An arch is a vertical curved structure that spans an elevated space and may or may not support the weight above it, or in case of a horizontal arch like an arch dam, the hydrostatic pressure against it. Arches may be synonymous with vaults, but a vault may be distinguished as a continuous arch forming a roof. Arches appeared as early as the 2nd millennium BC in Mesopotamian brick architecture, their systematic use started with the ancient Romans, who were the first to apply the technique to a wide range of structures. An arch is a soft compression form, it can span a large area by resolving forces into compressive stresses and, in turn eliminating tensile stresses. This is sometimes referred to as arch action; as the forces in the arch are carried to the ground, the arch will push outward at the base, called thrust. As the rise, or height of the arch decreases, the outward thrust increases. In order to maintain arch action and prevent the arch from collapsing, the thrust needs to be restrained, either with internal ties or external bracing, such as abutments.
The most common true arch configurations are the fixed arch, the two-hinged arch, the three-hinged arch. The fixed arch is most used in reinforced concrete bridge and tunnel construction, where the spans are short; because it is subject to additional internal stress caused by thermal expansion and contraction, this type of arch is considered to be statically indeterminate. The two-hinged arch is most used to bridge long spans; this type of arch has pinned connections at the base. Unlike the fixed arch, the pinned base is able to rotate, allowing the structure to move and compensate for the thermal expansion and contraction caused by changes in outdoor temperature. However, this can result in additional stresses, so the two-hinged arch is statically indeterminate, although not to the degree of the fixed arch; the three-hinged arch is not only hinged at its base, like the two-hinged arch, but at the mid-span as well. The additional connection at the mid-span allows the three-hinged arch to move in two opposite directions and compensate for any expansion and contraction.
This type of arch is thus not subject to additional stress caused by thermal change. The three-hinged arch is therefore said to be statically determinate, it is most used for medium-span structures, such as large building roofs. Another advantage of the three-hinged arch is that the pinned bases are more developed than fixed ones, allowing for shallow, bearing-type foundations in medium-span structures. In the three-hinged arch, "thermal expansion and contraction of the arch will cause vertical movements at the peak pin joint but will have no appreciable effect on the bases," further simplifying the foundation design. Arches have many forms, but all fall into three basic categories: circular and parabolic. Arches can be configured to produce vaults and arcades. Arches with a circular form referred to as rounded arches, were employed by the builders of ancient, heavy masonry arches. Ancient Roman builders relied on the rounded arch to span large, open areas. Several rounded arches placed. Pointed arches were most used by builders of Gothic-style architecture.
The advantage to using a pointed arch, rather than a circular one, is that the arch action produces less thrust at the base. This innovation allowed for taller and more spaced openings, typical of Gothic architecture. Vaults are "adjacent arches are assembled side by side." If vaults intersect, complex forms are produced with the intersections. The forms, along with the "strongly expressed ribs at the vault intersections, were dominant architectural features of Gothic cathedrals."The parabolic arch employs the principle that when weight is uniformly applied to an arch, the internal compression resulting from that weight will follow a parabolic profile. Of all arch types, the parabolic arch produces the most thrust at the base, but can span the largest areas, it is used in bridge design, where long spans are needed. The catenary arch has a shape different from the parabolic curve; the shape of the curve traced by a loose span of chain or rope, the catenary is the structurally ideal shape for a freestanding arch of constant thickness.
Types of arches displayed chronologically in the order in which they were developed: True arches, as opposed to corbel arches, were known by a number of civilizations in the ancient Near East and the Levant, but their use was infrequent and confined to underground structures, such as drains where the problem of lateral thrust is diminished. An example of the latter would be the Nippur Arch. Rare exceptions are an arched mudbrick home doorway in circa 2000BC Tell Taya and the Bronze Age arched Canaanite city gate of Ashkelon in modern-day Israel, dating to c. 1850 B. C. An early example of a voussoir arch appears in the Greek Rhodes Footbridge. Corbel arches were found in other parts of ancient Asia, Africa and the Americas. In 2010, a robot discovered a long arch-roofed passageway underneath the Pyramid of Quetzalcoatl, which stands in the ancient city of Teotihuacan north of Mexico City, dated to around 200 AD. In ancient Persia, the Achaemenid Empire built small barrel vaults known as iwan, which became massive, monumental structures during the Parthian Empire.
