A KÍNAI KARSZTVIDÉKEK KÜLÖNLEGES KARSZTOS MÉLYEDÉSEI, A TIANKENGEK 2. RÉSZ

Absztrakt

In the last decades, expeditions by karst and cave researchers have explored several huge depressions in the vast karst regions of China, reminiscent of classic dolines. However, due to their extreme extent they have been introduced as a new term in karst morphology under the name ”tiankengs” (”heavenly pits” or ”sky holes”). Tiankengs are giant dolines with steep walls and a depth of at least 100 m; their area both at the top and the bottom varies between 10,000 and 350,000 m2, and their volume exceeds 1,000,000 m3 (however, the biggest, Xiaozhai, has a volume of almost 120 million m3 ). Most of them were formed as a result of the collapse of a large underground cave, whose roof was increasingly dissolved by underground rivers from underneath until it finally collapsed, forming a massive doline. Another, a smaller part of the tiankengs, has been formed by erosion. Tiankengs exist also in other parts of the world, among others at the Mulu Karst in Borneo (Sulawesi) and in New Guinea, but most of them can be found in the South China Karst Region. The first part of this paper delt with some famous tiankengs in the Xingwen karst region (Sichuan Province), while this second part analyses the Wulong Karst region (Chongqing Municipality) including the famous Three Natural Bridges area. Their tiankengs are good examples of the origin and development of erosional tiankengs.