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101-587: The archipelago was formed from the ancient delta of the Geba and Grande de Buba rivers and spans an area of 12,958 km (5,003 sq mi). Twenty of its islands are populated year-round, including the most populated island, Bubaque . The administrative capital, Bolama is situated on the island of Bolama . There is a high diversity of ecosystems: mangroves with intertidal zones, palm forests, dry and semi-dry forests, secondary and degraded forests, coastal savanna, sand banks and aquatic zones. The archipelago

202-432: A density current that deposits its sediments as turbidites . When the river water is less dense than the basin water, as is typical of river deltas on an ocean coastline, the delta is characterized by hypopycnal flow in which the river water is slow to mix with the denser basin water and spreads out as a surface fan. This allows fine sediments to be carried a considerable distance before settling out of suspension. Beds in

303-471: A slave ship and asked if he was going to be eaten. Yet, the worst for slaves has only begun, and the journey on the water proved to be more harrowing. For every 100 Africans captured, only 64 would reach the coast, and only about 50 would reach the New World. Others believe that slavers had a vested interest in capturing rather than killing, and in keeping their captives alive; and that this coupled with

404-411: A "bycatch" who would have been killed if there had not been an export market for them. British explorer Mungo Park encountered a group of slaves when traveling through Mandinka country: They were all very inquisitive, but they viewed me at first with looks of horror, and repeatedly asked if my countrymen were cannibals. They were very desirous to know what became of the slaves after they had crossed

505-593: A ceremony known as the Annual Customs . As one of West Africa's principal slave states, Dahomey became extremely unpopular with neighbouring peoples. Like the Bambara Empire to the east, the Khasso kingdoms depended heavily on the slave trade for their economy. A family's status was indicated by the number of slaves it owned, leading to wars for the sole purpose of taking more captives. This trade led

606-493: A common location for civilizations to flourish due to access to flat land for farming, freshwater for sanitation and irrigation , and sea access for trade. Deltas often host extensive industrial and commercial activities, and agricultural land is frequently in conflict. Some of the world's largest regional economies are located on deltas such as the Pearl River Delta , Yangtze River Delta , European Low Countries and

707-545: A delta but enter into the sea in the form of an estuary . Notable examples include the Gulf of Saint Lawrence and the Tagus estuary. In rare cases, the river delta is located inside a large valley and is called an inverted river delta . Sometimes a river divides into multiple branches in an inland area, only to rejoin and continue to the sea. Such an area is called an inland delta , and often occurs on former lake beds. The term

808-533: A fan. The more often the flow changes course, the shape develops closer to an ideal fan because more rapid changes in channel position result in a more uniform deposition of sediment on the delta front. The Mississippi and Ural River deltas, with their bird's feet, are examples of rivers that do not avulse often enough to form a symmetrical fan shape. Alluvial fan deltas, as seen by their name, avulse frequently and more closely approximate an ideal fan shape. Most large river deltas discharge to intra-cratonic basins on

909-399: A few main distributaries. Once a wave-dominated or river-dominated distributary silts up, it is abandoned, and a new channel forms elsewhere. In a tidal delta, new distributaries are formed during times when there is a lot of water around – such as floods or storm surges . These distributaries slowly silt up at a more or less constant rate until they fizzle out. A tidal freshwater delta is

1010-545: A flat arid area splits into channels that evaporate as it progresses into the desert. The Okavango Delta in Botswana is one example. See endorheic basin . The generic term mega delta can be used to describe very large Asian river deltas, such as the Yangtze , Pearl , Red , Mekong , Irrawaddy , Ganges-Brahmaputra , and Indus . The formation of a delta is complicated, multiple, and cross-cutting over time, but in

1111-835: A hundred yards off on one side, and another of the women on the other side, looking on; they said an Arab who passed early that morning had done it in anger at losing the price he had given for her, because she was unable to walk any longer. 27th June 1866 – To-day we came upon a man dead from starvation, as he was very thin. One of our men wandered and found many slaves with slave-sticks on, abandoned by their masters from want of food; they were too weak to be able to speak or say where they had come from; some were quite young. The strangest disease I have seen in this country seems really to be broken-heartedness, and it attacks free men who have been captured and made slaves... Twenty one were unchained, as now safe; however all ran away at once; but eight with many others still in chains, died in three days after

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1212-573: A hypocynal delta dip at a very shallow angle, around 1 degree. Fluvial-dominated deltas are further distinguished by the relative importance of the inertia of rapidly flowing water, the importance of turbulent bed friction beyond the river mouth, and buoyancy . Outflow dominated by inertia tends to form Gilbert-type deltas. Outflow dominated by turbulent friction is prone to channel bifurcation, while buoyancy-dominated outflow produces long distributaries with narrow subaqueous natural levees and few channel bifurcations. The modern Mississippi River delta

1313-439: A mature delta with a distributary network. Another way these distributary networks form is from the deposition of mouth bars (mid-channel sand and/or gravel bars at the mouth of a river). When this mid-channel bar is deposited at the mouth of a river, the flow is routed around it. This results in additional deposition on the upstream end of the mouth bar, which splits the river into two distributary channels. A good example of

