OUCC Proceedings 8 (1976)
Pozo de Vega el Forcau
by Bill Collis, Steve Tarran, Mike Cowlishaw
|OUCC Proceedings 8 Index|
The major objective of this expedition, this pot at 258m deep and 1.6km long is one of the largest systems so far explored in the Picos. It is very varied with both large and small shafts, smooth and spiky walls, wet and dry, clean and muddy passages changing character from Mendip to Yorkshire to Continental types. The destiny of the water last seen in the flooded shaft of the final sump is unknown and the system probably still holds many secrets. A worthwhile cave, but not to be taken lightly.
From the bar at Lago de la Ercina follow the W.side of the lake and follow the causeway to the foot of a gully, which is ascended to a hut by a stream. Follow the stream to the left and up to another hut in a damp, large, flat-floored valley, continue across the valley to the next ascent up grass to another hut. Here turn sharp right (S) and follow a good shepherd's path up grass, then rock over an impressive saddle to a col, where the Vega el Forcau is entered The pot is about 150m almost straight ahead, slightly to the right of some ruinous walls. The small entrance is identified by a rock with the letters SIE emblazoned in red.
The first exploration of Pozo de Vega el Forcau was carried out in August 1964 by the Speleo Club Alpin Languedocien. They discovered the stream sump at - 150m and then reached the top of the 8th pitch, where a scratched set of initials and dates was found this year. They named the cave Cento Cenal and did not return to descend the pitch until 1975, when they had only a vague idea of its location. Meanwhile a shepherd had shown the Barcelona group ESIEC the entrance in 1974 and their exploration reached the same point. At Easter 1975 the same group, despite a considerable access problems due to surface snow conditions, spent 35 hours underground, exploring and surveying down to the inlet before having to leave.
July 1975 was arranged for the next Spanish expedition to the cave and several English cavers were invited to join. In the end the arrival of the Spanish group was delayed and the English group determined to inspect as much of the pot as they could, in conjunction with the SCAL group (Montpelier and Lunel sections) also camped at Lago de la Ercina, searching for Cento Cenal. A 15 hour trip, - much time being spent bolting all the pitches for SRT - allowed exploration to proceed almost to the 8th pitch. The identity of the pot was not realised by SCAL, who continued searching for their pot 1 Renewed plans were made for a large Anglo-Spanish expedition in July 1976, but the Spanish informed the British contingent that they could not arrive until August. By this time bookings had been made so Forcau '76 became an almost entirely Oxford University Cave Club venture !
The entrance is a shaft of llm, about 1m across. A snow plug was found at the bottom in early July, but would probably have gone by August, A short boulder slope leads to the second pitch of 7m into a boulder floored chamber. A short traverse leads to a convenient point for rigging the 3rd pitch, llm, free. The next pitch (6m) follows immediately, two short climbs then lead to the top of Acrobat pitch. This was originally named because the positioning of the bolt to ensure a free-hang necessitated certain acrobatics at the pitch head, the name was later Justified by the antics performed penduluming into an opening a short way down the shaft. The cave opens here into a very impressive, airy shaft landing in a chamber sloping down to the 6th pitch, which is in 3 sections (totalling 37m), and lands at the foot of an aven with water falling into a pool in which it sinks. So far the cave has been dry, with walls encrusted with powdery cave popcorn, but the foot of the 6th pitch reveals brecciated rock and the next passage contains much fill.
A loose and rather muddy section of passage with occasional small chambers leads to a light and spiky rift, the stream joins the passage at floor level, which is too narrow for progress. Traversing is possible at various levels, only one of which gives easy access to the 7th pitch. This is a 7m drop and is best laddered, it is tight at the top but opens out into a pleasant stream chamber, with a cascade upstream and a narrow winding, pleasantly clean passage downstream. A climb over a rock fall heralds the next stretch of passage, possibly developed in dolomite which has given rise to an awkward, spiky section of cave with occasional rock bridges. Near the end of this, a short duck enters a small chamber with what looks like an inlet sump underwater. The succeeding stream-way is superb - clean, scalloped walls gentle winding, about 1m apart. The cross section then becomes less simple and climbing out of the stream gives access to the oxbows. The stream carries on to a series of low ducks before it sumps.
The oxbows form a figure-of-eight, the two small passages to the S are about a metre lower than the larger, typically phreatic sections to the N. The walls are covered with mud and several fill stages are evident in pebble and mud deposits, some slumped and some calcited over. A single dry passage leads back to the streamway, emerging about 4m above the floor of a narrow rift, midway between a sump and the lip of the 8th pitch. This dry passage has a small slot in its mud floor cut by a minute trickle of water. The 8th pitch can be rigged dry by climbing into an oxbow to the left of the stream at the pitch head. The chamber reached by this forms the head of a 37m 85 sloping pitch, which is very pleasant. Climbing over some rocks at the bottom into a sloping rift, where a handline is useful, leads to the final pitch of 8m. Varied, sporting passages continue the route, usually with smooth, scalloped walls and frequently in sloping rifts. Progress is made mainly in the stream by walking, climbing cascades and occasionally by crawling. At one point the stream route is impassable and a traverse is necessary to attain an oxbow which regains the stream. A chamber with notable fill deposits marks the inlet, which has a small stream originating in the several avens at the end, some of which have well decorated grottos near the bottom. The passage to the sump provides easy walking, there is evidence of several different water levels in its numerous false floors at different levels on the passage sides and a stalactite immersed in water to a depth of 30cm in a deep pool. The passage then narrows and steepens, a final cascade entering the sump chamber. This has a clean flat floor with about 10cm of water all over, except where the vertical, fluted walls of the sump disappear downwards for at least l0m. There is a small perched sump giving a second inlet to the sump chamber - this appears to be short, air having been felt with feet, but the dive would be very tight and extremely cold.
No water-tracing has been done, to our knowledge - in this cave, and so the resurgence is unknown. Bearing in mind the general trend of the cave, it seems fairly likely that it may resurge in the Rio Pomperii.
All cavers on the expedition were involved in carrying out the survey at some time, in all 1569m of passage were surveyed with a vertical range of 258m. Closed loop errors were 1.3% comparison with the ESIEC survey supplied to us in 1975 is very interesting:
It appears that the surveying techniques used, at least in part, by the ESIEC were certainly capable of producing results as good as, or better than, ours. However, faulty and/or imaginative drawing together with inadequate surveying in the lower (admittedly arduous) reaches of the pot unfortunately casts doubt on the entire survey (and hence, by default, other similar surveys).