The Phong Nha – Ke Bang National Park in Vietnam contains the oldest karst system in Asia, between 400 – 450 million years old. Hang Son Doong itself is relatively young, with the analysis of sediment dating it to be only 3 million years old.
Formed on the edge of a fault zone, Hang Son Doong was carved out by the mighty Rao Thuong River as it eroded away the limestone, forming the enormous tunnel beneath the Truong Son Mountains. Giants dolines were created as parts of the ceiling fell in up to 300,000 years ago, creating massive openings to the outside world. Cave pearls the sizes of baseballs have been formed by water dropping from the ceiling.
The first expedition was halted by an 80 m high calcite barrier, which was affectionately named “The Great Wall of Vietnam”. It wasn’t until their second expedition in 2010, when the Great Wall was finally climbed and the end of the passage was found, that Hang Son Doong was determined to be the largest cave in the world.
At over 5 km long, with sections reaching up to 200 m tall and 150 m wide, Hang Son Doong is large enough to house an entire New York block, complete with 40-story skyscrapers. With a total measured volume of 38.5 million cubic meters, this comfortably surpasses Deer Cave in Malaysia, which was previously considered the record holder. Stalagmites up to 80 m high have also been surveyed, the tallest ever encountered.