1. Understanding karst


A karst environment is formed when certain types of rock which are water-soluble erode over millions of years. The likelihood that these conditions will occur is particularly heightened in situations where there is a lack of drainage that would otherwise allow for underground water to seep out of the bedrock.

And in some instances, that same eroding force of underground water flow that forms karst can also create a far more impressive sight: a sinkhole. And there was one in particular in China’s Fengshan County that was ripe for exploring, and its mere existence had only just come to the attention of the scientific world. From there on, it would only garner more attention.

2. Forging the path

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The research team’s special mission had taken them to the south of central China, in the country’s Guangxi Zhuang Autonomous Region, which borders Vietnam. It’s a place of unbelievably stunning and surprising natural beauty, crosshatched by rivers, and intersected by various mountains chains, each one having a unique, almost otherworldly shape.

Many of the mountains, both in terms of their shape and the way they abruptly jut out of the landscape, seem as though they belong on another planet. Among the breathtaking sweeps of otherworldly landscapes, one of the ranges in particular had a secret so surprising that it was about to make news headlines across the world.

3. The fellowship sets out

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On October 4, 2018, a team comprised of 19 scientists, both Chinese and British, assembled for a four-day trek through the mountain wilderness of Fengshan County. They represented two organizations: the Chinese Academy of Geological Sciences Institute of Karst Geology, led by Zhang Yuanhai, and the International Cave Association, led by Andy Evans.

The area of the mountain range where the sinkhole was located was exceptionally remote. Pushing forward, the team members passed the village of Haiting, and sought out the sinkhole located in the Nongle mountains. Once they had at long last reached its entrance, they then steadied themselves and got ready for a perilous undertaking.

4. A geologist’s dream

sinkhole china tourism
Huo Yan/Leye Fengshan World Geopark

Fengshan County, which is a part of the Guangxi Region, has become a tourist attraction thanks to its natural wonders, particularly its mountain caves. Fengshan itself means “phoenix mountain” in Chinese. The bizarre and bold beauty of the region’s geology makes it appealing for both photography enthusiasts and thrill seekers alike.

One key feature behind the geological processes that had given birth to this jagged landscape was also the reason behind the existence of this sinkhole. The region is especially notable for its high concentrations of karst topography — and this would be critical to understanding the scientific marvel the team was about to uncover.

5. Edge of glory

sinkhole researcher

It was this remote mountainside of rural China where an international team of researchers strapped on their harnesses, jumpsuits, and climbing gear, as they stood poised at the daunting edge of a precipice, peering into a sharp drop that was only for the strong of heart. They were prepared to venture into the unknown depths of the abyss.

The group of researchers were about to carry out a mission few would dare to risk: to descend into a massive sinkhole that remained yet uncharted, then document their findings for the very first time. As the earth yawned open below them, one by one, they seized the rope and took the plunge, unaware of the spectacle they’d soon find.

6. Revelations of danger

sinkhole china mountain cave

Recently, an enormous chunk of rock in the Fengshan mountains had crumbled and collapsed. The landslide allowed for the yawning chasm beneath it to finally be revealed to the light of day. While this offered the exciting possibility of exploring the sinkhole, it also meant the rock surrounding it was potentially unstable.

The entire area bore the continual risk of subsidence. If this international team of geological researchers had any hope of fulfilling their expedition’s goals without any loss of life or damage to their equipment, they would have to proceed with the utmost precision. Carefully, they stuck their climbing picks into the rock.

7. One by one

sinkhole china
YouTube/BBC News

The explorers carefully anchored their repelling rope into the karst on the lip of the sinkhole, making sure it was secure enough to handle the weight of each one of them. Using what is known as single-rope technique the scientific researchers lowered themselves into the opening of the sinkhole, one by one.

Descending with just the one rope, they made the plunge hundreds of feet through thin air, past cave walls with a nearly vertical drop, fringed by lush vegetation. It was by far not the safest possible method, but they were confident that they knew what they were doing. Only time would tell, though, whether the method would work or not.

8. Into thin air

sinkhole china guangxi

By using just one rope they lessened the risk of creating more fractures in the rock surrounding the mouth of the sinkhole. As each of the team members made their way safely to the cave floor, they looked back up, anxiously awaiting the arrival of the rest of the team.

They rappelled down into the belly of the beast. And finally, every single one of the intrepid geologists made it safely into the entrance of the sinkhole. Then, they could finally stand on their feet together and begin to explore. They looked around to acclimate to their surroundings, but what they saw left them speechless.

