Journeys into the depths of the Earth

The Thai cave rescue has thrown light on the dark and sometimes dangerous world of caving

When did caving begin?

Cave paintings found all round the world show that humans have been exploring the “dark zones” of caverns since prehistoric times. However, modern caving began in the late 19th century. In the 1880s and 1890s, a French lawyer named Édouard-alfred Martel travelled across France exploring its extensive cave networks and underground rivers. He visited caves across Europe – he was the first to complete the 98-metre descent into Gaping Gill in Yorkshire in 1895 – and the US. The sport was popularised in the 1930s and 1940s, when the availability of nylon ropes and wire scaling ladders made it easier; in Britain, the first caving clubs were formed in Somerset and the Yorkshire Dales.

What do cavers do?

Cavers, also known as potholers and sometimes spelunkers, explore cave systems, which are mostly formed by the action of underground streams cutting through limestone, eroding seams of calcium carbonate along their joints and fractures, and creating extensive networks. “A typical caving trip may involve climbing, abseiling, crawling, swimming and walking,” says the British Caving Association. It’s a challenging pastime, which involves passing through tight “squeezes”, “crawls” and “boulder chokes”, rappelling down steep shafts (and ascending back up them), and ducking through waterlogged “sumps”.

What is a sump?

The early cavers often found that their explorations ended at an underground pool of water – a “terminal sump”. On closer inspection, these often turned out to be mere watery U-bends, which could be passed through by taking a deep breath and “freediving” through to the next dry part of the cave. Some sumps, though, were bigger – and this gave birth to cave diving (see box). In 1936, Jack Sheppard and Graham Balcombe, two Post Office engineers, made a basic respirator from a football pump and a long tube, and used it to pass Sump 1 at Swildon’s Hole, the longest cave system in Somerset’s Mendip Hills. The pair formed the Cave Diving Group, using seadiving suits and air lines to walk along the underground riverbed in nearby Wookey Hole, discovering five new chambers, including the spectacular “Cathedral Cave”.

Is caving dangerous?

It can be. The main dangers include falling, being hit by falling rocks and the cold. Also, as in Thailand, water levels can rise fast in heavy rain. The UK’S worst caving accident happened in Mossdale Caverns on Conistone Moor in Yorkshire in 1967, when one inch of rain fell in three hours and the caves were flooded. Six young cavers were caught several hours from the entrance in the “Far Marathon Crawl”, a 275-metre crawl 25cm high and 60cm wide. Despite a heroic rescue effort mounted by fellow cavers – the only people with the skills to mount such attempts – they were found dead. Generally, though, as long as appropriate precautions are taken – checking weather forecasts is crucial – and groups are accompanied by experienced cavers, it is perfectly safe: thousands do it every weekend in Britain. The more extreme end of the sport, though, is a quite different matter.

What do extreme cavers get up to?

A world depth record was set by the Ukrainian Gennady Samokhin in 2012, who, with a 59-strong team, journeyed more than two kilometres down into the Krubera Cave in Georgia, one of the deepest known on Earth. They spent 37 days exploring the cave; when they reached the terminal sump, Samokhin donned his diving gear and descended to 2,197 metres down. Similar expeditions have taken place in another “supercave”, the Chevé system in Oaxaca, Mexico. In 2013 Phil Short, a British cave diver, and his Polish colleague Marcin Gala went 1,200 metres down and 12km horizontally before reaching the bottom of the J2 cave. They dived through four sumps, one 600 metres long, and spent 42 nights below the surface. These expeditions are like Everest ascents turned upside down, with base camps, underground camps and complex logistics, but they don’t end with a spectacular summit; they end with a wall or an impassable sump.

And this must be very dangerous?

Indeed. In 2014, Johann Westhauser, a German caver, suffered a traumatic brain injury in a rockfall about a kilometre from the surface in Bavaria’s gigantic Riesending cave. It took more than 700 people and 12 days to bring him to the surface. There are regular deaths on the more ambitious caving trips. Perils include histoplasmosis, a fungal infection acquired from bat guano; poisonous gas inhalation; and an illness known as “the rapture”: a kind of powerful anxiety attack caused by extreme darkness and depth. “At some level, everyone’s brain will start to say, ‘I don’t belong here. This is a very dangerous place,’” says James Tabor, author of Blind Descent, about the exploration of supercaves.

So why do people do it then?

Some cavers are geologists and biologists, and have made scientific discoveries: in Krubera, there are primitive eyeless insects that feed on fungi and decaying organic matter. But the thrill of exploration is the real draw: these are some of the last unknown places on Earth. Sometimes caves are beautiful, too: “caverns measureless to man” with spectacular mineral deposits and turquoise pools deep underground. Even in the UK, there are exciting discoveries to be made. Titan in Derbyshire, Britain’s deepest shaft cave, was only discovered in 1999. Sump 12 in Swildon’s Hole in the Mendips remains unpassed. In 2011, after more than a century of exploration, the final link in the “Three Counties System” was found, meaning that, as one caver put it: “It is now possible to go underground in Cumbria, travel below Lancashire and emerge in Yorkshire (if you are hard).”