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Surveying Gaping Gill

  • Written by  Kevin Dixon
  • Published in Explorers
An impressive straw filled chamber in Gaping Gill An impressive straw filled chamber in Gaping Gill
12 Dec
With the world accurately navigated by multi-constellation satellites, what is left to explore? Kevin Dixon is nearing completion of a five-year project to map the Gaping Gill cave system in the Yorkshire Dales, showing that you can still make new geographical discoveries even in a well-explored habitat

The Earth’s surface has been mapped with Radar and LiDAR (Light Detection and Ranging), so we not only know how many mountains there are, but have 3D models of them to virtually explore in our homes. What we have not been able to determine remotely is how many caves there are, their extent and depth. Here is a dark world, still largely unknown, where new discoveries can be made.

We know from geological mapping where cave-bearing limestone is, we can explore the surface, find an entrance and use satnav to position it. But once underground, what is round the next corner? A vertical drop, a climb, a swim, crawl or wallow? What equipment is required? How does the cave passage connect with other entrances and resurgences? How do we tell other people where we have gone if there are no named passages or known layout? What we need is a map, the means to produce it, and the original explorers who have the privilege of naming the cave and passages for future reference.



The Gaping Gill cave system lies deep below Ingleborough Peak within the Yorkshire Dales National Park. Documented exploration began in the 1800s and in 1895, EA Martel made the first descent of the 105m-deep main shaft using hemp rope and ladders, discovering the main chamber with water flowing out through the boulder-filled floor.

The water of Fell Beck entering the chasm of Gaping Gill was suspected of appearing again at the resurgence of Ingleborough Cave. A parson had tried to prove this by throwing wooden blocks down the main shaft, carved with his details and a reward for anyone subsequently finding one, without success. Early explorers were spurred on to find the underground passage that would prove the link from Gaping Gill to Ingleborough Cave. These ‘winch meets’ are still available to the public every year courtesy of Bradford Pothole Club for one week in May and Craven Pothole Club for one week in August.

The winch meets have facilitated exploration within Gaping Gill with maps produced in 1895, 1908, 1912, 1930, 1937, 1952, 1966 and 1975. These were completed by different caving clubs and individuals, often with older data, the majority of the original survey data has been lost.

In 2005, the University of Leeds used LiDAR to create a 3D model of the main chamber. It also conducted a Ground Penetrating Radar survey of the floor showing there to be boulders as deep as 30m through which the waterfalls from the surface filter through to the flooded phreas level below. By 2008, a new LiDAR survey was completed – by myself and Meg Stark – of the main chamber and main shaft as well as an area called Mud Hall.



Clothing and equipment for caving need to be appropriate for the cave passages being negotiated. Factors to take into consideration include the temperature – 9°C all year-round underground in the Yorkshire Dales – the amount of water, the amount of crawling, the number of vertical pitches and exposure to wind. Wind is a significant feature of the Gaping Gill system which is driven by the waterfalls of the main shaft and the chimney effect of the multiple entrances. Wind can indicate a new cave passage, but rapidly wicks heat away from the body especially when the caving suit is damp.

Sometimes, a change of clothing underground helps. While in Gaping Gill, a wetsuit was worn to get through a muddy water-filled canal and the 2m-long ‘Font’ which is negotiated on your back, helmet off, with nose in the limited roof airspace. On the other side is the lengthy, dry and sandy Whitsun Series for which ‘furry’ and oversuits protected in a waterproof drum replace the wetsuit. In this way, mud is not dragged through by the wetsuit, helping to preserve the clear and white formations.

Keeping on the move also helps to maintain body temperature. But surveying is slow work and this creates the problem of over-heating en-route to the furthest reaches of the cave system, then adding additional dry clothing to slow down the rapid cooling once the surveying starts. Every survey assistant was instructed to say when they were cold and the survey would end at that point. 

