A cave or cavern is a natural void in the ground a space large enough for a human to enter. Caves form by the weathering of rock and extend deep underground; the word cave can refer to much smaller openings such as sea caves, rock shelters, grottos, though speaking a cave is exogene, meaning it is deeper than its opening is wide, a rock shelter is endogene. Speleology is the science of study of all aspects of caves and the cave environment. Visiting or exploring caves for recreation may be called caving, potholing, or spelunking; the formation and development of caves is known as speleogenesis. Caves can range in size, are formed by various geological processes; these may involve a combination of chemical processes, erosion by water, tectonic forces, microorganisms and atmospheric influences. Isotopic dating techniques can be applied to cave sediments, to determine the timescale of the geological events which formed and shaped present-day caves, it is estimated that a cave cannot exceed 3,000 metres in depth due to the pressure of overlying rocks.
For karst caves the maximum depth is determined on the basis of the lower limit of karst forming processes, coinciding with the base of the soluble carbonate rocks. Most caves are formed in limestone by dissolution. Caves can be classified in various other ways as well, including a contrast between active and relict: active caves have water flowing through them. Types of active caves include inflow caves, outflow caves, through caves. Solutional caves or karst caves are the most occurring caves; such caves form in rock, soluble. Rock is dissolved by natural acid in groundwater that seeps through bedding planes, faults and comparable features. Over time cracks enlarge to become caves and cave systems; the largest and most abundant solutional caves are located in limestone. Limestone dissolves under the action of rainwater and groundwater charged with H2CO3 and occurring organic acids; the dissolution process produces a distinctive landform known as karst, characterized by sinkholes and underground drainage.
Limestone caves are adorned with calcium carbonate formations produced through slow precipitation. These include flowstones, stalagmites, soda straws and columns; these secondary mineral deposits in caves are called speleothems. The portions of a solutional cave that are below the water table or the local level of the groundwater will be flooded. Lechuguilla Cave in New Mexico and nearby Carlsbad Cavern are now believed to be examples of another type of solutional cave, they were formed by H2S gas rising from below. This gas mixes with groundwater and forms H2SO4; the acid dissolves the limestone from below, rather than from above, by acidic water percolating from the surface. Caves formed at the same time. Lava tubes are the most common primary caves; as lava flows downhill, its surface solidifies. Hot liquid lava continues to flow under that crust, if most of it flows out, a hollow tube remains; such caves can be found in the Canary Islands, Jeju-do, the basaltic plains of Eastern Idaho, in other places.
Kazumura Cave near Hilo, Hawaii is a remarkably deep lava tube. Lava caves are not limited to lava tubes. Other caves formed through volcanic activity include rifts, lava molds, open vertical conduits, blisters, among others. Sea caves are found along coasts around the world. A special case is littoral caves, which are formed by wave action in zones of weakness in sea cliffs; these weaknesses are faults, but they may be dykes or bedding-plane contacts. Some wave-cut caves are now above sea level because of uplift. Elsewhere, in places such as Thailand's Phang Nga Bay, solutional caves have been flooded by the sea and are now subject to littoral erosion. Sea caves are around 5 to 50 metres in length, but may exceed 300 metres. Corrasional or erosional caves are those that form by erosion by flowing streams carrying rocks and other sediments; these can form in any type including hard rocks such as granite. There must be some zone of weakness to guide the water, such as a fault or joint. A subtype of the erosional cave is the aeolian cave, carved by wind-born sediments.
