Digging in ernest at the most promising sites in Carno Adit started in October 1982 and the following account traces the progress and lack of progress made until the time of writing this account In May 1987.
In a brick lined section of the tunnel around the 1450-l500mm mark lay a five inch diameter hole in the right hand wall at about head height. This hole, as mentioned before, was noticed to issue a strong draught in summer and accept a strong draught in winter, so in October '82 it was decided to blast a way into the cavity beyond the brickwork to study the potential for cave. The hole was not initially enlarged but a crawl was blasted out from the end of the brick lined section back towards the hole. A few trips gave us a amall chamber with the hole at floor level and the draught being taken by a small fissure in the roof of this chamber. It was decided that excavation of the floor of this chamber might yield passage so the hole was enlarged to several feet in diameter so that fill could be thrown out into the tunnel. At the same time a sand-filled aven was noticed at the other end of the brick lined section and this was dug upwards concurrently, with spoil also thrown into the tunnel. By December '82 the chamber was a shaft 8ft deep with no wall features but about 12ft in diameter and looking at least partly natural in origin; evidence of the walls being squared-off was visible in places.
The sand-filled aven had reached 35ft in height with totally natural walls and, with easy removal and stacking of the sand and clay fill, it was progressing rapidly.
At the end of 1982 a small flat-out crawl was entered from the shaft which gave about 20ft of passage heading parallel to the tunnel at just below floor level, back towards the entrance. This crawl also accepted draught and ended in a sand, clay and boulder choke which was then dug with some enthusiasm the spoil being stacked in the tunnel.
On January 20th 1983 a small rift was discovered at a slightly lower level than the crawl and on the opposite wall of the shaft, heading away from the tunnel. This rift caused massive excitment as its draught was exceptional, blowing sand into your eyes as you entered it. Sadly It led to a small crossrift which became too tight for progress in both directions after only a few feet - blasting in one of the legs gave better access but only to a difficult bend and then boulder choke.
On February 3rd digging in the other crawl suddenly yielded a vertical pothole under the lefthand wall and all attention to the rift was diverted. The pot was descended and, at atout 40ft depth it spiralled back into a spoil filled chamber. It was immediately realised that this was the same spoil which floored the main shaft, so we had a spoil-filled shaft at least 50ft deep and probably l2ft In diameter, a rather large feature on our hands.
The pot was surveyed and a draught test done at the bottom in the following weeks, the draught going to the left of the spoil wall through a narrow shattered rift. It was decided that some blasting could be done in this rift without disturbing the large bank of spoil too much, so this was started on February 12th. By February 17th access had been gained to a small chamber and a boulder choked rift heading away from the spoil-filled shaft and accepting considerable draught. This choke was then persuaded and on March 3rd a way was forced through some large and unstable boulders into a chamber 20ft long, 8ft wide and 4ft high with a laminated clay floor and a dried-up stream channel meandering across its floor.
A small hole in the wall of this chamber near to the point where the missing stream sank into the floor gave access to an ascending boulder-filled rift heading almost vertically upwards with just about a foot thickness of rock separating it from the chamber alongside. This unexpected feature was repeated at the other end of the chamber with an aven doing the same. Laminated clays were on all the boulders and coated the floor and walls with not a sharp corner or chert nodule anywhere; we were in a very old and seemingly complicated phreatic maze.
Digging in the rift gave by March 17th access to another chamber at a higher level and a horrendous boulder choke. This constituted not only half the chambers walls but also the whole of its roof and, with access available only via the small hole and rift climb amongst boulders, it was decided that extreme care would be needed to persuade this choke and blasting would have to be done from the relative safety of the base of the pot. Each blast blocked the rift again and, after a few weeks effort the diggers withdrew for an assessment of the progress made so far and to plan alternative routes avoiding the problem chamber, now named "suicide".
We had in the past few months opened around 150ft of small but interesting passage which all seemed to meander around the area of the main spoil-filled shaft and end in boulder choke in fact the choke in "suicide" turned out to be only a few feet below the floor of the tunnel and no more than 15ft from the main shaft; blasting in it could be clearly heard and felt from the tunnel.
