An Intelligent Person's Guide to Gaping Gill, by Dick Glover

To the Memory of Dick Glover

Introduction

The Gaping Gill cave system consists of a series of shafts and passages, some water-filled, totalling nearly 14 km in length, over 150 m in depth, and with ten separate entrances. A further twelve or more separate caves and potholes in the area are thought to form a part of the same system but no physical connection has yet been discovered. (note 1)

The Main Shaft of Gaping Gill is located at an altitude of 396 m on the south-east flank of Ingleborough, where Fell Beck has cut a 10 m deep trench in the fluvio-glacial sands and boulders blanketing the plateau, left behind after the last major glaciation of the area, some 30,000 - 10,000 years ago. After running over a series of steps of dark coloured limestone, the stream normally drops vertically some 98 m down the 10 m by 20 m oval-shaped Main Shaft. The stream is not seen again above ground, until it emerges at Clapham Beck Head, nearly 150 m lower down, by the bridge a few metres up-valley from Ingleborough Cave.

The Winch Meets

These have been organised almost annually since 1896, apart from the war years and were initially run by the Yorkshire Ramblers Club, who carried out much of the early exploration and surveying. Since 1948, at the Whitsun and August Bank Holidays, a scaffolding platform has been erected by the Bradford Pothole Club (Whitsun) and the Craven Pothole Club (August), the stream diverted down the adjacent Rathole entrance by a metal and boulder dam, and a direct descent made by bosun’s chair (after payment of a fee) down the Main Shaft to the floor of the Main Chamber. Nowadays safety is ensured by use of a modern hydraulic winch.

The Main Shaft

The first full descent of the Main Shaft was made by the pioneer French caver E.A. Martel in 1895, and the first rock climbing ascent (GG Rider - 140 m. - Grade HVS, A2) of the North Wall of the shaft was made in August 1972 by two Leeds climbers, John Moore and Roger Baxter-Jones.

10 m down the shaft, the diverted Fell Beck water can be seen entering on the left, at 98 m forming the highest waterfall in Britain. A large ledge can be seen on the right at -58 m. This is known as Birkbeck’s Ledge, named after John Birkbeck, a local landowner who reached this point in 1842, being lowered on the end of a rope by his estate workers!

Below the ledge the back wall of the chamber slopes away to the south as one enters the Main Chamber, and, with the guide wire on the chair pulling it away from the nearly vertical north wall of the shaft, one feels like a spider dangling in an enormous black void.

The Main Chamber

On reaching the bottom of the shaft, moving away from the spray from the waterfall, and allowing your eyes to get used to the dim light filtering down the shaft, you will begin to appreciate the full dimensions of the Main Chamber, rightfully regarded as the most impressive cave in Britain. Figures do not do it justice, but for the record it is 150 m long, 30 m wide, and 35 m high, similar in size to York Minster, so it is said!

The first thing to note is a number of waterfalls cascading down the North Wall of the Main Chamber, to the left (north-west) of the Main Shaft. These waterfalls are derived partly from the diversion dam upstream of the Main Shaft and partly from natural sinks in the stream bed itself. (Rathole, Jib Tunnel, Spout Tunnel and Hamster Aven systems). The water forms a shallow pool from which streams run both right and left, eventually sinking through the boulders close to the walls of the chamber. This water is not seen flowing again until the furthest reaches of Ingleborough Cave, in passages which can only be reached by experienced cave divers.

In very high flood conditions, the diversion dam on the surface can be partially or wholly demolished, whereupon the full fury of the floodwater roars over the edge of, and down, the Main Shaft. In such conditions, the Main Chamber becomes filled with furious gales and spray, giving rise to the title Hall of the Winds, and the floor turns into a storm-tossed lake up to 15m deep. Winching operations in these conditions are, of course, suspended. Indeed, the winch itself has been known to become partially or wholly submerged.

The Main Chamber itself is aligned on an 290°-110° axis, and in low water conditions the water flows to the left, out of the pool, against the north wall, sinking at various points, including North Fissure (see later), before finally disappearing in a pile of shattered rocks just to the south of the base of the West Slope. Continuing around the south wall of the Main Chamber, it can be seen that the first 3 - 10 m of rock is vertical, capped by a metre thick bed of strikingly white rock before beginning to overhang the Main Chamber itself.