Many caves formed by solutional processes undergo a subsequent phase of erosional or vadose enlargement where active streams or rivers pass through them. Glacier caves are formed by flowing water within and under glaciers; the cavities are influenced by the slow flow of the ice, which tends to collapse the caves again. Glacier caves are sometimes misidentified as "ice caves", though this latter term is properly reserved for bedrock caves that contain year-round ice formations. Fracture caves are formed when layers of more soluble minerals, such as gypsum, dissolve out from between layers of less soluble rock; these rocks fracture and collapse in blocks of stone. Talus caves are formed by the openings among large boulders that have fallen down into a random heap at the bases of cliffs; these unstable deposits are called talus or scree, may be subject to frequent rockfalls and landslides. Anchialine ca
Niğde Province is a province in the southern part of Central Anatolia, Turkey. Population is 341,412; the population was 348,081 in 2000 and 305,861 in 1990. It covers an area of 7,312 km2. Neighbouring provinces are Kayseri, Mersin, Konya and Nevşehir; the province is surrounded on three sides by ranges of the Taurus Mountains, including Mount Hasan and the Melendiz mountains. To the west lies the plain of Emen, which opens up into the wide plain of Konya; the plain is covered with nutritious volcanic soil and Niğde is a successful agricultural region apples and potatoes. Surrounded by mountains and at a high altitude the area has a dry and chilly climate and is exposed to snows brought by cold north winds in winter. Average rainfall 0.9 mm, 78.5 mm in April zero in July and August. Therefore, the hillsides are more or less bare of vegetation, with some forest at the higher altitudes.. Niğde province is divided into 6 districts: Altunhisar Bor Çamardı Çiftlik Niğde UlukışlaSome of the towns within these districts are Bademdere, Bahçeli, Çiftehan, Darboğaz, Fertek and Kemerhisar.
Known in antiquity as Nakita or Nahita the named has mutated through Nekidâ, Nekide and Nikde to today's Niğde. The area has been settled since the Neolithic period of 8000-5500 BC, as proved excavations of burial mounds höyük in the district of Bor, tin mines on the district of Çamardı -Keste; the area was settled by the Hittites, who lived here for a thousand years up until 800BC. The name Nig˘de first occurs in written sources in the form na-hi-ti-ia in a Luwian inscription of king Saruanis from Andaval as was pointed out by Ignace Gelb. Came Assyrians and Phrygians, Armenians, Alexander the Great, who built the city of Tyana with its palaces and waterworks. Roman rule persisted from the Eastern capital of Byzantium until the area was occupied by the Seljuk Turks from 1166 onwards. By the early 13th century Niğde was one of the largest cities in Anatolia and a number of impressive mosques and tombs date from this period; the area was brought within the Ottoman Empire in 1471 and thus passed into the territory of the Turkish Republic in the 1920s.
In 2016, archaeologists discovered in Kınık Mound, an archeological site located in Yeşilyurt village of Altunhisar district at Niğde province, a temple dating back to the late Persian era. In 2018, they discovered a bull statue made from ceramics. Niğde benefits from its rich agriculture, its apples are particlularly famous, its location between the wealthy regions of Konya and Adana on the Mediterranean coast; because the province is near the tourist attractions of Cappadoccia it is close to the airports of Kayseri and Nevşehir. As well as apples important crops include potatoes, cabbages and sugar beet. Niğde has the most apple trees. Meat and dairy are important activities along with beekeeping and more trout farms. Niğde has a rich tradition of folk culture including song and dance and the famous proverb - "Bor's eastern market is over, ride your donkey to Niğde". Another Niğde tradition is to plum someone meaning if you have visitors sit them in the garden and fill them up with plums so you don't have to give them dinner.
The Aladağlar and Bolkar mountain ranges in the Taurus mountains are popular for winter sports and trekking through the high meadows and mountain villages. The mountains are attractive when the hills are covered in spring flowers; the Aladaglar mountains in particular are one of the most popular climbing venues in Turkey. Although the Aladaglar mountains border on their namesake Aladağ District, in Adana Province, they are reached from the villages of Demirkazık and Çukurbağ in Çamardı; the Bolkar mountains have a crater lake. Niğde is part of Cappadoccia and does attract some tourists to its historical sites, although nothing like as many as the centre of the area in Nevşehir. Sites of historical importance in Niğde include a large number of churches and underground cities. Another important site is the ancient city of Tyana and a number of Roman waterways in the district of Bor. An important underground city and ancient monastery is located in Gümüşler, Niğde, called Gümüşler Monastery. In Ulukışla, Öküz Mehmet Pasha Complex, a külliye is a 17th-century structure.
