# Ponor
A **ponor** is a natural opening in karst terrain, typically in the bottom or side of a closed depression, through which a surface stream or lake drains wholly or partly into an underground channel[1](https://en.wiktionary.org/wiki/ponor) • [2](https://termframe.ff.uni-lj.si/term/a3-0005-en/). The word comes from [Serbo-Croatian](https://www.edgepedia.org/serbo-croatian) and is one of several Slavic terms, along with *polje*, *uvala*, and *jama*, that entered international karst terminology[1](https://en.wiktionary.org/wiki/ponor) • [3](https://www.etd.ceu.edu/2020/lukic_dejan.pdf). In English-language literature the same feature is called a **swallow hole**, **swallet**, or **stream sink**[2](https://termframe.ff.uni-lj.si/term/a3-0005-en/).
| Key fact | Detail |
|---|---|
| Definition | Hole in the bottom or side of a closed depression through which water passes to or from an underground channel (Monroe, 1970)[2](https://termframe.ff.uni-lj.si/term/a3-0005-en/) |
| Synonyms | Swallow hole, swallet, stream sink; French *perte*, German *Schlund*, Greek *katavothra*, Spanish *sumidero*, Turkish *su yutan*[2](https://termframe.ff.uni-lj.si/term/a3-0005-en/) • [4](https://www.hinko.org/hinko/Dowloads/11/2/XI-2-09.pdf) |
| Etymology | From Serbo-Croatian; one of several Slavic karst terms adopted internationally[1](https://en.wiktionary.org/wiki/ponor) • [3](https://www.etd.ceu.edu/2020/lukic_dejan.pdf) |
| Hydrological role | Point at which a sinking stream, often carrying allogenic (non-karst) runoff, enters the karst groundwater system[2](https://termframe.ff.uni-lj.si/term/a3-0005-en/) |
| Flood control | No flooding of a polje occurs as long as the spring's total capacity is smaller than the ponor's total capacity (Milanović, 1981)[1](https://en.wiktionary.org/wiki/ponor) |
| Sea ponor | The only permanent sea ponor reported is the sea mill of Argostoli, on Kefalonia Island in the Ionian Sea, Greece[1](https://en.wiktionary.org/wiki/ponor) |
## Definition and related terms
According to a US Geological Survey glossary assembled by Watson H. Monroe, a ponor is an opening in the floor or wall of an enclosed depression that lets water flow into or out of a subterranean passage, while a stream sink is where a surface stream disappears into the ground[2](https://termframe.ff.uni-lj.si/term/a3-0005-en/). The British terms differ subtly in meaning: **swallow hole** typically suggests water vanishing within a closed depression or a blind valley, while **swallet** can describe water sinking into alluvium along a streambed even in the absence of any depression[2](https://termframe.ff.uni-lj.si/term/a3-0005-en/). Japanese references describe the ponor as the intake point where a surface river in limestone country becomes an underground (lost) stream, usually a vertical opening developed along limestone fissures[5](https://kotobank.jp/word/%E3%81%BD%E3%81%AE%E3%83%BC%E3%82%8B-3187031).
## Hydrological function
Ponors are the intake points of concentrated recharge. Water from allogenic sources, meaning streams that rise on non-karstic rock and flow onto the karst, sinks underground at these openings[2](https://termframe.ff.uni-lj.si/term/a3-0005-en/). Petar Milanović, a karst hydrogeologist and author of *Water Resources Engineering in Karst*, called ponors one of the symbolic features of karst regions and crucial features from a hydrogeological and geotechnical point of view[1](https://en.wiktionary.org/wiki/ponor).
The swallowing capacity of a ponor governs flooding in karst basins. In a polje, a large closed karst depression, water accumulates whenever inflow exceeds what the ponors can swallow; Milanović's 1981 formulation states that no flooding occurs as long as the total capacity of the outlet springs is smaller than the total capacity of the ponors[1](https://en.wiktionary.org/wiki/ponor) • [6](https://www.researchgate.net/publication/281691719_Poljes_Ponors_and_Their_Catchments). After heavy rain, when a ponor can no longer take in all the water, the surrounding area can temporarily become a lake[5](https://kotobank.jp/word/%E3%81%BD%E3%81%AE%E3%83%BC%E3%82%8B-3187031).
