www.sbss.info

Established: 1977

South Bristol Speleological Society

EAST TWIN SWALLET
A HISTORY OF THE SBSS DIG

(or the continuing search for the Burrington Master Cave)

BACKGROUND

East Twin Swallet is located at NGR ST47965814, in the East Twin Brook Valley which runs into Burrington Combe, in the Mendips, and was first dug into by the University of Bristol Speleological Society (UBSS) between 1934-36. In September 1936 UBSS entered East Passage (the present entrance crawl) and gained entry to the First Chamber which was choked at the lower end.

The cave was not visited again until March 1940 when some startling changes were discovered. The entrance crawl now ended on a ledge halfway up the wall of the First Chamber, the floor of which had been washed away and they had to slide down a sloping rock to the present floor level: the Chamber now being some 20 feet high instead of the previous 6 feet. The choke at the lower end had also been washed away and they were able to enter the Second Chamber; and following some excavation of the Squeeze, they gained access to the smaller Third Chamber.

The discovery of GB Cave at Charterhouse led to the discontinuation of the dig at East Twin. When work was eventually restarted the Squeeze between the Second and Third Chambers was again blocked. It has been blocked following flooding on a number of occasions since. The terminal choke at the lower end of the Third Chamber has been dug sporadically over the years by various Mendip clubs.

The stream flowing into the cave has been tested to Langford (circa 17 hours) and Rickford (circa 6 hours) Risings. The same stream re-appears in Pierre's Pot on the edge of the West Twin Brook valley lower down the Coombe. The stream presently sinks at a narrow rift on the right between the First and Second Chambers. Heavy rains over the past couple of years have washed much debris into the rift which has partially filled in and is now often completely flooded.

THE SBSS DIG

The SBSS as we now know it was re-formed in about January 1977. As membership began to grow in late '77/early '78, it seemed appropriate that the club might undertake a dig.

At a club meeting on 15/1/78, Dave Mockford and Mike Chalker agreed to look at prospective sites for a club dig. The August newsletter announced the "Grand Re-opening of the East Twin Swallet Dig," on Wednesday 8/8/78. The cave had been dug by the old SBSS in 1974.

On the first evening Dave Mockford, Dave Winter, brothers Fred and Malcolm "Miff" Smith, Andy Dann, and Barry Howe dug in the Squeeze for an hour and a half, lowering the floor by 18 inches. The stream which had been diverted down valley before entering the cave, sinking at the "Third Sink" (NGR ST 47965819), re-appeared in the tight rift on the left in the lower part of the Second Chamber. "A small probe to the left of the Squeeze revealed a small boulder and silt choke with fair size black spaces. Could we be digging too far to the right?" Dave Mockford, Dig Log: 9/8/78.

My own first visit to the cave on 30/12/78 with Miff and Dave Winter revealed that a little progress had been made. The dig face was, perhaps, 5 feet lower than where the winch is now. There are no further log book entries between the first one mentioned above and 17/1/79 when Phil Hodgkins took over the log. Phil's first entry in the log reveals that 3 feet of passage was dug out on 17/1/79, and part of the Squeeze collapsed on Tina Lewis. Progress over the next few weeks was phenomenal: on my next visit (as a new club member) on 21/2/79 the dig face was getting very close to what is now the entrance tube up to Spar Pot. From the logbook: "March '79- an exploratory dig at right angles into the silt was made for 8-10 feet but due to the unstable nature it was abandoned."

Progress over the next few months was so rapid that by May passing buckets from the dig face up the passage and through the Squeeze to the Second Chamber for emptying by the rope and human-chain method was becoming rather strained. Thus Phil Hodgkins and Martin Elsbury installed a "pre-designed runway" made from 1.5 inch Chevron angle iron, total length about 18 feet with a runner and hook on a length of rope to pull up the buckets: the Monorail #1.

This first runway worked quite well for about six weeks. However the rapidly advancing dig face meant that it needed to be extended which proved impractical due to its inflexible design. Hence with the help of Clive Lewis the Monorail #2 was designed, and installed on 11/7/79. The new design monorail could be extended as the dig face advanced with no major technical problems and by the end of July it was in full use. This second rail was made from dexion and is still installed today.

Progress could now continue unabated, apart from when the monorail fell down, which was quite a regular occurrence. We were also faced with the instability of the cave, mainly in the Squeeze. This has been the scene of two major collapses and several minor ones. The first major collapse has already been mentioned. The second occurred on 30/1/80. "Jane...straddled across the lower end of the Squeeze, when suddenly everything moved. Jane beat a hasty retreat to the Second Chamber, narrowly escaping injury." SBSS NL Feb. 1980.

