The Plura river disappears between the rocks to appear again some
3 kilometers downstream; this is the site of the Plura cave system.
The maximum depth and length of this system is still unknown. In
the 1970 a hydro plant was built on the site and the flow have since
seized. Before the hydro plant blocked the flow it was so strong
that locals have reported a water pillar 3 meters in height at the
spring. This suggests that Plura is a very extensive cave system.
Plura has been dived quite a bit in recent years with cave divers Vebjörn Karlssen and Nils Eldeby being the ones with the most dives in the cave. Together with the Norwegian dive team, NTD, they have also installed the expertly placed main line and explored large pa
rts of the cave. The goal with the
Ocean Discovery expedition was both video documentation and if time
allowed also exploration.
Exploration of this cave would prove, as expected, to be quite hazardous and complicated. The ice-cold water means that the divers faced the risk of freezing to death in case of a flooded suit. Some of the passages were also extremely silty and narrow. Some of these tunnels were inappropriate for scootering so the fast Gavin scooters could not bee used for parts of the dive. The cold water limited the time the divers could stay immersed so speed was of essence.
The cave begins with a rather narrow entrance. It then widens to a massive tunnel 10 m in height and 20m in width. This tunnel continues for about 450m and has several small side passages, some still unexplored. After 450m the tunnel becomes partially dry and continues an additional 400 meters. At the end of the main tunnel 950m in to the system the cave has collapsed and blocked the passage. At this point a smaller tunnel leads down to deeper regions of the cave. This smaller tunnel is winding down and gets smaller and smaller. Mounds of silt rest on the floor and in some of the tightest restrictions avoiding silt up is difficult. After about 100m the passage widens up to a big room. At one end of the room a hug
e tunnel leads down, slowly going deeper. This tunnel begins at 25m depth and the end is unknown. This is where the actual exploration took part. Previously explored to 57m by NTD, Ocean Discovery divers would attempt to push the line deeper and further in to the mountain.
A cunning plan
There were several logistical problems to be solved to conduct this dive as safely as possible. The team knew that the deep tunnel was at least 60m deep. Any diving deeper than 40m requires the use of Trimix as breathing gas. The depth of the passages leading to the deep tunnel was only 34 meters. A dive plan that was both safe and as simple as possible was required. The plan was to use a single stage bottle for the entire 950m long main passage swim and return. A mixture of 30% oxygen and balanced nitrogen was chosen. The use of a stage bottle rather than breathing the back gas enabled the divers to explore the deep tunnel with a completely full gas supply in the twin 15-liter tanks. Breathing Nitrox on the shallow part of the dive also gave an edge on decompression. The back tanks was filled with 16/45 Trimix and the maximum depth of the dive was set to 80 meters. Speed was of out most importance as the diver could only endure a limited time in the cold water. No setup divers qualified or equipped to carry deco gas in to the deep part of the system was available nor did the exploration team have time to do setup dives them selves. This meant that the exploration team had to transport the deco gas on the same dive. To improve speed and simplicity a single 7 liter deco bottle containing pure oxygen was carried. The deep parts of the deco were to be performed on back gas.
Everything went as planned on the way in to the deep section. The scooters were left before the restrictions at the end of the main passage. The Oxygen bottles were left on 9 meters and the divers carefully made their way down towards the deep tunnel trying their out most to avoid stirring up the silt. Some of the restrictions were so small that they had to squeeze trough. Finally in the big room the divers swam down in to the deep tunnel adding line as they went. The tunnel remained big and slowly went deeper and deeper. At some stages the floor was covered with small stones similar to aquarium stone. The visibility was unlimited and huge boulders were strayed around the floor. This was a truly impressive sight. After a swim of over 200m the divers approached the planned max depth of 80 meters. At this point the tunnel
seemed to level out, not increasing in depth. There
was no sign of the tunnel getting smaller, indicating that the tunnel
continues a lot further.
The line was tied off and the divers slowly commenced the exit. Approaching the big room again large puffs of silt came from the roof, completely destroying the visibility. At a quick glance it looked like rocks falling from the ceiling. This was however probably caused by heavy rainfall on the surface. The team proceeded by touch contact being careful not to lose the line.
The rest of the Trimix dive was uneventful, everything went as planned and the relatively short deco was carried out without incident.
A serious problem
On the way out, 10 minutes from the exit, one of the divers managed to rip a hole in his dry suit. A sharp stone had cut a large hole in the right leg of the suit. The suit flooded almost immediately. A human will not survive for a very long time in 5 C cold water. Expected time of survival in this temperature is between 20 and 30 min. Luckily the diver was using a DUI thinsulate undergarment that is designed to keep some of the warmth even when wet. This proved to help keeping the diver a little warmer. The unlucky diver managed to exit the cave without any serious injury. A slight hypothermia was all.
Text and pictures Ingemar Lundgren