On the occasion of the celebration of the International Year of Caves and Karst, the Portuguese Speleological Society – SPE started, on the 6th of June 2021, day of the celebration of the International Day of Caves & the Subterranean World, a series of events that will last until December 2021. These events are destined to the general public and specially to the teaching community.
Cave diving in Moinhos Velhos-Pena-Contenda System in the summer of 2009
Written by Luís Magro
On August 2nd we began a series of 7 dives with the basic aim of better understanding the flooded area of the Moinhos Velhos-Pena-Contenda System. It took 2 months of hard work equipping vertical shafts, pumping sumps and transporting gear over nearly 1 km (0.6 miles) of dry cave.
The first dive
For the first dive we had several immediate objectives:
• The last dive in this sector was 18 years ago, so we needed to check the condition of the line; • Get to know the gallery already explored and identify possible leads; • Get to intersection recorded in the survey map; • Start exploration of the tunnel that heads south based on the available survey data.
This first dive began with laying line from the built platform (the water level is about 10 meters down a vertical shaft, so a platform was built at water level), because the old line was broken. However the old line started at - 9 m (near the bottom of the shaft) and continues without interruption up to 120 m of penetration. The line is continuous and is in good condition, it is not necessary to be replaced.
The shaft from where we started our underwater exploration (Poço Final – Final Shaft) is about 10m deep with a sand bottom. From the moment we leave the pit and enter the gallery the cave morphology changes significantly. The walls are quite smooth, white, and there are several fallen blocks. The floor has a lot of sediment which easily becomes suspended.
On the way up to the limit of the surveyed area, we note a passage on the left side which was later found to be going north and connecting to the area of Rio Negro.
After 120 m (390 ft) of penetration we arrive at the intersection, and find that the main line is placed through the left (North) tunnel. The tunnel we were looking is on on the right. There is a T on the main line that leads South to this tunnel.
We placed a marker on the main line and started entering the tunnel. Once we entered we found the original reel from previous exploration. We decided to remove the reel and the old line and start remaking the penetration T with new line.
The cave once again changes in appearance. It is now a forced pipe with a diameter of about 1.5 m (5 ft). It´s almost impossible to do tie offs. The cave now is bit like a serpentine and because of its size requires an additional effort to progress, even though we are following the almost unnoticeable flow.
We turned the dive on gas just as we reached our MOD (30 meters) for this dive. The cave continues with general direction south.
The way back is painful. Although the flow is very weak, the size of the cave makes it difficult to get a smooth kick in.
We left the water still with enough gas to go back in to shoot some video.
On the following dives the distance explored within this tunnel grew and the number of stage bottles and dive time too. The logistics difficulty of each dive increases dramatically, and on last dives each diver was using 4 stage bottles (S80) and 1 bottle of deco (S40). The transport of 10 bottles, clothes and batteries through the dry cave was only possible due to the outstanding team that is the SPE, who over 3 months of exploration had the support of 30 members.
On the last dive we re-surveyed the new gallery, and shot some video of it. This dive lasted 3h10m, with a maximum depth of 47 meters (155 ft). The survey was completed to the end of the forced tunnel. There we found a crack that takes us back to - 35 m (115 ft) and this new gallery now looks like the dry cave we left behind. The cave continues, and now with our bubbles causing percolation that blinds our way back.
Data from dive 1:
• Day: 02/08/2009 • Start Time: 17h55m • Maximum depth: 28.4 m • Time: 55 min • Water temperature: 16 º C • Gas for each diver: 2x12L (21/35) + 2 S80 (32%) + 2 S40 (O2) on the surface • Divers: Ricardo Constantino (survey) and Luís Magro (line) • Surface Support: Ricardo Nogueira, Antonio Sobreira and Simone Constantino
Data from the 7th and last dive:
• Day: 29/08/2009 • Start Time: 15h16m • Maximum depth: 47.1 m • Time: 3h10m • Water temperature: 16 º C • Gas for each diver: 2x12L (21/35) + 4 S80 (21/35%) + 1 S40 (O2) • Divers: Delfim Machado (survey) and Luís Magro (video) • Surface Support: Ricardo Constantino and Piotr Gajek