1414-567: A nominal right to the islands to his brother Luis, Duke of Beja as well as generous trading rights. In 1535, Dom Luis sent a force to conquer the islands, but the islanders' strong navy destroyed it, leaving few survivors. For years afterwards the Bissagos refused to trade with the Portuguese and treated any shipwrecked sailors harshly, until relations were restored around 1550. The Bissago islanders then became important providers of slaves to

1515-423: A sedimentary deposit formed at the boundary between an upland stream and an estuary, in the region known as the "subestuary". Drowned coastal river valleys that were inundated by rising sea levels during the late Pleistocene and subsequent Holocene tend to have dendritic estuaries with many feeder tributaries. Each tributary mimics this salinity gradient from its brackish junction with the mainstem estuary up to

1616-447: A simple delta three main types of bedding may be distinguished: the bottomset beds, foreset/frontset beds, and topset beds. This three-part structure may be seen on small scale by crossbedding . Human activities in both deltas and the river basins upstream of deltas can radically alter delta environments. Upstream land use change such as anti-erosion agricultural practices and hydrological engineering such as dam construction in

1717-415: A trail of slaves: 19th June 1866 – We passed a woman tied by the neck to a tree and dead, the people of the country explained that she had been unable to keep up with the other slaves in a gang, and her master had determined that she should not become anyone's property if she recovered. 26th June. – ...We passed a slave woman shot or stabbed through the body and lying on the path: a group of men stood about

1818-551: Is a good example of a fluvial-dominated delta whose outflow is buoyancy-dominated. Channel abandonment has been frequent, with seven distinct channels active over the last 5000 years. Other fluvial-dominated deltas include the Mackenzie delta and the Alta delta. A Gilbert delta (named after Grove Karl Gilbert ) is a type of fluvial-dominated delta formed from coarse sediments, as opposed to gently sloping muddy deltas such as that of

1919-636: Is a major sign that Mars once had large amounts of water. Deltas have been found over a wide geographical range. Below are pictures of a few. History of slavery The history of slavery spans many cultures , nationalities , and religions from ancient times to the present day . Likewise, its victims have come from many different ethnicities and religious groups. The social, economic , and legal positions of slaves have differed vastly in different systems of slavery in different times and places. Slavery has been found in some hunter-gatherer populations, particularly as hereditary slavery, but

2020-424: Is a triangular landform created by the deposition of the sediments that are carried by the waters of a river , where the river merges with a body of slow-moving water or with a body of stagnant water. The creation of a river delta occurs at the river mouth , where the river merges into an ocean , a sea , or an estuary , into a lake , a reservoir , or (more rarely) into another river that cannot carry away

2121-604: Is also a current phenomenon. A Nigerien study has found that more than 800,000 people are enslaved, almost 8% of the population. Niger installed an anti-slavery provision in 2003. In a landmark ruling in 2008, the ECOWAS Community Court of Justice declared that the Republic of Niger failed to protect Hadijatou Mani Koraou from slavery, and awarded Mani CFA 10,000,000 (approximately US$ 20,000 ) in reparations. Sexual slavery and forced labor are common in

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2222-591: Is called by the Ionians ", including describing the outflow of silt into the sea and the convexly curved seaward side of the triangle. Despite making comparisons to other river systems deltas, Herodotus did not describe them as "deltas". The Greek historian Polybius likened the land between the Rhône and Isère rivers to the Nile Delta, referring to both as islands, but did not apply the word delta. According to

2323-420: Is estimated at 30,000 (2006) and the ethnic group Bissago ( Portuguese : Bijagó ) predominates. It has a relatively youthful population due to high birth rates and low life expectancy. The economy is largely rural, with many families living from subsistence farming and fishing. There is some tourist activity, mostly boat charters from neighboring Senegal . Lack of infrastructure and communication links prevent

2424-548: Is so named because the shape of the Nile Delta approximates the triangular uppercase Greek letter delta . The triangular shape of the Nile Delta was known to audiences of classical Athenian drama ; the tragedy Prometheus Bound by Aeschylus refers to it as the "triangular Nilotic land", though not as a "delta". Herodotus 's description of Egypt in his Histories mentions the Delta fourteen times, as "the Delta, as it

2525-667: Is spoken along with Portuguese and creole . Some authors argue that Bijago culture tends to be matriarchal, with women managing the household, the economy, law, as well as initiating courtship (women choose their husbands and terminate the matrimony). Other sources dispute this and suggest that closer examination has revealed a fundamentally patriarchal society where women, in spite of their substantial participation in material production and important roles in social, political, and religious matter, remain essentially unequal to men. A 2016 study suggested that female status in Bijagos society

2626-633: The 16th century , European merchants , starting mainly with merchants from Portugal , initiated the transatlantic slave trade . Few traders ventured far inland, attempting to avoid tropical diseases and violence. They mostly purchased imprisoned Africans (and exported commodities including gold and ivory ) from West African kingdoms, transporting them to Europe's colonies in the Americas . The merchants were sources of desired goods including guns, gunpowder, copper manillas , and cloth, and this demand for imported goods drove local wars and other means to

