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90-624: Southern Sudan may refer to: the southern regions of the present-day Republic of Sudan in North Africa South Sudan (est. 2011), the independent republic in East Africa Southern Sudan Autonomous Region (1972–1983) , part of the Republic of Sudan, that latterly mostly became the Republic of South Sudan Southern Sudan Autonomous Region (2005–2011) , part of

180-458: A condominium . The country's soils can be divided geographically into a few groups, the sandy soils of the northern and west central areas, the clay soils of the central region, and the laterite soils of the south. Less extensive and widely separated, but of major economic importance, is another group consisting of alluvial soils found along the lower reaches of the White Nile and Blue Nile, along

270-500: A dune slack . Dunes are most common in desert environments, where the lack of moisture hinders the growth of vegetation that would otherwise interfere with the development of dunes. However, sand deposits are not restricted to deserts, and dunes are also found along sea shores, along streams in semiarid climates, in areas of glacial outwash , and in other areas where poorly cemented sandstone bedrock disintegrates to produce an ample supply of loose sand. Subaqueous dunes can form from

360-555: A dune forms, plant succession occurs. The conditions on an embryo dune are harsh, with salt spray from the sea carried on strong winds. The dune is well drained and often dry, and composed of calcium carbonate from seashells. Rotting seaweed , brought in by storm waves adds nutrients to allow pioneer species to colonize the dune. For example, in the United Kingdom these pioneer species are often marram grass , sea wort grass and other sea grasses. These plants are well adapted to

450-617: A few square kilometers, but there are several large hill masses with internal valleys that cut through the mountains high above the plain. Sudan's third distinct region is the central clay plains that stretch eastward from the Nuba Mountains to the Ethiopian border, broken only by the Ingessana Hills , and from Khartoum in the north to the far reaches of southern Sudan. Between the Dindar and

540-590: A few tens of metres except at their nose, where vegetation stops or slows the advance of accumulating sand. Simple parabolic dunes have only one set of arms that trail upwind, behind the leading nose. Compound parabolic dunes are coalesced features with several sets of trailing arms. Complex parabolic dunes include subsidiary superposed or coalesced forms, usually of barchanoid or linear shapes. Parabolic dunes, like crescent dunes, occur in areas where very strong winds are mostly unidirectional. Although these dunes are found in areas now characterized by variable wind speeds,

630-569: A jumbled mass of hills where life is hard and unpredictable for the Beja inhabitants. Below the hills sprawls the coastal plain of the Red Sea, varying in width from about fifty-six kilometers in the south near Tawkar to about twenty-four kilometers near the Egyptian border. The coastal plain is dry and barren. It consists of rocks, and the seaward side is thick with coral reefs. Sudan has islands located in

720-711: A land area of 1,731,671 square kilometers (668,602 sq mi) and a total area of 1,861,484 square kilometers (718,723 sq mi). Approximately 18,900 square kilometers (7,300 sq mi) were irrigated as of 2012. The length of Sudan's borders are 6,819 kilometers (4,237 mi). Border countries are the Central African Republic (174 km (108 mi)), Chad (1,403 km (872 mi)), Egypt (1,276 km (793 mi)), Eritrea (682 km (424 mi)), Ethiopia (744 km (462 mi)), Libya (382 km (237 mi)), and South Sudan (2,158 km (1,341 mi)). Petroleum

810-407: A low-lying pan within the basin where the water evaporates, depositing the gypsum and forming crystals known as selenite . The crystals left behind by this process are eroded by the wind and deposited as vast white dune fields that resemble snow-covered landscapes. These types of dune are rare, and only form in closed arid basins that retain the highly soluble gypsum that would otherwise be washed into

900-505: A significant amount of crop cultivation, mainly of pearl millet , also occurs. Peanuts and sesame are grown as cash crops . Except for a small area in northeastern Sudan, where wadis discharge the sporadic runoff into the Red Sea and rivers from Eritrea that flow into shallow evaporating ponds west of the Red Sea Hills, the entire country is drained by the Nile and its two main tributaries,

990-412: A significant role in minimizing wave energy as it moves onshore. As a result, coastal dunes, especially those in the foredune area affected by a storm surge , will retreat or erode. To counteract the damage from tropical activity on coastal dunes, short term post-storm efforts can be made by individual agencies through fencing to help with sand accumulation. How much a dune erodes during any storm surge

