In karst country, rivers vanish underground and reappear with new names
Slovenia's Ljubljanica is nicknamed the river of seven names because it keeps disappearing into the ground and resurfacing somewhere else. That is typical of karst, landscapes carved by slightly acidic water dissolving limestone. Above ground you find sinkholes and bare rock; below lie caves, hidden rivers and some of the fastest-moving groundwater anywhere.
Rain picks up carbon dioxide from the air and more from the soil, forming a weak carbonic acid that slowly dissolves calcium carbonate. Karst develops best in dense, heavily fractured limestone with moderate to heavy rainfall; chalk, though chemically similar, is too porous to concentrate the flow. In rare cases a stronger agent is at work: sulfuric acid formed from sulfides helped hollow out Lechuguilla Cave in New Mexico and is still enlarging Italy's Frasassi Caves.
The name comes from a limestone plateau above Trieste, known in Slovene as Kras, and ultimately from an old Mediterranean word possibly linked to a root meaning rock. Johann Weikhard von Valvasor introduced it to European scholars in 1689 while describing the underground rivers of Lake Cerknica. Jovan Cvijić, called the father of karst geomorphology, catalogued its landforms in 1893. Cave exploration was long dismissed as sport rather than science, and karst hydrology became a formal discipline only in France in the late 1950s.
The landforms are striking. Small scale features include flutes and runnels etched into bare rock. Larger ones include sinkholes, vertical shafts, wide flat-floored basins called poljes, and in tropical regions whole fields of cone-shaped hills, as in Cuba, Jamaica and southern China. Along coasts, dissolution and bioerosion sculpt the towers of Phang Nga Bay in Thailand and Ha Long Bay in Vietnam. Ireland has turloughs, lakes that appear each year as groundwater wells up. Because the terrain is so hard to cross, karst forests often stay undisturbed, and their alkaline soils favour unusual orchids and palms.
Underground, water moves astonishingly fast. Dye traces at Barton Springs in Texas measured flows of up to 11 kilometres a day, which makes karst aquifers far more vulnerable to pollution than ordinary porous ones. Buried ancient karst also matters economically, since perhaps half the world's hydrocarbon reserves sit in carbonate rock.
Source: Karst