Niğde has a number of mineral hot-springs and other attractions, so with a little investment in hotels and other infrastructure the province could attract more tourists than at present. List of populated places in Niğde Province Niğde governor's official website Niğde municipality's official website Niğde weather forecast information Niğde University's official website
Mining is the extraction of valuable minerals or other geological materials from the earth from an ore body, vein, reef or placer deposit. These deposits form a mineralized package, of economic interest to the miner. Ores recovered by mining include metals, oil shale, limestone, dimension stone, rock salt, potash and clay. Mining is required to obtain any material that cannot be grown through agricultural processes, or feasibly created artificially in a laboratory or factory. Mining in a wider sense includes extraction of any non-renewable resource such as petroleum, natural gas, or water. Mining of stones and metal has been a human activity since pre-historic times. Modern mining processes involve prospecting for ore bodies, analysis of the profit potential of a proposed mine, extraction of the desired materials, final reclamation of the land after the mine is closed. De Re Metallica, Georgius Agricola, 1550, Book I, Para. 1Mining operations create a negative environmental impact, both during the mining activity and after the mine has closed.
Hence, most of the world's nations have passed regulations to decrease the impact. Work safety has long been a concern as well, modern practices have improved safety in mines. Levels of metals recycling are low. Unless future end-of-life recycling rates are stepped up, some rare metals may become unavailable for use in a variety of consumer products. Due to the low recycling rates, some landfills now contain higher concentrations of metal than mines themselves. Since the beginning of civilization, people have used stone and metals found close to the Earth's surface; these were used to make early weapons. Flint mines have been found in chalk areas where seams of the stone were followed underground by shafts and galleries; the mines at Grimes Graves and Krzemionki are famous, like most other flint mines, are Neolithic in origin. Other hard rocks mined or collected for axes included the greenstone of the Langdale axe industry based in the English Lake District; the oldest-known mine on archaeological record is the Ngwenya Mine in Swaziland, which radiocarbon dating shows to be about 43,000 years old.
At this site Paleolithic humans mined hematite to make the red pigment ochre. Mines of a similar age in Hungary are believed to be sites where Neanderthals may have mined flint for weapons and tools. Ancient Egyptians mined malachite at Maadi. At first, Egyptians used the bright green malachite stones for ornamentations and pottery. Between 2613 and 2494 BC, large building projects required expeditions abroad to the area of Wadi Maghareh in order to secure minerals and other resources not available in Egypt itself. Quarries for turquoise and copper were found at Wadi Hammamat, Tura and various other Nubian sites on the Sinai Peninsula and at Timna. Mining in Egypt occurred in the earliest dynasties; the gold mines of Nubia were among the largest and most extensive of any in Ancient Egypt. These mines are described by the Greek author Diodorus Siculus, who mentions fire-setting as one method used to break down the hard rock holding the gold. One of the complexes is shown in one of the earliest known maps.
The miners crushed the ore and ground it to a fine powder before washing the powder for the gold dust. Mining in Europe has a long history. Examples include the silver mines of Laurium. Although they had over 20,000 slaves working them, their technology was identical to their Bronze Age predecessors. At other mines, such as on the island of Thassos, marble was quarried by the Parians after they arrived in the 7th century BC; the marble was shipped away and was found by archaeologists to have been used in buildings including the tomb of Amphipolis. Philip II of Macedon, the father of Alexander the Great, captured the gold mines of Mount Pangeo in 357 BC to fund his military campaigns, he captured gold mines in Thrace for minting coinage producing 26 tons per year. However, it was the Romans who developed large scale mining methods the use of large volumes of water brought to the minehead by numerous aqueducts; the water was used for a variety of purposes, including removing overburden and rock debris, called hydraulic mining, as well as washing comminuted, or crushed and driving simple machinery.
The Romans used hydraulic mining methods on a large scale to prospect for the veins of ore a now-obsolete form of mining known as hushing. They built numerous aqueducts to supply water to the minehead. There, the water stored in large tanks; when a full tank was opened, the flood of water sluiced away the overburden to expose the bedrock underneath and any gold veins. The rock was worked upon by fire-setting to heat the rock, which would be quenched with a stream of water; the resulting thermal shock cracked the rock, enabling it to be removed by further streams of water from the overhead tanks. The Roman miners used similar methods to work cassiterite deposits in Cornwall and lead ore in the Pennines; the methods had been developed by the Romans in Spain in 25 AD to exploit large alluvial gold deposits, the largest site being at Las Medulas, where seven long aqueducts tapped local rivers and sluiced the deposits. Spain was one of the most important mining regions, but all regions of the Roman Empire were exploited.
