Chapter 7: CLIMATE, MORPHOLOGY AND GENESIS OF CAVES

Résumé - Abstract - Zusammenfassung  : The medium altitude caves that we explored in the SW Hubei are quite more vertical than those we explored in the Guizhou Province during 86 and 89 expeditions. The main caves are flood sinkholes in the blind valleys and the canyons (Dadong, Xiaoshuidong, Datiankeng, Puits Est, ...). The galleries are wide, the walls are polished by mechanical erosion and the shafts are beautiful. This is related to large basins and consequently, big discharge during the monsoon. Some deep potholes (more than 10 m sometimes) are very difficult to cross and oblige the caver to cross at the top of the shafts. They show the power of the mechanical erosion, linked with the sand, gravel and even big boulders carried by the water from sandstone outcrops in the catchment area. A second kind of caves is tunnel caves where allogenous rivers flow. The sizes of the entrances and the galleries are very large (up to 5 000 m2 !) because the flood discharge are very high (hundreds of m3/sec) . The third family of caves consists in resurgences. Some are very big, like Longdong and Donghe (Wufeng) where the flood discharges are over 50 m3/sec (1 m3/sec during the dry season). The caves are developed at various altitudes. This is related to the Tertiary and Quaternary uplift and must be studied along the sides of the canyons and in the long cave networks with fossil galleries and old fillings (Dadong). In some places, the difference between the altitude of the different caves is larger than 300 m (Songjiahe) and it reaches 1 000 m in the Daninghe canyon (Sichuan Province, northern border of Hubei). As far as we know, the caves explored date from Quaternary and sometimes Pliocene and Miocene.

Key-words: sinkhole, resurgence, blind valley, canyon, mechanical erosion, solution, speleogenesis, tectonics.