Collapse function of Furong Cave in Chongqing City and its environmental effects

Collapse of the Furong Cave in Chongqing City is studied by means of in situ investigation and the U-series and14 C isotopic dating of speleothems. The results show that the enormous collapse piles were formed in different stages:0.35 Ma earlier,0.2～0.35 Ma,0.026～0.1 Ma, and 0.025 Malater BP as well as recent collapses following the exploitation of the cave for tourism(collapses occurred in1995,2000,2003 and2008).Three collapse phenomena are considered: roof stoping, falling stalactites, and tipping or falling of stalagmites and columns. Upward stoping results from the adjustment of stresses in the parent rock as buoyancy decreases when the groundwater table lowers due to tectonic uplift. This results in upward void migration and enlargement of the Cave passage. Stalactites fall as their weight increases beyond the critical force on the contact plane between the stalactites and parent rock. Stalagmites and/or columns tip and fall occur when the speleothems or parent rock are hit by falling stalactites or shook by earthquakes. The collapse functions are of the environmental effects as enlarge the space of the cave, damage of the stalagmites and tourism facilities, and make the tourism path has to be changed. Therefore, some proposals on cave tourism development are put forward according to the features of the collapses in the Furong Cave.