An Expedition to the Picos de Europa (Tresviso 1979)

by Mark Sefton

Originally appeared in Caves and Caving No. 9

In the summer of 1979, a group from Lancaster University Speleological Society, reinforced by several members from K.C.G., U.L.S.A., C.P.C., Bristol University and S.E.I.I. (from Madrid) returned to the eastern massif of the Picos de Europa in Northern Spain, our fifth expedition to the area in a many years. Our short term objectives were to continue exploration of La Cueva del Agua, an 11km long resurgence cave at the bottom of the Urdon Gorge, below Tresviso, Marniosa, a 2km system further up the Sobra Valley and likely feeder to Agua; and the deep systems among the high peaks. Ultimately, we hoped to connect one of the sinks in the high peaks to Agua which would give a through trip over a vertical range of 1,300-1,500m or even greater.


As in the previous two years the expedition was split into two groups, a bottom camp situated at Tresviso to continue work on "Agua" and "Marniosa", and a top camp whose task was to explore the numerous surface shafts, mines and deep systems in the area. Some cavers alternated between the two camps.

In spite of four weeks of continuous caving from underground camps and a dozen leads from 1978, no major breakthrough was made in Agua. The leads either closed down or else went round in complex 3-dimensional loops. Nearer to the entrance, a promising bolt and peg climb to a black hole 20m above a perched sump ended when the passage at the top split into numerous tubes too small to squeeze into. The only promising lead still to be checked out is through the perched sump which could be drained, either by syphoning or by "chemical persuasion".

In Marniosa, a further 1,300m of passage was explored and surveyed. Attempts to by-pass the downstream sump in the main streamway by traversing at various levels were unsuccessful, although a breakthrough in this area in the future cannot be ruled out. Upstream, the 2km long streamway ended at a 60m aven inlet with two other avens nearby. Rather than begin the daunting task of a long bolt and peg climb, the Marniosa team began exploring the surface in the vicinity of the upstream terminus. Several small caves were entered and explored but none connected with Marniosa.

The top camp was considerably more successful. Enthusiasm for the area was high after the previous years success in pushing Sara to a terminal sump at a depth of -635m (ed. -578m) below the Sara mine and -701m below a higher level entrance. The whole area is littered with numerous shafts and abandoned zinc blende/galena mines. Most of the natural surface shafts are blocked at the bottom with rubble or snow plugs and the majority of our finds in the area were entered where mined passage intersects natural cave. This year's initial objectives were "Boulderosa", entered via the Boulderosa mine whose entrance was only 50m from our campsite; and "56", a good hours walk away.

Boulderosa was first entered in 1977 by several cavers from Whernside Manor who had joined the expedition that year. In days gone by the miners had presumably decided that it was easier to dump their rubble down a "bottomless pit" off the side of one of the main passages rather than carry it all the way to the surface. The result is an entrance rift packed with dangerously loose boulders, giving the cave its name. In 1978, members of L.U.S.S. and Spanish caves from S.E.I.I. reached the bottom of this rift which turned out to be 120m deep. With nine bolt changes on the way down and a variety of takeoffs, it provided excellent SRT practice for expert and novice alike. At the bottom, a second and much tighter rift led after 30m to the head of a 43m pitch which could only be reached by traversing above the floor. Below this pitch, another 120m of thrutching and traversing lead to a 14m pitch and climb down into a chamber with an aven inlet and, according to the Spanish team, a "duck" at the far end. That year's expedition drawing to a close, no further pushing was done and the system was detackled.

Last year, after several trips, the known limit was reached, initially via a different and much harder route which dropped down the aven inlet into the chamber just before the "duck". With the general water level being somewhat lower than the previous year, this turned out to be nothing more than a hands and knees crawl through a few centimetres of water and was instantly named "Donald Duck". At the far end, an 11 metre pitch onto a wide ledge was immediately followed by a very impressive 49m pitch into a large chamber. Following the stream with several climbs and pools, we continued to the head of a 43m pitch (not 53m as marked on the survey). This dropped into a massive chamber, over 50m across, the entire floor being littered with huge boulders. Despite several determined pushing trips no way through the boulder choke was found. The final depth from the beginning of the entrance rift was -313m.

Meanwhile, the exploration of 56 was continuing with greater success. The cave was first entered in 1978. A fine free hanging 122m entrance pitch down a dry shaft (Tigger's Pitch) had led us to "Fool's Blend Passage", a series of small chambers and passage amongst what our resident amateur geologists had assumed was high grade zinc blende until Pete Smart from Bristol University informed us that it was in fact a mixture of clay and calcite. At the far end, a 47m pitch into a large and impressive rift was followed immediately by a 17m pitch through a hole in the floor down to where the rift became small awkward. After 20m of traversing, the passage branched, one way leading to a small downstream sump. The other branch ended with a short pitch into a small chamber which we were told was far too dangerous to descend due to several large and very loose boulders at the top. These were thoughtfully rumbled on the detackling trip.