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1080-462: A star dune superimposed on its crest is the most common complex dune. Simple dunes represent a wind regime that has not changed in intensity or direction since the formation of the dune, while compound and complex dunes suggest that the intensity and direction of the wind has changed. The sand mass of dunes can move either windward or leeward, depending on if the wind is making contact with the dune from below or above its apogee. If wind hits from above,

1170-804: A unidirectional wind. In the sheltered troughs between highly developed seif dunes, barchans may be formed, because the wind is constrained to be unidirectional by the dunes. Seif dunes are common in the Sahara. They range up to 300 m (980 ft) in height and 300 km (190 mi) in length. In the southern third of the Arabian Peninsula, a vast erg , called the Rub' al Khali or Empty Quarter, contains seif dunes that stretch for almost 200 km (120 mi) and reach heights of over 300 m (980 ft). Linear loess hills known as pahas are superficially similar. These hills appear to have been formed during

1260-401: A violent dust storm, can occur in central Sudan when the moist southwesterly flow first arrives (May through July). The moist, unstable air forms thunderstorms in the heat of the afternoon. The initial downflow of air from an approaching storm produces a huge yellow/red wall of sand and clay that can temporarily reduce visibility to zero. Desert regions in central and northern Sudan are among

1350-457: A year to reach a maximum peak of about 45 °C (113 °F) in some places and averages high temperature remain above 24 °C (75.2 °F) in the northernmost region and above 30 °C (86 °F) in places such as Atbara or Meroe . Sudan faces some severe environmental problems, most related either to the availability of water or its disposal. Among them are desertification , land degradation , and deforestation. Desertification,

1440-404: Is Sudan's most important natural resource. The country also has significant deposits of chromium , copper , iron , mica , silver , gold , tungsten , and zinc . Dune A dune is a landform composed of wind- or water-driven sand . It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex . A large dune complex

1530-477: Is a type of sandstone that is formed when a marine or aeolian sand dune becomes compacted and hardened. Once in this form, water passing through the rock can carry and deposit minerals, which can alter the colour of the rock. Cross-bedded layers of stacks of lithified dunes can produce the cross-hatching patterns, such as those seen in Zion National Park in the western United States. A slang term, used in

1620-442: Is a very large aeolian landform, with a length of several kilometers and a height of tens to hundreds of meters, and which may have superimposed dunes. Dunes are made of sand-sized particles, and may consist of quartz, calcium carbonate, snow, gypsum, or other materials. The upwind/upstream/upcurrent side of the dune is called the stoss side; the downflow side is called the lee side. Sand is pushed (creep) or bounces ( saltation ) up

1710-570: Is an undulating land between Khartoum and Kassala that provides good grazing for cattle, sheep, and goats. East of the Butana is a geological formation known as the Qash Delta. Originally a depression, it has been filled with sand and silt brought down by the flash floods of the Qash River , creating a delta above the surrounding plain. Extending 100 kilometers north of Kassala, the whole area watered by

1800-410: Is blown along the beach. Dunes form where the beach is wide enough to allow for the accumulation of wind-blown sand, and where prevailing onshore winds tend to blow sand inland. The three key ingredients for coastal dune formation are a large sand supply, winds to move said sand supply, and a place for the sand supply to accumulate. Obstacles—for example, vegetation, pebbles and so on—tend to slow down

1890-445: Is by saltation , where sand particles skip along the ground like a bouncing ball . When these skipping particles land, they may knock into other particles and cause them to move as well, in a process known as creep . With slightly stronger winds, particles collide in mid-air, causing sheet flows . In a major dust storm , dunes may move tens of metres through such sheet flows. Also as in the case of snow, sand avalanches , falling down

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1980-400: Is called a dune field , while broad, flat regions covered with wind-swept sand or dunes, with little or no vegetation, are called ergs or sand seas . Dunes occur in different shapes and sizes, but most kinds of dunes are longer on the stoss (upflow) side, where the sand is pushed up the dune, and have a shorter slip face in the lee side. The valley or trough between dunes is called

2070-520: Is different from Wikidata All article disambiguation pages All disambiguation pages Geography of Sudan Sudan is located in Northeast Africa . It is bordered by Egypt to the north, the Red Sea to the northeast, Eritrea and Ethiopia to the east, South Sudan to the south, the Central African Republic to the southwest, Chad to the west and Libya to the northwest. Sudan

2160-572: Is divided into 18 states and one area with special administrative status. The states of Sudan are: As a result of the Comprehensive Peace Agreement signed in 2005, the Abyei Area was given special administrative status and following the independence of South Sudan in 2011, is considered to be simultaneously part of both the Republic of Sudan and the Republic of South Sudan , effectively

