Xiaozhai Tiankeng

The Xiaozhai Tiankeng (小寨天坑), also known as the Xiaozhai Heavenly Pit, is the world's deepest sinkhole and also the largest in the Shaanxi cluster. It is located in Fengjie County of Chongqing Municipality in China.

Dimensions
The Xiaozhai Tiankeng is 626 m long, 537 m wide, and between 511 and 662 m deep, with vertical walls. Its volume is 119,349,000 m³ and the area of its opening is 274,000 m2. This material has been dissolved and carried away by the river. The sinkhole is a doubly nested structure—the upper bowl is 320 m deep, the lower bowl is 342 m deep, and the two bowls are on average 257 to 268 m across. Between both these steps is a sloping ledge, formed due to soil trapped in the limestone. In the rainy season, a waterfall can be seen at the mouth of the sinkhole.

Discovery
The Xiaozhai Tiankeng has been well known to local people since ancient times. Xiaozhai is the name of an abandoned village nearby and literally means "little village", and "Tiankeng" means Heavenly Pit, a unique regional name for sinkholes in China. A 2,800-step staircase has been constructed in order to facilitate tourism.

Underground river and cave


The Tiankeng formed over the Difeng cave, which in turn had been formed by a powerful underground river which still flows underneath the sinkhole. The underground river starts in the Tianjin fissure gorge and reaches a vertical cliff above the Mekong River, forming a 46 m waterfall. The length of this underground river is approximately 8.5 km and during these 8.5 kilometres, it falls 364 m The median annual flow of this river is 8.77 m³ per second, but its flow rate can reach 174 m³/s. Both the river and Difeng Cave were explored and mapped by China Caves Project in 1994.

Flora and fauna
1,285 species of plants, including the ginkgo, and many rare animals like the clouded leopard and the Chinese Giant Salamander have been found in the sinkhole.