It's big enough to swallow cities, deep enough to hide skyscrapers and inside lies an ancient, thriving 'lost world' cut off from everything above

submitted by cm0002 to earthscience 21 points | 0 comments https://www.discoverwildlife.com/environment/deepest-sinkhole-xiaozhai-tiankeng > In China’s Chongqing Municipality, locals have known about the sinkhole for centuries. Xiaozhai is the name of a local abandoned village, whilst Tiankeng means Heavenly Pit, the local term for sinkhole. > > With a depth of 626 metres and a width of 527 metres, the enormous hole is twice as long as the Eiffel Tower and one a half times wider than London’s O2 Arena. With a volume of around 120,000,000 cubic metres, it could hold the equivalent of 40,000 Olympic-sized swimming pools or about 500 Hindenburg-class zeppelins. > > Sinkholes are deep holes in the ground that form when surface layers collapse into underground voids. They can appear gradually or suddenly, and are often caused by heavy rain, flooding, or human activities, such as building and mining. > > In the case of the Xiaozhai Tiankeng, forces from above and below ground shaped its formation. Over tens of thousands of years, rain water seeped into the region’s porous limestone bedrock, widening crevices and leading to erosion. At the same time, a powerful underground river was hollowing out a network of subterranean caves and caverns. Then, at some point the surface gave way and the sinkhole appeared.