World’s biggest cave is even bigger than we thought

CNN  — 

Thanks to discoveries made during a recent expedition in Vietnam, it appears the world’s largest cave, Son Doong, is even bigger than previously thought.

Last month, a trio of British divers – the same divers who aided in the rescue of the trapped soccer team in Thailand in 2018 – ventured to Phong Nha-Ke Bang National Park, in the jungle-filled Quang Binh Province of central Vietnam, to explore the cave’s waterways.

During the groundbreaking dive, they discovered an underwater tunnel that connects Son Doong (meaning “Mountain River Cave”) with another enormous cave called Hang Thung.

Son Doong currently measures a total of 38.5 million cubic meters (about 1.35 billion cubic feet). When it’s officially connected with Thung Cave, it will add an additional 1.6 million cubic meters in volume.

“It would be like someone found a lump on top of Mount Everest, making it another 1,000 meters higher,” says Howard Limbert, technical advisor of the Quang Binh-based Oxalis adventure tour company and one of the cave experts who helped organize the dive.

He tells CNN Travel, “Any cave in the world will be able to fit comfortably inside Song Dong when it’s connected – it’s just outrageous in size.”

Diving in Son Doong

British divers Jason Mallinson, Rick Stanton and Chris Jewell -- who helped rescue the trapped soccer team in Thailand in 2018 -- recently  dived in Vietnam's Son Doon Cave.

Oxalis, which is the only company licensed to bring travelers into Son Doong Cave, invited the British divers – Jason Mallinson, Rick Stanton and Chris Jewell – to visit the cave following the Thai rescue expedition.

“The divers did an amazing job rescuing the children in Thailand. We invited them on a trip to Son Doong to thank them for their great effort,” says Limbert.

“They wanted to do something interesting during the trip, so we came up with this idea of diving Son Doong, which had never been done before.”

Limbert says that the Oxalis team already knew that the water from Son Doong joined Thung Cave, through dye-testing, but no human has ever gone into these subterranean rivers.

During the mission, divers were able to reach a depth of about 78 meters while diving on air (oxygen and nitrogen) before turning around.

“When the divers reached 78 meters, they plumbed the depth below using a line and a lead weight. Hence, they believe the offshoot reaches a depth of 120 meters and continues for about 1 kilometer,” explains Limbert.

The team wasn’t expecting the tunnels to be so deep, because the other caves in the area are quite shallow.

“Now that we know how deep it is, we’ll bring the special gases [oxygen-helium mixture] with us next time to enable long, deep dives,” adds Limbert.

The divers plan to return in April again next year. This is the best time of year to dive, because water levels are relatively low, and visibility is better than usual – though still only about one to two meters.

“I think it’s incredible that something as important as the world’s largest cave is still being explored and better understood,” says Limbert.

“No one had ever set foot inside Son Doong until 2009 … and this latest discovery shows there are still an awful lot of things to uncover on this planet. It’s really exciting.”

Uncovering the cave