In Great Britain the natives had mined minerals for millennia, but after the Roman conquest, the scale of the operations increased as the Romans needed Britannia's resources gold, silver
World War I
World War I known as the First World War or the Great War, was a global war originating in Europe that lasted from 28 July 1914 to 11 November 1918. Contemporaneously described as "the war to end all wars", it led to the mobilisation of more than 70 million military personnel, including 60 million Europeans, making it one of the largest wars in history, it is one of the deadliest conflicts in history, with an estimated nine million combatants and seven million civilian deaths as a direct result of the war, while resulting genocides and the 1918 influenza pandemic caused another 50 to 100 million deaths worldwide. On 28 June 1914, Gavrilo Princip, a Bosnian Serb Yugoslav nationalist, assassinated the Austro-Hungarian heir Archduke Franz Ferdinand in Sarajevo, leading to the July Crisis. In response, on 23 July Austria-Hungary issued an ultimatum to Serbia. Serbia's reply failed to satisfy the Austrians, the two moved to a war footing. A network of interlocking alliances enlarged the crisis from a bilateral issue in the Balkans to one involving most of Europe.
By July 1914, the great powers of Europe were divided into two coalitions: the Triple Entente—consisting of France and Britain—and the Triple Alliance of Germany, Austria-Hungary and Italy. Russia felt it necessary to back Serbia and, after Austria-Hungary shelled the Serbian capital of Belgrade on the 28th, partial mobilisation was approved. General Russian mobilisation was announced on the evening of 30 July; when Russia failed to comply, Germany declared war on 1 August in support of Austria-Hungary, with Austria-Hungary following suit on 6th. German strategy for a war on two fronts against France and Russia was to concentrate the bulk of its army in the West to defeat France within four weeks shift forces to the East before Russia could mobilise. On 2 August, Germany demanded free passage through Belgium, an essential element in achieving a quick victory over France; when this was refused, German forces invaded Belgium on 3 August and declared war on France the same day. On 12 August and France declared war on Austria-Hungary.
In November 1914, the Ottoman Empire entered the war on the side of the Alliance, opening fronts in the Caucasus and the Sinai Peninsula. The war was fought in and drew upon each power's colonial empire as well, spreading the conflict to Africa and across the globe; the Entente and its allies would become known as the Allied Powers, while the grouping of Austria-Hungary and their allies would become known as the Central Powers. The German advance into France was halted at the Battle of the Marne and by the end of 1914, the Western Front settled into a battle of attrition, marked by a long series of trench lines that changed little until 1917. In 1915, Italy opened a front in the Alps. Bulgaria joined the Central Powers in 1915 and Greece joined the Allies in 1917, expanding the war in the Balkans; the United States remained neutral, although by doing nothing to prevent the Allies from procuring American supplies whilst the Allied blockade prevented the Germans from doing the same the U. S. became an important supplier of war material to the Allies.
After the sinking of American merchant ships by German submarines, the revelation that the Germans were trying to incite Mexico to make war on the United States, the U. S. declared war on Germany on 6 April 1917. Trained American forces would not begin arriving at the front in large numbers until mid-1918, but the American Expeditionary Force would reach some two million troops. Though Serbia was defeated in 1915, Romania joined the Allied Powers in 1916 only to be defeated in 1917, none of the great powers were knocked out of the war until 1918; the 1917 February Revolution in Russia replaced the Tsarist autocracy with the Provisional Government, but continuing discontent at the cost of the war led to the October Revolution, the creation of the Soviet Socialist Republic, the signing of the Treaty of Brest-Litovsk by the new government in March 1918, ending Russia's involvement in the war. This allowed the transfer of large numbers of German troops from the East to the Western Front, resulting in the German March 1918 Offensive.