2250-428: Is due to a number of pressures related to their proximity to the ocean and confinement to growth on sandy substrates. These include: Plants have evolved many adaptations to cope with these pressures: In deserts where large amounts of limestone mountains surround a closed basin , such as at White Sands National Park in south-central New Mexico , occasional storm runoff transports dissolved limestone and gypsum into

2340-404: Is related to its location on the coastal shoreline and the profile of the beach during a particular season. In those areas with harsher winter weather, during the summer a beach tends to take on more of a convex appearance due to gentler waves, while the same beach in the winter may take on more of a concave appearance. As a result, coastal dunes can get eroded much more quickly in the winter than in

2430-628: Is the absence of perennial streams; thus, people and animals must remain within reach of permanent wells. Consequently, the population is sparse and unevenly distributed. Western Darfur is an undulating plain dominated by the volcanic massif of Jabal Marrah towering 900 meters above the Sudanic plain; the drainage from Jabal Marrah onto the plain can support a settled population and a variety of wildlife (see East Saharan montane xeric woodlands ). Western Darfur stands in contrast to northern and eastern Darfur, which are semi-deserts with little water either from

2520-648: Is the smaller of the two rivers; its flow usually accounts for only one-sixth of the total. In August, however, the rains in the Ethiopian highlands swell the Blue Nile until it accounts for 90 percent of the Nile’s total flow. Sudan has constructed several dams to regulate the river’s flow, including the Roseires Dam , about 100 kilometers from the Ethiopian border and the largest, the 40-meter-high Sinnar Dam constructed in 1925 at Sinnar . The Blue Nile’s two main tributaries,

2610-769: Is the third largest country in Africa, after Algeria and the Democratic Republic of the Congo . It was the largest country on the continent until South Sudan split off from it in 2011. Northern Sudan –lying between the Egyptian border and Sennar – has two distinct parts, the desert and the Nile Valley . To the east of the Nile is the Nubian Desert and to the west, the Libyan Desert . Both are stony, with sandy dunes drifting over

2700-623: The Arabian Peninsula or moist southwesterly winds from the Congo River basin and southeasterly winds from the Indian Ocean . From January to March, the country is under the influence of dry northeasterlies. There is minimal rainfall countrywide except for a small area in northwestern Sudan where the winds have passed over the Mediterranean bringing occasional light rains. By early April,

2790-595: The Aswan High Dam in Egypt. The river flows slowly beyond Khartoum, dropping little in elevation, although five cataracts hinder river transport at times of low water. The Atbarah River , flowing out of Ethiopia, is the only tributary north of Khartoum, and its waters only reach the Nile from July to December. During the rest of the year, the Atbarah’s bed is dry, except for a few pools and ponds. Although Sudan lies within

Southern Sudan - Misplaced Pages Continue

2880-673: The Blue Nile and the White Nile where the great Gezira Scheme was developed. This project grows cotton for export and has historically produced more than half of Sudan's revenue and export earnings. Northeast of the central clay plains lies eastern Sudan, which is divided between desert and semi-desert and includes the Butana , the Qash Delta , the Red Sea Hills , and the coastal plain. The Butana

2970-506: The Dindar and the Rahad , have headwaters in the Ethiopian highlands and discharge water into the Blue Nile only during the summer high-water season. For the remainder of the year, their flow is reduced to pools in sandy riverbeds. The White Nile flows north from Central Africa, draining Lake Victoria and highland regions of Uganda , Rwanda , and Burundi . South of Khartoum, the British built

3060-495: The Jabal al-Awliya Dam in 1937 to store the water of the White Nile and then release it in the fall when the flow from the Blue Nile slackens. Much water from the reservoir has been diverted for irrigation projects in central Sudan and much of the remainder evaporates. By now, silt deposits have curtailed the overall flow. North of Khartoum, the Nile flows through the desert in a large S-shaped pattern to empty into Lake Nasser behind

3150-508: The Rahad rivers, a low ridge slopes down from the Ethiopian highlands contrasting the neighboring plains as do the occasional hills. The central clay plains provide the backbone of Sudan's economy because of the large amounts of settlements which are there due to the available water. In the heartland of the central clay plains lies the jazirah , (literally in Arabic "peninsula") the land between