2727-811: The Akkadian Empire , Assyria , Babylonia , Persia , ancient Israel , ancient Greece , ancient India , the Roman Empire , the Arab Islamic Caliphates and Sultanates , Nubia , the pre-colonial empires of Sub-Saharan Africa, and the pre-Columbian civilizations of the Americas. Ancient slavery consists of a mixture of debt-slavery , punishment for crime, prisoners of war , child abandonment , and children born to slaves. Writing in 1984, French historian Fernand Braudel noted that slavery had been endemic in Africa and part of

2828-853: The Dey of Algiers to free many slaves. The trading of children has been reported in modern Nigeria and Benin . In parts of Ghana , a family may be punished for an offense by having to turn over a virgin female to serve as a sex slave within the offended family. In this instance, the woman does not gain the title or status of "wife". In parts of Ghana, Togo , and Benin , shrine slavery persists, despite being illegal in Ghana since 1998. In this system of ritual servitude , sometimes called trokosi (in Ghana) or voodoosi in Togo and Benin, young virgin girls are given as slaves to traditional shrines and are used sexually by

2929-662: The Greater Tokyo Area . The Ganges–Brahmaputra Delta , which spans most of Bangladesh and West Bengal and empties into the Bay of Bengal , is the world's largest delta. The Selenga River delta in the Russian republic of Buryatia is the largest delta emptying into a body of fresh water, in its case Lake Baikal . Researchers have found a number of examples of deltas that formed in Martian lakes . Finding deltas

3030-621: The Kanem was about one third enslaved. It was perhaps 40% in Bornu (1396–1893). Between 1750 and 1900 from one- to two-thirds of the entire population of the Fulani jihad states consisted of slaves. The population of the Sokoto caliphate formed by Hausas in northern Nigeria and Cameroon was half-slave in the 19th century. It is estimated that up to 90% of the population of Arab - Swahili Zanzibar

3131-532: The Nile Delta and Colorado River Delta are some of the most extreme examples of the devastation caused to deltas by damming and diversion of water. Historical data documents show that during the Roman Empire and Little Ice Age (times when there was considerable anthropogenic pressure), there was significant sediment accumulation in deltas. The industrial revolution has only amplified the impact of humans on delta growth and retreat. Ancient deltas benefit

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3232-833: The Sahara , through the Red Sea, from the Indian Ocean ports and across the Atlantic. At least ten centuries of slavery for the benefit of the Muslim countries (from the ninth to the nineteenth)." He continues: "Four million slaves exported via the Red Sea , another four million through the Swahili ports of the Indian Ocean , perhaps as many as nine million along the trans-Saharan caravan route, and eleven to twenty million (depending on

3333-807: The United States , France , Spain , Portugal , Holland , West Africa and Arabia . The King of Bonny (now in Nigeria ) allegedly became dissatisfied of the British intervention in stopping the trade of slaves: "We think this trade must go on. That is the verdict of our oracle and the priests. They say that your country, however great, can never stop a trade ordained by God himself." Joseph Miller states that African buyers would prefer males, but in reality, women and children would be more easily captured as men fled. Those captured would be sold for various reasons such as food, debts, or servitude. Once captured,

3434-673: The private sector ; 15.4 million live in forced marriages. Forms of slavery include domestic labour, forced labour in manufacturing, fishing, mining and construction, and sexual slavery . Evidence of slavery predates written records; the practice has existed in many cultures and can be traced back 11,000 years ago due to the conditions created by the invention of agriculture during the Neolithic Revolution . Economic surpluses and high population densities were conditions that made mass slavery viable. Slavery occurred in civilizations including ancient Egypt , ancient China ,

3535-751: The 17th century. In Sierra Leone in the 19th century about half of the population consisted of slaves. In the 19th century at least half the population was enslaved among the Duala of the Cameroon , the Igbo and other peoples of the lower Niger , the Kongo , and the Kasanje kingdom and Chokwe of Angola . Among the Ashanti and Yoruba a third of the population consisted of slaves as well as Bono . The population of

3636-526: The 1840s, King Gezo of Dahomey said: "The slave trade is the ruling principle of my people. It is the source and the glory of their wealth...the mother lulls the child to sleep with notes of triumph over an enemy reduced to slavery." In 1807 the United Kingdom made the international trade of slaves illegal with the Slave Trade Act . The Royal Navy was deployed to prevent slavers from

3737-915: The 7th to the 20th century. Islamic law approved of enslavement of non-Muslims, and slaves were trafficked from non-Muslim lands: from the North via the Balkan slave trade and the Crimean slave trade ; from the East via the Bukhara slave trade ; from the West via Andalusian slave trade ; and from the South via the Trans-Saharan slave trade , the Red Sea slave trade and the Indian Ocean slave trade . Beginning in

3838-728: The American African Slave Trade Patrol , the abolition of slavery in the Americas, and the widespread imposition of European political control in Africa. In modern times, human trafficking remains an international problem. Slavery in the 21st century continues and generates an estimated $ 150 billion in annual profits. Populations in regions with armed conflict are especially vulnerable, and modern transportation has made human trafficking easier. In 2019, there were an estimated 40.3 million people worldwide subject to some form of slavery, and 25% were children. 24.9 million are used for forced labor , mostly in

