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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 rocks such as limestone, dolomite, and gypsum. It is characterized by underground drainage systems with sinkholes and caves. It has also been documented for more weathering-resistant ro ...
landscapes where the geology and the geomorphology is typically dominated by porous
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 ...
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 A cave or cavern is a natural void in the ground, specifically a space large enough for a human to enter. Caves often form by the weathering of rock and often extend deep underground. The word ''cave'' can refer to smaller openings such as sea ...
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 (from Latin ''alluvius'', from ''alluere'' 'to wash against') 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. Alluv ...
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 Attested language, unattested, linguistic reconstruction, reconstructed proto-language of all Slavic languages. It represents Slavic speech approximately ...
word ''nora'', meaning ''pit'', ''hole'', ''abyss''; the English word ''narrow'' probably has the same origin. 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 locally also known as ''vrtače'' and shakeholes, and to openi ...
(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 soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidate ...
system. Steady water erosion may have formed or enlarged the portal in (mainly
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 ...
) 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 ( sh, / , ), abbreviated BiH () or B&H, sometimes called Bosnia–Herzegovina and often known informally as Bosnia, is a country at the crossroads of south and southeast Europe, located in the Balkans. Bosnia and H ...
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. Roughly long, it is the third-longest European mountain range after the Urals at and the Scandinavian Mountains at . The range stretches ...
, the
Dinaric Alps The Dinaric Alps (), also Dinarides, are a mountain range in Southern and Southcentral Europe, separating the continental Balkan Peninsula from the Adriatic Sea. They stretch from Italy in the northwest through Slovenia, Croatia, Bosnia and Herz ...
, Greece, Turkey, and parts of the southern United States. File:Katavothra-Feneos ponor karst-depression Peloponnese Feneos mit katavothre.jpg, Polje of
Feneos Feneos (Greek: Φενεός, Latin: ''Pheneus'') is a village and a former municipality in Corinthia, Peloponnese, Greece. Since the 2011 local government reform it is part of the municipality Sikyona, of which it is a municipal unit. The municipal ...
,
Greece Greece,, or , romanized: ', officially the Hellenic Republic, is a country in Southeast Europe. It is situated on the southern tip of the Balkans, and is located at the crossroads of Europe, Asia, and Africa. Greece shares land borders with ...
, 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 ( sl, Notranjska Reka), is a river that starts as Big Creek ( hr, Vela voda) in Croatia, on the southern side of Mount Snežnik, and flows through western Slovenia, where it ...
disappears into
Škocjan Caves Škocjan Caves (; sl, Škocjanske jame, it, Grotte di San Canziano) is a cave system in Slovenia. Due to its exceptional significance, Škocjan Caves was entered on UNESCO’s list of natural and cultural World Heritage Sites in 1986. Internati ...
, Slovenia File:Ponor, Stubaier Alpen.jpg, A
Stubai Alps The Stubai Alps (in German ''Stubaier Alpen'') is a mountain range in the Central Eastern Alps of Europe. It derives its name from the Stubaital valley to its east and is located southwest of Innsbruck, Austria. Several peaks form the border betwee ...
stream terminates in an alluvial ponor 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 t ...
River disappears into a ponor between Ajou and
La Houssaye La Houssaye () is a commune in the Eure department in northern France. Population See also *Communes of the Eure department The following is a list of the 585 communes of the Eure department of France. The communes cooperate in the follo ...
(
Eure Eure () is a department in Normandy in Northwestern France, named after the river Eure. Its prefecture is Évreux. In 2019, Eure had a population of 599,507.Slovenia Slovenia ( ; sl, Slovenija ), officially the Republic of Slovenia (Slovene: , abbr.: ''RS''), is a country in Central Europe. It is bordered by Italy to the west, Austria to the north, Hungary to the northeast, Croatia to the southeast, an ...
File:Katavothra ponor Nestani-Polje Peloponnes Greece.jpg, In
Polje A polje, also karst polje or karst field, is a large flat plain found in karstic geological regions of the world, with areas usually . The name derives from the Slavic languages and literally means 'field', whereas in English ''polje'' specific ...
Argon Pedion Argon Pedion ( gr, Ἀργὸν Πεδίον, 3=untilled plain) is the geological name of a "closed karst basin" in the Arcadian highlands in the Peloponnese peninsula of southern Greece. The first known appearance of this name was in a publication ...
“ (untilled plain). Plain and ponor documented since 2nd century AD by
Pausanias Pausanias ( el, Παυσανίας) may refer to: *Pausanias of Athens, lover of the poet Agathon and a character in Plato's ''Symposium'' *Pausanias the Regent, Spartan general and regent of the 5th century BC *Pausanias of Sicily, physician of th ...


Dams and reservoirs in karst

Reservoir A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation. Reservoirs can be created in a number of ways, including contro ...
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, a ...
s to capture water in karst terrains may pose a great financial risk 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.


See also

*
Karst spring A karst spring or karstic spring is a spring (outflow of groundwater) that is part of a karst hydrological system. Description Because of their often conical or inverted bowl shape, karst springs are also known in German-speaking lands as a ''Top ...
*
Losing stream A losing stream, disappearing stream, influent stream or sinking river is a stream or river that loses water as it flows downstream. The water infiltrates into the ground recharging the local groundwater, because the water table is below the bo ...


References

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