A karst window, also known as a karst fenster, is a

geomorphic Geomorphology () is the scientific study of the origin and evolution of topography, topographic and bathymetry, bathymetric features generated by physical, chemical or biological processes operating at or near Earth#Surface, Earth's surface. Ge ...

feature found in

karst Karst () is a topography formed from the dissolution of soluble carbonate rocks such as limestone and Dolomite (rock), dolomite. It is characterized by features like poljes above and drainage systems with sinkholes and caves underground. Ther ...

landscapes where an underground river is visible from the surface within a sinkhole. In this feature, a spring emerges, then the discharge abruptly disappears into a

sinkhole A sinkhole is a depression or hole in the ground caused by some form of collapse of the surface layer. The term is sometimes used to refer to doline, enclosed depressions that are also known as shakeholes, and to openings where surface water ...

. The word ''fenster'' is German for 'window', as these features are windows into the

landscape. The term is used to denote an unroofed portion of a cavern which reveals part of a

subterranean river A subterranean river (also known as an underground river) is a river or watercourse that runs wholly or partly beneath the ground, one where the riverbed does not represent the surface of the Earth. It is distinct from an aquifer, which may flow ...

. A complex system of caves, known as

karst topography Karst () is a topography formed from the dissolution of soluble carbonate rocks such as limestone and Dolomite (rock), dolomite. It is characterized by features like poljes above and drainage systems with sinkholes and caves underground. Ther ...

, evolves from the effects of water erosion on

carbonate rocks Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two major types are limestone, which is composed of calcite or aragonite (different crystal forms of CaCO3), and Dolomite (rock), dolomite rock (also kn ...

such as

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

, dolomite or

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate Hydrate, dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, drywall and blackboard or sidewalk ...

. "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".*Ritter, Michael E. The Physical Environment: an Introduction to Physical Geography. 2006. Dec 2009. Theories in the creation of karst topography and karst fensters involve

vadose The vadose zone (from the Latin word for "shallow"), also termed the unsaturated zone, is the part of Earth between the land surface and the top of the phreatic zone, the position at which the groundwater (the water in the soil's pores) is at ...

water above the water table, and deep-circulating

phreatic ''Phreatic'' is a term used in hydrology to refer to aquifers, in speleology to refer to cave passages, and in volcanology to refer to a type of volcanic eruption. Hydrology The term phreatic (the word originates from the Greek , meaning "well" ...

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 the Kentucky Geological Survey, is Short Creek in Pulaski County, where a small river emerges and disappears in a space of less than 100 meters in length. An example of this formation on public parkland is

Cedar Sink Cedar Sink is a vertical-walled large depression or sinkhole in the ground, located in Edmonson County, Kentucky and contained within and managed by Mammoth Cave National Park. The sinkhole measures from the top sandstone plateau to the bottom of ...

Mammoth Cave National Park Mammoth Cave National Park is a national park of the United States in south-central Kentucky. It encompasses portions of Mammoth Cave, the longest known cave system in the world. The park's are located primarily in Edmonson County, with sma ...

, Kentucky, where small watercourses emerge and disappear at the bottom of a large

References

Karst springs, Sinkholes Dinaric karst formations Dinaric Alps {{geology-stub