Karst landscapes develop where thick layers of soluble bedrock (limestones or dolomites) lie close to the surface and where plentiful moisture (past or present) has dissolved channels and caverns in this bedrock. Rainfall, snowmelt or groundwater enter cracks in the rock and gradually erode channels; these open tunnels allow more water to flow into the bedrock, leading to the formation of caves and underground streams.
Some of the caves eventually collapse, forming sinkholes and "stealing" flow from surface streams. Where overlying, insoluble rock (such as sandstone) protects the eroded limestone, large, extensive cave systems may develop and "dripstone" formations (stalactites, stalagmites and flowstone) adorn the caverns. All of this underground water eventually returns to the surface via natural springs or enters regional acquifers. Karst topography is thus characterized by rolling terrain with numerous sinkholes and few surface streams. Caves underlie the region and their underground streams may surface some distance away, often emerging from limestone cliffs along a major river.
Tennessee, Kentucky and Missouri harbor a wealth of karst landscape. Tennessee has more caves than any other State and Kentucky is the home of Mammoth Cave; eroded in Mississippian limestone, this is thought to be the most extensive cave system on Earth. Most of Missouri's caves are found across the Ozark Plateau, where Ordovician dolomites predominate; the Mississippian limestones of southwest and central Missouri are also renowned for their karst features.
