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The Arrigonyena System
A considerable part of the 1975 Expedition's work was devoted to this system, in which we have now found and surveyed nearly 4km of passage. The system has a vertical extent of 80m at the moment - this includes a high aven at the highest point - and has a potential of 600m+. In over a dozen trips into the cave we succeeded in exploring all the open passages, but we retain hopes of extending the system, especially downwards. These possibilities are further discussed at the end of the article.
The entrance has been known for many years, being a remote rock shelter originally the scene of archaeological, not speleological, activity. In the summer of 1971 an archaeologist exposed a small hole from which a great draught blew. ARSIP were informed of this and investigated, returning with tales of pitches and streamways, and, boulders raining from the roof. We were asked to fully explore the system in 1972: it proved larger than we expected, necessitating our return this year to complete the work.
This area of the Pyrenees is one which has undergone tremendous geological upheaval. The angle of the bedding can change from horizontal to near vertical within yards, and the character of the system is consequently quite different from that of the Pierre which is only a few kilometres away. The area is still geologically active; in the 60's most of the village of Arrete was razed to the ground by earth tremors. Perhaps because of this the limestone around Betzula is shattered to a frightening degree. Not surprisingly many of the larger passages have boulder floors, and collapse has often obliterated their original shape.
Neglecting all the local variations in the bedding of the limestone, the system could be said to lie at the bottom of a syncline. The axis of this runs ESE, ascending slightly, towards the Spanish border, and under a hill which rises several hundred feet above the cave. Most of the passages trend (upstream) in this direction, and their extremities lie beneath a dry valley, running down to the NE behind the hill. A fault (along the main passage) is in the bottom of the syncline, running ESE, and the major joints are parallel to it. There are minor joints prominent in three places in the cave, orientated NE - SW. The known cave is almost entirely phreatic in origin, with extensive collapse and very little vadose modification. A large glaciated valley lies in front of the cave, and originally Entrance Passage and Lower Bear Passage would have been phreatic drains, via the entrance and Suicide Crawl respectively, resurging in the then valley floor. We conjecture that drainage along the minor joints was to the NE.
We had hoped to publish a copy of the complete survey, but the whole is far too big to reduce photographically to the required size. We include instead a schematic diagram of the cave to explain the description of the cave that follows. Parts not described below were detailed in last year's Journal.
(a) From Collapse Chamber,
This large, bouldery chamber had been entered the previous year and is the beyond of the ascending boulder-choke at the end of Lower Bear Passage. This part of the cave was known, from the survey, to be approaching the surface, and was deemed worthy of further investigation. Downstream the chamber chokes; upstream (back under the high level) it also chokes, at a point less than 10m from and at the same level as the Lower Bear Passage choke. A traverse to the left of the chamber (performed by Pete on three very shaky pegs after an ample amount of gardening) gives access to a 6m pitch onto a suicidal boulder slope. The passage continues for 80m, the last 12m being flat out over very mobile boulders (Suicide Crawl). Unlike a decent English or Welsh boulder ruckle this more resembles a pile of crushed roadstone. Pete pushed his way into it as far as he dared, and when attempting to return found that the passage had moved up through the boulders. The draught here is very strong, and a rough plot of the survey data showed us to be very near the surface, so the hillside in this area was searched and a draughting hole found. The survey's link to within a few feet; it is certain that the two are connected but we had no inclination to dig it through. It seems probable that the cave bears of Bear Passage entered the system by this entrance.
This is the upstream section of the large decorated passage that runs down to Collapse Chamber entered via Frenchman's Creek. Here the phreatic nature of the passage is clearly apparent, both upstream and downstream sections having the same tilted elliptical cross-section where they join, but the upstream passage has half the dimensions of the downstream. There is a small stal cascade to ascend to Lothlorien, which consists of 100m of very finely decorated passage terminating in a blind 3m pot.