At that date the Squeeze was not as shallow as it is today. In those days we were emptying buckets in the Second Chamber and for ease of passage the floor in the Squeeze was at least 4-5 feet lower than it is now and it was quite possible to walk through and to sit straddled across while waiting for buckets to come up or down.

The collapse included a particularly large boulder and several hundred weight of mud/silt, from the wall/ceiling. It was agreed that the area had become unacceptably unstable and we should seek advice on whether to shore it up or blast down the remaining loose material. In February 1980 the Wessex CC sent along several members who had a quick look at the Squeeze and recommended "banging" the remainder of the loose material which they undertook for us during March 1980. The debris was removed to the Second Chamber and the whole area cleared up.

By July/August 1980 the dig had advanced to a total of 45 feet. The monorail had been extended and strengthened on several occasions, and the winch had been installed to make it easier to pull up buckets over this distance. On 19 November 1980 after removing only a few buckets of spoil, the earth started to fall away to the left of the dig-face, eventually revealing a narrow inlet passage: "Burt Inlet". The entrance to the inlet was enlarged and John Stinchcombe was the first to try and push the passage. However after about 8 feet a constriction was encountered stopping further progress. John reported that the passage continued with muddied formations and seemed to widen out again past the constriction but was still very narrow and very muddy.

As no progress could be made in Burt Inlet work continued at the main dig face, however over the next year very little progress was actually made and during the latter half of 1981 the dig was virtually unvisited. Around that time I acquired a copy of Barrington and Stanton's "Mendip - The Complete Caves...". Until this point our aim had always been a link with Lionel's Hole across the Combe, with various surveys undertaken to prove that we were working in the right direction. After a little scientific arithmetic and map work, the January 1982 newsletter carried the first mention of a possible link with Spar Pot.

Whether it was this that sparked off interest in the dig again I cannot tell, however by February 1982 the dig was on again. A survey by Martin Elsbury and Mike Hinds on 21/2/82 claimed to have disproved the connection with Spar. This was also the year of Martin Elsbury's "Water Erosion Thesis".

THE CASE FOR WATER EROSION IN EAST TWIN SWALLET (THIRD CHAMBER)

If a large enough stream was released in the Third Chamber it would start to carry with it some of the choke material that has been deposited by too slow a flow of water in the past. A flow of this nature would gradually erode the top of the choke away and leave a large space. A stream diverted down the full length of the chamber would, however, take with it an unnecessary amount of choke material, causing more choking at the dig face. Therefore what is needed is a supply of clean water at the face to erode from that point onwards. This could be done by piping the water from the First Chamber to the face and releasing it there.

The water would have two weeks between our dig nights to erode the choke material away. It could be stopped while we removed any loose material by the existing bucket and monorail method on dig nights."

The summer months of 1982 were therefore spent on gathering the necessary items to put the theory to the test. By August everything was ready: a concrete dam had been built across the passage (parallel to East Passage) where the stream enters the First Chamber, various pipes were joined up and water flowed to the bottom for the first time in a number of years. The dam is still in place and can be seen at the outflow of the parallel passage when you descend the incline at the end of East Passage. Unfortunately all the experiment proved was that if you send a lot of water to the bottom all you get is a wet, muddy dig where nobody wants to work!

Whilst work was being carried out on Martin's theory, interest was still being shown in Burt Inlet. Various methods were employed to enlarge the passage, including the "hammer and chisel" method. However eventually the inlet was banged on 17/8/82. Mud and rubble were removed the following evening, and John Stinchcombe was able to get up about 14 feet to see the passage bending to the right. It was clear that further banging would be needed if we intended to follow the inlet further and Mike Hinds had now established by survey that the passage was unlikely to take us into Long Crawl in Spar Pot, but a connection between the two caves still seemed likely at anytime.

With a return to organised digging in September '82, came a group of "weekenders" (John Stinchcombe, Mark Yandell, Kevin Johnson, et al) who began digging out the passage which had been dug and filled in again in 1979, due to its instability. Work continued at the main dig face on Wednesday evenings but this was often under difficult conditions due to the build up of mud and water. Time was also spent cementing the wall of spoil in the Second Chamber and piles of loose rocks in the Third.

With the onset of winter and even worse conditions at the bottom of the dig, fuller attention was paid to the inlet passage dig which appeared to have stabilised since 1979 and now seemed to be going somewhere. For a while it was assumed to be a surface connection due to the strange infill found (eg: silver foil, crisp bags, an old boot...) and a strong draught. However when it was worked out that we must still be 50 feet below ground this seemed less likely. A second opinion was that it might be a connection with Lionel's Hole.

