Features of Karst Landscapes

Cave Formation Underground Creates Distinct Topography Above Ground

Aug 13, 2009

Karst landscapes are defined by several key features. These features form due to geologic processes occurring in cavern systems below ground.

Karst topography typically forms in areas where the local bedrock is made of limestone, a type of sedimentary rock composed of the mineral calcite. Calcite is easily dissolved by acidic rain and groundwater, leading to the formation of caves underground. Continued dissolution of calcite and groundwater movement cause changes in the cave system, creating unique landforms visible above ground.

Cave Formation

All rain is naturally acidic. As it falls, the rainwater reacts with carbon dioxide in the atmosphere to form weak carbonic acid. This acid is stronger in areas of heavy air pollution. The acid rain dissolves limestone rock exposed at the Earth’s surface, but also percolates underground and dissolves the limestone below the surface.

Caves form at or near the water table, where the slightly acidic groundwater slowly dissolves the surrounding limestone over time. If the water table drops, the groundwater will drain away, leaving behind the empty cavern.

Groundwater will continue to move through the now-empty cave as it travels down through the bedrock. As the water drips from the cave ceiling or along its walls, the carbon dioxide will evaporate out of the water, making it less acidic. At that point, any calcite already dissolved in the water will begin to precipitate. This process creates cave formations, called speleothems. The continual movement of groundwater through the cave and the rest of the cavern system constantly changes the shape of the cave and its speleothems, which in turn changes the shape of the landscape above ground.

Karst Topography

In Earth: Portrait of a Planet, Stephen Marshak lists several identifying features of a karst landscape. These features are a clear indication that cave processes are occurring underground.

The most prominent karst feature is the sinkhole. Sinkholes form when a cave’s roof collapses, causing the ground above to subside. Cave collapse often occurs when groundwater drains from a cavern, leaving no way of supporting the cave’s roof. Sinkholes can cause extensive damage to structures and roads. Sometimes, sinkholes fill with water, forming lakes.

Natural bridges are formed when most of a cave collapses, but the roof is left. Erosion over time exposes the empty space.

Disappearing streams and emerging springs are water features of karst landscapes. Disappearing springs occur when water traveling above ground vanishes into the subsurface, becoming an underground stream. Emerging springs, conversely, form when water traveling through a cave system escapes to the surface.

Areas of China are known for their tower karst formations. Tower karst develops when formations of stronger, less soluble bedrock remains between sinkholes. Erosion eventually destroys the limestone bedrock, leaving formations of the stronger bedrock behind.

Relationship Between Topography and Underground Processes

Karst topography has several features that make it unique. Geologists can use these features to pinpoint areas of underground cave systems. The evolution of these systems – the constant interaction between acidic water and limestone rock – is what creates these exceptional formations.

The copyright of the article Features of Karst Landscapes in Geography is owned by Dianne Turgeon. Permission to republish Features of Karst Landscapes in print or online must be granted by the author in writing.