3939-529: The Americas. The Dutch imported slaves from Asia into their colony at the Cape of Good Hope (now Cape Town ) in the 17th century. In 1807 Britain (which already held a small coastal territory, intended for the resettlement of former slaves, in Freetown , Sierra Leone ) made the slave trade within its empire illegal with the Slave Trade Act 1807 , and worked to extend the prohibition to other territory, as did

4040-529: The Bidyogo people. The London School of Hygiene and Tropical Medicine is conducting research into infectious diseases on the islands. Because they are so isolated there is less danger of contamination of the results than in other places. Due to difficulties of communication with mainland Guinea-Bissau that persist to this day, the population has a considerable degree of autonomy and has shielded its ancestral culture from outside influence. The Bijago language

4141-734: The Democratic Republic of Congo. Many pygmies in the Republic of Congo and Democratic Republic of Congo belong from birth to Bantus in a system of slavery. Evidence emerged in the late 1990s of systematic slavery in cacao plantations in West Africa; see the chocolate and slavery article. According to the U.S. State Department , more than 109,000 children were working on cocoa farms alone in Ivory Coast in "the worst forms of child labour " in 2002. On

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4242-700: The Greek geographer Strabo , the Cynic philosopher Onesicritus of Astypalaea , who accompanied Alexander the Great 's conquests in India , reported that Patalene (the delta of the Indus River ) was "a delta" ( Koinē Greek : καλεῖ δὲ τὴν νῆσον δέλτα , romanized:  kalei de tēn nēson délta , lit.   'he calls the island a delta'). The Roman author Arrian 's Indica states that "the delta of

4343-624: The Khasso into increasing contact with the European settlements of Africa's west coast, particularly the French . Benin grew increasingly rich during the 16th and 17th centuries on the trade of slaves with Europe; slaves from enemy states of the interior were sold, and carried to the Americas in Dutch and Portuguese ships. The Bight of Benin 's shore soon came to be known as the "Slave Coast". In

4444-503: The Mississippi. For example, a mountain river depositing sediment into a freshwater lake would form this kind of delta. It is commonly a result of homopycnal flow. Such deltas are characterized by a tripartite structure of topset, foreset, and bottomset beds. River water entering the lake rapidly deposits its coarser sediments on the submerged face of the delta, forming steeping dipping foreset beds. The finer sediments are deposited on

4545-1032: The Philippines during the Iberian Union (1580–1640). The Middle Passage , the crossing of the Atlantic to the Americas , endured by slaves laid out in rows in the holds of ships, was only one element of the well-known triangular trade engaged in by Portuguese, American, Dutch, Danish-Norwegians, French, British and others. Ships having landed with slaves in Caribbean ports would take on sugar, indigo, raw cotton, and later coffee, and make for Liverpool , Nantes , Lisbon or Amsterdam . Ships leaving European ports for West Africa would carry printed cotton textiles, some originally from India, copper utensils and bangles, pewter plates and pots, iron bars more valued than gold, hats, trinkets, gunpowder and firearms and alcohol. Tropical shipworms were eliminated in

4646-623: The Portuguese, putting aside inter-island rivalries to raid the mainland. In 1849, with the people of the Bissagos still fiercely independent, the British and French mounted a joint expedition to 'pacify' the islands, but they were repulsed. The Portuguese tried several times to put down 'tax revolts' in the islands in the early 20th century but largely failed. The islands were not formally annexed by Portugal until 1936. The Bissagos were visited by Austrian anthropologist and photographer Hugo Bernatzik in 1930–1931, who documented daily life among

4747-528: The United States in 1808. In Senegambia , between 1300 and 1900, close to one-third of the population was enslaved. In early Islamic states of the Western Sudan , including Ghana (750–1076), Mali (1235–1645), Segou (1712–1861), and Songhai (1275–1591), about a third of the population was enslaved. The earliest Akan state of Bonoman which had third of its population being enslaved in

4848-472: The ability to pile up and accumulate due to the sediment traveling into a steep subduction trench rather than a shallow continental shelf . There are many other lesser factors that could explain why the majority of river deltas form along passive margins rather than active margins. Along active margins, orogenic sequences cause tectonic activity to form over-steepened slopes, brecciated rocks, and volcanic activity resulting in delta formation to exist closer to

4949-524: The arrival of the Portuguese . Because it had been established within his kingdom, Afonso I of Kongo believed that the slave trade should be subject to Kongo law. When he suspected the Portuguese of receiving illegally slaves to sell, he wrote letters to the King João III of Portugal in 1526 imploring him to put a stop to the practice. The kings of Dahomey sold their war captives into transatlantic slavery, who otherwise may have been killed in