Main Passage is on a fault with a throw of about 6m all the way along. Because of the vertical weakness, the phreatic passage that formed did so over a large vertical range (at least 50m) and often has a series of levels. Not all of these are everywhere reachable; and we quite probably have not found the full depth of the passage. Main Chamber was formed by the sideways collapse of Bear Passage, which runs on a shelf on one side of the Chamber into Main Passage. Main Chamber measures 25m across the two passages, and is almost this high on the Main Passage side. The line of Main Passage is continued downstream in Entrance Passage, and also in a low, collapsed passage underneath it below floor level in the chamber. A complete roof bedding has peeled away and lies in a shallow V on the floor; descending beneath this, everything is choked, but last year, in wet weather this was one of the points in the system at which water could be heard beneath the floor. This passage is lower than any point reached in Main Passage.
A cross joint enters in one corner of the chamber, and probably had considerable influence on its formation. A continuation is evident 10m up this corner, and was climbed to by Steve E-S, William and a couple of pegs; a further very muddy 3m climb gives onto a slope of muck and boulders ascending at 40 degrees. At the top of this one is on a level with the roof of Main Chamber, and at the bottom of a 10m aven. The passage ahead is sealed with clastic fill and overhangs. Although there is a very inviting black hole overhead, the most climbable thing is the vertical wall to the left, a prospect which completely deterred us. We conjecture that a passage continues on this joint, which is that on which the Large Chamber a Long Way from Anywhere is orientated - possibly the passage continues over Main Chamber as well. The passage ascending the muck-slope has a solid arched rock roof and might have been a phreatic downtube draining the upper passage into the main (phreatic) drains below.
Proceeding from Main Chamber, Main Passage is at first high, with some low ascending beddings on the left, but the boulder floor ascends until a 10m blind pot is reached. Skirting this, a 6m climb takes to a higher level; here the rift is narrow and heavily calcited, some of the deposits being very soft and powdery. Looking back, one can plainly see upper levels of main passage. Ahead the rift gradually widens and descends to a small chamber. On the left a hole leads to a 12m pitch into a lower level of the passage that cannot be followed far. Around here are some very large (up to a foot in diameter), shattered stal bosses or columns, with clear growth rings. From the chamber the obvious way on is back, up right round an elbow bend on the other joints. The passage ascends as a large, shattered cockled rift to a 6m climb up to the French Camp.
At the chamber at the elbow bend in Main Passage a steep slope may be climbed on the right. A passage ascends on the major joint line and after 40m gives on to another, almost parallel one. Backwards this passes over Main Passage (where the floor has a hollow ring to it) before choking. At one point another parallel passage can be glimpsed through a too-tight crack in the left wall. Forwards also leads to a (slightly draughting) choke. At this point Julian descended a small hole on the left for 20m or so, first in a steep bedding, and then in a rift, to a small, unexpected streamway. The descent is made dangerous by the quantity of loose debris which is funelled down the slope. Sound also, like the rocks, only travels downwards. Near the bottom a convenient 2cwt boulder jammed in the rift could be set swinging through 180 degrees, but was not dislodged. The streamway downstream can be followed for a few hundred feet, with at one point a small chamber over which there is a phreatic enlargement of the passage, typical of the cave, which might continue at a higher level, before the rift is choked. This can probably be dug.
Upstream is a very small rift which soon becomes pretty hopelessly choked: an hour's digging only served to confirm this. This end of the streamway is trending beneath a 30m shaft in the dry valley. This is on the fault, but is completely choked with boulders, and a day's digging didn't make it look any less choked. There is little hope of entering the system that way, but it remains probable that the water in Julian's Streamway is drainage down the fault.
