Kents Cavern, Torquay, Devon - British Geological Survey

Kents Cavern is a show cave in the town of Torquay in the south of Devon, at the heart of the English Riviera and part of UNESCO’s English Riviera Global Geopark. It contains spectacular cave formations (or ‘speleothems’) such as stalagmites, stalactites and flowstone and is world-famous because a piece of jawbone discovered here in 1927 is the oldest known, modern human fossil from north-west Europe.

Geology

Kents Cavern is found within the Torquay Limestone Formation, which is approximately 388 to 393 million years old, making it Devonian in age. This is unusual in the UK, as most cave systems here have formed in Carboniferous limestones (359 to 299 million years old).

Geological map of the Torquay area, with the location of Kents Cavern marked by the red dot. Pink: igneous intrusion; purple: interbedded mudstone and limestone; pale green: limestone (including the Torquay Limestone Formation); dark blue: interbedded mudstone, siltstone, sandstone and limestone; grey: interbedded mudstone, siltstone and sandstone; orange: interbedded breccia and sandstone; yellow: interbedded sandstone and conglomerate. BGS © UKRI.

During the Devonian, Great Britain lay to the south of the equator and the Torquay Limestone Formation formed in shallow, tropical seas. Hundreds of millions of years later in the Pleistocene — at least half a million years ago — water began to percolate through joints and fractures in the rock and started to dissolve it away. Over time, the cracks widened into fissures and then small passages. These would have been completely filled with water, which flowed through them creating long, circular cave passages and huge caverns as the water dissolved away more rock. Eventually, the water table dropped and the caves became dry.

The caves didn’t stay empty, however; they began to fill up with sediment carried in by debris flows entering at the far end of the cave system. The sediment included not only mud and rocks, but also the bones of animals and stone tools made by ancient humans. Animals like cave bears and hyenas also used the caves for hibernation and dens and left both their remains and the remains of their prey behind amongst the infilling sediment.

The sediment was then covered by a layer of calcium carbonate (calcite) called a stalagmite floor, which came from water dripping from the roofs of the caves, forming stalactites hanging from the cave ceilings and sealing in the sediment beneath it. This floor was subsequently covered by another influx of sediment during the last ice age, about 10 000 years ago, and again this was sealed in by another stalagmite floor on top.

Brown and pale layers of sediment and rock — The brownish material at the bottom of the picture is a debris flow deposit that was sealed by the paler, layered band above it, which is the stalagmite floor. The stalagmite floor can be traced throughout the whole cave. © Jacqueline Hannaford.

Speleothems

Kents Cavern has many spectacular and beautiful rock formations within it, including stalagmites, stalactites, pillars, flowstone and straws.

Victorian excavations involved destroying speleothems to gain access to the sediments buried beneath the stalagmite floors. The destruction reveals the layered nature of the floor, built up from drops of water depositing calcite over thousands of years. © Jacqueline Hannaford.

Stalactite straws, stalagmite columns and piles of flowstone. © Jacqueline Hannaford.

Each straw has a drop of water hanging from its tip, indicating that the speleothems are still actively growing. © Jacqueline Hannaford.

A face in the dark. © Jacqueline Hannaford.

Archaeological discoveries

Although the cavern had been known about since Roman times, it wasn’t until the nineteenth century that people began to explore the cave passages and come to realise their significance to Quaternary geology, archaeology and palaeoanthropology (the study of human evolution).

A few archaeological excavations had been made in the caves in the 1820s but it was the work of William Pengelly that brought fame to Kents Cavern. Pengelly worked in the caves for fifteen years between 1865 and 1880 with his small team of diggers. His pioneering techniques, including the first 3D grid mapping system, are the foundations on which modern archaeological methods are based. He was diligent in recording his finds and his team found bones of extinct animals including hyenas, cave bears, cave lions and woolly mammoths, and tools made by both modern humans and human ancestors. The oldest stone axes date back half a million years and would have been made by species such as Homo erectus, a direct ancestor of modern humans.

Animal bones from Kents Cavern, including cave bear, hyena, horse and reindeer. Nilfanion, CC BY-SA 4.0, via Wikimedia Commons.

The most famous find, however, was made in 1927 by Arthur Ogilvy: a human jawbone.

How do we know how old the finds are?

The stalagmite floors in Kents Cavern sealed in the debris flow sediments beneath them. Samples taken of the stalagmites can be accurately and precisely using uranium–thorium dating methods, so individual growth bands in a speleothem can be dated. This allows us to to investigate climate constrain the age of the sediments either above or below the stalagmite floor: for example, anything below the 500 000-year old stalagmite floor must be more then 500 000 years old.

Visiting Kents Cavern

Kents Cavern is open to the public Monday to Sunday from 10:30, with the first guided tour starting at 10:30. The cave stays at a constant temperature of around 13°C no matter what the weather outside, which can feel nice and warm in winter but a bit chilly in summer so choose your clothes carefully! Underfoot the caves can be a little slippery and rough in places, so take care if you are not steady on your feet.