In the spring of 1983 we met a boulder ruckle approximately 15 feet up the tube. It was extremely unstable. This ruckle held us up for some time as we toyed with various ideas for its disposal or passing. In May 1983 the ruckle was banged for us by Tim Large of Bristol Exploration Club (BEC) and a number of the more menacing boulders removed.

On 8/6/83 a number of diggers entered East Twin to tidy up the ruckle and to see what progress had been or could be made. A "letter-box" had been noticed shortly after blasting, but had been thought too hazardous to squeeze through. However all those who entered the cave that evening made it through the Letter-Box and became the first to stand in Spar Pot since its closure in 1971. A message in a bottle, from the original diggers told us of their finds and asked us to respect the cave as they had done.

After the initial euphoria of the discovery and re-exploration of Spar Pot had ended, interest in the dig waned and by December the same year the dig had fallen into inactivity. We had lost a number of the active diggers through marriage, work commitments and although there had been an influx of new members there were none interested in digging. The East Twin dig was officially abandoned in January 1985.

Efforts were made to find another dig site. For a short time we thought about the East Twin top sink, but this would have required civil engineering on a scale with the Channel Tunnel to have been successful - it appear others have since made attempts to dig this sink unsuccessfully from visits to the site over recent years. A dig was also made at Trat's Crack, a few hundred yards up the Combe on the opposite side, for about eighteen months. However after a period of rain the dig sumped and despite various valiant efforts by the emptying buckets and siphoning techniques and for a while the discussion of the purchase of a club pump, the dig there was eventually abandoned in 1987.

However the old diggers had never really let go of the dream of finding the Burrington Master Cave, and with another influx of members, digging at East Twin restarted. There had been infill due to flooding which needed to be dug out before any further real progress could be made.

For the next few years progress continued slowly onwards and downwards. There were several attempts (by non-digging enthusiasts) to abandon the dig but on each occasion it was agreed to keep the dig going even if things were not exactly active.

In September 1994 Martin Smith, et al, digging at the bottom of East Twin, approximately 40-50 feet below the connection with Spar Pot, discovered a small tube off to the right. Ecstatic at the find, Martin described it as "Better Than Sex" at the club AGM just after the discovery. He also described it as a small chamber, which brought out a number of re-enthused diggers including myself on the following few trips - only to be disappointed to find that the small "chamber" was in fact a tight, wet, muddy tube.

The following winter was one of the wettest for a number of years: after a particularly heavy period of rain the diggers were dismayed to visit the dig one Wednesday night to find that water had swept through the cave carrying away large amounts of mud and boulders particularly from the floor of the 2nd chamber which had then blocked the squeeze. The squeeze was dug out to reveal even more damage beyond. The sheer volume of water had scoured away the mud floor all down the passage leaving various precariously placed boulders. The dig face itself had infilled considerably and water had sumped back up the passage. When the dig was next visited the water had drained away but had left a very wet dig face, in addition the end of the monorail was now buried under mud and boulders and the entrance to the new inlet tube had been lost. Immediate measures were taken to prevent any further damage. A "dam" consisting of dig spoil in bags, topped by a layer of boulders was built across the top of the 2nd chamber just below the rift where the stream normally sinks, and a further "holding" wall was constructed at the lower end of the chamber above the squeeze.

Work continued at the dig face and by the end of 1995 we were back to where we were before the flood, with the end of the monorail clear, the new inlet passage visible again and into new ground. By this time however the number of regular diggers had tailed off again - Martin Smith had moved to Yorkshire and, with concerns about thefts from cars, one of the team had to remain on car-sitting duty in the lay-by while everyone else was digging.

It was becoming more difficult to maintain the dig's progress with the decrease in numbers and it was agreed that the dig would only be held every third week rather than every other week.

Progress during 1996 continued, with a main core of 4-6 regular diggers: Ian Mildon, Brian Clemenson, Keith Emery and Jane Osborne (joined by Trevor Timmins and Tim Fell during the climbing off-season). By this time we were dumping dig spoil in the 3rd Chamber in sacks in an effort to fill in the areas that had been washed away by the flood and because this was now easier with fewer diggers than trying to get buckets through the Squeeze to be emptied in the 2nd Chamber. It was decided that we would park cars in the Burrington Inn car park at the bottom of the Combe and walk up to the cave - we were now regularly using this as our post-digging pub, and this would also obviate the need for someone to remain with the cars for several hours in the cold and dark.

We were now digging below Better Than Sex, which was bringing in a constant trickle of water, which made the dig itself rather wet and the area behind the diggers rather unstable with a constant slurry of mud. It was decided to install a framework of scaffolding poles at the bottom which would hopefully stabilise the area, assist diggers in getting to and from the dig face which was now getting to be a rather steep climb in and out, and a point to which the monorail could be extended and attached. The slurry continued however and eventually Ian produced a lightweight aluminium ladder about 5 feet long which was installed to assist in getting to and from the face.

