The pit is home to a number of rare plants and animals.
First discovered by experts in 1994, the world’s deepest sinkhole can be found in Fengjie Province, Chongqing Municipality, China. Xiaozhai Tiankeng, or the Xiaozhai Heavenly Pit, measures approximately 537 meters in diameter and sinks between 511 and 662 meters into the Earth.
With nearly vertical walls, the volume of this important geological feature is 119.349 million cubic meters. During heavy rains, sometimes a waterfall can be seen on the steep walls of the hole. The structure is double nested, meaning it is composed of two distinct “bowls” that dissect it into two layers, each bowl measuring over 300 meters deep.
Difeng Cave, on which the sinkhole is located, was formed by a powerful underground river. This river can now be seen deep in the pit where it carries clear water through the interior cave systems.
The river flows about 8.5 kilometers from the underground gorge of the Tianjing fissures before reaching daylight at the vertical cliff of the Migong River, where the underground water system forms a 46-meter waterfall.
A paradise of rare plants and animals
There are 1,285 species of plants recorded in the depths of the Xiaozhai sinkhole, creating its own thriving, unique and rare ecosystem. Ginkgo biloba, a rare species of tree, can be found living in the pit, as well as rare animal species such as the clouded leopard, of which there are estimated to be less than 10,000 in the wild.
The sinkhole is composed of Triassic limestone found in thick pure blocks. It is believed to have formed gradually over the past 128,000 years, making it relatively young compared to other sinkholes in the area.
In fact, China is home to a number of sinkholes, commonly referred to as “tiankeng”. The word tiankeng means “sky pit” or “sky hole” in Chinese and refers to a very specific group of geological structures.
To be a tiankeng, the sinkhole must be at least 100 meters deep and wide, with a river flowing through it. All tiankengs are composed of carbonate rock, except for two Venezuelan structures that consist of sandstone. They are formed by a karst process when their composition is carbonate rock and by a suffusion process when they are made of sandstone.
The conditions required for the formation of a tiankeng are very specific, which makes their formation rare. The rock must be above sea level and thick without layers of impurities. Heavy rainfall is also required to form these structures, which in turn helps form their underground rivers.
Although the term refers to any sinkhole within these criteria, of the 75 identified, 50 of the largest are found in China, so the term Chinese has become the common name for such structures.