Oxford University Cave Club
Proceedings 5 (1970)
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J G Sheppard
Length - 400 m (approx)
Height - 16 m (very approx)
La Boriza survey: High; Medium; Low resolution
This is a resurgence cave upstream from the Cueva de Bolugo. It is situated at the foot of a large, heavily vegetated cliff at the end of a dry hanging valley. A medium sized stream, one of the two main feeders of Bolugo, flows from the cave; this is the Arroyo Bolugas proper.
The cave was fully explored over a period of a week or so, about five separate trips being made in all. All of these were made in more or less flood conditions, as water levels in the area were, according to local information, abnormally high for the time of year. The entrance is about 10 m high, and a wade of 20 m leads to the first cascade (2 m) immediately followed by a second cascade (3 m). An alternative high level route in the roof to above the second cascade is possible, but there is no means of descent back into the stream passage and the rock is extremely slippery. On the roof and walls above the second cascade some rather beautiful months were observed.
A fine meandering stream passage then leads to a large which chamber, which can also be reached via a dry oxbow. The water enters from a passage high up in the roof, strikes a step about 5 m down and then sprays out in all directions, so that it is impossible to keep dry anywhere within 4 m of the pitch. Owing to all this water the chamber is extremely noisy, and communication is difficult. A climb up to the left into the roof of the chamber leads into a bedding plane which seems to lead back to the stream passage above the pitch, but the crawl closes down so much that it is impassable. A traverse to the right appeared more likely to go, so we attempted it and after about two hours of pegging and a few hairy moves we reached the top of the pitch and rigged a ladder. If hung straight down, the ladder would have given an extremely wet pitch, so we clipped it to the pegs in the traverse and used it as a handline cum footrail.
The stream passage above the pitch is smaller than that below, and the water deeper. A twisting passage full of deep holes, some of which require swimming across, leads to a double cascade after about 70 m. There were several dry passages leading off in the roof, but all of these turned out to be oxbows. A small inlet passage was found to be impenetrable. The stream passage is almost completely devoid of formations, apart from occasional stal flows, and this was found to be the case in the rest of the cave as well. The rock itself, however, is quite interesting, ranging in colour from black to light brown with many quartz veins in it.
The double cascade (7 m), the last part of which is vertical and only just climbable, then leads to the final part of the cave. The passage widens considerably above the cascade, the stream gradually deepens and after up 40 m, sumps. We free-dived the sump as it was only about 0.5 m long, and found ourselves in a large airbell (5 m). The second sump was not attempted, as we could not feel an airspace on the other side. The water in the sumps is superbly clear, and it is possible to stand on one side of the first sump and see the feet of the person on the other side. An exceedingly rare occurrence in British caves!
Coming back after driving the sump a wet passage of to the left was noticed. "Aha, a sump bypass!" We thought, but no such luck. The passage goes up and along in the right direction, first over shingly sand and then mud, but finally degenerates into a 3-dimensional maze of passages which all close down and are impenetrable. A very strong cold draught blows through all this passage, and at the extreme end the air definitely smelt earthy, so it is our opinion that at this point the surface is very close, possibly within 10 m or so. This would certainly fit in with our above-ground observations as the Arroyo Bolugas sinks in a boulder choke not too far above the cliff face from which it resurges.