Oxford University Cave Club
Proceedings 5 (1970)
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Pozo de Fresno survey: High; Medium: Low resolution
This cave is part of the Bolugo - Caldue˝in system at El Mazuco. Although its entrance is a large and obvious shaft, I doubt that it would have been entered but for the dismal weather experienced while we were in this part of Spain. The entrance shaft, although large, looks singularly unpromising and has been used as a burial place for all the nastiest dead animals of the village. In spite of this Jim Sheppard and I threw down 20 m of ladder and drew lots as to who was to descend.
I had the good fortune to lose, descended the shaft and, finding the refuse less unpleasant than anticipated, inspected the first of the two ways on. This was the route followed by my unwitting predecessors, and leads immediately to "spare parts chamber". The litter of bones made this a strangely desolate place, and there was no way on.
The opposite route quickly leads into a large dry passage decorated by crumbling stalagmite formations and a frosting of calcite. This passage soon collects a minute stream and widens into a bagpipe-shaped chamber, and it is here that the wonders begin. The floor of this chamber is a whole series of rimstone pools, and the walls are tastefully embellished by occasional large stal flows. On the roof are some very fine helictites. The lower end of this chamber leads to the 10 m pitch into the main chamber.
This pitch is curtained off by a collonade of stalactites, and this shields a truly wonderful vista. Towering up into the vastness of this chamber is a row of immense stalagmites, like a row of distillation columns in an oil refinery, the largest being some 12 m tall. Yet they seem almost to be lost, at the walls and roof remain out of sight. The floor of the chamber consists entirely of calcite, brown and dead in parts, but on the whole clean, white and glistening. As in the chamber above, the walls are only occasionally decorated, and the head of the chamber is curtained off by a stalactites collonade. Giant stalactites hang from the roof; they can be seen from the top of the pitch but are more or less out of sight from the bottom. The steep stalactite slope leads to a lower part of the main chamber; on climbing down we found that the water sinks to a mud floor and all possible ways on are blocked.
This lower chamber runs almost parallel to the upper main chamber and is older and more decayed. One has to climb over boulder falls and old stal flow, until eventually it peters out completely, once again behind a stalactite curtain. This is obviously the oldest part of the cave as it lacks the vitality of the other part of the system.
Leading from the entrance series is a second route, of which spirals downwards to a final depth of some 140 m. A short crawl leads to a 7 m pitch, beyond which the way bifurcates. One route leads to a pitch into the lower main chamber, while the other leads, via a rope pitch, into a small chamber. From this a magnificent 15 m pitch hangs free into the centre of a pear-shaped chamber, where a small stream is met. A steep stal slope, which needs a rope, leads to the head of a 35 m pitch.
This we called M÷bius pitch, because of the strange manner in which the ladder hangs. On the lower half of the pitch one climbs with one's back to the wall of in a veritable shower bath of water. Free the exit from this aven was blocked by a stalagmite barrier, which quickly succumbed to the hammer, but within a few metres the passage was again impeded, this time by a boulder, well cemented in with calcite. After a vain attempt to remove it, Jim Sheppard and I wriggled through the small gap left above. We soon reached a further 12 m pitch, at the foot of which we found ourselves in a small chamber, with no way on. The stream sinks through boulders, which might prove diggable, but it would be a mammoth undertaking. Returning, we found it much harder to get past the boulder in an upward direction, and we therefore named it the Shottky barrier.
All in all, this route formed a most satisfying trip, and used a large amount of our tackle, but it was a pity that a way through into the Bolugo master system could not be found. We calculate that the master stream runs some 200 m below the Fresno entrance shaft, so in the unlikely event of the connection being made it would make an exceptionally fine through trip. Even as it is, El Pozo de Fresno is a very fine cave, with something in it to suit every taste.