THE TIANKENG CLUSTER OF HANZHONG
—The Latest Geological Discovery
Now with the help of Google Earth and other modern technologies, people might think that even the most remote and unexplored corners of the world conceal secrets no more. Yet the discovery of at least 49 karst sinkholes (“Tiankeng” in Chinese) in Hanzhong, Shaanxi Province proves that our planet is far beyond our imagination.
Now, in the 21st century even the most remote and unexplored corners of the world can be brought to our living rooms by Google Earth. Modern equipment allows amateur explorers to tame a wilderness where once only the bravest dared to venture. There are still, however, surprising discoveries to made, secrets that have evaded even the most prying of modern technologies—at the end of 2016 in Hanzhong, Shaanxi Province, people discovered a group of karst sinkholes of the scale that almost defied imagination—49 in total, of a variety of sizes. This article is a first-hand account of this geographical discovery, of a phenomenon now known as tiankeng or “heavenly well”.
lying south to north across China in early summer, once your plane clears Daba Mountains, mist usually shrouding their summits, the squares of paddies of Hanzhong Basin start appearing under the jet’s wings. As the plane descends, the landscape fills with the hustle and bustle of life— you can start to make out people and vehicles hurrying around the roads on the edges of the paddies.
The plane lands at the airport near Liulin Town of Hanzhong. Twenty kilometers to the northeast of the airport stands an irrigation system, called Wumenyan (or Wumen Dam), still operational today, which was built at the very start of the first millennium AD. Another 20 kilometers, this time to the northwest, is an ancient tunnel named Shimen Tunnel with its inner wall and surrounding cliffs carved with hundreds of inscriptions. What I found striking and confused, was that amongst all this human activity and historical heritage, it took people until the year 2016 to discover the local tiankeng cluster, or karst sinkholes, and no fewer than 49 of them!
A Long Story of Discoveries
When I got to the bottom of Boniu Tiankeng located in Xiaonanhai Town of Nanzheng County, I could not help but feel even more confused. My guide told me that back in 1964, a 77-year-old man
called Luo Rongfu had in fact been frequenting these sinkholes. At that time Luo and a dozen others would go down the sinkhole to harvest swallow droppings, which were then used as fertilizer, collecting as much as almost half a ton per day. Why do we then claim to have “discovered” these sinkholes last year when the locals had known about them for decades?
I guess that one of the reasons is that tiankeng is a new concept in the scientific circles, whose exact definition and categorizations are still being fixed. This natural wonder has been around since time immemorial, but it was not until 2005 that Zhu Xuewen, a researcher at Institute of Karst Geology of the Chinese Academy of Geological Sciences, put forward the term of “karst tiankeng” which was subsequently formally accepted by the scientific circles. Zhu Xuewen, together with Tony Waltham of Nottingham Trent University defined tiankeng as: “a type of very large collapse doline (“doline” is another term for “sinkhole”) that has evolved by roof collapse over a large cave chamber where a huge mass of breakdown debris has been removed by a substantial cave river”.
However, all this scientific jargon and the fact of the “discovery” of tiankeng mean nothing to the locals who have for generations lived side by side with these karst caves. Perhaps that’s why they were not discovered until recently.
The tiankeng, as a matter of fact, could have been “discovered” earlier, in 2012. In June that year Zhenba County of Hanzhong produced a promotional video about the local sights. Jiang Zongxiang, one of the people who took part in this project, then posted the video online. A tiankeng momentarily appears in the video— this was the first ever record of a Hanzhong tiankeng, but nobody at the time gave it a second thought.
This lasted until 2016 when Chinese government launched a nationwide survey to record geological sites. The survey gradually gathered momentum,
capturing public attention, and the government of Shaanxi Province took to the survey in earnest, pouring a great deal of resources and manpower to search for interesting geological formations in the province. Only then were the tiankeng finally “discovered”.
In March 2016, Zhang Yuanhai, senior researcher at Institute of Karst Geology of the Chinese Academy of Geological Sciences filed an application to China’s Ministry of Land and Resources, to invite experts from the Czech Republic to inspect the karst cave system in Hanzhong.
Before coming to Hanzhong, Zhang Yuanhai got an amateur caver, who goes under the nickname of “Raven”, to find out, using Google Earth, if Hanzhong had tiankeng. Raven is a curious character—his real name is Wu Hongying, he is a native of Guangxi Zhuang Autonomous Region whose daytime job is working at a power station. He is so tanned from spending a lot of time outside looking for caves, that his friends started to call him “Raven”, which he then took as his Internet nickname. Raven is an expert when it comes to locating karst caves and tiankeng using Google Earth—in his native Guangxi he discovered over 200 caves using this method, many of which were then confirmed by experts in the field. In the caving circles his prodigious skills earned him a tongue- in- cheek title of Master Raven.
I asked Raven how he got to be this good, but he just laughed it off, saying that anyone with an eye for detail can learn to do what he does. He mentioned that you must, first—look at the topography, second—pay close attention to edges and depth of shadows, third—look at the same place from different angles, fourth—cross-check against old maps. He also said that he hopes to share the experience that he has gained with people: “In the past, exploration required a lot of walking, the progress was, slow, painstaking, but now, satellites make this job so much easier.”
