A group of Chinese and foreign explorers have recently found rare species in a cluster of huge sinkholes, also known as tiankengs, in northwest China's Shaanxi Province.
The rare species of plants and animals discovered by Chinese researchers and experts from the United Nations Educational Scientific and Cultural Organization (UNESCO) included the Chinese yew, rhododendron hybrids, Paris polyphylla, the southern-China-inhabited cobra.
The survey team is working hard searching answers to the problem of how these sinkholes were formed. And the discovery of the large-scaled underground caves and rivers in the central parts of the sinkholes may offer some clues to the mystery.
"Tiankengs (sinkholes) and caves are in separable. This time we have put emphasis on the study of the caves. If we have got clear about the caves, we would be able to deduce or further study how the sinkholes were formed and their further development trend," said Hong Zenglin, head of the Shaanxi Provincial Institute of Geological Survey.
Research results have shown that 54 sinkholes have been discovered in an area of over 5019 square kilometres. Of these, the mouth diameters of two are bigger than 500 metres, ranking fifth and sixth among the world's super-sinkholes. This has made Hanzhong a world-class sinkhole cluster. The sinkhole survey will end on May 10.
The sinkhole clusters have brought the total number of sinkholes in the world up to 217 and has altered the previous thought that sinkhole clusters are mostly concentrated in alpine and low latitude wet climate regions on the equator, as China's sinkholes are located in an area between 32 degrees and 33 degrees north latitude, the northernmost karst landform region ever found in the world. All previous discoveries were between 24 and 31 degrees north latitude.
Tiankengs are dolines, or huge pits, with special geological features found in karst regions formed by repeated cave-ins.
They are mainly found in China, Mexico and Papua New Guinea. In 2001, geologist Zhu Xuewen proposed the Chinese name tiankeng for the sinkholes over 100 meters in depth, as there was no special term yet to define this unique geological feature.