The original diggers of the tunnel in 1905 had noted a draughting fissure in this area which we think must have been the shaft and had obviously squared-off the fissure so as to use the void to put in spoil excavated from the tunnel. We assessed therefore that the shaft must be the main feature in the area and the fact that they put effort into trimming its shape should mean it is either very deep or leads to a large chamber capable of holding a considerable volume of spoil. After all a large depositary for spoil one mile inside the tunnel must have been a real bonus to the diggers extending the tunnel.
On April 14th therefore it was decided to put all our efforts into digging out the shaft and entering the presumed large passages at its base so between May 1983 and November 1985 the shaft was painstakingly emptied of spoil firstly by bucket and pulley and then by a hand winch kindly donated from a local colliary store (along with a couple of interested miners). By November 1985 it was over 60ft deep, still about 12ft in diameter and with only one extra passage found leading from it. The spoil heaps in the tunnel reached nearly 200m down the tunnel and contained we estimate over 600 tonnes of limestone shale, chippings and boulders.
The extra passage I will describe now followed by an account of the bottoming of the shaft.
On October 6th 1983 a small crawl was excavated in the wall of the shaft directly below the tight draughting rift and adjacent to the bottom of the pot, which by this time was able to be entered at its bottom as well as its top from the shaft. The crawl again carried a substantial draught and led at 90 degrees to the shaft going gently downwards with the dip of the strata. Removal of boulders jammed in the crawl gave us steady progress to an overall length of 80ft by May 1984. The crawl had a boulder-filled aven on its right-hand side a few feet inside, a tight rift in the floor some 60ft further on and ended in a series of small solution tubes after about 80ft, each taking draught in winter and feeding draught in summer. Blasting these tubes did not seem profitable so the crawl was abandoned but not until the aven and rift had been thoroughly examined and persuaded gently to reveal their secrets, all to no avail.
On November 20th 1985 the shaft was bottomed, to solid rock; amazement and disappointment spread through the diggers, why was the shaft squared off so diligently, why was the bottom 15ft totally man-made, where were the draughting fissures mentioned in the Lapworth Report?
The conclusion must be that the fissure was the shaft before
it was modified and the draught goes off down all the various
rifts,crawls and boulder chokes already found.
During 1984 and 1985 forays were made to other areas in the tunnel
by several diggers to look for other possibilities and to relieve
the monotony of endless shaft deepening for a week or two.
February 3rd 1984 saw CSS members excavate a 70ft crawl on the east side of the tunnel around the 1300m mark; small in cross section, it turned out to be another phreatic remnant with a laminated clay floor and fine shelving. It ended at a small sand-filled chamber only a few metres from another cave remnant discovered earlier.
On several occasions in 1984 and 1985 attempts were made to probe a way into the dripping aven which lies around the 1700m mark and again on the eastern side of the tunnel. Removal of boulders and mud from the bottom of this aven revealed another aven about lOft away which was filled with large boulders and another similar feature nearby likewise filled. Some boulder removal was done over the years by several diggers but the fact that this area of the tunnel was wet and muddy whereas the shaft and its satellite passages were dry and sandy meant progress was slow and the work spasmodic.
From December 1985 until September 1986 the digging in Carno Adit tended to diminish in frequency and enthusiasm waned. The discovery of Daren Cilau, work in the Clydach Gorge and extensions in Agen Allwedd took their toll, along with the growing view that with the shaft bottomed, where do we dig now?
Some attempts were made to blast through into the Suicide chamber near the shaft via a nearby aven which would enable work to be carried out in the choke without the danger involved in climbing the boulder filled rift. The effort did not succeed in producing a better route.
The area of the dripping aven around the 1700m mark in the tunnel contains a few interesting features; the small stream which flows from the hole excavated for water further into the tunnel sinks here and feeds Ffynnon Gisfaen in the Clydach Gorge in under 48 hours at a distance of over 3 miles and there are at least three avens nearby, one open to a height of 25ft, the others partially blocked with boulders and some mud.
