Akarst window, also known as akarst fenster, is ageomorphic feature found inkarst landscapes where an underground river is visible from the surface within a sinkhole.[1][2] In this feature, a spring emerges, then the discharge abruptly disappears into asinkhole. The wordfenster is German for 'window', as these features are windows into thekarst landscape.
The term is used to denote an unroofed portion of a cavern which reveals part of asubterranean river.[3] A complex system of caves, known askarst topography, evolves from the effects ofwater erosion oncarbonate rocks such aslimestone,dolomite orgypsum. "A karst fenster is caused by a caving in of portions of the roof of a subterranean stream, thus making some of the underground stream visible from the surface".[4] Theories in the creation of karst topography and karst fensters involvevadose water above the water table, and deep-circulatingphreatic water (water in the zone of saturation) eroding away subsurface rock. Karst fensters may also form because of weathering from above.
An example of a karst window or fenster, recognized by theKentucky Geological Survey, isShort Creek in Pulaski County, where a small river emerges and disappears in a space of less than 100 meters in length.[5] An example of this formation on public parkland isCedar Sink inMammoth Cave National Park, Kentucky, where small watercourses emerge and disappear at the bottom of a largesinkhole.