5050-692: The author) across the Atlantic Ocean" Zanzibar was once East Africa's main slave-trading port, during the Indian Ocean slave trade and under Omani Arabs in the 19th century, with as many as 50,000 slaves passing through the city each year. Prior to the 16th century, the bulk of slaves exported from Africa were shipped from East Africa to the Arabian peninsula . Zanzibar became a leading port in this trade. Arab traders of slaves differed from European ones in that they would often conduct raiding expeditions themselves, sometimes penetrating deep into

5151-1256: The basins feeding deltas have reduced river sediment delivery to many deltas in recent decades. This change means that there is less sediment available to maintain delta landforms, and compensate for erosion and sea level rise , causing some deltas to start losing land. Declines in river sediment delivery are projected to continue in the coming decades. The extensive anthropogenic activities in deltas also interfere with geomorphological and ecological delta processes. People living on deltas often construct flood defences which prevent sedimentation from floods on deltas, and therefore means that sediment deposition can not compensate for subsidence and erosion . In addition to interference with delta aggradation , pumping of groundwater , oil , and gas , and constructing infrastructure all accelerate subsidence , increasing relative sea level rise. Anthropogenic activities can also destabilise river channels through sand mining , and cause saltwater intrusion . There are small-scale efforts to correct these issues, improve delta environments and increase environmental sustainability through sedimentation enhancing strategies . While nearly all deltas have been impacted to some degree by humans,

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5252-411: The best clothing, meaning they were even more exposed to diseases. On top of the fear of disease, people were afraid of why they were being captured. The popular assumption was that Europeans were cannibals . Stories and rumours spread that whites captured Africans to eat them. Olaudah Equiano accounts his experience about the sorrow slaves encountered at the ports. He talks about his first moment on

5353-422: The bird's-foot of the Mississippi or Ural river deltas), pushing its mouth into the standing water. As the deltaic lobe advances, the gradient of the river channel becomes lower because the river channel is longer but has the same change in elevation (see slope ). As the gradient of the river channel decreases, the amount of shear stress on the bed decreases, which results in the deposition of sediment within

5454-450: The channel and a rise in the channel bed relative to the floodplain . This destabilizes the river channel. If the river breaches its natural levees (such as during a flood), it spills out into a new course with a shorter route to the ocean, thereby obtaining a steeper, more stable gradient. Typically, when the river switches channels in this manner, some of its flow remains in the abandoned channel. Repeated channel-switching events build up

5555-631: The cold Atlantic waters, and at each unloading, a profit was made. The Atlantic slave trade peaked in the late 18th century when the largest number of people were captured and enslaved on raiding expeditions into the interior of West Africa. These expeditions were typically carried out by African states, such as the Bono State , Oyo empire ( Yoruba ), Kong Empire , Kingdom of Benin , Imamate of Futa Jallon , Imamate of Futa Toro , Kingdom of Koya , Kingdom of Khasso , Kingdom of Kaabu , Fante Confederacy , Ashanti Confederacy , Aro Confederacy and

5656-542: The conditions of agriculture with increasing social and economic complexity offer greater opportunity for mass chattel slavery . Slavery was institutionalized by the time the first civilizations emerged (such as Sumer in Mesopotamia , which dates back as far as 3500 BC). Slavery features in the Mesopotamian Code of Hammurabi (c. 1750 BC), which refers to it as an established institution. Slavery

5757-534: The continent. They also differed in that their market greatly preferred the purchase of enslaved females over male. The increased presence of European rivals along the East coast led Arab traders to concentrate on the overland slave caravan routes across the Sahara from the Sahel to North Africa. The German explorer Gustav Nachtigal reported seeing slave caravans departing from Kukawa in Bornu bound for Tripoli and Egypt in 1870. The trade of slaves represented

5858-429: The crew. Death was so common that ships were called tumbeiros, or floating tombs. What shocked Africans the most was how death was handled in the ships. Smallwood says the traditions for an African death were delicate and community-based. On ships, bodies would be thrown into the sea. Because the sea represented bad omens, bodies in the sea represented a form of purgatory and the ship a form of hell. Any Africans who made

5959-662: The crossing. They described their only pain in the heart, and placed the hand correctly on the spot, though many think the organ stands high up in the breast-bone. African states played a key role in the trade of slaves, and slavery was a common practice among Sub Saharan Africans even before the involvement of the Arabs , Berbers and Europeans . There were three types: those who were enslaved through conquest, instead of unpaid debts, or those whose parents gave them as property to tribal chiefs. Chieftains would barter their slaves to Arab, Berber, Ottoman or European buyers for rum, spices, cloth or other goods. Selling captives or prisoners

6060-413: The development of the islands' tourism potential. Starting in the early 2000s, several of the islands began to be used as transit depots for narcotraffic , which is quickly changing the social and economic fabric of the islands. In pre-European colonial times, the islands were central to the trade along the coast of West Africa and they built up a powerful navy. In 1532, King Joao III of Portugal ceded

6161-410: The disproportionate removal of males and the introduction of new crops from the Americas ( cassava , maize) would have limited general population decline to particular regions of western Africa around 1760–1810, and in Mozambique and neighbouring areas half a century later. There has also been speculation that within Africa, females were most often captured as brides , with their male protectors being

