<P> Karst topography is a landscape formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum . It is characterized by underground drainage systems with sinkholes and caves . It has also been documented for more weathering - resistant rocks, such as quartzite, given the right conditions . Subterranean drainage may limit surface water, with few to no rivers or lakes . However, in regions where the dissolved bedrock is covered (perhaps by debris) or confined by one or more superimposed non-soluble rock strata, distinctive karst surface developments might be totally missing, the features occurring at subsurface levels . </P> <P> The study of karst is considered of prime importance in petroleum geology since as much as 50% of the world's hydrocarbon reserves are hosted in porous karst systems . </P>

Numerous circular pits found in the karst region are called