Published : 2023-02-24
Tiankeng (天坑), or "heavenly pit", which is a giant sinkhole and a magnificent karst landscape resembling a gateway to the underground world, preserves the most primitive ecological environment.
China boasts 90% of the world's Tiankeng, and one place, renowned for having the highest number and largest scale of Tiankengs, is hailed as the "Tiankeng Museum"—Guangxi Proinvce.
7 of the world's top 10 standard Tiankengs are in Guangxi
According to statistics, as of the end of 2021, about 300 standard Tiankengs have been discovered worldwide, of which more than 270 are in China.
South China's Guangxi alone boasts 90 Tiankengs, including the world's largest three Tiankeng groups. They occupy seven of the top 10 standard Tiankengs in the world, earning Guangxi the title "Museum of Tiankengs".
What is a "Tiankeng"? It is a special type of karst landform.
Thick soluble rock layers, eroded and dissolved by underground rivers over many years, which constantly collapsed and ultimately formed a sinkhole on the surface.
A Tiankeng's walls consist of sheer cliffs, enclosing a seemingly bottomless depression with an average depth and width exceeding 100 metres. This creates a relatively isolated ecosystem that preserves remarkably diverse primeval forests and rare flora and fauna.
Is the term "Tiankeng" derived from Chinese Pinyin?
Interestingly, the term "Tiankeng" was first proposed by Chinese karst scientists in 2001 and was recognised by the international karst academic community in 2005, becoming internationally known by the Chinese pinyin "Tiankeng".
This is the third karst landform terminology defined and named by the Chinese, following "Fenglin" (峰林) and "Fengcong" (峰叢).
Read more: "Rebirth" of Tang Dynasty Tianfu Guanyi in the bottom of 300-metre Wulong Tiankeng
As one of the representative regions of China's karst landforms, Guangxi has thick limestone layers, abundant annual rainfall, and the highest number of underground rivers in the country. These natural conditions have created this "Kingdom of Tiankengs".
If the world's Tiankengs are best represented in Guangxi, then Guangxi's Tiankengs find their finest expression in Leye.
Leye County in Baise City, Guangxi, is home to the largest Tiankeng group in the world – the Dashiwei Tiankeng Group (大石圍天坑群), which includes 29 Tiankengs and 2 super Tiankengs.
Among them, the Dashiwei Tiankeng, with a volume of nearly 80 million cubic metres, is the "big brother" of the Leye County Tiankeng family.
This is the world's second-largest standard Tiankeng, with a maximum depth of 613 metres, an east-west length of 600 metres across the opening, a north-south width of 420 metres, and an underground primeval forest covering an area of 96,000 square metres, home to thousands of plant species.
High-definition imaging technology aids Tiankeng exploration
In May 2022, the Institute of Karst Geology, China Geological Survey discovered another new Tiankeng in Leye and named it "Shenying Tiankeng" (神鷹天坑).
Its maximum depth is 192 metres, and its bottom preserves an intact primeval forest system. Researchers also discovered marine fossils from 200 million years ago in the limestone.
This discovery has increased the total number of Tiankengs in China to 32.
Unlike other Tiankeng groups in Leye County, the "Shenying Tiankeng" was not formed by the Bailang Underground River but by the Fugui Underground River. It represents a completely new Tiankeng family, with the potential for more Tiankengs to be discovered in the future.
Researchers point out that the discovery of the "Shenying Tiankeng" benefited from high-definition satellite imaging technology.
By analysing shadows, they located potential Tiankeng positions, followed by field surveys for confirmation.
Zhang Yuanhai, a senior engineer at the Institute of Karst Geology, China Geological Survey, stated that satellite images have helped them identify thousands of "potential" Tiankengs, but less than 30% have been confirmed, requiring substantial time and effort for further exploration.
Read more: The secret to local longevity lies in Guangxi's Qianlong Tiankeng?