9. A hole to the sky

opening sinkhole china geology

The underground world stretching out before the scientists’ eyes inside the sinkhole was beautiful beyond description, and filled with unknown possibilities. Everything they would document would be a new revelation to the world of geological science. In Chinese, this specific sort of sinkhole formation would be classified as “tiankeng,” literally meaning skyhole.

Tiankeng is the term used to describe a category of sinkholes that are deeper than 100 feet. Considering the magnanimous forces of erosion required even to create a sinkhole in the first place, the amount of force it took to create this natural wonder was extraordinary. And what the scientists would proceed to see was exceedingly rare.

10. A rare geological find

sinkhole cave researchers

Less than 100 giant sinkholes of this variety have been discovered across the planet. That rarity heightened the importance of the scientific mission, bringing it to a whole new magnitude. The team of researchers was truly in one of the deepest sinkholes on the planet, and now it was time to map out its course.

Once they were on stable ground in the slippery environs of the sinkhole, the scientific researchers set up their equipment and got ready to discover the cave’s secrets. Anything was possible, and their flashlights and headlamps revealed the extent of this untouched and unexplored underground world of which they were pioneers. Facing an expanse of an unknown size, they’d prepared a plan to reach all the secret chambers and hallows of the vicinity.

11. 3D scanning

stalactite cavern sinkhole

Thanks to sophisticated advancements in science, the explorers would not have to trek the entirety of the cave in order to comprehend its extent. Utilizing the technology of 3D scanning, the team of researchers and geologists would be able to document the full scale of this underground cavern of the sinkhole.

Water trickled from the bizarre rock formations on the roof of the sinkhole. Every nook and cranny of the cave hidden for millions of years from human view was new information yet to be documented and shared with the world of geological researchers. With the method of 3D scanning, the team would soon uncover something they hadn’t expected.

12. Underground network

rock sinkhole
Alessio Romeo/ESA

By means of 3D scanning, the team would not only map out the obvious areas that were immediately apparent to them, such as the entrance and the main hall of the cavern. The scanners would be able to uncover layers of the system hidden deep beneath eons of rubble, rock cover, and debris that would reveal an incredible discovery.

They could now see the other hidden passageways that made up the entirety of the vast subterranean network, including some of the tunnel systems of the sinkhole which were concealed deep below its rock floor. What the results of the 3D scanning would show would put the sinkhole in the record books.

13. Immense proportions

sinkhole photography

The size of this discovery was nothing short of monumental. The basement of the main hall of the cavern, the initial room that they had rappelled down into, plunged down to 400 feet below the entrance. It turned out that the sinkhole measured 650 feet in length with a mouth of approximately 330 feet wide.

But to understand the nerve-wracking plunge that the expedition team members had taken in the name of science, the sinkhole must be seen in proportion. In fact, if measured from the tip of the mountain surrounding it, the entire complex meant a terrifying 1,476 foot drop. Just how this massive geological site came to be specifically, could only be explained by it’s remarkable genesis story.

14. Tectonic history

sinkhole china

This entire region of China had once been under a primordial ocean, between 400 to 250 million years ago. Due to the shifting of tectonic plates, the Fengshan Mountains in Guangxi had been pushed up above sea level and covered in limestone that had been deposited in the former ocean.

This limestone had been dissolved ever so slowly to create this massive sinkhole near Nongle. The team of researchers were already aware of these tectonic processes as they set out for their expedition, though they hadn’t expected something quite this dramatic. But the 3D scanning was about to reveal to them yet another secret.

15. Water defeats rock

river sinkhole cave
South China Morning Post

In addition to the caves themselves, the 3D scanning exposed to the scientists yet another aspect of the cave system and the likely culprit of the sinkhole’s creation in the first place: an entire network of rivers. There were only hints of these bodies of water that had conquered the area, in the form of several small pools in the cavern.

Flowing deep beneath the Earth’s surface hidden from the human eye, since the Fengshan Mountains had been raised from the prehistoric ocean floor, these rivers were responsible for shaping the topography of the region. All of them drained into the Panyang River in the “above world.” But that paled in comparison to the greatest discovery yet.