3240-512: The Western Desert of Egypt . The largest crescentic dunes on Earth, with mean crest-to-crest widths of more than three kilometres, are in China's Taklamakan Desert . Abundant barchan dunes may merge into barchanoid ridges, which then grade into linear (or slightly sinuous) transverse dunes, so called because they lie transverse, or across, the wind direction, with the wind blowing perpendicular to

3330-454: The southwest US , for consolidated and hardened sand dunes is "slickrock", a name that was introduced by pioneers of the Old West because their steel-rimmed wagon wheels could not gain traction on the rock. Sand dunes can have a negative impact on humans when they encroach on human habitats. Sand dunes move via a few different means, all of them helped along by wind. One way that dunes can move

3420-667: The 1970s and 1980s saw the southwesterlies frequently fail, with disastrous results for the Sudanese people and economy. Temperatures are highest at the end of the dry season when cloudless skies and dry air allow them to soar. The far south, however, with only a short dry season, has uniformly high temperatures throughout the year. In Khartoum, the warmest months are May and June, when average highs are 41 °C (105.8 °F) and temperatures can reach 48 °C (118.4 °F). Northern Sudan, with its short rainy season, has very high daytime temperatures year round, except for winter months in

3510-459: The Blue Nile and the White Nile. The longest river in the world, the Nile flows for 6,737 kilometers from its farthest headwaters in Central Africa to the Mediterranean. The importance of the Nile has been recognized since biblical times; for centuries the river has been a lifeline for Sudan. The Blue Nile flows out of the Ethiopian highlands to meet the White Nile at Khartoum. The Blue Nile

3600-581: The Blue Nile, large areas are used for mechanized rainfed crops. West of the White Nile, these soils are used by traditional cultivators to grow sorghum , sesame , peanuts , and (in the area around the Nuba Mountains) cotton . The southern part of the clay soil zone lies in the broad floodplain of the upper reaches of the White Nile and its tributaries, covering most of Aali an Nil and upper Bahr al Ghazal in South Sudan. Subject to heavy rainfall during

3690-741: The Nile and other rivers, in lakes and reservoirs and in the Red Sea. Tuti Island , Aba Island , Badien Island , Sai Island . Mukawwar Island (Jazirat Magarsam), Jazirat Mayteb, Jazirat Bayer, Juzur Telat. Talla Talla, Kebir Island, Taimashiya Island, Dar Ah Teras, Andi Seli, Masamarhu Island, Abu Isa Island, Dahrat ed Dak Hillat Island, Ed Dom esh Sheikh Island, Darrakah, Miyum, Zahrat Ghab, Jazirat Zahrat Abid, Gazirat Iri, Sayl Bahr, Gazirat Abid, Gazirat Wahman, Jaza'ir Amarat, Quban Island, Bakiyai Islands, Gazair Hayyis Wa Karai, Saqir Island, Sumar Island, Long Island, Gap Island, Two Islands. Jazirat Maqanza, Jazirat Abu Ushar, Jazirat Muluwwa. Gazerat Jene't. Four small islands and several islets. Sudan

Southern Sudan - Misplaced Pages Continue

3780-792: The Nile to Lake Nubia , in the delta of the Qash River in the Kassala area, and in the Baraka Delta in the area of Tawkar near the Red Sea in Kassala State. Agriculturally, the most important soils are the clays in central Sudan that extend from west of Kassala and southern Kurdufan. They are known as cracking soils because of the practice of allowing them to dry out and crack during the dry months to restore their permeability and are used in Al Jazirah and Khashm al Qirbah for irrigated cultivation. East of

3870-497: The Qash is a rich grassland with bountiful cultivation long after the river has spent its waters on the surface of its delta. Trees and bushes provide grazing for the camels from the north, and the rich moist soil provides an abundance of food crops and cotton. Northward beyond the Qash lie the Red Sea Hills. Dry, bleak, and cooler than the surrounding land, particularly in the heat of the Sudanese summer, they stretch northward into Egypt,

3960-428: The Republic of Sudan, that latterly mostly became the Republic of South Sudan See also [ edit ] [REDACTED] Search for "southern Sudan" , "south Sudan" , "south of Sudan" , or "Sudan South" on Misplaced Pages. All pages with titles beginning with Southern Sudan All pages with titles containing Southern Sudan Sudan (disambiguation) Topics referred to by