This light-coloured band of rock, known as the Porcellaneous Band, can also be clearly seen running along the full length of the north wall of the Main Chamber. It appears to have been deposited during a fall of sea level during an Ice Age some 300 million years ago, traces of which have been found in the Sahara desert, when that part of Africa was located in the Antarctic region, and the Yorkshire Dales were located approximately at the same latitude as the Bahamas are today, and where limestone sands and mudstones are being formed. These latter deposits will eventually turn into the type of “Great Scar” limestones, including varieties of Porcellaneous Bands found in the Yorkshire Dales today.

The Main Chamber Fault

Back in the Main Chamber, it can be seen that the overhang of the south wall of the Main Chamber starts along the top surface of the Porcellaneous Band. Careful levelling of this lithological horizon around the Main Chamber shows that it is continuous around the West Slope, but is displaced downwards by some 4 m where the south wall meets the East Slope. Further to the east, at the end of Old East Passage, in Mud Hall, the downthrow to the south is in excess of 13 m. The Main Chamber, Mud Hall, and much of the passage beyond, have thus been formed as a result of enhanced erosion along the line of a major wrench fault - the Main Chamber Fault.

In addition, the effects of the Main Chamber Fault can be traced in a number of associated potholes to the east of Gaping Gill, and across Clapham Bottoms into Crummackdale. It may therefore be related to a fault in the highly folded and faulted rocks underlying the whole area, and which are very well exposed in Crummackdale itself.

The Main Chamber Fault is one of three major faults which can be seen in various parts of the Gaping Gill system, and which have played a major role in controlling the direction of many of the major passages in it. Equally, the Porcellaneous Band appears to have controlled the horizon of a large part of the known system.

It is not surprising to find that these faults and most of the major joints in the Gaping Gill area run along a north-west - south-east line, parallel to the North and South Craven Faults, less than a mile to the south, and along which downward displacement of the rocks to the south in excess of 1800m have been shown to have occurred intermittently, over the last 300 million years. The last recorded movement along these faults occurred in 1947, resulting in a minor earthquake which was severe enough to cause several chimneys and old buildings to be damaged in Skipton.

The floor of the Main Chamber is more or less level, and is composed of rounded gritstone boulders and pebbles, but one part consists of a 1m high plateau of a sticky and slippery mixture of sand and mud. In 1895, on his first descent, Martel stated that the floor was completely flat and sandy. Since then, the effects of recent and extensive moor drainage (gripping) has resulted in greatly increased runoff rates, which are slowly removing the sand and mud deposits. Fell Beck can rise 1 - 3 m in a few hours after heavy rain, and grass, peat and old fence posts have been found washed up as high as 20 m above the present floor level!

The West Slope

At the west end of the Main Chamber, the 12 m high West Slope leads up past the “letter-box” squeeze entrance to the 30 m deep West Pot, which ends in a tight sump. At the top, a crawl to the left leads to a 6 m drop into the sand-floored West Chamber.

The only exit is a high-level roof tube, reached by a difficult climb up via a polished limestone chimney. The roof tube runs south-east, passing beneath a hole in the roof where the floor of an older, higher-level roof tube is revealed to be choked solid with a mixture of sand, clay and rounded gritstone pebbles. The roof tube ends abruptly at a 6 m slippery climb down into the pool at the north-east end of Pool Chamber, more easily reached via South Passage.

It is clear that in high flood conditions water rises high enough up the West Slope to enter West Chamber, where most of it sinks through the sand along the base of the north-west wall. Occasionally, however, West Chamber must completely fill with water, and overflow via the roof tube into Pool Chamber. The top of the Porcellaneous Band is visible at the lowest point of the chamber.

The East Slope

At the east end of the Main Chamber, the East Boulder Slope rises some 25 m above the Main Chamber floor level. At the top, an awkward overhanging climb up a rigid ladder (care) leads to Old East Passage.

From here, the passage runs, at much the same level, in an eastward direction as far as Mud Hall; most of it very old, in excess of 300,000 years - as shown by uranium/thorium dating of sections of the latest stalagmite floor deposits.

This is a chamber almost as large as the Main Chamber, and although its floor level is some 20 m lower than that of the former, it is completely dry. Its size (the roof is too high to be seen with caving lamps), the absence of daylight and the noise of falling water from high up on the far side, make Mud Hall one of the most foreboding parts of the Gaping Gill system. (note 2)

It is clear that Mud Hall was once almost completely filled with alternating layers of sand and mud, but the points of entry and exit of the vast amounts of water required to fill and then remove these sediments are a mystery, both underground and on the surface.

South Passage

In the south-east corner of the Main Chamber, several large blocks, composed mainly of pieces of the Porcellaneous Band limestone which have fallen away from the wall, are presently being undermined by water sinking here in wet weather. They hide the entrance to South Passage, which is entered by an easy climb up the right-hand edge of the blocks. The passage consists of a low arched tunnel, usually mud-floored, with the remains of several alternating thin layers of sand, clay, pebbles and stalagmite visible on either side.