16. Gargantuan sinkhole

sinkhole lagoon

When all the calculations from the 3D scan search of the karst sinkhole had been completed, the international research team of geologists was flabbergasted to realize that the entire sinkhole and the connecting arteries of caves constituted a total volume of 236 million cubic feet. This was truly a discovery of unfathomable proportions.

These numbers alone look impressive, but to truly understand the monumental size of the Nongle sinkhole, it has to be put into context. The entire space contained underground in the sinkhole could hold the entirety of the Great Pyramid of Giza — TWICE! Little did the team know, though, but their timing was more critical than they knew.

17. Collapsing cavern


The expedition team had been right to take extra precautions as they spelunked down into the sinkhole. As it turned out, it was highly likely the entire cavern was in the process of collapse, steadily imploding even as they explored it. After all, a rockslide had revealed the sinkhole in the first place.

Now, the team had been able to chart its previously unnavigated chambers before the sinkhole crumbled in on itself. Most ironic of all, there was one huge twist about this group of scientists. They had not been the only humans to peer into this abyss. They owed their achievement to someone else.

18. Finders keepers

Chinese Geological Survey

Funnily enough, the intrepid 19 British and Chinese geological scientists were not the first researchers to have discovered the sinkhole at Nongle. A team from Hong Kong had recently beat them to it. They had been the key to learning the location of the sinkhole after the landslide had exposed it.

It was the tantalizing news of this discovery in Fengshan County that had acted as the catalyst for the team to further investigate and document the scale of the cavern. But they made sure to do one thing so that they could recognize the work of those who had gone before.

19. Hong Kong Haiting Hall

rock cave sinkhole

The new team, gracious to the people who had tipped them off and given them the impetus for their trek, decided to give the sinkhole an official name: the Hong Kong Haiting Hall; Haiting after the name of the closest village, and Hong Kong after the place of origin of the first explorers who had discovered the sinkhole.

The teams of researchers had it as their goal to bring the Fengshan region to the forefront of geological research and understanding, to give its impressive and unusual topographical features a name on the world stage. And once news broke of their new subterranean finding, it would shoot to inconceivable heights.

20. A superlative find

sinkhole china
Wikimedia Commons/Public Domain

Once its size had been calculated, the Hong Kong Haiting Hall sinkhole would be ranked among the top 10 largest in the world. The largest sinkhole on Earth is also located in China. It’s known as Xiaozhai Tiankeng. Measuring 2,054 feet long, the enormous limestone formation was formed over the Difeng cave and caused by an underground river’s erosion.

But these karst sinkholes are ones that exist in mountainous areas relatively isolated from civilization, having been developed and shaped by intricate geological processes taking millions of years. On the other hand, sometimes sinkholes can open when you least expect it — and humans often have something to do with it, as you’ll soon see.

21. Nearly swallowed

sinkhole china bus
People’s Daily

The year prior, in a separate area of the Guangxi Region, in the city of Nanning, a sinkhole opened up from manmade circumstances — and very nearly could have cost dozens of lives. A harrowing video from a traffic camera showed a packed passenger bus rocketing down the road, just before the earth opened up beneath it.

The bus and the 20 passengers on board barely missed the sinkhole at the last second, its back tires grazing the asphalt even as the sinkhole opened. Investigations showed that Nanning’s city subway line passed directly underneath the same road, likely the cause for the terrifying incident. But this is far from the only manmade culprit for sinkholes.

22. A real threat

sinkhole backyard manmade

Sinkholes continue to fascinate geologists and laymen alike, certainly because of their destructive potential as seen in the human imagination. But although they are not a common occurrence, the processes behind the creation of more short-term sinkholes differ greatly from the karst sinkholes in China that formed over millions of years.

Manmade disruptions, such as sewage drainage issues and particularly mining, can often cause irreparable damage of subterranean conditions in a given area. In the most dangerous situation, layers of bedrock belie the clay beneath them, which absorbs water and eventually gives way. Mankind’s interference has even created sinkholes alongside one of the world’s most iconic wonders.

23. The Dead Sea

dead sea sinkhole
Travel Therapy Blog

The Dead Sea, shared between Israel, Jordan, and the Palestinian Territories is a world-renowned place of extremes. At 1,412 feet below sea level, it is the lowest point on the Earth’s surface that is not submerged beneath the ocean. It is also 10 times saltier than the ocean, causing anyone swimming in it to float without even trying.

But even though this unique formation has mystified and enthralled visitors for generations, both for its buoyancy and the supposedly therapeutic minerals in its muds and salts, something is terribly wrong with the Dead Sea: it’s receding and truly dying. And as it does, something incredibly dangerous happens along its shores.