4050-551: The action of water flow ( fluvial processes) on sand or gravel beds of rivers , estuaries , and the sea-bed. Some coastal areas have one or more sets of dunes running parallel to the shoreline directly inland from the beach . In most cases, the dunes are important in protecting the land against potential ravages by storm waves from the sea . Artificial dunes are sometimes constructed to protect coastal areas. The dynamic action of wind and water can sometimes cause dunes to drift, which can have serious consequences. For example,

4140-409: The coastal environment of the sand dune vital to their species' survival. Over the course of time coastal dunes may be impacted by tropical cyclones or other intense storm activity, dependent on their location. Recent work has suggested that coastal dunes tend to evolve toward a high or low morphology depending on the growth rate of dunes relative to storm frequency. During a storm event, dunes play

4230-604: The concave sides of the dunes. These dunes form under winds that blow consistently from one direction (unimodal winds). They form separate crescents when the sand supply is comparatively small. When the sand supply is greater, they may merge into barchanoid ridges, and then transverse dunes (see below). Some types of crescentic dunes move more quickly over desert surfaces than any other type of dune. A group of dunes moved more than 100 metres per year between 1954 and 1959 in China 's Ningxia Province , and similar speeds have been recorded in

4320-405: The corridors between individual dunes. Because all dune arms are oriented in the same direction, and, the inter-dune corridors are generally swept clear of loose sand, the corridors can usually be traversed in between the trailing arms of the dune. However to cross straight over the dune by going over the trailing arms, can be very difficult. Also, traversing the nose is very difficult as well because

4410-484: The desert is the Nile Valley, whose alluvial strip of habitable land is no more than two kilometers wide and whose productivity depends on the annual flood. Sudan's western front encompasses the regions known as Darfur and Kurdufan that comprise 850,000 square kilometers. Traditionally, this has been regarded as a single regional unit despite the physical differences. The dominant feature throughout this immense area

4500-491: The direction (s) of prevailing winds, are known as lunettes, source-bordering dunes, bourrelets and clay dunes. They may be composed of clay, silt, sand, or gypsum, eroded from the basin floor or shore, transported up the concave side of the dune, and deposited on the convex side. Examples in Australia are up to 6.5 km long, 1 km wide, and up to 50 metres high. They also occur in southern and West Africa , and in parts of

4590-657: The distance between the water line and where vegetation can grow. Coastal dunes can be classified by where they develop, or begin to take shape. Dunes are commonly grouped into either the Primary Dune Group or the Secondary Dune Group. Primary dunes gain most of their sand from the beach itself, while secondary dunes gain their sand from the primary dune. Along the Florida Panhandle, most dunes are considered to be foredunes or hummocks. Different locations around

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4680-522: The driest and the sunniest places on Earth: the sunshine duration is always uninterrupted year-round and rise to above 4,000 hours or about 91% of the time with the sky being cloudless all the time. Areas around Wadi Halfa and along the Egyptian border can easily pass many years or many decades without seeing any rainfall at all. They are also among the hottest places during their summertime and their "wintertime": averages high temperatures routinely exceed 40 °C (104 °F) for four to nearly six months

4770-604: The dune and underlying soils . The stability of the dunes was once attributed to the vegetative cover but recent research has pointed to water as the main source of parabolic dune stability. The vegetation that covers them—grasses, shrubs, and trees—help anchor the trailing arms. In inland deserts, parabolic dunes commonly originate and extend downwind from blowouts in sand sheets only partly anchored by vegetation. They can also originate from beach sands and extend inland into vegetated areas in coastal zones and on shores of large lakes. Most parabolic dunes do not reach heights higher than

4860-513: The dunes and provide horticultural benefits, but instead spread taking land away from native species. Ammophila arenaria , known as European beachgrass, has a similar story, though it has no horticulture benefits. It has great ground coverage and, as intended, stabilized the dunes but as an unintended side effect prevented native species from thriving in those dunes. One such example is the dune field at Point Reyes, California . There are now efforts to get rid of both of these invasive species. As

4950-593: The dunes, washing humus into the slacks, and the slacks may be much more developed than the exposed tops of the dunes. It is usually in the slacks that more rare species are developed and there is a tendency for the dune slacks' soil to be waterlogged where only marsh plants can survive. In Europe these plants include: creeping willow, cotton grass, yellow iris , reeds, and rushes. As for vertebrates in European dunes, natterjack toads sometimes breed here. Dune ecosystems are extremely difficult places for plants to survive. This