Where a ponor leads, tracing experiments show, can vary sharply over short distances. In the Fatničko Polje of eastern [Herzegovina](https://www.edgepedia.org/herzegovina), water sinking in one ponor zone reappears at the Bregava River spring, water from another zone about 2 km away reappears at the Trebišnjica spring, and a third zone feeds both springs depending on groundwater levels; the two springs lie more than 35 km apart in a straight line[6](https://www.researchgate.net/publication/281691719_Poljes_Ponors_and_Their_Catchments).
## Terminology history
Ponor entered scientific usage from the Dinaric karst of the Balkans. Although the Serbian geographer [Jovan Cvijić](https://www.edgepedia.org/jovan-cvijic) is often credited with introducing Slavic terminology into the classification of karst forms, terms of Slavic origin including *ponor*, *uvala*, *jama*, and *polje* were already in use; Cvijić asserted their precise meaning in geomorphological discourse rather than coining them[3](https://www.etd.ceu.edu/2020/lukic_dejan.pdf). In Slovenia, the karst researcher Ivan Gams noted in 1962 that Slovene workers had begun to distinguish more precisely among the terms *ponor*, *ponikva*, and *požiralnik*[7](https://www.researchgate.net/publication/334433827_Contribution_of_Ivan_Gams_to_the_Development_of_Slovene_Karst_Terminology).
## Special cases
A **sea ponor** is an opening where seawater flows or is drawn into karstified rock[4](https://www.hinko.org/hinko/Dowloads/11/2/XI-2-09.pdf). The cited example is the sea mill of [Argostoli](https://www.edgepedia.org/argostoli) on Kefalonia, described in the *Encyclopedia of Caves and Karst Science* as the only permanent sea ponor in the world[1](https://en.wiktionary.org/wiki/ponor). In glaciokarst, landscapes shaped by glaciers, ponors characteristically formed in karstic depressions or in glacial erosional depressions[1](https://en.wiktionary.org/wiki/ponor).
## References
1. [Ponor, Wiktionary (quotations from Milanović 1981; Gunn 2004; Milanovic 2004; Veress 2018)](https://en.wiktionary.org/wiki/ponor)
2. [Ponor, swallow hole, stream-sink, swallet, stream sink, Termframe (definitions from Fleury 2009; Ford and Williams 2007; Monroe 1970)](https://termframe.ff.uni-lj.si/term/a3-0005-en/)
3. [Lukić, Dejan (2020). CEU thesis on karst terminology and flooding](https://www.etd.ceu.edu/2020/lukic_dejan.pdf)
4. [A Lexicon of Cave and Karst Terminology (multilingual synonyms)](https://www.hinko.org/hinko/Dowloads/11/2/XI-2-09.pdf)
5. [ポノール, Kotobank (最新地学事典; ブリタニカ国際大百科事典)](https://kotobank.jp/word/%E3%81%BD%E3%81%AE%E3%83%BC%E3%82%8B-3187031)
6. [Bonacci, Ognjen (2013). Poljes, Ponors and Their Catchments, Treatise on Geomorphology](https://www.researchgate.net/publication/281691719_Poljes_Ponors_and_Their_Catchments)
7. [Contribution of Ivan Gams to the Development of Slovene Karst Terminology](https://www.researchgate.net/publication/334433827_Contribution_of_Ivan_Gams_to_the_Development_of_Slovene_Karst_Terminology)
---
*Topic: Encyclopedia › Places and geography › Landforms and terrestrial features › Caves and subsurface landforms › Karst landforms and regions › Karst hydrology, springs and subterranean waters › Ponors, swallets, and sink points*
*Initially written Sep 17, 2026 · Reviewed: Oct 21, 2026 · Edited: Oct 11, 2026; Oct 15, 2026; Oct 21, 2026 · Last review: Oct 21, 2026*
*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*
License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license