Sinkholes more than 100 meters deep formed by limestone weathering in China can contain many lush, ancient trees.
The giant sinkholes scattered across southwestern China are nicknamed “tiankeng” which means “heavenly holes”. Not only do they stand out among the mountainous landscape, but they also contain primitive jungle and pristine ecosystems, according to UNESCO Courier.
Southwest China is home to karst terrain, a weathering phenomenon typical of limestone mountains eroded by flowing water. Over hundreds of thousands of years, rainwater seeps through the ground to the bedrock and gradually erodes the limestone. The slightly acidic river water widened the cracks into tunnels and caves, eventually unable to support the rock ceiling. As a result, the rock ceiling collapsed to the bottom, creating a giant sinkhole.
According to Zhu Xuewen, a researcher at the Institute of Limestone Geology at the Chinese Academy of Geological Sciences, the paradise hole is very unique. They are among the largest sinkholes in the world, especially the Xiaozhai Tiankeng sinkhole located in Fengjie district, Chongqing. This is the deepest sinkhole on Earth. To become a paradise hole, the sinkhole must be at least 100 m deep and wide. The paradise hole must also have steep sides and rivers running along the bottom, according to Xuewen. For example, in Xiaozhai Tiankeng, the rainy season feeds an underground river that snakes through the cave.
China has about 200 paradise holes, mainly distributed from Shaanxi province in the central region to Guangxi in the southwest. About one-third of China has karst terrain, the highest proportion of any other country in the world.
“Due to differences in geology, climate and many other factors, the way karst terrain appears on the ground can be very different,” said George Veni, a hydrogeologist specializing in karst terrains and director of Executive Director of the US National Institute of Karst and Cave Research, shared. “China has particularly impressive karst terrain with giant sinkholes and huge cave entrances. In other parts of the world, you can walk on karst terrain without even noticing it.”
Despite its massive size, China’s paradise hole can be difficult to spot amid the rugged mountains and luxuriant jungle that cover much of the southwest. That’s why dozens of new holes have been discovered recently. The most recent was discovered in May 2022 in Guangxi. A cave exploration team climbed into a sinkhole located near Ping’e village in Lac Nghiep district and measured the hole to be 192 m deep and 306 m wide. This discovery brings the total number of paradise holes in Lac Nghiep to 30. At the bottom of the hole there is a primeval forest with ancient trees up to 40 m high. The trees growing below are very dense and reach shoulder height, according to Chen Lixin, leader of the expedition team.