Why has the giant sinkhole only just been discovered?
Nguyen Van Uy, a cave expert with the National Speleological Society (NSS) of the US and deputy director of Jungle Boss, was among 24 members of an expedition that surveyed the giant sinkhole in Phong Nha-Ke Bang National Park, Quang Tri Province.
Speaking to Dantri/Dtinews, Uy described the trip as a special experience and a remarkable new discovery.
To reach the sinkhole, he and the other expedition members had to trek 20km through dense forest without established trails, navigating sharp limestone formations and facing severe water shortages during the dry season. The survey lasted a full week.
Cave expert Nguyen Van Uy (right) and expedition members abseil down a sheer rock face to reach the sinkhole floor (Photo: Jungle Boss).
“The sinkhole lies in rugged forest with no streams nearby. Local people travelling through the forest have little reason to visit or pass through this area, so it has largely gone unnoticed. Although we have spent many years exploring Phong Nha-Ke Bang, this area was relatively unfamiliar to us,” Uy said.
The cave expert added that the entire sinkhole and its surroundings are covered by pristine forest. The green canopy acts as an effective camouflage, making the enormous depression almost invisible from above.
The giant sinkhole in Phong Nha - Ke Bang National Park seen from above (Photo: Jungle Boss).
The discovery began when Kevin Ditamore, a veteran member of the NSS, noticed an unusually large dark patch in Phong Nha-Ke Bang National Park while reviewing satellite images on Google Earth.
“Satellite imagery has its limitations, so locating the sinkhole was far from straightforward. We carried out three drone surveys before gradually pinpointing its exact location. Several months of preparation were needed before the expedition could begin,” Uy said.
Uy said the newly discovered sinkhole was the largest he had encountered during more than 20 years of trekking and exploration in Phong Nha-Ke Bang. The team installed a safety system and descended ropes along a sheer rock face to a depth of 120 metres to survey the sinkhole floor.
He believes the area may have contained an underground stream millions of years ago. Geological processes later disrupted the flow, causing layers of rock and soil to collapse and form the sinkhole seen today.
“The floor of the sinkhole supports a thriving, pristine ecosystem with many mature trees, suggesting that it formed millions of years ago. Temperatures and humidity inside are also lower than outside, creating favourable conditions for vegetation,” Uy said.
At the bottom of the sinkhole is a thriving primary ecosystem with many ancient trees (Photo: Jungle Boss).
The expedition also found piles of seashells and snail shells along the rock walls, as well as several monkey skeletons inside the sinkhole.
During the survey, the team searched for geological signs that might lead to an underground cave but found no promising route. It discovered a fissure five metres high and 12-15 metres deep, but there was no airflow through it. Rock and soil deposits from previous landslides had completely buried the base of the cliff and the former watercourse, leaving no visible direct passage into an underground chamber.
A vast cave system may lie beneath the sinkhole
Le Luu Dung, an experienced cave explorer who has conducted expeditions in Vietnam and abroad and is also affiliated with the NSS, said the sinkhole in Phong Nha-Ke Bang National Park appeared to have resulted from a major geological collapse.
Dung suspects that a very large cave system may lie beneath it. However, the expedition has yet to find an entrance leading into the underground chambers. If the sinkhole connects to a main cave, its overall depth could be greater than currently measured.
Cave expert Le Luu Dung (Photo: Provided by the subject).
“The sinkhole covers a vast area, so searching for passages connecting it to the main cave will be difficult and time-consuming. The pristine forest inside could be the largest forest within a cave in Phong Nha-Ke Bang, and possibly in Vietnam, at present,” Dung said.
He noted that Phong Nha-Ke Bang contains several other deep and large sinkholes, including Kong Sinkhole in the Tiger Cave system, Nightmare Sinkhole in the Hung Thoong cave system, and Dinosaur Eye Sinkhole in Son Doong Cave.
Unlike the newly discovered formation, however, these other sinkholes are connected to underground cave passages, making exploration more straightforward.
“This new sinkhole is in extremely rugged terrain, far from accessible routes, and some areas have no nearby water sources for drinking. Survey work will therefore be very demanding,” Dung said.
“The sinkhole narrows at the top and widens towards the bottom, so there is a strong possibility that the cave beneath it is enormous. At present, it may be buried under a massive accumulation of collapsed rock and soil.”
Le Luu Dung suspects there may be a very large cave system beneath the sinkhole (Photo: Jungle Boss).
Jungle Boss, the NSS and the management board of Phong Nha-Ke Bang National Park in Quang Tri Province recently announced the survey and measurements of the previously unexplored giant sinkhole in the Cha Noi-Khe Gat area of the park.
The sinkhole has an inverted-bowl shape, widening towards the bottom. Its oval opening measures 190 metres by 140 metres, while the interior is 250 metres long and 200 metres wide, with a depth of 120 metres.
The sinkhole covers an estimated two hectares, equivalent to about three standard football pitches.
The exploration company has submitted a detailed report and field measurements to the national park’s management board, recommending further research in the Cha Noi-Khe Gat area and surveys of additional access routes from outside the sinkhole.