This architectural tradition was continued by the Sasanian Empire, which built the Taq Kasra at Ctesiphon in the 6th century, the largest free-standing vault until modern times. The ancient Romans learned the arch from the Etruscans, refined it and were the first builders in Europe to tap its full potential for above ground buildings: The Romans were
Shale is a fine-grained, clastic sedimentary rock composed of mud, a mix of flakes of clay minerals and tiny fragments of other minerals quartz and calcite. Shale is characterized by breaks along thin laminae or parallel layering or bedding less than one centimeter in thickness, called fissility, it is the most common sedimentary rock. Shale exhibits varying degrees of fissility, breaking into thin layers splintery and parallel to the otherwise indistinguishable bedding plane because of the parallel orientation of clay mineral flakes. Non-fissile rocks of similar composition but made of particles smaller than 0.06 mm are described as mudstones or claystones. Rocks with similar particle sizes but with less clay and therefore grittier are siltstones. Shales are composed of clay minerals and quartz grain, are grey. Addition of variable amounts of minor constituents alters the color of the rock. Black shale results from the presence of greater than one percent carbonaceous material and indicates a reducing environment.
Black shale can be referred to as black metal. Red and green colors are indicative of ferric oxide, iron hydroxide, or micaceous minerals. Clays are the major constituent of other mudrocks; the clay minerals represented are kaolinite and illite. Clay minerals of Late Tertiary mudstones are expandable smectites whereas in older rocks in mid- to early Paleozoic shales illites predominate; the transformation of smectite to illite produces silica, calcium, magnesium and water. These released elements form authigenic quartz, calcite, ankerite and albite, all trace to minor minerals found in shales and other mudrocks. Shales and mudrocks contain 95 percent of the organic matter in all sedimentary rocks. However, this amounts to less than one percent by mass in an average shale. Black shales, which form in anoxic conditions, contain reduced free carbon along with ferrous iron and sulfur. Pyrite and amorphous iron sulfide along with carbon produce the black coloration; the process in the rock cycle which forms shale is called compaction.
The fine particles that compose shale can remain suspended in water long after the larger particles of sand have deposited. Shales are deposited in slow moving water and are found in lakes and lagoonal deposits, in river deltas, on floodplains and offshore from beach sands, they can be deposited in sedimentary basins and on the continental shelf, in deep, quiet water.'Black shales' are dark, as a result of being rich in unoxidized carbon. Common in some Paleozoic and Mesozoic strata, black shales were deposited in anoxic, reducing environments, such as in stagnant water columns; some black shales contain abundant heavy metals such as molybdenum, uranium and zinc. The enriched values are of controversial origin, having been alternatively attributed to input from hydrothermal fluids during or after sedimentation or to slow accumulation from sea water over long periods of sedimentation. Fossils, animal tracks/burrows and raindrop impact craters are sometimes preserved on shale bedding surfaces.
Shales may contain concretions consisting of pyrite, apatite, or various carbonate minerals. Shales that are subject to heat and pressure of metamorphism alter into a hard, metamorphic rock known as slate. With continued increase in metamorphic grade the sequence is phyllite schist and gneiss. Before the mid-19th century, the terms slate and schist were not distinguished. In the context of underground coal mining, shale was referred to as slate well into the 20th century. Bakken Formation Barnett Shale Bearpaw Formation Burgess Shale Marcellus Formation Mazon Creek fossil beds Oil shale – Organic-rich fine-grained sedimentary rock containing kerogen Shale gas Shale gas in the United States Wheeler Shale Wianamatta Shale Media related to Shale at Wikimedia Commons
The Sperrgebiet is a diamond mining area in southwestern Namibia, in the Namib Desert. It spans the Atlantic Ocean-facing the coast from Oranjemund on the border with South Africa, to around 72 kilometres north of Lüderitz, a distance of 320 km north; the Sperrgebiet renamed Tsau ǁKhaeb National Park, extends to around 100 km inland, its total area of 26,000 km2, makes up three percent of Namibia's land mass. However, mining only takes place in five percent of the Sperrgebiet, with most of the area acting as a buffer zone. Members of the public are banned from entering most of the area, despite the creation of a national park there in 2004. In September 1908, the German government created the Sperrgebiet in its colony of German South West Africa, giving sole rights for mining to the Deutsche Diamantengesellschaft. In 1915, during World War I, South African forces led by General Jan Smuts and Louis Botha, the South African Prime Minister, invaded the country; the South Africans defeated the Germans, taking control of modern-day Namibia, including the Sperrgebiet.