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6262-556: The economy due to their well-sorted sand and gravel . Sand and gravel are often quarried from these old deltas and used in concrete for highways , buildings, sidewalks, and landscaping. More than 1 billion tons of sand and gravel are produced in the United States alone. Not all sand and gravel quarries are former deltas, but for ones that are, much of the sorting is already done by the power of water. Urban areas and human habitation tend to be located in lowlands near water access for transportation and sanitation . This makes deltas

6363-419: The enslavement of Africans in ever greater numbers. In India and throughout the New World, people were forced into slavery to create the local workforce. The transatlantic slave trade was eventually curtailed after European and American governments passed legislation abolishing their nations' involvement in it. Practical efforts to enforce the abolition of slavery included the British Preventative Squadron and

6464-442: The extent that a crisis in the social system would have negative effects" on the natural system. In particular, it was the lack of harmony between the community, ancestors and the supernatural world that was seen as causing environmental dissonance. The Bissagos peoples produce many artifacts for daily use and ritual following a traditional iconography that is unique to their culture, and shows variations from island to island. Among

6565-414: The flow enters the standing water, it is no longer confined to its channel and expands in width. This flow expansion results in a decrease in the flow velocity , which diminishes the ability of the flow to transport sediment . As a result, sediment drops out of the flow and is deposited as alluvium , which builds up to form the river delta. Over time, this single channel builds a deltaic lobe (such as

6666-506: The fresh stream feeding the head of tidal propagation. As a result, the tributaries are considered to be "subestuaries". The origin and evolution of a tidal freshwater delta involves processes that are typical of all deltas as well as processes that are unique to the tidal freshwater setting. The combination of processes that create a tidal freshwater delta result in a distinct morphology and unique environmental characteristics. Many tidal freshwater deltas that exist today are directly caused by

6767-466: The geomorphology and ecosystem. Deltas are typically classified according to the main control on deposition, which is a combination of river, wave , and tidal processes, depending on the strength of each. The other two factors that play a major role are landscape position and the grain size distribution of the source sediment entering the delta from the river. Fluvial-dominated deltas are found in areas of low tidal range and low wave energy. Where

6868-425: The incident. According to police, approximately 276 children were taken in the attack, of whom 53 had escaped as of 2 May. Other reports said that 329 girls were kidnapped, 53 had escaped and 276 were still missing. The students have been forced to convert to Islam and into marriage with members of Boko Haram, with a reputed " bride price " of ₦ 2,000 each ( $ 12.50/ £ 7.50). Many of the students were taken to

6969-521: The journey to the coast killed many and weakened others. Disease engulfed many, and insufficient food damaged those who made it to the coasts. Scurvy was common, and was often referred to as mal de Luanda ("Luanda sickness," after the port in Angola). The assumption for those who died on the journey died from malnutrition . As food was limited, water may have been just as bad. Dysentery was widespread and poor sanitary conditions at ports did not help. Since supplies were poor, slaves were not equipped with

7070-426: The journey would have survived extreme disease and malnutrition, as well as trauma from being on the open ocean and the death of their friends. In Algiers during the time of the Regency of Algiers in North Africa in the 19th century, up to 1.5 million Christians and Europeans were captured and forced into slavery. This eventually led to the Bombardment of Algiers in 1816 by the British and Dutch , forcing

7171-484: The kingdom of Dahomey . Europeans rarely entered the interior of Africa, due to fear of disease and moreover fierce African resistance. The slaves were brought to coastal outposts where they were traded for goods. The people captured on these expeditions were shipped by European traders to the colonies of the New World . It is estimated that over the centuries, twelve to twenty million slaves were shipped from Africa by European traders, of whom some 15 percent died during

7272-406: The lake bottom beyond this steep slope as more gently dipping bottomset beds. Behind the delta front, braided channels deposit the gently dipping beds of the topset on the delta plain. While some authors describe both lacustrine and marine locations of Gilbert deltas, others note that their formation is more characteristic of the freshwater lakes, where it is easier for the river water to mix with

7373-594: The lakewater faster (as opposed to the case of a river falling into the sea or a salt lake, where less dense fresh water brought by the river stays on top longer). Gilbert himself first described this type of delta on Lake Bonneville in 1885. Elsewhere, similar structures occur, for example, at the mouths of several creeks that flow into Okanagan Lake in British Columbia and form prominent peninsulas at Naramata , Summerland , and Peachland . In wave-dominated deltas, wave-driven sediment transport controls

7474-583: The land of the Indians is made by the Indus river no less than is the case with that of Egypt". As a generic term for the landform at the mouth of the river, the word delta is first attested in the English-speaking world in the late 18th century, in the work of Edward Gibbon . River deltas form when a river carrying sediment reaches a body of water, such as a lake, ocean, or a reservoir . When

7575-530: The major source of revenue for the state of Bornu as late as 1898. The eastern regions of the Central African Republic have never recovered demographically from the impact of 19th-century raids from the Sudan and still have a population density of less than 1 person/km . During the 1870s, European initiatives against the trade of slaves caused an economic crisis in northern Sudan, precipitating