This offensive was successful, but the Allies rallied and drove the Germans back in their Hundred Days Offensive. Bulgaria was the first Central Power to sign an armistice—the Armistice of Salonica on 29 September 1918. On 30 October, the Ottoman Empire capitulated. On 4 November, the Austro-Hungarian empire agreed to the Armistice of Villa Giusti after being decisively defeated by Italy in the Battle of Vittorio Veneto. With its allies defeated, revolution at home, the military no longer willing to fight, Kaiser Wilhelm abdicated on 9 November and Germany signed an armistice on 11 November 1918. World War I was a significant turning point in the political, cultural and social climate of the world; the war and its immediate aftermath sparked numerous uprisings. The Big Four (Britain, the United States, It
Germany the Federal Republic of Germany, is a country in Central and Western Europe, lying between the Baltic and North Seas to the north, the Alps to the south. It borders Denmark to the north and the Czech Republic to the east and Switzerland to the south, France to the southwest, Luxembourg and the Netherlands to the west. Germany includes 16 constituent states, covers an area of 357,386 square kilometres, has a temperate seasonal climate. With 83 million inhabitants, it is the second most populous state of Europe after Russia, the most populous state lying in Europe, as well as the most populous member state of the European Union. Germany is a decentralized country, its capital and largest metropolis is Berlin, while Frankfurt serves as its financial capital and has the country's busiest airport. Germany's largest urban area is the Ruhr, with its main centres of Essen; the country's other major cities are Hamburg, Cologne, Stuttgart, Düsseldorf, Dresden, Bremen and Nuremberg. Various Germanic tribes have inhabited the northern parts of modern Germany since classical antiquity.
A region named Germania was documented before 100 AD. During the Migration Period, the Germanic tribes expanded southward. Beginning in the 10th century, German territories formed a central part of the Holy Roman Empire. During the 16th century, northern German regions became the centre of the Protestant Reformation. After the collapse of the Holy Roman Empire, the German Confederation was formed in 1815; the German revolutions of 1848–49 resulted in the Frankfurt Parliament establishing major democratic rights. In 1871, Germany became a nation state when most of the German states unified into the Prussian-dominated German Empire. After World War I and the revolution of 1918–19, the Empire was replaced by the parliamentary Weimar Republic; the Nazi seizure of power in 1933 led to the establishment of a dictatorship, the annexation of Austria, World War II, the Holocaust. After the end of World War II in Europe and a period of Allied occupation, Austria was re-established as an independent country and two new German states were founded: West Germany, formed from the American and French occupation zones, East Germany, formed from the Soviet occupation zone.
Following the Revolutions of 1989 that ended communist rule in Central and Eastern Europe, the country was reunified on 3 October 1990. Today, the sovereign state of Germany is a federal parliamentary republic led by a chancellor, it is a great power with a strong economy. As a global leader in several industrial and technological sectors, it is both the world's third-largest exporter and importer of goods; as a developed country with a high standard of living, it upholds a social security and universal health care system, environmental protection, a tuition-free university education. The Federal Republic of Germany was a founding member of the European Economic Community in 1957 and the European Union in 1993, it is part of the Schengen Area and became a co-founder of the Eurozone in 1999. Germany is a member of the United Nations, NATO, the G7, the G20, the OECD. Known for its rich cultural history, Germany has been continuously the home of influential and successful artists, musicians, film people, entrepreneurs, scientists and inventors.
Germany has a large number of World Heritage sites and is among the top tourism destinations in the world. The English word Germany derives from the Latin Germania, which came into use after Julius Caesar adopted it for the peoples east of the Rhine; the German term Deutschland diutisciu land is derived from deutsch, descended from Old High German diutisc "popular" used to distinguish the language of the common people from Latin and its Romance descendants. This in turn descends from Proto-Germanic *þiudiskaz "popular", derived from *þeudō, descended from Proto-Indo-European *tewtéh₂- "people", from which the word Teutons originates; the discovery of the Mauer 1 mandible shows that ancient humans were present in Germany at least 600,000 years ago. The oldest complete hunting weapons found anywhere in the world were discovered in a coal mine in Schöningen between 1994 and 1998 where eight 380,000-year-old wooden javelins of 1.82 to 2.25 m length were unearthed. The Neander Valley was the location where the first non-modern human fossil was discovered.