With the close of the evening climbing season we began to see more of Trevor and Tim and progress became more rapid. The dig was now going downhill at a much steeper angle and generally speaking provided fairly easy digging - mainly pulling out fair size boulders, although the winter rains did mean that most digs started off being rather wet with attempts to drain the excess water as much as possible. Trevor began digging in Better Than Sex - a thankless task as the inlet is extremely tight, muddy and wet, Trevor being the only member of the team thin enough to be able to do so.

1997 saw the dig progressing onwards and downwards, and Trevor's dig in Better Than Sex continued until the early summer. In mid-August with an extremely full complement of diggers it looked like being a promising evening's dig - particularly in view of progress over recent dig nights. "Girl Power" ruled and myself and the other girlies were despatched to the dig face. Lizzie Mildon, having joined me at the dig face a few weeks previously, went on ahead of my daughter Abi and myself.

The next thing we knew Lizzie had reached the dig face rather more quickly than anticipated - the wall of "slurry" at the end of the monorail having finally "gone". I carefully joined Lizzie, who was winded but unhurt, at the bottom to survey the damage. The red ladder had been pushed down into the dig face by the landslide and I managed to secure this to one side of the scaffolding below Better Than Sex in order that Lizzie and I might actually get out from the dig face without causing further collapse.

Ian (Lizzie's father) came down to see what had happened. Having deduced that most of what was going to go, had gone, and at least the wall/floor to the left hand side was solid rock and the infill below Better Than Sex looked fairly solid and not in danger of collapse, Ian estimated that a fixed ladder about 8 feet long was long was needed and we exited the cave.

On Wednesday 27 August 1997 the fixed ladder which Ian had constructed from dexion was taken into the cave in two halves and installed at the bottom of the dig, being fixed to the existing scaffolding at the end of the monorail. There appeared to have been a further, smaller, landslide. The old bunk bed ladder was hoisted back up above the new ladder and tied on to a length of rope from the bottom of the scaffolding below Burt Inlet.

Sunday 31 August 1997 will long be remembered for a number of reasons: the death of Diana, Princess of Wales, Abi's 15th birthday and one of the most severe thunder storms on Mendip for many a long year. We were staying at my brother-in-law's home at East Harptree over-night, and awoke at about 9.00 a.m. to a severe thunder storm which continued until after 12 noon. About 1.15 p.m. we went out for a quick walk around the local lanes. Heading back to the cottage we took a left up Water Street to have a look at the local stream. Having seen what is normally a clear shallow stream turned to a thundering brown torrent I began to wonder how things were at East Twin. Leaving East Harptree at about 4.15 p.m. I persuaded the family that we should drive back via Burrington Combe to investigate.

Pulling into the lay-by the water flowing across the road from the valley was about 6 inches deep and cars were having to slow down considerably to pass it. I had to wade through the stream as there was no way round. The water at the entrance was about 12 inches above the grill. There wasn't much water going into the cave itself as the grill was bunged up with debris but I managed to free some of this. The sheer volume of water had washed over the earth dam which normally ensures that water flows into the cave rather than on down the valley to the road. Having done what I could, I returned to the car noting on the way that about half the water was actually flowing off, and presumably sinking, into the depression behind the lay-by. The flood water from the East Twin Valley flowed all the way down the Combe to the Garden Centre. There was no overflow however from the West Twin Valley.

Fortunately the dig had not flooded - Ian Mildon had also been up to the entrance earlier on the day of the storm and had wondered whether our flood defences would hold, or whether water would enter further down the cave. However it appeared that not much flood water had actually entered and our flood defences in the Second Chamber had held out.

We were joined on a trip later in September 1997 by Alex Gee (ex-SBSS) now with BEC. Ian had seen him at the BCRA conference in Bristol and he had offered to survey the dig for us. (At the time of writing - over 18 months later - we are still awaiting the results of the survey!)

Over the past year and a half the dig has been plagued by technical difficulties with the monorail needing extension and several repairs, although the dig itself has continued downwards in spite of this. Unfortunately the exceptionally heavy rains have meant that in both winter 1997/8 and 1998/9 the dig has flooded up as high as the link with Spar Pot however the water always drains away when the rain stops and due to our earlier flood defences there appears to be little impact on the face other than very slow progress. Flooding this year has been so severe that the cave has been undiggable since late November 1998. The spring appears to have now arrived and itís getting drier so the search for the Burrington Master Cave should continue shortly (and Trevor's masochistic dig in Better Than Sex will continue to intrigue the rest of us.)

JANE OSBORNE, 26th March 1999
Adapted from the SBSS 21st Anniversary Journal





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