12.3: Karst Topography

Karst Topography

The sedimentary rock limestone is composed of the mineral calcite, which is water soluble; this means it will dissolve in water that is weakly acidic. In humid areas where limestone is present, water dissolves away the rock, forming large cavities and depressions that vary in size and shape. As more dissolution occurs, the caves become unstable and collapse, creating sinkholes Links to an external site. (Figure 12.6).

Left, a Google Earth view of central Florida. Top right, and aerial image of a sinkhole. — **Figure 12.6:** *Top right:* The Winter Park sinkhole of Central Florida. *Bottom left:* Every circular feature in this aerial photo is a sinkhole filled with water. (Public Domain; USGS Links to an external site.)

These broad, crater-like depressions are typical of karst topography, named after the Karst region in Slovenia. Karst topography Links to an external site. is characterized by sinkholes, sink lakes (sinkholes filled with water), caves, and disappearing streams (surface streams that disappear into a sinkhole) (Figure 12.7).

Far left, rainwater and groundwater percolate through underground fissures and bedding planes, dissolving carbonate minerals, creating wider cavities and conduits. Left middle, conduits continue to widen, creating underground network of cavities, frequently along one or more discrete zones. Larger conduits have larger flows and enlarge faster. Flow moves towards the local base level. Right middle, rocks above cavities and voids subside or collapse forming dissolution holes and sinkholes. Lake and rivers may disappear underground.
Far right, sinkholes overlap and eventually fill with surficial debris. Soils develop and vegetations is established across a rolling landscape. — **Figure 12.7:** *Top right:* The Winter Park sinkhole of Central Florida. *Bottom left:* Series of generalized cross-sectional views of the development of a karst landscape. (Public Domain; USGS Links to an external site.)

Living on a karst landscape poses unique challenges, and approximately one fourth of Americans in the lower 48 states live in these regions (Figure 12.8).

Map illustrating locations of karst in the US. — **Figure 12.8:** Karst and potential karst areas in soluble rocks in the contiguous United States. (Public Domain; USGS Links to an external site.)