a tiankeng is defined as a distinctive type of very large collapse doline that is more than 100 m wide and deep, with a depth to width ratio close to unity, and vertical cliffs round most of its perimeter. they are massive negative karst landforms of extraordinary size and shape with huge volumes and dramatic enclosing cliffs. developed in a great thickness of carbonate rock in the unsaturated zone, the tiankengs range in depth and width from 100 m up to several hundred meters, some connecting to underground rivers.
dashiwei tiankeng group covers 100 square kilometers area ranging 22 km east to west and 5 km north to south. so far 28 tiankengs have been discovered in the tiankeng group, 23 of which are in the geopark. five additional tiankengs have been found in the east part (fengshan) of the geopark. of the tiankengs in the geopark, dashiwei tiankeng has the largest scale and the greatest depth (613 m, the second deepest in the world). at the rim, dashiwei tiankeng is 600 m wide from east to west and 420 m wide from north to south, with a total volume of 67.1 million cubic meters. the area at the rim is 16.6 ha, while the area of the virgin forest at the bottom is 10.5 ha, the largest in the world.