The owner of the mine, De Beers, had total control of the area until the 1990s, when the Namibian government purchased a fifty percent stake. They formed; the mining area close to Bogenfels is called "Pocket Beaches", one of Namdeb's northern coastal mines. The Sperrgebiet has a diverse range of flora and fauna, due to little human intervention in the area for 100 years. Forty percent of the landscape is desert, thirty percent is grassland, twenty-eight percent is rocky. Roter Kamm, an impact crater in the southern Namib Desert within Sperrgebiet, has a diameter of 2,5 km. In the Sperrgebiet you find the Tsaus Mountains, Mount Aurus, Mount Heioab, Mount Höchster, the Klinghardt Mountains and the permanent water spring Kaukausib; the highest point of the Sperrgebiet is 1488m. There are 776 types of plants in the Sperrgebiet, with 234 being endemic to southwest Namibia, despite the Orange River being the only permanent water supply in the area. A study has shown that climate change will affect the plant life in the area the Succulent Karoo.
Drier winters may lead to the extinction of these plants. According to Morgan Hauptfleisch, a scientist who works at the Southern African Institute for Environmental Assessment, the Sperrgebiet "is the only arid biodiversity hotspot and this makes it a special area", it has more biodiversity than anywhere else in Namibia, supporting animals such as the gemsbok and brown hyena. Bird species resident in the Sperrgebiet include the African oystercatcher, the black-headed canary, the dune lark; the Sperrgebiet was designated as a national park in June 2004. De Beers still controls the area, but will relinquish control to the Namibian Ministry for Environment and Tourism once a management plan for the park has been completed, it is a proclaimed diamond area which needs thorough control so as to keep possible diamond theft at bay. In April 2008, a 500-year-old shipwreck named Bom Jesus containing Iberian coins, bronze cannons and ivory was found in the Sperrgebiet. Under Namibian law, the Namibian government is entitled to all the items found on board.
These items will be showcased at a museum in Oranjemund. Today, there are several ghost towns in the Sperrgebiet, built in the late 19th century, the best known of these being Kolmanskop and others including Pomona and Elizabeth Bay; the wind has excavated a number of half-mummified bodies at a graveyard outside one of these ghost towns. Noli, Gino: Desert Diamonds. Gino Noli, Plettenberg Bay 2010, ISBN 978-0-620-40680-2. Christian Goltz. Sperrgebiet National Park Visitor's Information Materials
Lüderitz is a harbour town in the ǁKaras Region of southern Namibia. It lies on one of the least hospitable coasts in Africa, it is a port developed around Shark Island. The town is known for its colonial architecture, including some Art Nouveau work, for wildlife including seals, penguins and ostriches, it is home to a museum, lies at the end of a decommissioned railway line to Keetmanshoop. The bay on which Lüderitz is situated was first known to Europeans when Bartolomeu Dias encountered it in 1487, he erected a padrão on the southern peninsula. In the 18th century Dutch adventurers and scientists explored the area in search of minerals but did not have much success. Further exploration expeditions followed in the early 19th century during which the vast wildlife in the ocean was discovered. Profitable enterprises were set up, including whaling, seal hunting and guano-harvesting. Lüderitz thus began its life as a trading post; the town was founded in 1883 when Heinrich Vogelsang purchased Angra Pequena and some of the surrounding land on behalf of Adolf Lüderitz, a Hanseat from Bremen in Germany, from the local Nama chief Josef Frederiks II in Bethanie.