In 1979 some of us were determined to go and have a look at this chamber, subsequently named the "Abbattoir", which was entered via a slot at floor level and 4m pitch. On the opposite side of the chamber, as luck would have it, the rift continued. 120m of traversing above the water brought us to a 14m pitch back down to the streamway. The passage quickly developed a reputation for destroying caving gear. Three boiler suits were ruined in as many trips and a brand new Enduro suit was shredded beyond repair after four. Tackle bags and Petzl suits faired little better.

On a subsequent trip, two gallons of Rhodamine concentrate were added to the streamway which begins at an inlet into the Abbatoir. Two weeks of drought did nothing to help move the dye along and we spent many a trip caving among little pink waterfalls and cascades. Then, after two days of torrential rain, the dye was visible in the main streamway of Agua, 1500m below.

Beyond The Slasher, the rift continued, interspaced with several large chambers and pitches of 12m (The Ramp), 31m and 23m (Pink Pitch). At the bottom of the" Pink Pitch" the stream flowed along a tube and down another pitch which could only be hung in the water. 5m down and under the full force of the water, a precarious pendulum brought us onto a sloping shelf and a further two pitches, one of 14m and the second, reached by climbing up in the rift just before the "Pink Pitch" was discovered on a subsequent surveying trip and it seemed a much safer bet. This turned out to be a spectacular 142m shaft with a wide ledge 118m down and the water from the streamway entering from an inlet near the bottom. Excitement among the top camp personal rapidly turned to disappointment when the next party reached a sump at -494m. However, we still have some leads to go back to in 1980 and "56" is by no means finished yet.

Another major success in 1979 was Tere which, like so many other caves in the area, was entered via a mine. The entrance had been discovered in 1977 but as it was tight and wet and there being some more interesting caves to explore at the time, it was not pushed further. During the first few weeks of the 1979 expedition Boulderosa and "56" took up almost all out tackle, over 100m of rope in all; so much so that when Boulderosa ended at the terminal chamber, we were down to our last couple of ropes and contemplating detackling one system so that we could continue the other. Once these two systems had been detackled we were able to turn our attention more fully to Tere which at that stage had been extended through a long and tight crawl and down pitched of 17m, 9m and 32m to a 4th undescended pitch. Another three pitches brought us to a breakdown chamber (Pebble Hall). There were two ways on, a flat out crawl with the water and a large dry high level route. During the next few days we extended the system by a further eight pitches, ending at a tight rift with a 20cm squeeze in the middle at -342m. Beyond lay a 146m deep shaft broken by several ledges. The squeeze severely limited the manpower available to explore the bottom end, several fruitless hours being spent trying to batter away the rock with a bolting hammer. Time for the expedition was running out and there could only be one more pushing trip before surveying and detackling took priority. Two cavers went through the squeeze and reached the bottom of the shaft. There was no way on, the shaft, surprisingly, closed up to an impenetrable crack in the floor and this route, at any rate, was finished at -487m.

The other discovery of note in 1979 was made by the Spaniards from S.E.I.I. who entered the main shaft of Sara from the top via another high level route also beginning in the Sara mine. This extended the depth of the natural cave from -635m to -848m. (ed. Sara turned out to be -578m) At -230m deep, the main shaft must be one of the worlds more impressive drops.

Perhaps the most notable achievement of the expedition was the film made for the BBC by Chris Baxter (cameraman) and Nick Airey (sound) based on the exploration of Agua and Tere. They were rewarded for the limitless hours of work they put in both above and below ground by winning the Mick Burke award (part 1, part 2) for 1979.

And what of the future? This year a group of us will be returning to the Picos. There are still several leads in "56" and the tight passage where the water disappearing in Tere wants a good push, as do one or two possible high level routes. Marniosa has by no means been worked to death and who knows, maybe several kilometres of passage lie beyond the perched sump at the end of "The Road to Certain Death" in Agua. So far we've explored nearly 200 mines, shafts and caves in the area including over 60 in 1979 alone and there are a large number more still to be looked at. Really, there's no limit to the things still to be done.

A full account of the 1979 expedition, including surveys, photographs and cave descriptions may be found in the L.U.S.S. journal "Tresviso '79, An Expedition to the Picos de Europa, Northern Spain 1979".