A team of Chinese scientists has discovered a giant new sinkhole with a forest at its bottom. 

The sinkhole is 630 feet (192 meters) deep, according to the Xinhua news agency, deep enough to just swallow St. Louis’ Gateway Arch. A team of speleologists and spelunkers rappelled into the sinkhole on Friday (May 6), discovering that there are three cave entrances in the chasm, as well as ancient trees 131 feet (40 m) tall, stretching their branches toward the sunlight that filters through the sinkhole entrance.

“This is cool news,” said George Veni, the executive director of the National Cave and Karst Research Institute (NCKRI) in the U.S., and an international expert on caves. Veni was not involved in the exploration of the cave, but the organization that was, the Institute of Karst Geology of the China Geological Survey, is NCKRI’s sister institute.

A site for sinkholes

This image shows a typical karst sinkhole called a tiankeng in Chongqing, China. (Image credit: Eastimages/Getty Images)
The discovery is no surprise, Veni told Live Science, because southern China is home to karst topography, a landscape prone to dramatic sinkholes and otherworldly caves. Karst landscapes are formed primarily by the dissolution of bedrock, Veni said. Rainwater, which is slightly acidic, picks up carbon dioxide as it runs through the soil, becoming more acidic. It then trickles, rushes and flows through cracks in the bedrock, slowly widening them into tunnels and voids. Over time, if a cave chamber gets large enough, the ceiling can gradually collapse, opening up huge sinkholes.

“Because of local differences in geology, climate and other factors, the way karst appears at the surface can be dramatically different,” he said. “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. Cave entrances might be very small, so you have to squeeze your way into them.” 

In fact, 25% of the United States is karst or pseudokarst, which features caves carved by factors other than dissolution, such as volcanics or wind, Veni said. About 20% of the world’s landmass is made of one of these two cave-rich landscapes. 

The new discovery took place in the Guangxi Zhuang Autonomous Region, near Ping’e village in the county of Leye, according to Xinhua. Guangxi is known for its fabulous karst formations, which range from sinkholes to rock pillars to natural bridges and have earned the region UNESCO world heritage site designation.

Why sinkholes matter

The sinkhole’s interior is 1,004 feet (306 m) long and 492 feet (150 m) wide, Zhang Yuanhai, a senior engineer with the Institute of Karst Geology, told Xinhua. The Mandarin word for such enormous sinkholes is “tiankeng,” or “heavenly pit,” and the bottom of the sinkhole did indeed seem like another world. Chen Lixin, who led the cave expedition team, told Xinhua that the dense undergrowth on the sinkhole floor was as high as a person’s shoulders. Karst caves and sinkholes can provide an oasis for life, Veni said.

“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. 

In one West Texas cave, Veni said, tropical ferns grow abundantly; the spores of the ferns were apparently carried to the sheltered spot by bats that migrate to South and Central America.

Not only do sinkholes and caves offer refuge for life, they are also a conduit to aquifers, or deep stores of underground water. Karst aquifers provide the sole or primary water source for 700 million people worldwide, Veni said. But they’re easily accessed and drained — or polluted.

“Karst aquifers are the only types of aquifers that you can pollute with solid waste,” Veni said. “I’ve pulled car batteries and car bodies and barrels of God-knows-what and bottles of God-knows-what out of the active cave stream.” 

The new discovery brings the number of sinkholes in Leye County to 30, according to Xinhua. The same researchers have previously discovered dozens of sinkholes in Northwest China’s Shaanxi province and a cluster of interconnected sinkholes in Guangxi, China Daily reported.

The supervolcano that lies beneath Yellowstone National Park in the US is far larger than was previously thought, scientists report.

A study shows that the magma chamber is about 2.5 times bigger than earlier estimates suggested.

A team found the cavern stretches for more than 90km (55 miles) and contains 200-600 cubic km of molten rock.

The findings are being presented at the American Geophysical Union Fall Meeting in San Francisco.

Prof Bob Smith, from the University of Utah, said: “We’ve been working there for a long time, and we’ve always thought it would thought it would be bigger… but this finding is astounding.”

If the Yellowstone supervolcano were to blow today, the consequences would be catastrophic.

The last major eruption, which occurred 640,000 years ago, sent ash across the whole of North America, affecting the planet’s climate.

Now researchers believe they have a better idea of what lies beneath the ground.

The team used a network of seismometers that were situated around the park to map the magma chamber.

Dr Jamie Farrell, from the University of Utah, explained: “We record earthquakes in and around Yellowstone, and we measure the seismic waves as they travel through the ground.

“The waves travel slower through hot and partially molten material… with this, we can measure what’s beneath.”

The team found that the magma chamber was colossal. Reaching depths of between 2km and 15km (1 to 9 miles), the cavern was about 90km (55 miles) long and 30km (20 miles) wide.It pushed further into the north east of the park than other studies had previously shown, holding a mixture of solid and molten rock.

“To our knowledge there has been nothing mapped of that size before,” added Dr Farrell.

The researchers are using the findings to better assess the threat that the volatile giant poses.

“Yes, it is a much larger system… but I don’t think it makes the Yellowstone hazard greater,” explained Prof Bob Smith.

“But what it does tell us is more about the area to the north east of the caldera.”

He added that researchers were unsure when the supervolcano would blow again.

Some believe a massive eruption is overdue, estimating that Yellowstone’s volcano goes off every 700,000 years or so.

Although fascinating, the new findings do not imply increased geologic hazards at Yellowstone, and certainly do not increase the chances of a ‘supereruption’ in the near future. Contrary to some media reports, Yellowstone is not ‘overdue’ for a supereruption.

Media reports were more hyperbolic in their coverage.

A study published in GSA Today, the monthly news and science magazine of the Geological Society of America, identified three fault zones where future eruptions are most likely to be centered. Two of those areas are associated with lava flows aged 174,000–70,000 years, and the third is a focus of present-day seismicity.

In 2017, NASA conducted a study to determine the feasibility of preventing the volcano from erupting. The results suggested that cooling the magma chamber by 35 percent would be enough to forestall such an incident. NASA proposed introducing water at high pressure 10 kilometers underground. The circulating water would release heat at the surface, possibly in a way that could be used as a geothermal power source. If enacted, the plan would cost about $3.46 billion. On the other hand, according to Brian Wilson of the Jet Propulsion Laboratory, such a project might trigger rather than prevent an eruption.