated by stalactites and flowstone, but my apprehension vanished when I saw the wide conduit that beckoned to us. Once through, we made our way west towards the inland systems, with the cave ultimately dictating our direction. As we moved through the cave on our first dive, depth remained shallow for the most part. The cave morphology and wall colors changed abruptly and continuously, and we made our way past canyons and a beautiful bedding plane. As we continued, ripples in the sand suggested that there was flowing water through this passage and the likelihood of large passage upstream; though emptying the reel was definitely not what we expected on this dive, the game was on.

In the ensuing month, Stefano, Mauro, and I dived the cave, and specifically this passage, about six more times. We experienced both enthusiastic moments with multiple reels laid and unproductive dives where the lead was lost. The diversity of this cave was amazing, as it changed from shallow, restricted, and silt-free to about 15 m (50 ft) wide at 30 m (100 ft) of depth; a mixture of sand and tiny gravel covered the bottom of the phreatic cross section. Big passages led to rooms with apparently no ongoing passage, and smaller conduits led us inland and to open passages. This pattern repeated a few times throughout the cave. 

On one of our longer dives, we reached the end of an open section, where going forward led to a silty restriction and to the left, there was only a collapse. As we poked around, we found multiple areas where we could surface, so we checked the dry parts hoping to encounter other sumps. One of these areas specifically grabbed our attention. After surfacing and climbing on a sandy slope, we continued about 200 m (656 ft) into the dry passage and found an oval-shaped passage where the flow of water must have been substantial; following the carved rock and perfectly and evenly shaped turns of the conduit, we abruptly entered a massive room with incredibly shiny and smooth rocks. As we made our way, we came to a drop beneath that was crystal clear water—actually, quite far below us. This meant we needed rope and single rope technique (SRT) caving gear.

The following dive was exhausting yet hilarious; after passing through the restriction with two stages per diver and a dry caving bag, installing the rope in the dry section, lowering down gear, and gearing up, we found ourselves almost on top of the line we laid the previous days. Unfair.

As with many European caves, what poses the greatest challenge to the explorer is not the fact that there is a restriction but rather where the restriction rests, as it is many times a fair distance from the entrance; in this case, it is about 600 m (1,970 ft) from the entrance. This required a team of divers able and willing to carry safety cylinders, stages, DPVs, and extra stages and caving gear across the restriction.

In the end, we managed to explore and survey more than 1.4 km (0.9 miles) of underwater passages as well as some short, dry sections. 

Decompression here was not an issue. Even though dives were as long as seven hours, shallow depths rendered decompression manageable. The only variable that needed careful management was coordination with the boat and surface crew, as they provided access to the cave. Weather and sea condition changes required efficient communication between divers and surface support. This resulted in a plan of a 6-hour dive time and the staging of two mobile phones in a predetermined location in the event of worsening weather and team separation.

This year, the Phreatic Project, which we we conduct annually in Sardinia, will include at least two or three weeks in Cala Luna. Continued exploration of these caves is necessary, and hopefully, we will locate more signs of flow to help us find ongoing leads. We also intend on dedicating our efforts to creating a complete map of the newly discovered branches. Ultimately, we hope to collaborate with other groups in Sardinia to combine the information we’ve gathered and finally unveil the mysteries of this stunning and complex underwater maze. 

By Andrea Marassich

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