There was one occasion when I got cold before the assistant had said anything and when asked, their response was that they had stopped shivering – time to eat the emergency rations and get out fast in order to warm up. 


stalactiteAdmiring a large stalactite at the far end of the North West Extension of Gaping Gill



Detailed weather forecasts are essential viewing prior to a descent as a number of cave passages flood to the roof, becoming ‘sumped’, which could trap a party at the far reaches of the system or in certain places lead to drowning. Evidence of these events can be seen with grass wrapped around stalactites and sometimes calcited over – a sobering thought when passing underneath them.

In August 2016, there was an exceptional flooding event during the CPC Gaping Gill winch meet. Four cavers plus myself, all with extensive experience of the system, descended from the Bar Pot entrance. Normally dry, this had a waterfall halfway down. Progress to the main chamber was stopped because the southeast passage was sumped to the roof with a raging stream pouring out of the main chamber.

An alternative route was used to reach the main chamber where we discovered a deep lake. A stone marker left in place at the water edge was subsequently measured using the survey stations to calculate a water depth of 8.5m. The lake vanished into the cave system within five hours. Water has been timed via dye to take 11 days to travel from the main chamber to Ingleborough Cave, however the resulting pressure surge burst through the concrete at the entrance of the Ingleborough Show Cave within just a few hours.

On a trip to the appropriately named Avalanche Inlet, a handhold, being used on a climb by a survey assistant, peeled off and smashed into the legs of the other assistant standing below. The injured party was evacuated from the fell via tracked vehicle and then on to a local hospital for X-rays showing nothing broken, just severely bruised legs.

Leakey’s Cavern in Stream Passage Pot had not been visited for many years. This required a pendulum on the rope to the entrance ledge before installing stainless steel anchors to drop a rope into the cavern. Two of us negotiated this drop without incident but on the return of the first, a large tombstone-sized slab started moving from the wall. The climber was able to inch past holding it in place with his knees while I ran to the far end of the cavern and made myself as small as possible before the tombstone came crashing down, the cavern filling with a distinctive smell of crushed rock.

The Blowhole, so called because of the strong airflow indicating that Southgate is not sumped (a good thing), is a very restricted space which has to be passed to gain access to the Far Country and Far Waters. Many cavers are physically too large to fit through, while small and thin cavers slide through with ease.

I am in the middle category which requires me to push with my legs and arms to compress my rib cage and hold my breath to negotiate the tight bit. Gravity helps the slide in but this only exacerbates the anticipated return. It is very much mind over matter whether to go through - sometimes you have to know when to back off. The cave will always be there.



The biggest discovery has been just how long the Gaping Gill cave system has become. When last assessed in 1991 by the Northern Caves Volume 2 caving guide book, the length was 10.8km. The new survey currently has a length of 22.15km showing just how much of the cave has been discovered in the last 26 years.

There is a significant difference in some cave passages to the prior surveys and it is all too easy to think that the prior work had errors. What needs to be appreciated is the nature of some of the cave passages and the difficulty in taking readings from a compass and clinometer in a freezing passage as small as 25cm high, wearing woollen clothing.

For instance, three sumps in Far Country and Far Waters are all at the same elevation, 27m vertically above the sump level along the Mud Pot to Deep Well geological fault with the waters known to be connected via die tracing. This indicates that there is a new dry cave passage to be found, which has peaked the interest of some cave divers to revisit these sumps.

The Northern Line is not as far north as the original survey, making it less likely to be connected to the Whitsun Series – an earlier survey had these two passages crossing which had spurred many cavers to try to connect the two.

Our new survey is the first of Gaping Gill that will provide a detailed 3D model and this clearly shows the extensive horizontal passage development at the porcellanous band level – a slightly more impervious oolitic strata than the more typical limestone surrounding it. The current deepest point reached by cave divers in the phreas lies 30.4m vertically below the resurgence at Clapham Beck Head Cave. This deepest level is believed to be at the base of the limestone.



