It’s October in southern China, and a group of explorers are teetering on the edge of a vast sinkhole. Bravely, they descend into the darkness, with just a single rope between them and certain death. But as they near the bottom, they discover an incredible landscape hidden beneath the earth.
In recent years, a considerable number of sinkholes have made the news. Like, for example, the vast void that almost swallowed up a Florida resort in 2013. Or the chasm that destroyed a huge chunk of road in Fukuoka, Japan in 2016. But what exactly is behind the sudden appearance of these terrifying holes?
Simply put, sinkholes occur when the surface of the ground collapses. And most of the time, this happens as the result of natural processes. For example, in areas rich in carbonate rocks like limestone, the flow of groundwater can dissolve the rock over time, causing underground spaces to form.
As this process continues, these spaces grow to form caverns beneath the surface of the earth. And even though the land above them might appear to be completely sound, it is, in fact, precariously balanced on top of a gaping hole – making it prone to an abrupt and dramatic collapse.
However, erosion isn’t the only process that can cause vast underground holes to form. “Sometimes sinkholes are a purely natural phenomenon, but they may also be associated with previous industrial activities, most commonly mining,” Dr. Jamie Pringle and Professor Peter Styles from England’s Keele University wrote in a piece for The Conversation in September 2018.
Additionally, underground piping can sometimes shift, creating a hole through which water begins to pour. Over time, these leaks erode the rock around them, eventually causing sinkholes to form. And though these caverns form gradually, they can often appear on the surface overnight.
In cities, the sudden appearance of sinkholes can lead to great destruction. Roads, and even whole buildings, can disappear in a matter of seconds. But these phenomena can also offer a fascinating opportunity to investigate ecosystems that have largely gone unexplored.
In fact, all around the world, sinkholes have long appealed to climbers and explorers seeking to discover uncharted terrain. And in places as diverse as Michigan, Lebanon and Japan, thrill-seekers gather to experience the excitement of descending deep into the earth through these vast craters. This is the case too in rural Fengshan County, located in South Central China’s Guangxi Zhuang Autonomous Region.
Fengshan means phoenix mountain – a name inspired by the distinctive range that straddles the region. And below the surface, the county’s geography is equally notable. In fact, it’s an area known for its karst, a landscape rich in sinkholes and caves.
Amazingly, Fengshan County boasts some 50 caves in excess of 20,000 square feet, with almost 20 reaching upwards of 100,000. And in some places, such as Yuanyang Cave in the east and Shuiyuan Cave in the village of Poxin, these natural features have become tourist attractions, drawing visitors to the region.
In China, sinkholes that reach sizes of over 100 feet are known as tiankengs – translated as ‘skyholes’. According to experts, there are fewer than 100 in existence worldwide. One of these, Nongle, is located in Fengshan County, in the village of Haiting.
Beginning on October 4, 2018, a team of 19 researchers from both China and Britain went on an expedition into the depths of the Nongle tiankeng. The team was led by Zhang Yuanhai from the Chinese Academy of Geological Science’s Institute of Karst Geology and Andy Evans of the International Cave Association. And while on their excursion, the group were amazed by what they found.
Apparently, a section of rock around a dozen feet thick had collapsed, revealing a vast cavern underneath. Using what’s known as single rope technique – a method that sees cavers scale and cascade on a solitary vertical line – the explorers entered the sinkhole. And they discovered an incredible landscape hidden within.
They found a huge underground cavern, stretching almost 400 feet beneath the surface of the earth. At some 650 feet long, and with an entrance almost 330 feet wide, the cave is among the biggest of its kind ever discovered anywhere in the world. Incredibly, it’s thought to cover a staggering 236 million cubic feet.
For context, that means that the cavern is large enough to contain Egypt’s Great Pyramid of Giza two times over. According to explorer Yuanhai, the cave boasts steep sloping sides, as well as a number of separate structures within its walls. These include formations dubbed the ‘basement’, the ‘corridor’ and the ‘hall’.
In order to better understand the fascinating geology inside the sinkhole, the team employed 3D scanning techniques to examine the cave hall. And amazingly, they discovered yet another structure within the cavern. Dubbed the ‘courtyard’, this sub-hall stretches to nearly 165 feet wide by almost 500 feet tall.
According to Yuanhai, this courtyard contains evidence that the cave may have been mid-collapse when it was discovered. Furthermore, the scans also revealed a network of nearby waterways. These flow underground before breaching the surface and becoming Guangxi’s Panyang River.
However, Yuanhai confessed to journalists that his team was not the first to discover the impressive cave. Apparently, a group of researchers from Hong Kong pipped them to the post. And to honor them, Yuanhai and his colleagues have opted to name the cavern “Hong Kong Haiting Hall.”
Now, experts hope that the cave will allow for a better understanding of the unique landscape of Fengshan County. And now that video footage captured within the cave has been released online, armchair explorers across the globe have been treated to a rare glimpse into this unexplored realm.
Meanwhile, sinkholes continue to occur in many corners of the globe. In fact, just days after Yuanhai and his team plunged through the depths of the Nongle cavern, four people died when a sinkhole opened up in the city of Dazhou hundreds of miles away. But will expeditions like Yuanhai’s help to prevent such tragedies occurring? Only time will tell.