Gaping Gill cave system

Gaping Gill landscape

Chemical weathering results in a number of characteristic solution features in the landscape around areas of massive limestone.

Elsewhere in this section you can find information about underground features formed by solution and precipitation. We will look at one example of a cave system in more detail: Gaping Gill (sometimes known as Gaping Ghyll).

The safest way to see spectacular caverns is to visit a show cave, which have been made safe for visiting tourists and have expert guides and equipment at hand. There are a number in Yorkshire, but the one relevant to this section is Ingleborough Show Cave.

Caves and potholes are dangerous places and should not be entered without expert guidance and equipment.

The evolution of Gaping Gill

Gaping Gill landscape

The Gaping Gill cave system has an ancient history that goes back several million years.

The caverns and underground passageways that make up the Gaping Gill cave system were formed by the passage of water.

Acidic water picked out the weak joints and bedding planes, gradually widening them first to a few millimetres, then a few centimetres and eventually to several metres.

In places where the joints, bedding planes and geological faults made a particular site even weaker than the rest, wide caverns developed, many tens of metres high.

Erosion in flood

Although the caves are made almost entirely by solution, a small part of cave formation is due to erosion, especially when the river is in flood. Sand and pebbles are used by the river to scour and erode away its channel.

Banks of sand and gravel are found in Sand Cavern and towards the back of the Ingleborough Show Cave just before the visitor reaches the so called 'Pool of Reflections'.

Ice age interruption

During the last ice age, Gaping Gill swallow hole was blocked and the meltwater from the retreating glaciers that fed Fell Beck cascaded into Clapdale. Today, Fell Beck follows tunnels and caves below Gaping Gill.

Fell Beck does not use all the caves and passageways to move through the cave system. Some are dry fossil caves. These caves and passageways were created by solution by water, but they are now dry.

During the last ice age, glaciers eroded the valleys and carried the rock away as moraine. This caused a lowering of the valley floor; the water table dropped and the resurgence level lowered. As a result, the water formed new passageways, found other routes to move through the limestone and abandoned the old passageways.

Younger precipitation features

The stalagmites and stalactites that have grown in the cave system are much younger. It is possible to date the calcite within stalagmites and stalactites by radioactive materials such as uranium, which occurs naturally in very small amounts.

The oldest stalagmites from the passages between the caverns, called Main Chamber and Mud Hall, are between 230 000 and 350 000 years old, while some in the area around Mountain Hall are up to 135 000 years old.

Schematic section through Gaping Gill and Clapdale valley

Gaping Gill swallow hole

Gaping Gill waterfall

The waters that feed the Gaping Gill cave system enter mainly through three potholes:

  • Gaping Gill
  • Disappointment Pot
  • Stream Passage Pot

(There are three other entrances to the system — Car Pot, Bar Pot and Flood Entrance Pot.)

Fell Beck, which drains Simon Fell on the eastern side of Ingleborough, cascades down the vertical shaft of Gaping Gill to the cave floor 110 m below. It forms Britain's largest unbroken waterfall.

The upper part of the shaft is about 10 m in diameter but it widens out dramatically about 70 m down where it reaches the roof of Gaping Gill Main Chamber.

This is Britain's largest cavern, 140 m long, 30 m wide and 30 m high. The known mapped cave system below Gaping Gill is over 16 km in length, although the smaller uncharted caves and passages extend many more kilometres.

The cave system

The water that falls down through Gaping Gill disappears into the floor of the cave on its way to the resurgence.

Dry, fossil caves extend out from the Main Chamber. They are mainly tube-like passages that formed when the water table was much higher and the cave system was flooded (they formed in the phreatic zone) and in part follow faults through the limestone.

There are several large caverns in the cave system that can be reached only by expert cavers. To the east of the Main Chamber is Mud Hall and to the south is Sand Cavern.

Rivers flowing deep underground

Deep within the cave system are the Far Country passages, which were deeply trenched by a river that once flowed through the caves (they were formed in the vadose zone) and the cavern called Mountain Hall is also found there.

The waters of Fell Beck flow through some of the passages in the cave system and, a little to the north of the Ingleborough Show Cave, is another series of passages and caverns called the Inauguration Series.

These partially flooded caves follow bedding planes in the limestone: one to Beck Head Stream Cave and the Clapham Beck resurgence; another down formerly phreatic tube passages to Ingleborough Cave, and a third to Foxholes resurgence.

Precipitation features

Water flowing through the cave system created a spectacular cave that is now open to the public: Ingleborough Show Cave. It is possible to walk about 400 m into the cave and see many examples of the solution and precipitation features characteristic of karst areas.

Ingleborough Show Cave is an important tourist attraction in the area (and tourism is a major source of income in the Yorkshire Dales).

Ingleborough Show Cave

Stalactites

Stalactites are common. They formed by the precipitation of calcite from mineralised water on the cave roof. Some are given names according to their resemblance to everyday objects, for example the 'Coffee Pot'.

One part of Ingleborough Show Cave has been called Eldon Hall. It contains a group of very thin helictites, stalactites that appear to defy gravity, twisting and turning in different directions.

Although the method of their formation is not understood in detail, these kinds of speleothem are often caused by changes in the direction of calcite crystal growth, possibly due to air drafts.

Jockey Cap stalagmite

Stalagmites

Stalagmites are also forming in the cave and they are often given names. The 'Jockey's Cap', for example, is a large stalagmite about 3 m in circumference, and about 1 m high.

Stalagmites are also formed by precipitation of calcite, derived from water dripping from the ceiling.

Great Pillar

Pillars

Pillars are present in the show cave. Here the water dripping from the end of a stalactite lands on the cave floor below, liberating more calcite.

The stalactite grows downwards and the stalagmite grows upwards until the two unite to form a pillar. The water then flows down the outside of the pillar, thickening it further by precipitating calcite on it surface.

An example of this can be seen in Ingleborough Show Cave where the 'Elephant's Legs' are two thick pillars that formed by stalagmites and stalactites uniting into one.

Clapham Beck Head resurgence

Clapham Beck resurgence

Fell Beck drains the eastern side of Ingleborough and flows underground at Gaping Gill and re-emerges (resurges) in Clapdale.

It was not until 1983 that it was discovered that the outlet passages were near Clapham. This was established by releasing fluorescent dye into Fell Beck and waiting until it flowed out at a resurgence. However, the route was not explored until the 1980s, when cave divers explored the caves.

Surprisingly, although the water that tumbles down Gaping Gill drops 110 m to the Main Chamber floor, it flows vertically down only another 70 m of rock before it reaches the resurgence at Beck Head.

Underground watercourses

The underground watercourse of Fell Beck flows through the cave system on its way to the resurgence at Clapham.

One of the best places to see the resurgence is at Ingleborough Cave. Although it is not the main resurgence of the cave system it is the most accessible because in 1837 a calcite dam about 20 m inside the entrance was removed, releasing Fell Beck. The water level of the dammed water can be seen on the cave wall.

Most water sinks lower in the cave system, below the level of the show cave, and flows through other cave systems. There are several outlets for the water from Fell Beck including one just below the mouth of the show cave, but the main resurgence takes place at Clapham Beck Head Cave, about 70 m north of Ingleborough Cave. This flooded cave is inaccessible and the route that the water takes through the cave system is still not known.

The rocks below the Carboniferous limestone at Clapham are ancient grits and shales, and more impermeable than the limestone. Water does not pass through them easily. Fell Beck follows the limestone on top of this impermeable rock at Clapham Beck Head resurgence, over the North Craven Fault and down to the lake at Clapham.