The Neanderthal 1 fossils are known to be 40,000 years old. Evidence of modern humans dated, has been found in caves in the Swabian Jura near Ulm; the finds included 42,000-year-old bird bone and mammoth ivory flutes which are the oldest musical instruments found, the 40,000-year-old Ice Age Lion Man, the oldest uncontested figurative art discovered, the 35,000-year-old Venus of Hohle Fels, the oldest uncontested human figurative art discovered. The Nebra sky disk is a bronze artefact created during the European Bronze Age attributed to a site near Nebra, Saxony-Anhalt, it is part of UNESCO's Memory of the World Programme. The Germanic tribes are thought to date from the Pre-Roman Iron Age. From southern Scandinavia and north Germany, they expanded south and west from the 1st century BC, coming into contact with the Celtic tribes of Gaul as well
The Euphrates is the longest and one of the most important rivers of Western Asia. Together with the Tigris, it is one of the two defining rivers of Mesopotamia. Originating in eastern Turkey, the Euphrates flows through Syria and Iraq to join the Tigris in the Shatt al-Arab, which empties into the Persian Gulf; the Ancient Greek form Euphrátēs was adapted from Old Persian Ufrātu, itself from Elamite ú-ip-ra-tu-iš. The Elamite name is derived from a name spelt in cuneiform as, which read as Sumerian language is "Buranuna" and read as Akkadian language is "Purattu". In Akkadian the river was called Purattu, perpetuated in Semitic languages and in other nearby languages of the time; the Elamite and Sumerian forms are suggested to be from an unrecorded substrate language. Tamaz V. Gamkrelidze and Vyacheslav Ivanov suggest the Proto-Sumerian *burudu "copper" as an origin, with an explanation that Euphrates was the river by which the copper ore was transported in rafts, since Mesopotamia was the center of copper metallurgy during the period.
The earliest references to the Euphrates come from cuneiform texts found in Shuruppak and pre-Sargonic Nippur in southern Iraq and date to the mid-3rd millennium BCE. In these texts, written in Sumerian, the Euphrates is called Buranuna; the name could be written KIB. NUN. or dKIB. NUN, with the prefix "d" indicating that the river was a divinity. In Sumerian, the name of the city of Sippar in modern-day Iraq was written UD. KIB. NUN, indicating a strong relationship between the city and the river; the Euphrates is the longest river of Western Asia. It emerges from the confluence of the Kara Su or Western Euphrates and the Murat Su or Eastern Euphrates 10 kilometres upstream from the town of Keban in southeastern Turkey. Daoudy and Frenken put the length of the Euphrates from the source of the Murat River to the confluence with the Tigris at 3,000 kilometres, of which 1,230 kilometres is in Turkey, 710 kilometres in Syria and 1,060 kilometres in Iraq; the same figures are given by Mikhailova. The length of the Shatt al-Arab, which connects the Euphrates and the Tigris with the Persian Gulf, is given by various sources as 145–195 kilometres.
Both the Kara Su and the Murat Su rise northwest from Lake Van at elevations of 3,290 metres and 3,520 metres amsl, respectively. At the location of the Keban Dam, the two rivers, now combined into the Euphrates, have dropped to an elevation of 693 metres amsl. From Keban to the Syrian–Turkish border, the river drops another 368 metres over a distance of less than 600 kilometres. Once the Euphrates enters the Upper Mesopotamian plains, its grade drops significantly; the Euphrates receives most of its water in the form of rainfall and melting snow, resulting in peak volumes during the months April through May. Discharge in these two months accounts for 36 percent of the total annual discharge of the Euphrates, or 60–70 percent according to one source, while low runoff occurs in summer and autumn; the average natural annual flow of the Euphrates has been determined from early- and mid-twentieth century records as 20.9 cubic kilometres at Keban, 36.6 cubic kilometres at Hīt and 21.5 cubic kilometres at Hindiya.
