A cave exploration team in China has discovered an enormous sinkhole with a well-preserved primitive forest at the bottom. The forest likely contains a variety of species of small animals that are unknown to science, George Veni, executive director of the National Cave and Karst Research Institute who was not involved in the research, told the Washington Post’s Marisa Iati last month.
The large hole measures over 1,000 feet in length, almost 500 feet wide and 630 feet deep, with a volume of over 176 million cubic feet, per a release from the Chinese government’s state-owned news agency, Xinhua.
The giant sinkhole—also called tiankeng, or “heavenly pit,” in Chinese—is located in south China's Guangxi Zhuang Autonomous Region in the Leye County, raising the number of giant sinkholes in the county up to 30.
The exploration team rappelled down more than 320 feet and trekked for several hours to reach the bottom. They were met with undergrowth as high as their shoulders and trees towering over 100 feet high, according to Chen Lixin, leader of the team, per the Xinhua news release.
Geologists would argue that the discovery is not surprising because of southern China’s karst topography, Veni, who works for a sister agency of the organization that explored the Chinese sinkhole, told Live Science’s Stephanie Pappas. Karst is a “type of landscape where the dissolving of the bedrock has created sinkholes, sinking streams, caves, springs, and other characteristic features,” per the National Park Service. Common rock types in karst landscapes are limestone, marble and gypsum.
30th giant karst sinkhole discovered in south China's Guangxi pic.twitter.com/52ZxFnyuWF— CGTN (@CGTNOfficial) May 11, 2022
Karst forms when rainwater picks up carbon dioxide as it falls through the atmosphere, creating H2CO3, carbonic acid. The lightly acidic water seeps through the ground, moving through fractures and openings in the rock. The water dissolves calcite, a mineral in limestone, marble and dolostone, creating the characteristic sinkholes, caves and streamways.
Karst areas are ideal for storing groundwater because water flows quickly through the porous rock. They are, however, highly vulnerable to contamination. Around 700 million people worldwide rely on karst aquifers as their primary source of water, writes Accuweather’s Marianne Mizera.
“Because of local differences in geology, climate and other factors, the way karst appears at the surface can be dramatically different,” Veni told Live Science. “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. Sinkholes might be quite subdued, only a meter or two in diameter.”
Because of its unique karst features and landscapes, the South China Karst is a Unesco World Heritage Site.
“The property contains the most spectacular, scientifically significant and representative series of karst landforms and landscapes of South China from interior high plateau to lowland plains and constitutes the world’s premier example of humid tropical to subtropical karst: one of our planet’s great landscapes,” per Unesco.