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

geomorphic Geomorphology (from Ancient Greek: , ', "earth"; , ', "form"; and , ', "study") is the scientific study of the origin and evolution of topographic and bathymetric features created by physical, chemical or biological processes operating at or ...

feature found in karst 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 locally also known as ''vrtače'' and shakeholes, and to openi ...

. The word ''fenster'' is German for 'window', as these features are windows into the karst landscape. The term is used to denote an unroofed portion of a cavern which reveals part of a

subterranean river A subterranean river is a river that runs wholly or partly beneath the ground surface – one where the riverbed does not represent the surface of the Earth. It is distinct from an aquifer, which may flow like a river but is contained within a per ...

. A complex system of caves, known as karst topography, evolves from the effects of

water erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is dist ...

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 (also known as doloston ...

such as

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

, dolomite or

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate 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, blackboard or sidewalk chalk, and drywal ...

. "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, 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 atmospheric pressure ("vadose" is fr ...

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 The Kentucky Geological Survey (KGS) is a department of the University of Kentucky that provides information on the geology of Kentucky Kentucky ( , ), officially the Commonwealth of Kentucky, is a state in the Southeastern region of the U ...

, is Short Creek in Pulaski County, 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, that is 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 ...

in Mammoth Cave National Park, Kentucky, where small watercourses emerge and disappear at the bottom of a large

References

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