In September 86 therefore it was decided to study this area of Carno Adit more carefully and then probe the avens or the stream sink.
The first step was to radio-locate accurately the shaft and dripping avens from the surface; this was decided upon because of the expertise of a recent addition to the digging patty. The shaft proved to be below the edge of a forestry plantation a little to the south of Llangynidr reservoir at a depth of around 40m; the aven proved to be below a large dollne on open moorland to the east of this reservoir at a depth of 70m. This latter depth determination proved to be much more accurate than the former and can be stated with some certainty.
A depth of 70m (220ft) seemed encouraging so work commenced on trying to clear the largest aven of its boulders. The open aven was not originally probed because, from below it seemed to close down at 25ft to an impenetrable crack which issued water, hence the "dripping aven" name.
Removal of boulders and copious quantities of orange mud followed with stacking again taking place in the tunnel and steadily a strong draught was produced; so strong in fact that it was audible and lying in the base of the aven shovelling mud and stones became a very cold and uncomfortable activity. It seemed that a very large feature existed here also like the shaft along the tunnel so, to estimate its size and maybe to bypass the boulder and mud problems, it was decided to blast out a few bricks from the far side of the tunnel wall near to several small draughting holes. This was duly done on September 24th 1986 only to encounter yet more large boulders and even more copious amounts of orange mud; however the draught by now was quite extraordinary, a roaring wind no less and work proceeded removing boulders and mud from the hole in the brickwork, stacking it (or rather letting it fall) into the tunnel. This ever increasing pile of spoil caused some concern as it dammed the stream which flows In the tunnel at this point and on several occasions almost blocked off the tunnel itself. Still progress was being made and by December you could climb inside the cavity behind the bricks and wonder at the unstable boulder piles which enclosed you, making a hasty retreat after only a few seconds.
On December 14th a very cold frosty day, a party of volunteers was dispatched to walk the open moor near to the radio-located doline whilst another party of would-be arsonists burned numerous sticks of yellow phosphorus at the entrance to the choke in the hole in the brickwork. The immense volume of white smoke was swallowed easily by the choke but no reports of white fumes were given by the surface party. This gave added impetus to investigating the dripping aven area and spirits rose yet again.
The boulder choked aven and the hole in the bricks were steadily worked for several weeks and the piles of spoil once again started spreading up and down the tunnel whilst the draught increased at both sites.
On February 1st 1987 a free climb of 25ft up the dripping aven and a close inspection of the impenetrable crack at its top led us to believe it was not so impenetrable after all. There was obviously a narrowing of the aven at this point but the crack was in fact a space between two large slabs of rock jammed in the aven. These were therefore removed by blasting and access was gained to an extension of the aven of about l2ft.
Above, the narrow section it opened out into a small chamber with a large window in one wall filled with the inevitable boulder choke. By March 25th this choke had 'been destroyed and transported to the tunnel spoil heaps and a sloping scree was climbed into yet another chamber.
The dripping aven had by now captured moat of the draught from the other two avens and it was literally howling up into the choke. The aven consisted of a 23ft pitch narrowing at its top from 5ft diameter to 2ft at the constriction, then opening out to around 4ft diameter for an 8ft vertical distance. A large opening in the wall giving access to a scree slope of some 6ft vertical range and then a larger chamber of some l2ft diameter and l2ft in height. The constriction, the window and the walls of the upper chamber all had phreatic shelving marking their level and seemed to correspond to layers of resistant rock between more soluble beds. There were some fine phreatic pendants and flutes on the sides of the aven and its upper chambers and the whole feature, being in black limestone had a Yorkshire feel about it; the constant trickle of water from the top choke added to this feel and with the draught produced a very uncomfortable place in which to dig. Still digging did continue and at the time of writing this account we have penetrated the choke a few feet more and are at present confronted by the largest boulder yet seen in Carno. It is "small car" size and hangs above our heads in a most unnerving way, seemingly not supported by anything. All attempts to remove it have yet failed and, with the draught now reversed for the summer period making blasting awkward, it may have some months to survive yet.