Zhang Yuanhai has full trust in Raven’s ability to track down tiankeng using maps, and Raven does not disappoint—he finds that there are tiankeng in two places of Hanzhong! Xiaonanhai Town of Nanzheng County, and Luojiaba Town in Xixiang County both have tiankeng and Raven provides coordinates for both. The team choses one as the first objective, and, having visited it, they find it worth investigating—it is a very large tiankeng indeed. It is no other than Boniu Tiankeng mentioned at the start of the article— the longest axis of its opening is around 200 meters, and the shortest 145 meters. The depth of this tiankeng stands at 215 meters.
When Zhang Yuanhai made it to the bottom of the Boniu Tiankeng for the first time, a carpet of bright green moss on the ground made him reluctant to tread on it, Zhang recalls. But what really made an impression, was a rhododendron tree covered by long threads of pine lichen: “Finding a rhododendron in bloom, with red flowers, right at the bottom of a karst sinkhole, this is not something you can forget easily!”
Using Raven’s coordinates and aided by a guide, the team discovered many other tiankeng around Boniu, reaching a conclusion that they have come across a large tiankeng group, or cluster. Then more news came from Raven—using Google Earth, he found an even larger tiankeng in Zhenba County. The team headed straight there, wasting no time, but an extensive search failed to uncover any evidence of tiankeng. Disappointed, they went on to make enquiries and came across a local photographer who said that he had photographed a local tiankeng! Having looked at his photos, there was no doubt in their minds that it was indeed a tiankeng. Unfortunately, a landslide destroyed the road leading to that tiankeng and there was no way to get there to have a look. Zhang Yuanhai then made a report to Dong Ying, the leader of the project documenting the geological heritage nationwide. Dong Ying, in his turn, noti-
fied Shaanxi Center of Geological Surveys and the large- scale survey of Hanzhong tiankeng was thus launched.
Didonghe Tiankeng: A Young and Growing One
In order to collect the first-ever data about Hanzhong tiankeng, Chinese national geography Magazine sent a team to do a survey. On the 28th of January 2017, the team members assembled at the house of the photographer Sun Jiaqi and drove off towards the Didonghe Tiankeng in Chanjiayan Town.
The decision to come to tiankeng during the winter was done after a lot of careful deliberation. Hanzhong tiankeng are special in that they are the northernmost of the distribution range of China’s tiankeng, which was something that Sun Jiaqi wanted to show in photographs. The higher the latitude, the colder the winter, and what can show the cold better than snow? Sun Jiaqi hoped to be able to capture the snowy tiankeng landscape, and in the days before the departure, he would carefully scan the weather reports, searching for the news of incoming snow. To his great disappointment, none such news came.
When we drove into Xi’an, the capital of the Shaanxi Province, to our great excitement, a large snowfall descended on Chanjiayan. However, the snow turned the road treacherously slippery, and we did not have chains fixed to our tyres. Getting to Chanjiayan on the same night was too much of a risk, and so we had to abandon our original plan and
spend an extra night in Xi’an. By the time we got to Didonghe Tiankeng, the snow had already melted.
We had too many things to do to feel disappointed, a rappel system was rigged up, and a small recce team went down to the bottom of the tiankeng to take the first photographs. The entire team followed them by the evening, and we all camped out at the bottom of the tiankeng. The following morning, having wriggled out of our tents we were left stupefied by the sight of snowflakes floating down from the mouth of the tiankeng. As it only snowed for less than two hours, and with the temperature at the bottom of the tiankeng being around 10 °C, the snowflakes melted as they fluttered down. We could not obtain the desired effect of a snow-white cover, but at least we managed to get those elusive shots of snow in a tiankeng.
The gigantic size of Didonghe Tiankeng made the survey team gasp in astonishment—the longest axis of the mouth of the tiankeng turned out to exceed 400 meters, with the shortest axis surpassing 200 meters, and the maximum depth of the tiankeng was measured at over 300 meters. The walls of the tian-
keng were stratified into three different zones, each with its distinct vegetation—the tree-covered zone at the top of the mouth of the tiankeng, and then in the two zones below the vegetation transitioned from shrubs to grasses with very clear boundaries, creating a remarkable sight. Even more astonishing was that every one of the three terraces of each zone had a waterfall, and the sight of the columns of water descending down to the bottom of the tiankeng left the observers speechless.
The beauty of the Didonghe Tiankeng did not just stop there. After having passed through the opening of the cave we discovered a large hidden cave system. The team chose one of the tunnels, going against the current of a river that was flowing through it. It was dry season and parts of the riverbed ran completely dry, leaving the riverbed exposed, which made walking easy. The riverbed was of large size, wide with high banks, so much so that it seemed that the team was walking through one large cave chamber. After having walked four kilometers, the ceiling of the cave suddenly rose and a small mountain of debris from a collapse in the ceiling or in the walls of the cave blocked the way. The river descended this barrier and then its course went up at a slant. Another kilometer and the team came across a man-made bamboo fence, then it was the opening of the cave, and a small village presented itself the eyes of the team—lu- oshuidong Village, which means “Village of Water and Caves”. It was during the Spring Festival and the village looked resplendent in its decorations, festooned in lanterns and streamers.
