Karst

Karst develops where water circulates through soluble rock and gradually enlarges cracks, fractures and other openings. Limestone and dolomite are common bedrock, while marble and gypsum can also form karst landscapes. Rainwater that absorbs carbon dioxide in soil becomes mildly acidic; over long periods, it dissolves carbonate rock and widens passages underground. The resulting terrain may contain caves, underground streams and springs as well as sinkholes—depressions formed when bedrock dissolves below the surface or a cave roof collapses. A stream may disappear into a fissure or sinkhole and re-emerge at a spring. Because drainage often runs beneath the surface, some karst regions have few permanent surface streams or lakes. Caves are one visible part of karst systems, but the term describes a broader landscape and drainage pattern.

Karst does not have a single appearance. Local rock type, fractures, rainfall and groundwater circulation help determine which features dominate. Some areas have exposed, grooved limestone pavement; others are marked by enclosed depressions, cave networks, or cone-shaped and tower-like hills. The name comes from the Karst (Kras) region of Slovenia, where limestone terrain displays characteristic karst forms. Similar landscapes occur in many parts of the world, although their surface features and underground drainage differ from place to place.

Karst formations can store and transmit substantial groundwater, and springs fed by karst aquifers are important water sources. Their open, connected flow paths also create a vulnerability: water and contaminants entering at the surface can move rapidly through underground conduits, often with less filtration than in many other aquifers. Understanding where water enters, travels and emerges is therefore important for protecting drinking-water supplies. Sinkhole formation is another practical concern; when underground dissolution or a cave collapse removes support beneath the surface, the ground above can subside suddenly and damage buildings or infrastructure.