Fengyu Cave is located in Shanhe, 110 km southeast of Guilin (Photograph, left).  It is a limestone cavern, a solution cave large enough for people to walk in.  Cave development has been a mystery to many scientists.  How do caves form thousands of meters below karst landforms when karst is essentially a surface process?  The vadose theory, which appears to be the formation process of the Fengyu Cave, implies that caves develop in the zone of aeration by downward moving vadose, or , water.  Along bedding joints and planes, the vadose water solution mixing with limestone, developed passageways large enough to carry underground rivers.  Surface rivers are necessary to drain the subterranean river.
The Fengyu Cave has an entire length 5.3 kilometers and a subterranean river of 4.1 km.  Fengyu red fish, how the Cave gets it's name, are abundant in this underworld environment.  Speleothems, cave deposits from water, take on very delicate shapes in the Fengyu Cave.  As karst limestone dissolves by water, the pH of the limestone/water mixture rises in the same ratio as a comparable high carbon dioxide pressure.  The limestone/water solution enters the aerated Fengyu Cave and excess carbon dioxide diffuses into the cave atmosphere.  Calcite is deposited forming principal speleothems; stalactites and helictites that grow downward from cave roofs and stalagmites that build upward (Photograph, right).  Stalagmites in the Fengyu Cave are young and grow quickly.  They are also very slender.  For example, a stalagmite named Dinghaishenzhen (marvelous needle) is 9.8 m high but only 15 cm in diameter.  Stalactite stone curtains are also abundant in the Cave, where calcite flows coat cave walls.
Outside Fengyu Cave is the Fengcong Valley.  The karst peaks, about 300 m high, meander the banks of the Shanhe River.  Behind the cliffs are typical Fencong depressions displaying orderly, closed polygonal patterns.  This is caused by the distinctive weathering surface of  limestone.

The subterranean river (Photograph, below) descends from a surface stream, 3 km away from the Fengyu Cave entrance, that originates from the southern sandstone Dayao Mountains.  The river enters the cave between a boundary of sandstone and Devonian limestone.The Shanhe River, a tributary of the Lipu River, recharges the subterranean river by karst fissures, increasing the discharge in small increments.  As a seasonal river, the Shanhe is flooded in the summer and almost parched in the winter.  Sinkholes on the surface also recharge the subterranean river.
The width of the subterranean river is 5-6 m wide.  The water depth and discharge are quite different throughout the length of the river.  At Ganghu Cave, the entrance of Fengyu Cave, the river is 0.3 m deep and has a discharge of 0.5 cubic meters per second.  In the Dabayan Cave, where the river exits, it is more than 1 m deep and has a discharge of 1.6 cubic meters per second.
The subterranean river is daily traversed by tourism boats.  The gaudy lights are to make the river tour "mystical" for the tourists, as they meander through a paradise of stalagmites and stalactites.  Near the entrance of the cave is a big hall where the tourist can choose to drink, sing, and dance.  Where the Earth has undergone and is undergoing dynamic geologic processes, an automatic remote light and stereo system allows the "Flinstone" tourists to engage in a modern Discotheque.

The United Nations Educational, Scientific, and Cultural Organization, the International Union of Geological Sciences, and the International Geological Correlation Programme. Karst Geological Hazard in Zhemu Village, Guilin

Karst Dynamics Laboratory Ministry of Land and Resources Guilin, Guangxi Desertified Karstland Fengyu Cave

Major and Minor Karst Landforms Fengcong Versus Fenglin Karst Environmental Change and Karst Processes

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