7676-659: The most striking Bidyogo art pieces are the portable ancestor shrines ("iran") and the zoomorphic masks representing cows ("vaca-bruta"), sharks, stingrays and, occasionally, other local animals. Traditionally-decorated artifacts are also produced for "fanado" coming-of-age ceremonies (wood masks, spears, shields, headgear, bracelets), daily activities (fishing, agriculture) and personal use (stools, basketry, foodware). Its unique aesthetics make Bidyogo art easily distinctive from other African tribal arts. 11°15′N 16°05′W  /  11.250°N 16.083°W  / 11.250; -16.083 River delta A river delta

7777-545: The neighbouring countries of Chad and Cameroon , with sightings reported of the students crossing borders with the militants, and sightings of the students by villagers living in the Sambisa Forest , which is considered a refuge for Boko Haram. On 5 May 2014 a video in which Boko Haram leader Abubakar Shekau claimed responsibility for the kidnappings emerged. Shekau claimed that "Allah instructed me to sell them...I will carry out his instructions" and " [s]lavery

7878-683: The night of 14–15 April 2014, a group of militants attacked the Government Girls Secondary School in Chibok , Nigeria. They broke into the school, pretending to be guards, telling the girls to get out and come with them. A large number of students were taken away in trucks, possibly into the Konduga area of the Sambisa Forest where Boko Haram were known to have fortified camps. Houses in Chibok were also burned down in

7979-524: The onset of or changes in historical land use, especially deforestation , intensive agriculture , and urbanization . These ideas are well illustrated by the many tidal freshwater deltas prograding into Chesapeake Bay along the east coastline of the United States. Research has demonstrated that the accumulating sediments in this estuary derive from post-European settlement deforestation, agriculture, and urban development. Other rivers, particularly those on coasts with significant tidal range , do not form

8080-481: The period from the late 19th century and early 20th century, demand for the labour-intensive harvesting of rubber drove frontier expansion and forced labour . The personal monarchy of Belgian King Leopold II in the Congo Free State saw mass killings and slavery to extract rubber. Surviving the voyage was the main struggle. Close quarters meant everyone was infected by any diseases that spread, including

8181-581: The priests in addition to providing free labor for the shrine. An article in the Middle East Quarterly in 1999 reported that slavery is endemic in Sudan . Estimates of abductions during the Second Sudanese Civil War range from 14,000 to 200,000 people. During the Second Sudanese Civil War people were taken into slavery; estimates of abductions range from 14,000 to 200,000. Abduction of Dinka women and children

8282-487: The result of this process is the Wax Lake Delta . In both of these cases, depositional processes force redistribution of deposition from areas of high deposition to areas of low deposition. This results in the smoothing of the planform (or map-view) shape of the delta as the channels move across its surface and deposit sediment. Because the sediment is laid down in this fashion, the shape of these deltas approximates

8383-509: The rise of Mahdist forces. Mahdi 's victory created an Islamic state , one that quickly reinstituted slavery. European involvement in the East African trade of enslaved people began when Portugal established Estado da Índia in the early 16th century. From then until the 1830s, c.  200 enslaved people were exported from Portuguese Mozambique annually and similar figures has been estimated for enslaved people brought from Asia to

8484-579: The river delta, causing the delta to retreat. For deltas that form further upriver in an estuary, there are complex yet quantifiable linkages between winds, tides, river discharge, and delta water levels. Erosion is also an important control in tide-dominated deltas, such as the Ganges Delta , which may be mainly submarine, with prominent sandbars and ridges. This tends to produce a "dendritic" structure. Tidal deltas behave differently from river-dominated and wave-dominated deltas, which tend to have

8585-414: The river water is nearly equal in density to the basin water, the delta is characterized by homopycnal flow , in which the river water rapidly mixes with basin water and abruptly dumps most of its sediment load. Where the river water has a higher density than basin water, typically from a heavy load of sediment, the delta is characterized by hyperpycnal flow in which the river water hugs the basin bottom as

8686-485: The salt water. I told them that they were employed in cultivation the land; but they would not believe me ... A deeply-rooted idea that the whites purchase negroes for the purpose of devouring them, or of selling them to others that they may be devoured hereafter, naturally makes the slaves contemplate a journey towards the coast with great terror, insomuch that the slatees are forced to keep them constantly in irons, and watch them very closely, to prevent their escape. During

8787-399: The sediment is never piled up in thick sequences due to the sediment traveling and depositing in deep subduction trenches. At the mouth of a river, the change in flow conditions can cause the river to drop any sediment it is carrying. This sediment deposition can generate a variety of landforms, such as deltas, sand bars, spits, and tie channels. Landforms at the river mouth drastically alter

8888-514: The sediment source. When sediment does not travel far from the source, sediments that build up are coarser grained and more loosely consolidated, therefore making delta formation more difficult. Tectonic activity on active margins causes the formation of river deltas to form closer to the sediment source which may affect channel avulsion , delta lobe switching, and auto cyclicity. Active margin river deltas tend to be much smaller and less abundant but may transport similar amounts of sediment. However,

