A new underground tunnel is discovered in Son Doong, revealing more mysteries from the world's largest cave (Photo: Jason Speth)

An international press conference on Tuesday in Hanoi announced the discovery, which was made during a research dive by a British Cave Research Association team. Some of the team’s members took part in the rescue of the Wild Boar football team in Tham Luang, Thailand in 2018. 

The purpose of the research trip was to find a connection between Son Doong Cave and Thung Cave. The team conducted a dive to the depth of 77 metres looking for a passage to Thung Cave, but didn't succeed. At this depth, it becomes impossible to use ordinary compressed air. According to a dive expert Jason Mallinson, the depth of the tunnel could be 100m or more, and the team couldn’t go any deeper due to the limitation of their equipment. The dive team plans to use compressed helium for the next dive. 
On this expedition, the cave experts found a new tunnel system at a depth of 60 metres. The deeper it goes the wider the underground cave system opens up.  Howard Limbert of the British Cave Research Association team said Son Doong does not end where the river flows into the passage, but expands into the underground tunnel. The team will return to Son Doong Cave in the near future to continue exploring the cave with equipment that will allow them to dive to greater depths and map the cave. 
The discovery has made Son Doong even more mysterious to cave experts and scientists. With a total measured volume of 38.5 million cubic metres, it comfortably surpasses Deer Cave in Malaysia, the previous record holder.