Caving traffic along this passage has been heavy enough to wear pits in the mud floor, exposing the bedrock as being the Porcellaneous Band. This bed of limestone appears to be much less soluble than the coarsely crystalline limestones above it, and many kilometres of passage in Gaping Gill appeared to have been originally developed at this level. Several high joint-controlled chambers are passed, including one leading down to the left. This is one end of the Booth-Parsons Crawl, which connects with Old East Passage, and also passes the entry to the notorious Hensler’s Long Crawl, and which is a tributary of Hensler’s Master Cave, described in a later section.

Keeping right, past the exit of Booth-Parson’s Crawl, the passage changes into an upward sloping, wet, muddy flat-out crawl for a few yards, by-passing on the left an entrance to a series of low chambers with pools of water on the floor, until a final upward gentle squeeze (The Portcullis) leads into a high cross-joint chamber. This is known as Pool Chamber, since the right-hand end contains a long chest-deep pool. This ends in a slippery 6 m climb (care) into the high-level passage, mentioned earlier, leading south-west from the far end of West Pot.

To the left, a gentle slope leads down past several small and low blind chambers containing shallow pools, and then levels off, forming a walking-sized, mud and sand-floored passage which runs in a generally southerly direction. All signs of human visitation in this part are regularly removed by heavy flooding of the system.

Rock ledges on either side of the passage are formed of the Porcellaneous Band, and over much of its length the roof is noticeably flat due to solution when the passage was full of static water for long periods.

Several joint-controlled chambers running north-east - south-west intersect the passage, some over 10 m high, and show by the strangely shaped pocketing of their higher levels that they were also formed underwater. Large flowmarks on the walls of the passage indicate that it was originally formed deep underwater by water flowing slowly in a southerly direction. Later, the water level fell, and the passage became a long canal, being refilled regularly by flood water. The great pressure and speed of these flood waters is shown by the large stalagmite boss, lying on its side, and half buried by sand, which can be seen halfway along this section of South Passage, and which can only have come from Pool Chamber.

At the end of South Passage, T-junction is reached, where much smaller passages lead left along South East Passage towards the base of the Bar Pot entrance, and right towards Sand Cavern and Stream Chamber beyond.

Sand Cavern

Turning right at T-junction, 15 m of low passage lead into a chamber which rises over large mound of sand and gravel to the left, and slopes steeply down to the right to a choke. This is known as 'D1' (Dig 1), since it has been excavated intermittently since the early 1900’s. Occasionally, a draught and the distant sound of falling water can be detected at this point, but it would take an major engineering exercise to make any worthwhile progress. The Porcellaneous Band can be seen forming a rock ledge on the right at the point of entry to the chamber, and since in all other points in the Gaping Gill system where passages have been developed below the Porcellaneous Band horizon, major extensions occur, a major dig at the bottom of D1 seems a likely place for new discoveries.

Turning left up and over the mounds of fill leads past a high cross rift in the roof into Sand Cavern proper. This is over 90 m long and some 15 m high and 9 m wide. The roof is a large arch commencing at a prominent bedding plane seen on both sides. Below this level, breakdown has left both sidewalls as vertical rock-faces. Very large flowmarks in the roof show the chamber was originally formed as a large phreatic tube, deep underwater, which flowed very slowly for a very long time, in a northerly direction, i.e. towards D1. The chamber was subsequently filled almost to roof level by vast quantities of mud, sand and rounded gritstone pebbles, which were probably washed in from some unknown entrance to the south, at the end of a major glaciation, when the melting ice released huge amount of water and sediments.

Since then, major floods have been slowly clearing the fill, and have left two deep depressions in the floor, one on either side of the ridge running along the centre of the chamber. In times of heavy flood, water rises up from the bottom of these pits, and can fill the chamber to its highest point at the northern end, as can be shown by the presence of pieces of dried grass, moss and heather on the walls at this level. Presumably it then overflows down D1, and then slowly drains back down the floor pits, taking with it some of the remaining sediments. At the lowest point of the floor pit on the right, a little excavation exposes the top of the Porcellaneous Band.

The southern end of Sand Cavern ends in a near vertical wall of two thick beds of sticky clay separated by a 5 m thick bed of alternate thin bands of light-coloured sand and darker brown clay (The Sand Wall). These are the highest and oldest remains of the sediments which once filled the chamber. The laminated section is thought to be the remains of sediments washed in during the annual spring floods which occurred during the decay of a static ice sheet covering the area at the end of a major glaciation. At the end of each flood, the heavier sand grains settled out first, followed by the finer mud particles.

