In a remarkable discovery, a team of cave explorers in China has stumbled upon a colossal sinkhole that is home to a pristinely preserved ancient forest.
George Veni is the Executive Director of the National Cave and Karst Research Institute. He said the forest likely contains a variety of species of small animals that are unknown to science.
The sinkhole, or “tiankeng” as referred to in Chinese, translates to “heavenly pit.” It is situated in the Guangxi Zhuang Autonomous Region’s Leye County. This discovery brings the tally of giant sinkholes in the county to 30.
The dimensions of this enormous sinkhole are staggering. According to a press release from Xinhua, the Chinese government’s state-owned news agency, the sinkhole stretches over 1,000 feet in length. It is almost 500 feet wide, and plunges to a depth of 630 feet. All told, the tiankeng encompasses a volume exceeding 176 million cubic feet.
Zhang Yuanhai is a senior engineer at the Institute of Karst Geology of the China Geological Survey. He also told Xinhua that the site had a well-preserved ancient forest at the bottom and three caves in it’s walls.
The exploration team, led by Chen Lixin, descended more than 320 feet and hiked for several hours to reach the bottom. There, they encountered undergrowth reaching up to their shoulders and trees soaring over 100 feet high.
While this discovery is astounding, it aligns with the expectations of geologists, given the karst topography prevalent in southern China.
Karst topography is defined by the National Park Service as a type of landscape where the dissolving of the bedrock has created sinkholes, sinking streams, caves, springs, and other characteristic features. It typically involves common rock types such as limestone, marble, and gypsum.
Veni, who is affiliated with a sister agency of the organization that conducted the exploration, explained to Live Science that the formation of karst occurs when rainwater, after absorbing carbon dioxide from the atmosphere, transforms into carbonic acid (H2CO3).
This mildly acidic water permeates the ground, dissolving calcite, a mineral found in limestone, marble, and dolostone. This ultimately forms the characteristic sinkholes, caves, and streamways of karst regions.
Karst terrains are highly conducive for groundwater storage due to the rapid flow of water through the porous rock. However, they are also exceedingly susceptible to contamination.
Accuweather’s Marianne Mizera reports that around 700 million people globally depend on karst aquifers as their primary water source.
“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.”
The South China Karst, due to its distinct karst features and landscapes, has been designated as 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,” stated Unesco.
Sinkholes are depressions or holes in the ground caused by the collapse of a surface layer. They can range in size from just a few feet in diameter to hundreds of acres, and can be shallow or more than 100 feet deep. Here’s a comprehensive overview of sinkholes:
Sinkholes are primarily formed by the dissolution of soluble bedrock (a process called chemical weathering) and by the subsequent removal of the loosened material, creating voids underground. Over time, these voids can cause the ground above to collapse, forming a sinkhole.
Solution sinkholes: These form where rainwater, which is slightly acidic due to dissolved carbon dioxide, reacts with the soluble bedrock, such as limestone or gypsum, leading to its gradual dissolution.
Collapse sinkholes: These occur suddenly when the ground above an underground void collapses, forming a hole. They are often triggered by changes in groundwater levels or heavy surface loading.
Subsidence sinkholes: These form slowly and gradually when loose, unconsolidated material is washed into cracks in the bedrock. This creates a depression on the surface.
Natural processes: Most sinkholes form due to natural processes. These can include the dissolution of soluble rocks, changes in groundwater levels, and the natural erosion of the ground beneath the surface.
Human activities: Over-extraction of groundwater, construction activities, drilling, mining, leaking sewerage or stormwater pipes, and the collapse of underground mines can also trigger sinkholes.
While sinkholes can be found worldwide, they are especially common in areas with large amounts of limestone, gypsum, or salt beds. Notable regions with a history of sinkholes include Florida, Kentucky, and other parts of the U.S., the Dead Sea area, parts of China, and the Yucatán Peninsula in Mexico.
Sinkholes can pose significant risks to infrastructure, properties, and human safety. A sudden collapse sinkhole can swallow cars, homes, or even larger structures. They can also disrupt transportation, contaminate water supplies, or lead to other environmental problems.
Detecting potential sinkholes before they collapse can reduce the associated risks. Techniques such as ground-penetrating radar, electrical resistivity testing, and microgravity surveys can be used to detect underground voids. If an area is identified as high-risk for sinkhole formation, certain mitigation techniques can be used to stabilize the ground. These include grouting or underpinning.
Some notable sinkholes around the world include the Great Blue Hole in Belize, the Sima Humboldt in Venezuela, and the Xiaozhai Heavenly Pit in China.
Areas with a high frequency of sinkholes are often referred to as “karst landscapes.” These regions display other features like caves, springs, and underground drainage systems due to the dissolution of soluble rocks.
Understanding sinkholes and the processes leading to their formation is crucial, especially in regions prone to their occurrence. Proper urban planning, construction practices, and water resource management can help minimize the risks associated with sinkholes.
Credit for images: Xinhua News Agency