The surface of the Gaping Gill area is dominated by peat, limestone pavement, escarpments and shakeholes. The latter are conical depressions within the limestone, are often cave entrances, many are still filled with boulder clay from the last glacial period. The available topographical data, from Ordnance Survey or Shuttle Radar Topography Mission or Environment Agency, lacks detail especially with respect to shakeholes so it was decided to conduct a new surface survey using kinematic post processing of the professional GPS, mounted on a backpack, with position accuracies of 10cm every second. Every shakehole was walked in a spiral pattern round the cone down to the bottom and back out again. The end result is a very detailed surface map to go with the new 3D model of Gaping Gill to help understand the geological development and where there may be new entrances to be found.



Laser Rangefinder

DistoX2 – £350 to £400

A Leica Geosystems Disto X310 laser rangefinder with the internal processor board replaced with a DistoX2 cave surveying board and a non-magnetic battery. Capable of recording 1,000 measurements and communicating via Bluetooth. Records magnetic azimuth, inclination and slope distance.


Waterproof Notepads

Muddy Duck – £2.95

Extra heavy-duty waterproof paper and plastic binders. Survives cave water, grit and mud. Allows measurements and drawings of cave passage to be recorded by pencil.



Petzl Elios – £35

Protects the head from changes in roof height and loose rocks.



Warmbac wetsocks, hood, Warmtex kneepads and elbow pads. Aldi builders gloves

Protects the extremities from knocks, prolonged crawling and exposure to wet conditions. Gloves essential to prevent finger ends becoming worn down from prolonged exposure to water and grit. Thin enough to provide tactile feel of buttons on DistoX2. Kneepads doubled up for trips to the far reaches of Gaping Gill.



Warmbac Cordura Oversuit/Furry Undersuit – £100/£80

Furry one-piece undersuit for warmth and quick draining of water. One-piece Cordura oversuit to protect from mud, grit, sand and sharp limestone.



Fenix HL55 headlamp/PD32 torch – £52/£44

Equipped with 18650 Lithium 3400mAh batteries. The HL55 provides four levels of wide-beam lighting while the PD32 provides a long-range spot beam for looking up avens and down pitches. Waterproof to 2m water depth. Two lights provide full redundancy.



Dunlop Acifort Heavy Duty Wellingtons – £19.99

Better without the steel toecaps because extensive crawling tends to wear the toes down quickly. Good grip, flexibility and feel of the rock through the soles.



Warmbac Tackle bag – £57

Flexible enough to squeeze through small passages, shoulder straps and grab handles for a variety of carrying options. Drag loop for attaching to harness for crawls up and down vertical drops.


Safety Gear

Petzl SuperAvanti Harness, Ascenders and Stop Descender – £250

A complete Single Rope Technique kit for negotiating vertical drops, lightweight, robust and lasts many years of abrasive grit and mud covered rope and cave passage.


Wetsuit Combination

Lomo Farmer John Wetsuit and Bolero Jacket – £40 and £29

For really wet and muddy caves. Provides 3mm neoprene thickness on the limbs for flexibility, while giving 6mm on the torso for core warmth.



Blackfriars Flapjacks, Aldi Hike Bars and HiGates Flapjacks to maintain energy and warmth levels while underground. The packaging is good enough to survive being dropped in mud and water, or even squashed in a helmet or undersuit.


floodAn exceptional flooding event hit the cave system in August 2016


Kevin Dixon is a Geodetic Surveyor who has worked on all seven continents and more than 120 countries. He has been involved with the development of Professional GPS since 1988 and has more recently been applying LiDAR technology to underground surveying as featured on the BBC’s The One Show, Coast and Channel 5’s Underground Britain. For more information on visiting Gaping Gill and Ingleborough Cave, visit www.bpc-cave.org.uk/wp/gaping-gill

This was published in the December 2017 edition of Geographical magazine.

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