When Adolf Lüderitz did not return from an expedition to the Orange River in 1886, Angra Pequena was named Lüderitzbucht in his honour. In 1905, German authorities established a concentration camp on Shark Island; the camp, access to, restricted, operated between 1905 and 1907 during the Herero Wars. Between 1,000 and 3,000 Africans from the Herero and Nama tribes died here as a result of the tragic conditions of forced labour, their labour was used for expansion of the city, port and on the farms of white settlers. In 1909, after the discovery of diamonds nearby, Lüderitz enjoyed a sudden surge of prosperity due to the development of a diamond rush to the area. In 1912 Lüderitz had 1,100 inhabitants, not counting the indigenous population. Although situated in harsh environment between desert and Ocean, trade in the harbour town surged, the adjacent diamond mining settlement of Kolmanskop was built. After the German World War I capitulation South Africa took over the administration of German South West Africa in 1915.
Many Germans were deported from Lüderitz, contributing to its shrinking in population numbers. From 1920 onwards, diamond mining was only conducted further south of town in places like Pomona and Elizabeth Bay; this development led to the loss of Lüderitz' importance as a trading place. Only small fishing enterprises, minimal dock activity and a few carpet weavers remained. In an effort to remove colonial names from the maps of Namibia, in 2013 the Namibian government renamed the constituency ǃNamiǂNûs, its name prior to 1884; the harbour has a shallow rock bottom, making it unusable for modern ships. However, the addition of a new quay has allowed larger fishing vessels to dock at Lüderitz; the town has re-styled itself in an attempt to lure tourists to the area, which includes a new waterfront area for shops and offices. Just outside Lüderitz lies the ghost town of a prominent tourist destination; this bustling diamond town is now abandoned, fights a constant struggle against being buried under the shifting sand dunes of the Namib desert.
The coastline in the area is recognised by Bird Life and other global conservation groups as one of the Important Bird Areas for important coastal seabird breeding. Mercury Island, Ichaboe Island, Halifax Island and the Possession Islands support the entire Namibian breeding population of Cape gannets, 96% of the Namibian population of the endangered African penguin, nearly one quarter of the global breeding population of crowned cormorants. 80% of the global population of the endangered Bank cormorant breeds on Mercury Island and in the Ichaboe Islands. In April 2009, an oil spill from an oil tanker risked hundreds of African penguins and other flora and fauna. Several species of cetaceans, most notably Haviside's dolphins, can be seen close to the shore while larger whales such as southern right, minke, pygmy right, are less common but increasing in numbers. Lüderitz has a desert climate, with moderate temperatures throughout the year; the average annual precipitation is 17 millimetres. Windy and cold conditions can occur due to the cold South Atlantic current on the coast.
Lüderitz is home to the Lüderitz Speed Challenge, the only international sporting event held in the town. This is an annual month-long speed sailing event held in the last quarter of the year under the auspices of the International Sailing Federation World Sailing Speed Record Council. In 1984 Lüderitz was the starting point for explorer and sailor Amyr Klink's successful solo crossing of the Atlantic Ocean, rowing for 101 days all the way to the Brazilian coast with no other form of propulsion. In October 2011, Turkish-born American adventurer Erden Eruç departed from Lüderitz Bay for the final ocean crossing of his Guinness world record-setting solo human-powered circumnavigation of the Earth. Eruç rowed to South America in an oceangoing rowboat, taking five months for the crossing to the town of Güiria, Venezuela. Construction of a new port at Shearwater Bay, 30 kilometres south of Lüderitz, has been proposed for the export of coal from Botswana with a 1,600-kilometre railway connecting the two.