Attempts have been made to measure the magnetic properties of the laminated sediments of the Sand Wall in an attempt to correlate them with other areas. Although a consistent set of readings were obtained, it could not be matched with any parts of the known sequence, and the sediments may well have been deposited during one of the earlier glaciations which are thought to have commenced some three million years ago.

Stalagmite Chamber

An easy scramble up the right hand side of the Sand Wall leads into a small joint chamber, from which a turn to the right leads into a complex area of low, wide clay-floored chambers, known collectively as Stalagmite Chamber, once beautifully decorated by many straw stalactites descending from the roof. Large numbers of stalagmite columns grew up from the clay floor, which in places was covered with large sheets of pure white crystalline flowstone. However, the constant caving traffic over the last ninety years has largely destroyed all formations.

In several places, obvious routes down to the right lead to 3 m deep rock trench which, if followed back to the right, leads back to a window overlooking Sand Cavern. Known as the Opera Box from its peculiar position, many parties have been lured there and wondered how to get down to the passage below. To the left, the trench enters a high north-west - south-west cross-rift, floored by large blocks which have fallen from the walls and from the roof. In wet weather a heavy shower, source unknown, enters from high in the roof.

Stream Chamber

After a scramble up and through the blocks, and a turn to the right, an obvious track in sticky mud skirts the 15 m deep shattered-looking Mud Pot to the head of a steep slippery mud slope overlooking Stream Chamber. This runs for a total length of some 360 m to the north-west, and although it is 15 m wide and 12 m high at the start, it gradually gets too low and muddy for the visitor. After a muddy calcite squeeze into North-West Extension, a crawl leads to an awkward 10 m pitch into a streamway. Upstream, the passage finally emerges into Terminal Aven, down which the water forming the streamway falls. The aven been scaled to a height of over 30 m to where it ends in a tight slot. A crawl continues for a short distance beyond Terminal Aven.

It would appear that the whole of the North-West Extension consists of a large phreatic tube developed along the line of a joint or fault. At some time in the past, the passage was completely filled with in-washed sediments, which have subsequently been partially removed by water entering from Terminal Aven. The source of the water which originally formed the passage, as well as the source of sediment fill, remain, as in the case of Sand Cavern, a mystery.

The whole of Stream Chamber, South-East Passage and Stream Passage Pot have been developed along the line of a wide zone of parallel and closely-packed set of faults, the South-East Passage Fault System. This can be traced, at intervals, for over 600 m, along a line running north-east - south-west i.e. parallel to the North Craven Fault. Little sign of vertical movement along this fault zone has been found, but in one or two places evidence of lateral movement can be seen.

Back in Stream Chamber, at the foot of the muddy slope, a house-sized boulder which has fallen from the roof, occupies the centre of the chamber floor, around and under which a normally small stream flows before sinking among shattered boulders. An obscure climb down here allows cavers to reach the bottom of Mud Pot. After a further descent through a large boulder choke, the stream is again seen in a short passage ending in a 15 m shaft and sump. This has been dived through three more sumps, separated by short sections of stream passage, to a final 10m deep sump which ends in a boulder choke. This point is directly below the bottom of the deepest pit in Sand Cavern.

In flood, water from the whole of the lower system backs up into Sand Cavern, where water has been observed bubbling up from the bottom of the deepest pit in the floor.

Stream Passage

The stream in Stream Chamber flows from a large, high rift passage on the left side of the chamber itself. This can be followed upstream past the remains of thick beds of sand and rounded boulder fill to where the water enters from a series of 25 m high holes in the roof.

Stream Passage Pot

These spray-filled avens form the last pitch of Stream Passage Pot, yet another of the surface entrances to the Gaping Gill system, located where a stream sinks in a deep shakehole about 300 m south-west of the Main Shaft. It consists of a meandering stream passage with four pitches, the largest being some 34 m deep. This is often used as a sporting entrance to the system.

South-East Passage

Returning through Sand Cavern back to T junction, the passage continues to the south-east as a hands-and-knees grovel (using the Gaping Gill Gorilla Gait!) past several low sand-choked passages to the left, and through several high cross-rift chambers containing remnants of cemented boulder-fill high in the roof.

Ignoring the first passage to the right, the way on follows a small rocky tube into a large chamber with the 40 m deep South East Pot on the right, and a waterfall dropping down the 43 m final pitch of Flood Entrance from above.

