A cave or cavern is a natural void under the Earth's 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 underground. Caves which extend further underground than the opening is wide are called endogene caves.
Karst is a topography formed from the dissolution of soluble carbonate rocks such as limestone and dolomite. It is characterized by features like poljes above and drainage systems with sinkholes and caves underground. There is some evidence that karst may occur in more weathering-resistant rocks such as quartzite given the right conditions.
The Amblyopsidae are a fish family commonly referred to as cavefish, blindfish, or swampfish. They are small freshwater fish found in the dark environments of caves, springs and swamps in the eastern half of the United States. Like other troglobites, most amblyopsids exhibit adaptations to these dark environments, including the lack of functional eyes and the absence of pigmentation. More than 200 species of cavefishes are known, but only six of these are in the family Amblyopsidae. One of these, Forbesichthys agassizii, spends time both underground and aboveground. A seventh species in this family, Chologaster cornuta, is not a cave-dweller but lives in aboveground swamps.
In Greek mythology, the river Phlegethon or Pyriphlegethon was one of the five rivers in the infernal regions of the underworld, along with the rivers Styx, Lethe, Cocytus, and Acheron.
The Marble Arch Caves are a series of natural limestone caves located near the village of Florencecourt in County Fermanagh, Northern Ireland. The caves are named after the nearby Marble Arch, a natural limestone arch at the upstream end of Cladagh Glen under which the Cladagh River flows. The caves are formed from three rivers draining off the northern slopes of Cuilcagh mountain, which combine underground to form the Cladagh. On the surface, the river emerges from the largest karst resurgence in Ireland, and one of the largest in the United Kingdom. At 11.5 kilometres (7.1 mi) the Marble Arch Caves form the longest known cave system in Northern Ireland, and the karst is considered to be among the finest in the British Isles.
Troglofauna are small cave-dwelling animals that have adapted to their dark surroundings. Troglofauna and stygofauna are the two types of subterranean fauna. Both are associated with subterranean environments – troglofauna are associated with caves and spaces above the water table and stygofauna with water. Troglofaunal species include spiders, insects, myriapods and others. Some troglofauna live permanently underground and cannot survive outside the cave environment. Troglofauna adaptations and characteristics include a heightened sense of hearing, touch and smell. Loss of under-used senses is apparent in the lack of pigmentation as well as eyesight in most troglofauna. Troglofauna insects may exhibit a lack of wings and longer appendages.
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 bottom of the stream channel. This is the opposite of a more common gaining stream which increases in water volume farther downstream as it gains water from the local aquifer.
Subterranea are underground structures, both natural and human-made.
The Punkva is a 29 km (18 mi) long river in South Moravia, Czech Republic. It is a subterranean river in the Moravian Karst and a left tributary of the Svitava. It is the longest underground river in the Czech Republic.
The Reka, 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 Creek. The river is 54 km (34 mi) long, of which 51 km (32 mi) is in Slovenia. At the village of Škocjan it disappears underground through Škocjan Caves, flowing 38 km (24 mi) underneath the Slovenian Karst. The river continues as part of the Timavo in Italy. Tracer studies have shown that it also feeds springs elsewhere on the Adriatic Coast between Trieste and Monfalcone. It has a pluvial regime.
A ponor is a natural opening where surface water enters into underground passages; they may be found in karst landscapes where the geology and the geomorphology is typically dominated by porous limestone rock. Ponors can drain stream or lake water continuously or can at times work as springs, similar to estavelles. Morphologically, ponors come in forms of large pits and caves, large fissures and caverns, networks of smaller cracks, and sedimentary, alluvial drains.
An underground lake is a lake underneath the surface of the Earth. Most naturally occurring underground lakes are found in areas of karst topography, where limestone or other soluble rock has been weathered away, leaving a cave where water can flow and accumulate.
The Cladagh River is a small river in County Fermanagh, formed from three rivers and a number of streams draining off the northern slopes of Cuilcagh mountain, which combine underground in the Marble Arch Cave system. On the surface, the River Cladagh emerges from one of the largest karst resurgences in the UK, before flowing through Cladagh Glen Nature Reserve and eventually draining into the Arney River.
The Timavo River, known in Slovene as the Timava or Timav, is a two-kilometre stream in the Province of Trieste. It has four sources near San Giovanni near Duino and outflows in the Gulf of Panzano 3 kilometres (2 mi) southeast of Monfalcone, Italy.
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. After gaining independence from Yugoslavia in 1991, Slovenia made a commitment to actively protect the Škocjan Caves area. To fulfill this commitment, Škocjan Caves Regional Park was established, along with its managing authority, the Škocjan Caves Park Public Service Agency.
Škocjan Caves Regional Park is located in the Škocjan Karst, a vast flat landscape that lies at an elevation between 420 and 450 m in the southeast part of the Karst area. Following its independence, Slovenia committed itself to protecting the Škocjan Caves area; for this reason, it established Škocjan Caves Regional Park and its managing authority, the Škocjan Caves Park Public Service Agency.
The Ombla is a short river in Croatia, northeast of Dubrovnik. Its course is approximately 30 metres long, and it empties into the Rijeka Dubrovačka, ria formed by the Adriatic Sea near Komolac in Dubrovnik-Neretva County. Rijeka Dubrovačka is actually a ria, a flooded river valley formed through changes in sea surface elevation on a geologic time scale. The river rises as a karst spring fed by groundwater replenished by Trebišnjica, which is an influent stream flowing in Popovo Polje, in the immediate hinterland of the Ombla. The elevation difference between the river's source and its mouth is just over 2 metres. The average discharge of the river is 24.1 cubic metres per second. The drainage basin of the Ombla encompasses 600 square kilometres and, besides the short surface course, includes only groundwater flow.
The Punkva Caves are a cave system of the Czech Republic located north of the city of Brno, near the town of Blansko. The Punkva River flows through it. Part of it is the Macocha Abyss, its sinkhole is about 138.7 meters deep and also the deepest of its kind in Central Europe. It is a popular tourist attraction for casual visitors to the region, in addition to cavers and advanced technical divers.
The Zalomka is a karstic river in the southern part of Bosnia and Herzegovina, and as part of the Neretva river system it is one of the largest sinking rivers in the country and Dinarides. It rises under the Morine plateau, near Brajićevići village in Gacko municipality, but also collects its upper course waters from Gatačko Polje.
The Northern Karst Belt is a limestone karst landscape located in the northwestern region of Puerto Rico. A karst is a topographical zone formed by the dissolution of soluble porous rocks, such as limestone, with features such as mogotes, canyons, caves, sinkholes, streams and rivers, all of which are common on this region of the island. Some of the island's main rivers, including its longest, traverse the karst and form some of the most distinctive Puerto Rican geographical features such as the Camuy caverns. Many of these rivers feed into and are important in the formation of many marshy areas such as the Caño Tiburones wetlands.
