Deep within the southwestern landscapes of China, a breathtaking natural wonder remains hidden beneath the rugged terrain—giant sinkholes, or “tiankeng”, that shelter ancient forests untouched by time. These massive chasms, some spanning over 1,000 feet (306 meters) across, have intrigued scientists for decades, offering a glimpse into an ecosystem preserved for thousands of years. Unlike typical sinkholes, these formations are so immense that they house dense, thriving forests at their base, teeming with life.
Discovered primarily in the karst regions of Guizhou, Guangxi, Yunnan, and Chongqing, these sinkholes result from the gradual dissolution of limestone over millennia. The unique geology of the region has created some of the largest sinkholes on Earth, with China home to over 200 known tiankeng. Scientists continue to uncover new ones, with one of the latest major discoveries made in 2022 in Guangxi, where a team of explorers descended into a vast sinkhole harboring 131-foot (40-meter) trees.
A Window into Earth’s Ancient Past
The first scientific studies on China’s tiankeng formations were conducted by the Institute of Karst Geology at the Chinese Academy of Geological Sciences. According to geologist Zhu Xuewen, these sinkholes qualify as true tiankeng only if they are at least 330 feet (100 meters) deep and wide, feature steep rock walls, and are carved by underground rivers or ancient water flow patterns. Among them, the Xiaozhai Tiankeng in Fengjie County holds the title of the deepest sinkhole in the world, plunging an astonishing 2,172 feet (662 meters) into the Earth.
What makes China’s karst landscape unique is the sheer scale and beauty of its formations. “Because of local differences in geology, climate and other factors, the way karst appears at the surface can be dramatically different,” explained George Veni, a hydrogeologist specializing in karst terrains and executive director of the National Cave and Karst Research Institute in the U.S. “So in China, you have this incredibly visually spectacular karst with enormous sinkholes and giant cave entrances and so forth. In other parts of the world, you walk out on the karst and you really don’t notice anything.”
© Song Wen
How These Giant Sinkholes Were Formed
The formation of China’s giant sinkholes is a result of a geological process that takes hundreds of thousands of years. The region’s karst topography consists of highly soluble limestone, which gradually erodes as rainwater seeps into the ground, forming underground rivers and massive cavern systems. Over time, these caverns expand until the rock ceiling collapses, leaving behind the jaw-dropping sinkholes we see today.
Unlike typical sinkholes, China’s tiankeng often contain their own microclimates, with temperatures, humidity levels, and light conditions differing significantly from the surface. This allows for the preservation of ancient plant species that may have disappeared elsewhere due to climate change or human activity. In some cases, underground rivers still flow through these massive pits, further carving and shaping the landscapes over time.
The Guangxi region, which has been a UNESCO World Heritage site since 2007, is home to the highest concentration of these sinkholes, including the recently discovered tiankeng in Leye County. Scientists believe that new sinkholes are still waiting to be uncovered, hidden beneath the lush forests and towering limestone cliffs of southwestern China.
A Lost World: Ancient Forests Hidden Below the Surface
Perhaps the most remarkable feature of these sinkholes is their ability to preserve ancient ecosystems, creating biological time capsules at the bottom of these immense pits. Some of the deepest sinkholes contain forests that have remained isolated for thousands of years, shielding them from human interference and environmental changes that have transformed the surface world.
When a Chinese cave exploration team descended into a previously unexplored sinkhole in Guangxi in May 2022, they discovered towering trees reaching 131 feet (40 meters) into the sky and dense undergrowth so thick it reached their shoulders. The expedition leader, Chen Lixin, expressed excitement over the potential for new, undiscovered species living within these subterranean forests. “I wouldn’t be surprised to know that there are species found in these caves that have never been reported or described by science until now,” Lixin said.
Such discoveries suggest that China’s tiankeng could hold hidden species of plants and animals, offering new insights into evolution, biodiversity, and ancient ecosystems. These environments remain largely unexplored, and future expeditions could reveal extraordinary new life forms thriving in the shadows of these deep, forgotten forests.