A slippery and dangerous climb to the right, up cemented sand and gravel fill, leads into a higher level of the same fault chamber. It is clear that this chamber represents the choked remnant of the main continuation of South-East Passage in a north-westerly direction. From this chamber, a tight sandy crawl has been pushed for a considerable distance towards Sand Cavern.

The pot can be by-passed by a traverse on the left, on the top surface of the Porcellaneous Band, up a rocky slope into a high rift passage. A deep and dangerous hole on the right should be passed with the greatest of care. Beyond the mud-floored passage, the route descends a mound of mud-covered boulders into the large chamber at the base of the Bar Pot Big Pitch. Solutional pocketing in the roof at the top of the rise shows lateral displacement of about 1 cm along the line of one of the South-East Passage faults.

An oval hole, seen some 3 m up the south-west wall of the chamber, opposite the base of the ladder or rope down the Big Pitch, leads into the Wild Cat Rift series, also reached by the traverse round the left-hand edge of the head of the pitch.

Bar Pot

At the head of Trow Gill, on the walk up to Gaping Gill past Ingleborough Cave, a semicircular flat boggy area is seen just before the stile. A small stream drains from the bog, and sinks at its southern end.

Over the stile, the large, 15 m deep, rock-walled collapse pit, Bar Pot, lies along side the track. To the right of the track, a short distance beyond Bar Pot, two narrow pothole entrances can be seen at the foot of the mound of peat-covered to the north. These are Flood Entrance (formerly called Flood Exit) and Wade’s Entrance Pots. These join some 15 m down, and after two further pitches of 15 m and 43 m land on the edge of the 40 m deep South-East Pot, in the floor of South-East Passage.

A few hundred metres further, the track passes between two narrow holes in solid rock. The pot on the right is called OBJ (Oh, Be Joyful!) Hole, 40 m deep, and ends in a choked fissure where voice connection has been made through a narrow rift part-way down Flood Entrance Pot. (note 3)

Bar Pot is the most frequently used alternative entrance to the Gaping Gill system. A scramble down the rocky slope leads to a narrow hole through boulders at the lowest point. An excavation through the boulders, made in 1949, leads to the head of a tight pitch, 17 m deep, which widens abruptly after about 6 m, landing on the sloping rocky floor of the first chamber. At least three alternative routes lead on down from this point, but the most direct route leads down through a hole at the lowest point of the chamber to the top of a slippery slab which drops some 6 m into the large Bridge Chamber whose boulder floor descends steeply to the north. (note 4)

From the lowest point of Bridge Chamber a passage leads left via a short crawl into a muddier descending passage which opens out and passes under another rock bridge to the head of the Big Pitch. A drop to the left over a boulder leads to the pitch but this route is broken partway by a large ledge. An alternative way passes on the left and over yet another small rock bridge to enter a chamber at the head of the Big Pitch. This is 30 m deep and lands on the flat floor of South-East Passage. At the far end of the head of the Big Pitch, a 6m climb leads to a bedding plane crawl which leads through to Flood Entrance Pot near the head of the final pitch.

Far South-east Passage

To the south-east of the base of the Bar Pot Big Pitch, the rift passage rises over and then down a mud-covered slope of boulders to enter another high aven chamber with a small stream entering from the roof.(note 5)

At the lowest point of this aven chamber, near where the stream sinks, a tight slot down through the boulders leads via a series of wet, low and muddy crawls, which merge before gradually enlarging to form the start of one of the inlets leading to Hensler’s Master Cave, and the extensive system of passages beyond.

Far South-East Passage continues beyond this point, up a muddy 3 m climb on the right, as a rift passage along the line of the South-East Passage Fault. Immediately to the right of the head of the climb, a low glutinous crawl leads into a high cross rift, yet another part of the Wild Cat Rift series.

To the south-east of the climb up into the main rift passage, large flowmarks on the walls indicate that this section of passage originated deep underwater, by slow phreatic flow, over a long period, from an as yet unknown source to the south-east, possibly from Clapham Bottoms via the Hurnel Moss Fault. The passage terminates in an aven full of stalagmite covered boulders, down which a small inlet descends. This point is directly below the small stream sink at the lower end of the boggy patch on the Trow Gill side of the Bar Pot stile.

The flow-marked undercut sidewalls of the rift disappear below the terminal choke, indicating the possibility (by excavation) of discovering further extensions to Far South-East Passage running towards Clapham Bottoms and the junction of the South-East Passage Fault zone with the Hurnel Moss Fault.