However, these averages mask the high inter-annual variability in discharge. The discharge regime of the Euphrates has changed since the construction of the first dams in the 1970s. Data on Euphrates discharge collected after 1990 show the impact of the construction of the numerous dams in the Euphrates and of the increased withdrawal of water for irrigation. Average discharge at Hīt after 1990 has dropped to 356 cubic metres per second; the seasonal variability has changed. The pre-1990 peak volume recorded at Hīt was 7,510 cubic metres per second, while after 1990 it is only 2,514 cubic metres per second; the minimum volume at Hīt remained unchanged, rising from 55 cubic metres per second before 1990 to 58 cubic metres per second afterward. In Syria, three rivers add their water to the Euphrates; these rivers rise in the foothills of the Taurus Mountains along the Syro–Turkish border and add comparatively little water to the Euphrates. The Sajur is the smallest of these tributaries; the Balikh receives most of its water from a karstic spring near'Ayn al-'Arus and flows due south until it reaches the Euphrates at the city of Raqqa.
In terms of length
A subterranean river is a river that runs wholly or beneath the ground surface – one where the riverbed does not represent the surface of the Earth. It should not be confused with an aquifer which may flow like a river but is contained within a permeable layer of rock or other unconsolidated materials. Subterranean rivers may be natural, flowing through cave systems. In karst topography, rivers may disappear through continuing underground. In some cases, they may emerge into daylight further downstream; some fish and other troglobite organisms are adapted to life in subterranean lakes. The longest subterranean river in the world is located in Mexico. Subterranean rivers can be the result of covering over a river and/or diverting its flow into culverts as part of urban development. Reversing this process is known as daylighting a stream and is a visible form of river restoration. One successful example is the Cheonggyecheon in the centre of Seoul. Examples of subterranean rivers occur in mythology and literature.
There are many natural examples of subterranean rivers. Among others: In Bosnia and Herzegovina: Unac; the Cross Cave system in Loška Dolina, Slovenia includes 22 subterranean lakes The Lost River in the Appalachian Mountains of West Virginia disappears underground and reappears as the Cacapon River The Mojave River in southern California flows underground in most places The Phong Nha-Kẻ Bàng National Park in Vietnam has an underground river flowing through its cave system The Puerto Princesa Subterranean River on the island of Palawan, Philippines flows underground before emerging into the West Philippine Sea The Punkva in Moravian Karst, Czech Republic underground river flowing through cave system - Punkva Caves and Macocha gorge. The Santa Fe River in northern Florida drops into a large sinkhole in O'Leno State Park and reappears in the adjacent River Rise Preserve State Park, 3 miles downstream In many cities there are natural streams which have been or built over; such man-made examples of subterranean urban streams are too numerous to list, but notable examples include: The Bièvre underneath Paris, France The Fleet and other subterranean rivers of London The Frome underneath Bristol The Hobart Rivulet in Tasmania Mill Creek in Philadelphia The Neglinnaya River, which runs through a series of tunnels underneath the central part of Moscow The Tank Stream underneath Sydney, Australia The River Team underneath the Team Valley Trading Estate, United Kingdom The Zenne underneath Brussels, following the covering of the Zenne between 1865 and 1871 Castle Frank Brook, Garrison Creek, Russell Creek, Taddle Creek, other subterranean urban streams in Toronto The Park River underneath Hartford Some fish and other troglobite organisms are adapted to life in subterranean rivers and lakes.
Greek mythology included the Styx, Acheron and Lethe as rivers within the Underworld. Dante Alighieri, in his Inferno, included the Acheron and Styx as rivers within his subterranean Hell; the river Alph, running "Through caverns measureless to man / Down to a sunless sea" is central to the poem Kubla Khan, by Samuel Taylor Coleridge. The characters in Jules Verne's A Journey to the Centre of the Earth encounter a subterranean river: "Hans was not mistaken," he said. "What you hear is the rushing of a torrent." "A torrent?" I exclaimed. "There can be no doubt. Several other novels feature subterranean rivers; the subterranean rivers of London feature in e.g. the novel Drowning Man by Michael Robotham as well as in the novel Thrones, Dominations by Dorothy L. Sayers and Jill Paton Walsh in which a character remarks: "You can bury them deep under, sir. Hamza River Abîme – A vertical shaft in karst terrain that may be deep and opens into a network of subterranean passages Karst – Topography formed from the dissolution of soluble rocks Losing stream Speleology – Science of cave and karst systems Subterranean rivers of London Subterranean rivers in Hong Kong Subterranean waterfall Underground lake