5040-592: The dunes. Typically these are heather , heaths and gorses . These too are adapted to the low soil water content and have small, prickly leaves which reduce transpiration. Heather adds humus to the soil and is usually replaced by coniferous trees, which can tolerate low soil pH , caused by the accumulation and decomposition of organic matter with nitrate leaching. Coniferous forests and heathland are common climax communities for sand dune systems. Young dunes are called yellow dunes and dunes which have high humus content are called grey dunes . Leaching occurs on

5130-401: The effective winds associated with the growth and migration of both the parabolic and crescent dunes probably are the most consistent in wind direction. The grain size for these well-sorted, very fine to medium sands is about 0.06 to 0.5 mm. Parabolic dunes have loose sand and steep slopes only on their outer flanks. The inner slopes are mostly well packed and anchored by vegetation, as are

5220-522: The end of December they cover the entire country. Khartoum has a three-month rainy season (July–September) with an annual average rainfall of 161 millimeters (6.3 in); Atbarah receives showers in August that produce an annual average of only 74 millimeters (2.9 in). In some years, the arrival of the southwesterlies and their rain in central Sudan can be delayed, or they may not come at all. When that happens, drought and famine follow. The decades of

5310-519: The geological record . All these dune shapes may occur in three forms: simple (isolated dunes of basic type), compound (larger dunes on which smaller dunes of same type form), and complex (combinations of different types). Simple dunes are basic forms with the minimum number of slipfaces that define the geometric type. Compound dunes are large dunes on which smaller dunes of similar type and slipface orientation are superimposed. Complex dunes are combinations of two or more dune types. A crescentic dune with

5400-595: The globe have dune formations unique to their given coastal profile. Coastal sand dunes can provide privacy and/or habitats to support local flora and fauna. Animals such as sand snakes, lizards, and rodents can live in coastal sand dunes, along with insects of all types. Often the vegetation of sand dunes is discussed without acknowledging the importance that coastal dunes have for animals. Further, some animals, such as foxes and feral pigs can use coastal dunes as hunting grounds to find food. Birds are also known to utilize coastal dunes as nesting grounds. All these species find

5490-408: The harsh conditions of the foredune, typically having deep roots which reach the water table , root nodules that produce nitrogen compounds, and protected stoma , reducing transpiration . Also, the deep roots bind the sand together, and the dune grows into a foredune as more sand is blown over the grasses. The grasses add nitrogen to the soil, meaning other, less hardy plants can then colonize

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5580-470: The intermittent streams known as wadis or from wells that normally go dry during the winter months. Northwest of Darfur and continuing into Chad lies the unusual region called the jizzu , where sporadic winter rains generated from the Mediterranean frequently provide excellent grazing into January or even February. The southern region of western Sudan is known as the qoz , a land of sand dunes that in

5670-483: The landscape. There is virtually no rainfall in these deserts. Water in the Libyan desert is limited to a few small watering holes, such as Bir an Natrun , where the water table reaches the surface to form wells that provide water for nomads , caravans , and administrative patrols, although insufficient to support an oasis and inadequate to provide for a settled population. The Nubian Desert has no oases. Flowing through

5760-478: The last ice age under permafrost conditions dominated by sparse tundra vegetation. Star dunes are pyramidal sand mounds with slipfaces on three or more arms that radiate from the high center of the mound. They tend to accumulate in areas with multidirectional wind regimes. Star dunes grow upward rather than laterally. They dominate the Grand Erg Oriental of the Sahara. In other deserts, they occur around

5850-515: The margins of the sand seas , particularly near topographic barriers. In the southeast Badain Jaran Desert of China, the star dunes are up to 500 metres tall and may be the tallest dunes on Earth. Oval or circular mounds that generally lack a slipface. Dome dunes are rare and occur at the far upwind margins of sand seas. Fixed crescentic dunes that form on the leeward margins of playas and river valleys in arid and semiarid regions in response to

5940-406: The moist southwesterlies have reached southern Sudan, bringing heavy rains and thunderstorms. By July, the moist air has reached Khartoum, and in August it extends to its usual northern limits around Abu Hamad , sometimes the humid air reaches as far as the Egyptian border. The flow becomes weaker as it spreads north. In September the dry northeasterlies begin to strengthen and to push south and by

6030-520: The northwest where there is some precipitation in January and February. Conditions in highland areas are generally cooler, and the hot daytime temperatures during the dry season throughout central and northern Sudan fall rapidly after sunset. Lows in Khartoum average 15 °C (59 °F) in January and have dropped as low as 6 °C (42.8 °F) after the passing of a cool front in winter. The haboob ,

