How Halong Got Its Karst

Karst -- a name derived from a limestone plateau in Slovenia -- refers to outcroppings of readily soluble rock, commonly limestone, that are eaten away by chemical reactions catalyzed by dripping water. The karst outcroppings in Halong -- and in places like Guilin in China or Krabi in Thailand -- are made of this porous sedimentary rock and tend to develop dynamic caves that drip minerals and form stalactites and stalagmites. Other features of limestone karst deposits and erosion are wide fissures and underground streams -- in short, a constantly changing, dynamic landscape caused by chemical erosion. Some of Halong's many caves are actually "dead," meaning that the leaching process is over, but others are constantly changing.

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