24. Desert sinkholes

sinkhole dead sea israel jordan
Atlas Obscura

The Dead Sea is fed by the Jordan River, which flows in from the Sea of Galilee in the north of Israel. As the Jordan River has been diverted over the past decades, the Dead Sea’s water level has dropped dramatically. To make matters worse, water has been diverted to nearby factories for mineral product extraction.

As the Dead Sea receives roughly 20 percent of the incoming water flow that it used to, vast expanses of shoreline are no longer touched by saltwater. When groundwater collects there, it more easily washes out salts in cracks in the ground — making the surface more susceptible to collapse. The scope of the problem is expected to get even worse.

25. Perilous shores

sinkhole israel
The Times of Israel

Exacerbating the situation of the Dead Sea sinkholes even further is the fact that the entire region lies on the fault lines of the Syrian-African Rift Valley, causing craters, canyons, and fissures that can easily open up as the Dead Sea retreats. The western shore is now covered by some 4,000 sinkholes.

Signs on the side of the highway warn tourists and adventurers from exploring off the road for vast expanses of shoreline, due to danger of death. While no humans have been killed by Dead Sea sinkholes yet, local wildlife has occasionally fallen victim. There’s one last hope for this crumbling shore, however.

26. Saved by the river

sinkhole israel jordan dead sea
The Jerusalem Post

As the Dead Sea sinkholes open up closer and closer to the highway lining its shores, and the world wonder continues on its way to ecological disaster and utterly drying up, scientific researchers in Israel and Jordan are scrambling to find ways to save their landmark from completing its disappearing act.

A pipeline has been proposed that would funnel water all the way from the Red Sea in the south of both countries up to the expiring Dead Sea. Despite the danger in mixing outside water with the unique chemical composition that the Dead Sea has borne for millennia, it may be the only choice. But elsewhere, pits have not been formed by water — but fire.

27. A drilling accident

turkmenistan sinkhole

It began as a mining expedition. Soviet engineers in the Karakum Desert of present-day Turkmenistan were looking for a site rich in oil so they could build a new extraction facility. Curious about one spot in particular, they began to drill. It turned out to be a huge mistake the scale of which they couldn’t have fathomed.

The crust of the earth was far thinner than they had expected. As they drilled to investigate, it quickly crumbled under the weight of the heavy machinery. Piece by piece, the earth opened up under the engineers, sending them fleeing for their lives. Their equipment was destroyed. But what seeped out was about to produce a catastrophe.

28. The sinkhole leaks

turkmenistan sinkhole
Wikimedia Commons

As an enormous sinkhole quickly opened in the deserts of Turkmenistan, swallowing earth and machine alike, the thin layer of rock that had been ruptured now exposed a devilish secret it had been hiding: a reservoir of methane gas. Now the engineers had not only lost their equipment, but were endangering nearby towns.

Fearful that the gas cloud would escape and harm local villages, the engineers had to act. Local wildlife began dying from the methane, and though humans could breathe it with difficulty, just a small percentage in the air could cause an explosion. So they came up with a wild plan for the sinkhole.

29. ‘Gateway to Hell’

sinkhole desert fire

The Soviet engineers decided the best way to save both local fauna as well as the human population nearby was to light the methane gas on fire. This was a standard practice in mining and drilling, known as a controlled burn. It was the quickest solution to the problem the sinkhole was emitting.

So the engineers set it ablaze, figuring it would burn off relatively quickly. There was just one problem: that’s exactly the opposite of what happened. While the immediate threat to the surrounding area was averted, the fire didn’t stop. It kept burning, the methane deposits barely expended. Something had to be done.

30. Welcome to the sinkhole

sinkhole turkmenistan

At present, it’s been more than 47 years, and the sinkhole in the Turkmen Desert has not stopped burning. Scientists soon realized there was nothing they could do. The methane gas in the sinkhole continues to add an eerie glow to the desert night, and has been nicknamed the Gateway to Hell.

One look, and the description becomes immediately apparent. The Darvaza Gas Crater, as it is officially known, is 226 feet across and 98 feet deep. Several years ago, Turkemistan’s leader declared the area a nature reserve. This sinkhole is a testament both to the folly of mankind, as well as the wondrous sights the world can create.

Sources: Boredom TherapyScience Alert