The following day, the team went to Didonghe Tiankeng again, this time from Luoshuidong Village, and explored another branch of the cave, discovering a stalactite chamber on their way. Even though the chamber was not large, suddenly coming across such an intricate natural work of art, sheltered in the brutal vastness of a cave large enough to harbour a river, was extraordinary.
Dr. Zhao Xinnan of Xi’an Jiaotong University
took a sample of a stalagmite from Didonghe Tiankeng, sending it to be aged at the university’s isotope laboratory. The results revealed that the age of the stalagmite, and hence of the cave and of the collapse of the cave roof, was less than 340,000 years, a surprisingly short stretch of time for geologists!
According to Dr. Zhao, the stalagmite sample was collected from the mid-section of the cave wall, about 50 meters from the cave entrance. From the angle of the stalagmite Dr. Zhao deduced that this tiankeng was not formed by a single collapse from the top. She judged it to be more likely that first an ancient river had eroded out the large cave system,
which was followed by the collapse of the roof. Then the modern river carved out yet another layer in the existing caves. This is the most widely accepted and applied consensus of tiankeng formation, but more evidence is still required.
The Discovery and Frustration
According to Sun Jiaqi, the most unforgettable tiankeng expedition that he had done was to Luoquanya Tiankeng in Hanzhong’s Xixiang County.
On the 5th of April 2017, the team arrived in Luojiaba Town in Xixiang, with plans to explore a tiankeng known as Shuangxuanwo Tiankeng, which means a tiankeng of two vortexes. However, the very same evening, they were joined by a team from Xi’an Geological Investigations Center who gave them three pieces of bad news. First, the 20 kilometers from Luojiaba Town to Shuangxuanwo Tiankeng were not really doable in a day with heavy loads. Second,
Creeks Running Underground There is a small cave hidden beneath the bottom of Boniu Tiankeng. After searching step by step for about 800 meters, team members found a pound where three tiny creeks converge.
Firsthand Photos and Data
At the end of 2016, after the discovery of the Hanzhong Tiankeng cluster was reported, Chinesenationalgeogra
phy immediately organized a professional team, consisting of explorers, photographers and writers, and sent them deep into the forests of Hanzhong to obtain firsthand photos and data. That is how this report was created.
Inside the Boniu Tiankeng ➲
The opening on the land surface is not the only one— there are two other openings through the inside walls, just like the windows of a house. With headlamps, team members are able to check the interior structure of Boniu Tiankeng thoroughly. ➲
In another cave at the bottom of Boniu Tiankeng, team members found a natural opening in its roof. A ray of sunshine shone through this “skylight,” shedding light into the cave and awakening the dark underground world sleeping in silence.
Ecology of the Tiankeng System Apart from the rich vegetation found in the tiankeng system, we also found some intriguing creatures living in these karst environments, such as the giant flying squirrel, a vigilant rodent that is hard to capture with our lens. In the caves at the bottom of the tiankeng, we found some albino arthropods living in complete darkness. Some scientists believe that such isolated underground environments are likely to have new species waiting for us to discover them. Petauristaalborufus
Larvae of ground beetle
Albino species of Diestrammena
Didonghe Tiankeng: A Giant Footprint on the Ground Most tiankeng have openings that are round, or nearly round, in shape, but the Didonghe Tiankeng is an exception. Its opening forms a giant footprint on the ground, with its widest place at over 433 meters and a depth of about 340 meters. With the help of drones, we see that this tiankeng’s opening is surrounded by extremely steep cliffs, making it quite difficult to approach.
Complicated Cave System under Didonghe Tiankeng At the bottom of Didonghe Tiankeng, there is a large cave that has an opening of 50 meters in height and 100 meters in width. Yet that is not what surprised us the most—after we explored the underground cave system thoroughly, we found that the whole system is over 9,000 meters long with a main cave and more than 40 branch ones. There are grand halls with a height of 70-80 meters, as well as narrow passages that barely allow one person through.
“Farmlands” and “Pillars” In most karst caves, people often find “side dams”—carbonatite sediments that gather around water bodies, forming small walls that look like ridges and dams used to hold water in farmlands. The giant pillar was a stalagmite formed by dripping water from the cave’s ceiling—when the water evaporated, the carbonatite it contained remained on the ground, presenting us with this amazing formation standing in this underground world.
The Didonghe Tiankeng and Its Cave System Ponor’s opening N Aven connecting upper and middle layers Ruin of ancient saltpeter mine Legends Dry Clay Wet Clay Stalactite Water Body Scarp Slope Gravel and Scree Water flow Airflow Entrance Shield-shaped rocky sediment Scale 0 50 100 200m Didonghe Tiankeng mite