8989-814: The sediment supplied by the feeding river. Etymologically, the term river delta derives from the triangular shape (Δ) of the uppercase Greek letter delta . In hydrology , the dimensions of a river delta are determined by the balance between the watershed processes that supply sediment and the watershed processes that redistribute, sequester, and export the supplied sediment into the receiving basin. River deltas are important in human civilization , as they are major agricultural production centers and population centers. They can provide coastline defence and can impact drinking water supply. They are also ecologically important, with different species' assemblages depending on their landscape position. On geologic timescales , they are also important carbon sinks . A river delta

9090-424: The shape of the delta, and much of the sediment emanating from the river mouth is deflected along the coastline. The relationship between waves and river deltas is quite variable and largely influenced by the deepwater wave regimes of the receiving basin. With a high wave energy near shore and a steeper slope offshore, waves will make river deltas smoother. Waves can also be responsible for carrying sediments away from

9191-504: The structure of everyday life throughout the 15th to the 18th century. "Slavery came in different guises in different societies: there were court slaves, slaves incorporated into princely armies, domestic and household slaves, slaves working on the land, in industry, as couriers and intermediaries, even as traders". During the 16th century, Europe began to outpace the Arab world in the export traffic, with its trafficking of slaves from Africa to

9292-477: The surrounding areas in northern Nigeria at the turn of the 20th century, approximately 2 million to 2.5 million people living there were enslaved. Slavery in northern Nigeria was finally outlawed in 1936. Writing in 1998 about the extent of trade coming through and from Africa, the Congolese journalist Elikia M'bokolo wrote "The African continent was bled of its human resources via all possible routes. Across

9393-623: The terrible voyage, many during the arduous journey through the Middle Passage . The great majority were shipped to the Americas, but some also went to Europe and Southern Africa. While talking about the trade of slaves in East Africa in his journals, David Livingstone said To overdraw its evil is a simple impossibility. While travelling in the African Great Lakes Region in 1866, Livingstone described

9494-656: The trailing edges of passive margins due to the majority of large rivers such as the Mississippi , Nile , Amazon , Ganges , Indus , Yangtze , and Yellow River discharging along passive continental margins. This phenomenon is due mainly to three factors: topography , basin area, and basin elevation. Topography along passive margins tend to be more gradual and widespread over a greater area enabling sediment to pile up and accumulate over time to form large river deltas. Topography along active margins tends to be steeper and less widespread, which results in sediments not having

9595-772: Was a common practice among Africans, Turks, Berbers and Arabs during that era. However, as the Atlantic trade of slaves increased its demand, local systems which primarily serviced indentured servitude expanded. European trading of slaves, as a result, was the most pivotal change in the social, economic, cultural, spiritual, religious, political dynamics of the concept of trading in slaves. It ultimately undermined local economies and political stability as villages' vital labour forces were shipped overseas as slave raids and civil wars became commonplace. Crimes which were previously punishable by some other means became punishable by enslavement. Slavery already existed in Kingdom of Kongo prior to

9696-595: Was common. In Mauritania it is estimated that up to 600,000 men, women and children, or 20% of the population, are currently enslaved, many of them used as bonded labor . Slavery in Mauritania was criminalized in August 2007. During the Darfur conflict that began in 2003, many people were kidnapped by Janjaweed and sold into slavery as agricultural labor, domestic servants and sex slaves. In Niger , slavery

9797-425: Was declared a UNESCO Biosphere Reserve in 1996. The site has been designated an Important Bird Area (IBA) by BirdLife International because its intertidal mudflats and mangroves support significant populations of non-breeding and wintering waterbirds , especially large numbers of migratory Palaearctic waders , gulls and terns , as well as greater flamingos and pink-backed pelicans . The population

9898-477: Was diminished during the slave trade era (likely due to European influence) but has become more valued again in more recent times. In 2012, a study by Bissau-Guinean sociologist Boaventura Santy examined the social representations of the people of the island of Formosa Bijagó about possible threats from climate change . The study concluded that for "the Bijagó the natural and the social are inextricably linked, to

9999-546: Was enslaved. Roughly half the population of Madagascar was enslaved. Slavery in Ethiopia persisted until 1942. The Anti-Slavery Society estimated that there were 2,000,000 slaves in the early 1930s, out of an estimated population of between 8 and 16 million. It was finally abolished by order of emperor Haile Selassie on 26 August 1942. When British rule was first imposed on the Sokoto Caliphate and

10100-732: Was first coined by Alexander von Humboldt for the middle reaches of the Orinoco River , which he visited in 1800. Other prominent examples include the Inner Niger Delta , Peace–Athabasca Delta , the Sacramento–San Joaquin River Delta , and the Sistan delta of Iran. The Danube has one in the valley on the Slovak–Hungarian border between Bratislava and Iža . In some cases, a river flowing into

10201-696: Was widespread in the ancient world in Europe, Asia, the Middle East, and Africa. Slavery became less common throughout Europe during the Early Middle Ages but continued to be practiced in some areas. Both Christians and Muslims captured and enslaved each other during centuries of warfare in the Mediterranean and Europe. Islamic slavery encompassed mainly Western and Central Asia, Northern and Eastern Africa, India , and Europe from

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