6120-654: The nose is usually made up of loose sand without much if any vegetation. A type of extensive parabolic dune that lacks discernible slipfaces and has mostly coarse grained sand is known as a zibar . The term zibar comes from the Arabic word to describe "rolling transverse ridges ... with a hard surface". The dunes are small, have low relief, and can be found in many places across the planet from Wyoming (United States) to Saudi Arabia to Australia. Spacing between zibars ranges from 50 to 400 metres and they do not become more than 10 metres high. The dunes form at about ninety degrees to

6210-440: The prevailing wind which blows away the small, fine-grained sand leaving behind the coarser grained sand to form the crest. Occurring wherever winds periodically reverse direction, reversing dunes are varieties of any of the above shapes. These dunes typically have major and minor slipfaces oriented in opposite directions. The minor slipfaces are usually temporary, as they appear after a reverse wind and are generally destroyed when

6300-494: The rainy season is characterized by a rolling mantle of grass and has more reliable sources of water with its bore holes and hafri (sing., hafr ) than does the north. A unique feature of western Sudan is the Nuba mountain range of southeast Kurdufan in the center of the country, a conglomerate of isolated dome-shaped, sugarloaf hills that ascend steeply and abruptly from the great Sudanic plain. Many hills are isolated and extend only

6390-573: The rainy season, the floodplain proper is inundated for four to six months — a large swampy area, the Sudd in South Sudan, is permanently flooded — and adjacent areas are flooded for one or two months. In general this area is poorly suited to crop production, but the grasses it supports during dry periods are used for grazing. The sandy soils in the semi-arid areas south of the desert in North Kurdufan and North Darfur support vegetation used for grazing. In

6480-478: The resultant direction of sand movement (hence the name "longitudinal"). Some linear dunes merge to form Y-shaped compound dunes. Formation is debated. Ralph Bagnold , in The Physics of Blown Sand and Desert Dunes , suggested that some seif dunes form when a barchan dune moves into a bidirectional wind regime, and one arm or wing of the crescent elongates. Others suggest that seif dunes are formed by vortices in

6570-426: The ridge crest. Seif dunes are linear (or slightly sinuous) dunes with two slip faces. The two slip faces make them sharp-crested. They are called seif dunes after the Arabic word for "sword". They may be more than 160 kilometres (100 miles) long, and thus easily visible in satellite images (see illustrations). Seif dunes are associated with bidirectional winds. The long axes and ridges of these dunes extend along

6660-464: The same term [REDACTED] This disambiguation page lists articles associated with the title Southern Sudan . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Southern_Sudan&oldid=1242856389 " Categories : Disambiguation pages Place name disambiguation pages Hidden categories: Short description

6750-415: The sand in the dune migrates forward. In plan view, these are U-shaped or V-shaped mounds of well-sorted, very fine to medium sand with elongated arms that extend upwind behind the central part of the dune. There are slipfaces that often occur on the outer side of the nose and on the outer slopes of the arms. These dunes often occur in semiarid areas where the precipitation is retained in the lower parts of

6840-425: The sand particles move leeward; the leeward flux of sand is greater than the windward flux. Conversely, if sand hits from below, sand particles move windward. Further, if the wind is carrying sand particles when it hits the dune, the dune's sand particles will saltate more than if the wind had hit the dune without carrying sand particles. Coastal dunes form when wet sand is deposited along the coast and dries out and

6930-438: The sea. A nabkha , or coppice dune, is a small dune anchored by vegetation. They usually indicate desertification or soil erosion, and serve as nesting and burrow sites for animals. Sub-aqueous ( underwater ) dunes form on a bed of sand or gravel under the actions of water flow. They are ubiquitous in natural channels such as rivers and estuaries, and also form in engineered canals and pipelines. Dunes move downstream as

7020-468: The size of livestock herds since the 1960s that have overused grazing areas. Deforestation has occurred at an alarming rate. Sudan as a whole might have lost nearly 12 percent of its forest cover between 1990 and 2005, or about 8.8 million hectares, a loss driven primarily by land clearance and energy needs. Compounding Sudan’s environmental problems are long years of warfare and the resultant camps for large numbers of internally displaced people, who scour

7110-471: The southern part of these states and the West Darfur and South Darfur are the so-called qoz sands. The qoz sands are the principal area from which gum arabic is obtained through tapping of Acacia senegal (known locally as hashab ). This tree grows readily in the region, and cultivators occasionally plant hashab trees when land is returned to fallow. Though livestock raising is this area's major activity,

