A ponor is a natural opening where surface water enters into underground passages; they may be 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 the geology and the geomorphology is typically dominated by porous

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) ...

rock. Ponors can drain stream or lake water continuously or can at times work as springs, similar to

estavelle In karst geology, estavelle or inversac is a ground orifice which, depending on weather conditions and season, can serve either as a sink or as a source of fresh water. It is a type of ponor or sinkhole A sinkhole is a depression or hole in ...

s. Morphologically, ponors come in forms of large pits and

cave Caves or caverns are natural voids under the Earth's Planetary surface, surface. Caves often form by the weathering of rock and often extend deep underground. Exogene caves are smaller openings that extend a relatively short distance undergrou ...

s, large

fissure A fissure is a long, narrow crack opening along the surface of Earth. The term is derived from the Latin word , which means 'cleft' or 'crack'. Fissures emerge in Earth's crust, on ice sheets and glaciers, and on volcanoes. Ground fissure A ...

s and caverns, networks of smaller cracks, and sedimentary,

alluvial Alluvium (, ) is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. Alluvium is also sometimes called alluvial deposit. Alluvium is ...

drains.

Etymology

The name for the karst formation ponor comes from Croatian and Slovene. It derives from the

proto-Slavic Proto-Slavic (abbreviated PSl., PS.; also called Common Slavic or Common Slavonic) is the unattested, reconstructed proto-language of all Slavic languages. It represents Slavic speech approximately from the 2nd millennium BC through the 6th ...

word ''*nora'', meaning ''pit'', ''hole''. Several places in southeast Europe (Bulgaria, Croatia, Czech Republic, Hungary, Romania, Montenegro, Slovenia) bear the name ''Ponor'' due to associated karst openings.

Description

Whereas 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 ...

(doline) is a depression of surface topography with a pit or cavity directly underneath, a ponor is kind of a portal where a surface stream or lake flows either partially or completely underground into a karst

groundwater Groundwater is the water present beneath Earth's surface in rock and Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. About 30 percent of all readily available fresh water in the world is groundwater. A unit ...

system. Steady water erosion may have formed or enlarged the portal in (mainly

) rock, in a conglomerate, or in looser materials. Karst terrains are known for surface water losses through small ponors and its resurgence after having traveled through vast underground systems.

Prevalence

Ponors are found worldwide, but only in karst regions. The entire Adriatic watershed within

Bosnia and Herzegovina Bosnia and Herzegovina, sometimes known as Bosnia-Herzegovina and informally as Bosnia, is a country in Southeast Europe. Situated on the Balkans, Balkan Peninsula, it borders Serbia to the east, Montenegro to the southeast, and Croatia to th ...

sits on Dinaric karst, with numerous explored and probably many more unexplored ponors and underground flows. There are significant geological ponors in the

Carpathian Mountains The Carpathian Mountains or Carpathians () are a range of mountains forming an arc across Central Europe and Southeast Europe. Roughly long, it is the third-longest European mountain range after the Ural Mountains, Urals at and the Scandinav ...

, the

Dinaric Alps The Dinaric Alps (), also Dinarides, are a mountain range in Southern Europe, Southern and Southcentral Europe, separating the continental Balkan Peninsula from the Adriatic Sea. They stretch from Italy in the northwest through Slovenia, Croatia ...

, Greece, Turkey, and parts of the southern United States. File:Katavothra-Feneos ponor karst-depression Peloponnese Feneos mit katavothre.jpg, Polje of Feneos,

Greece Greece, officially the Hellenic Republic, is a country in Southeast Europe. Located on the southern tip of the Balkan peninsula, it shares land borders with Albania to the northwest, North Macedonia and Bulgaria to the north, and Turkey to th ...

, lake until late 19. Century. Rain showers flood large parts even today File:Avenul campeneasca.jpg, Closeup of ponor in Câmpeneasca cave near Izbuc village, Romania File:Skocjanske-Ponor3.jpg, A ponor where the

Reka River The Reka (literally, 'river' in Slovene), also the Inner Carniola Reka (), is a river that starts as Big Creek () in Croatia, on the southern side of Mount Snežnik, and flows through western Slovenia, where it is also initially known as Big Cre ...

disappears into

Škocjan Caves Škocjan Caves (; , ) is a cave system located in Slovenia. Škocjan Caves was included on UNESCO’s list of natural and cultural World Heritage Sites in 1986. Škocjan Caves is a significant underground phenomenon on the Karst Plateau and in ...

, Slovenia File:Risle ponor.jpg, The

Risle The Risle (; less common: ''Rille'') is a long river in Normandy, left tributary of the Seine. The river begins in the Orne department west of L'Aigle, crosses the western part of the department of Eure flowing from south to north and out into ...

River disappears into a ponor between

Ajou Ajou () is a former commune in the Department of Eure in Normandy. It is located in northern France. On 1 January 2016, it was merged into the new commune of Mesnil-en-Ouche.La Houssaye La Houssaye () is a commune in the Eure department in northern France. Geography The commune along with another 69 communes shares part of a 4,747 hectare, Natura 2000 conservation area, called Risle, Guiel, Charentonne. Population See al ...

(

Eure Eure ( ; ; or ) is a department in the administrative region of Normandy, northwestern France, named after the river Eure. Its prefecture is Évreux. In 2021, Eure had a population of 598,934.Logatec Logatec (; , ) is a town in Slovenia. It is the seat of the Municipality of Logatec. It is located roughly in the centre of Inner Carniola, between the capital Ljubljana and Postojna. The town of Logatec has seen rapid industrial development and ...

Slovenia Slovenia, officially the Republic of Slovenia, is a country in Central Europe. It borders Italy to the west, Austria to the north, Hungary to the northeast, Croatia to the south and southeast, and a short (46.6 km) coastline within the Adriati ...

File:Katavothra ponor Nestani-Polje Peloponnes Greece.jpg, In

Polje A polje, also called karst polje or karst field, is a large flat plain found in karstic geological regions of the world, with areas usually in the range of 5–400 km2 (2–154 sq mi). The name derives from the Slavic languages, ...

" Argon Pedion" (untilled plain). Plain and ponor documented since 2nd century AD by Pausanias

Dams and reservoirs in karst

Reservoir A reservoir (; ) is an enlarged lake behind a dam, usually built to water storage, store fresh water, often doubling for hydroelectric power generation. Reservoirs are created by controlling a watercourse that drains an existing body of wa ...

s in karst are prone to losses due to leakage through ponors. The construction of

dam A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, aqua ...

s to capture water in karst terrains may pose a great

financial risk Financial risk is any of various types of risk associated with financing, including financial transactions that include company loans in risk of default. Often it is understood to include only downside risk, meaning the potential for financi ...

despite initial investigations and thorough sealing treatments. It wasn't until the twentieth century that the first dams in karst were built, some of which famously failed.

References

{{Rivers, streams and springs . Karst formations Dinaric Alps Dinaric karst formations Sinkholes

Etymology

Description

Prevalence

Dams and reservoirs in karst

See also

References