Lüderitz is the terminus of the 318 kilometres railway line to Seeheim where
A ghost town is an abandoned village, town, or city one that contains substantial visible remains. A town becomes a ghost town because the economic activity that supported it has failed, or due to natural or human-caused disasters such as floods, prolonged droughts, government actions, uncontrolled lawlessness, pollution, or nuclear disasters; the term can sometimes refer to cities and neighbourhoods that are still populated, but less so than in past years. Some ghost towns those that preserve period-specific architecture, have become tourist attractions; some examples are Bannack, Centralia and South Pass City in the United States, Barkerville in Canada, Craco in Italy, Elizabeth Bay and Kolmanskop in Namibia, Pripyat in Ukraine, Danushkodi in India. The town of Plymouth on the Caribbean island of Montserrat is a ghost town, the de jure capital of Montserrat, it was rendered uninhabitable by volcanic ash from an eruption. The definition of a ghost town varies between individuals, between cultures.
Some writers discount settlements that were abandoned as a result of a natural or human-made disaster or other causes using the term only to describe settlements that were deserted because they were no longer economically viable. Some believe. Whether or not the settlement must be deserted, or may contain a small population, is a matter for debate. Though, the term is used in a looser sense, encompassing any and all of these definitions; the American author Lambert Florin's preferred definition of a ghost town was "a shadowy semblance of a former self". Factors leading to abandonment of towns include depleted natural resources, economic activity shifting elsewhere and roads bypassing or no longer accessing the town, human intervention, massacres and the shifting of politics or fall of empires. A town can be abandoned when it is part of an exclusion zone due to natural or man-made causes. Ghost towns may result when the single activity or resource that created a boomtown is depleted or the resource economy undergoes a "bust".
Boomtowns can decrease in size as fast as they grew. Sometimes, all or nearly the entire population can desert the town; the dismantling of a boomtown can occur on a planned basis. Mining companies nowadays will create a temporary community to service a mine site, building all the accommodation and services required, remove them once the resource has been extracted. Modular buildings can be used to facilitate the process. A gold rush would bring intensive but short-lived economic activity to a remote village, only to leave a ghost town once the resource was depleted. In some cases, multiple factors may remove the economic basis for a community. S. Route 66 suffered both mine closures when the resources were depleted and loss of highway traffic as US 66 was diverted away from places like Oatman, Arizona onto a more direct path. Mine and pulp mill closures have led to many ghost towns in British Columbia, Canada including several recent ones: Ocean Falls which closed in 1973 after the pulp mill was decommissioned, Kitsault B.
C. whose molybdenum mine shut after only 18 months in 1982 and Cassiar whose asbestos mine operated from 1952 to 1992. In other cases, the reason for abandonment can arise from a town's intended economic function shifting to another, nearby place; this happened to Collingwood, Queensland in Outback Australia when nearby Winton outperformed Collingwood as a regional centre for the livestock-raising industry. The railway reached Winton in 1899, linking it with the rest of Queensland, Collingwood was a ghost town by the following year; the Middle East has many ghost towns that were created when the shifting of politics or the fall of empires caused capital cities to be or economically unviable, such as Ctesiphon. The rise of condominium investment caused for real estate bubbles leads to a ghost town, as real estate prices rise and affordable housing becomes less available; such examples include China and Canada, where housing is used as an investment rather than for habitation. Railroads and roads bypassing or no longer reaching a town can create a ghost town.