7200-673: The southward shift of the boundary between desert and sem-idesert, has occurred at an estimated rate of 50 to 200 kilometers since records of rainfall and vegetation began in the 1930s. Its impact has been most notable in North Darfur and North Kordofan. Desertification is likely to continue its southward progression because of declining precipitation and will lead to continued loss of productive land. Agriculture, particularly poorly planned and managed mechanized agriculture, has led to land degradation, water pollution, and related problems. Land degradation has also resulted from an explosive growth in

7290-402: The steeper slip face facing downstream. Ripple marks preserved in sedimentary strata in the geological record can be used to determine the direction of current flow, and thus an indication of the source of the sediments. Dunes on the bed of a channel significantly increase flow resistance, their presence and growth playing a major part in river flooding . A lithified (consolidated) sand dune

7380-604: The stoss side, and slides down the lee side. A side of a dune that the sand has slid down is called a slip face (or slipface). The Bagnold formula gives the speed at which particles can be transported. Five basic dune types are recognized: crescentic, linear, star, dome, and parabolic. Dune areas may occur in three forms: simple (isolated dunes of basic type), compound (larger dunes on which smaller dunes of same type form), and complex (combinations of different types). Barchan dunes are crescent-shaped mounds which are generally wider than they are long. The lee-side slipfaces are on

7470-663: The summer. The converse is true in areas with harsher summer weather. There are many threats to these coastal communities. Some coastal dunes, for example ones in San Francisco, have been completely altered by urbanization; reshaping the dune for human use. This puts native species at risk. Another danger, in California and places in the UK specifically, is the introduction of invasive species. Plant species, such as Carpobrotus edulis , were introduced from South Africa in an attempt to stabilize

7560-506: The surrounding land for water, fuel, and food. Experts from the United Nations predict that Sudan’s current program of dam construction on the Nile and its tributaries will cause riverbank erosion and loss of fertilizing silt. In urban areas, rapid and uncontrolled population influx into Khartoum and other cities and towns and the general lack of facilities to manage solid waste and sewage are among major environmental concerns. Sudan has

7650-509: The town of Eucla, Western Australia , had to be relocated in the 1890s because of dune drift. The modern word "dune" came into English from French around 1790, which in turn came from Middle Dutch dūne . A universally precise distinction does not exist between ripples, dunes, and draas , which are all deposits of the same type of materials. Dunes are generally defined as greater than 7 cm tall and may have ripples, while ripples are deposits that are less than 3 cm tall. A draa

7740-408: The tropics, the climate ranges from hyper-arid in the north to tropical wet-and-dry in the far southwest. Temperatures do not vary greatly with the season at any location; the most significant climatic variables are rainfall and the length of the wet and dry seasons. Variations in the length of the wet and dry seasons depend on which of two air flows predominates: dry northern winds from the Sahara and

7830-471: The upstream slope is eroded and the sediment deposited on the downstream or lee slope in typical bedform construction. In the case of sub-aqueous barchan dunes, sediment is lost by their extremities, known as horns. These dunes most often form as a continuous 'train' of dunes, showing remarkable similarity in wavelength and height. The shape of a dune gives information about its formation environment. For instance, rivers produce asymmetrical ripples, with

7920-534: The western United States, especially Texas. U-shaped mounds of sand with convex noses trailed by elongated arms are parabolic dunes. These dunes are formed from blowout dunes where the erosion of vegetated sand leads to a U-shaped depression. The elongated arms are held in place by vegetation; the largest arm known on Earth reaches 12 km. Sometimes these dunes are called U-shaped, blowout , or hairpin dunes, and they are well known in coastal deserts. Unlike crescent shaped dunes, their crests point upwind. The bulk of

8010-402: The wind and lead to the deposition of sand grains. These small "incipient dunes or "shadow dunes" tend to grow in the vertical direction if the obstacle slowing the wind can also grow vertically (i.e., vegetation). Coastal dunes expand laterally as a result of lateral growth of coastal plants via seed or rhizome . Models of coastal dunes suggest that their final equilibrium height is related to

8100-483: The wind next blows in the dominant direction. Draas are very large-scale dune bedforms; they may be tens or a few hundreds of metres in height, kilometres wide, and hundreds of kilometres in length. After a draa has reached a certain size, it generally develops superimposed dune forms. They are thought to be more ancient and slower-moving than smaller dunes, and to form by vertical growth of existing dunes. Draas are widespread in sand seas and are well-represented in

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