By turning left just before the climb up to the French Camp and traversing round a 20m pitch leading to a passage vertically beneath one reaches Cairn Passage. Another hole on the left contains a 12m pitch to the lower passage, but the easiest access to it is by climbing down a further hole on the right. Cairn Passage continues, turning into a wide bedding passage. Here is one of the few vadose effects in the cave - a deep trench incised across the bedding. A 15m pitch descends to a streamway, which cascades down from a number of slippery waterfalls; alternatively the bedding ascending steeply to the right of Cairn Passage holds a hairy traverse above the trench. The inlet has not been pushed upstream. Cairn Passage closes down beyond the 'rench. Downstream, the water gains an inlet which emerges from an inpenetrable passage above a 4m waterfall. The water enters a larger passage and sinks in the floor. A choke can be passed to the right to follow the passage (but not the water) for some 100m at which point it joins the passage that descends, via a number of bouldery climbs and a 6m pitch, beneath the floor of Cairn Passage. This constitutes the Round Trip.
The Main Drag is the westerly continuation of the passage beneath Cairn Passage. A tricky climb up was subsequently laddered; the passage is at first boulder-strewn, then mud floored, with spasmodic occurences of boulders and typically a flat roof and a parallelogram cross section. It runs for some 180m and gives onto a large passage orientated on the minor joints (The Big Chamber a Long Way From Anywhere). Although 60m long, it doesn't go; an inlet enters from a high level at the SW end, and the water flows down a steeply descending passage (boulder slope) to the left to a choke. A little before the chamber, in the Main Drag, a drip on the left runs away through a hole under the passage. This was followed via a 6m pitch to a complex of boulders and bedding chambers, one of which, Shivering Chamber, was of a rather fragile nature, debris falling steadily from the roof without provocation. A stream runs through the lowest level, but cannot be followed far in either direction.
The French Camp is a rather squalid mess left by the ARSIP Party in a little loop of passage above the aforementioned climb. It returns to Cairn Passage half way along, where an inlet enters and runs away down the 12m pitch from Cairn Passage. From this area a number of small passages ascend the bedding, which rises quite steeply to the South. They tend to go on and on and end rather inconclusively. Similar passages ascend the bedding at the end of Cairn Passage, beyond the trench, and one of these was followed to a point where it gave onto a chamber - Guy's "15 Foot Chamber". In reality two pitches, respectively 10m and 12m, were laddered to descend Guy's "15 Foot Chamber" Pot to the floor of the chamber with no way on. A very high aven ascends as far as the party could see with the afterburner effect of stinkies with 6" reflectors.
This point of the system is again beneath the dry valley. Prospecting in this valley, an active shakehole had previously been found in this very area. A hole 2m deep was blocked at the bottom by a big boulder, though stones fell a considerable distance, which we did not attempt to move, not realising the significance of this at the time. There remains the possibility of opening up a top entrance to the system, perhaps with a pitch of several hundred feet.
The known vadose drainage consists of several streams for the most part running down the major joints at the bottoms of the passages. In some places (beneath Main Chamber and Lower Bear Passage) we only know of their existence because water was audible beneath boulder floors the previous year. ARSIP had told us, somewhat imprecisely, that they had found a 30m pitch down to a substantial streamway. Having investigated thoroughly all the passages we believe them to have found, we conclude that either this phenomenon is hidden down a very inconspicuous hole, or, more probably, they are exaggerating some feature of the cave, the most likely being the 15m pitch in the trench, the one major vadose feature of the system. The stream here could be quite large in wet weather. Betzula should capture all the drainage from the dry valley, and this inlet is in the right place to receive its full share. In contrast, Julian's Streamway is phreatic in character, and would seem never to take much water; however, as the fault line crosses the dry valley lower down it is not surprising that most of the water is captured before reaching here. All our streams sink in boulder floors or are choked by boulders.
At present we can only speculate as to what happens to the water. It may just diversify and seep out of beddings some 200m below. Alternatively we hope it may descend sufficiently in a cross joint, flowing back to the SW, to pass out of the control of this syncline and into the next, where there is a very large resurgence some 450m below the level of the entrance. Although the following or finding of the streams beneath boulder chokes will be difficult, if the latter hypothesis can be verified by dye-testing this year, the effort would be well worth while for a system with a depth potential of 600m.
|CU 1974 Contents Page||Next:|
The Arrigonyena System