This was the case in many of the ghost towns along Ontario's historic Opeongo Line, along U. S. Route 66 after motorists bypassed the latter on the faster moving highways I-44 and I-40; some ghost towns were founded along railways where steam trains would stop at periodic intervals to take on water. Amboy, California was part of one such series of villages along the Atlantic and Pacific Railroad across the Mojave Desert. River re-routing is one example being the towns along the Aral Sea. Ghost towns may be created when land is expropriated by a government, residents are required to relocate. One example is the village of Tyneham in Dorset, acquired during World War II to build an artillery range. A similar situation occurred in the U. S. when NASA acquired land to construct the John C. Stennis Space Center, a rocket testing facility in Hancock County, Mississippi; this required NASA to acquire a large (approximately 34-square-mile (88
Namibia the Republic of Namibia, is a country in southern Africa. Its western border is the Atlantic Ocean. Although it does not border Zimbabwe, less than 200 metres of the Zambezi River separates the two countries. Namibia gained independence from South Africa on 21 March 1990, following the Namibian War of Independence, its capital and largest city is Windhoek, it is a member state of the United Nations, the Southern African Development Community, the African Union, the Commonwealth of Nations. Namibia, the driest country in Sub-Saharan Africa, was inhabited since early times by the San and Nama peoples. Around the 14th century, immigrating Bantu peoples arrived as part of the Bantu expansion. Since the Bantu groups, the largest being the Ovambo, have dominated the population of the country. In 1878, the Cape of Good Hope a British colony, had annexed the port of Walvis Bay and the offshore Penguin Islands. In 1884 the German Empire established rule over most of the territory as a protectorate.
It began to develop infrastructure and farming and maintained this German colony until 1915, when South African forces defeated its military. In 1920, after the end of World War I, the League of Nations mandated the country to the United Kingdom, under administration by South Africa, it imposed its laws, including racial rules. From 1948, with the National Party elected to power, South Africa applied apartheid to what was known as South West Africa. In the 20th century and demands for political representation by native African political activists seeking independence resulted in the UN assuming direct responsibility over the territory in 1966, but South Africa maintained de facto rule. In 1973 the UN recognised the South West Africa People's Organisation as the official representative of the Namibian people. Following continued guerrilla warfare, South Africa installed an interim administration in Namibia in 1985. Namibia obtained full independence from South Africa in 1990. However, Walvis Bay and the Penguin Islands remained under South African control until 1994.
Namibia has a population of a stable multi-party parliamentary democracy. Agriculture, herding and the mining industry – including mining for gem diamonds, gold and base metals – form the basis of its economy; the large, arid Namib Desert has resulted in Namibia being overall one of the least densely populated countries in the world. The name of the country is derived from the Namib Desert, considered to be the oldest desert in the world; the name Namib itself is of Nama origin and means "vast place". Before its independence in 1990, the area was known first as German South-West Africa as South-West Africa, reflecting the colonial occupation by the Germans and the South Africans; the dry lands of Namibia have been inhabited since early times by San and Nama. Around the 14th century, immigrating Bantu people began to arrive during the Bantu expansion from central Africa. From the late 18th century onward, Oorlam people from Cape Colony crossed the Orange River and moved into the area that today is southern Namibia.
Their encounters with the nomadic Nama tribes were peaceful. They received the missionaries accompanying the Oorlam well, granting them the right to use waterholes and grazing against an annual payment. On their way further north, the Oorlam encountered clans of the Herero at Windhoek and Okahandja, who resisted their encroachment; the Nama-Herero War broke out in 1880, with hostilities ebbing only after the German Empire deployed troops to the contested places and cemented the status quo among the Nama and Herero. The first Europeans to disembark and explore the region were the Portuguese navigators Diogo Cão in 1485 and Bartolomeu Dias in 1486, but the Portuguese did not try to claim the area. Like most of interior Sub-Saharan Africa, Namibia was not extensively explored by Europeans until the 19th century. At that time traders and settlers came principally from Sweden. In the late 19th century, Dorsland Trekkers crossed the area on their way from the Transvaal to Angola; some of them settled in Namibia instead of continuing their journey.
Namibia became a German colony in 1884 under Otto von Bismarck to forestall perceived British encroachment and was known as German South West Africa. The Palgrave Commission by the British governor in Cape Town determined that only the natural deep-water harbor of Walvis Bay was worth occupying and thus annexed it to the Cape province of British South Africa. From 1904 to 1907, the Herero and the Namaqua took up arms against brutal German colonialism. In calculated punitive action by the German occupiers, government officials ordered extinction of the natives in the Herero and Namaqua genocide. In what has been called the "first genocide of the 20th century", the Germans systematically killed 10,000 Nama and 65,000 Herero; the survivors, when released from detention, were subjected to a policy of dispossession, forced labor, racial segregation, and