The headwaters of theApurímac River onNevado Mismi had been considered, for nearly a century, theAmazon basin's most distant source until a 2014 study found it to be the headwaters of theMantaro River on the Cordillera Rumi Cruz inPeru.[28] The Mantaro andApurímac rivers join, and with other tributaries form theUcayali River, which in turn meets theMarañón River upstream ofIquitos, Peru, forming what countries other thanBrazil consider to be themain stem of the Amazon. Brazilians call this section theSolimões River above its confluence with theRio Negro[29] forming what Brazilians call the Amazon at theMeeting of Waters (Portuguese:Encontro das Águas) atManaus, the largest city on the river.
The Amazon River has an average discharge of about 215,000–230,000 m3/s (7,600,000–8,100,000 cu ft/s)—approximately 6,591–7,570 km3 (1,581–1,816 cu mi) per year, greater than the next seven largest independent rivers combined. Two of the top ten rivers by discharge aretributaries of the Amazon river. The Amazon represents 20% of the global riverine discharge into oceans.[30] The Amazon basin is the largestdrainage basin in the world, with an area of approximately 7,000,000 km2 (2,700,000 sq mi).[5] The portion of the river's drainage basin in Brazil alone is larger than any other river's basin. The Amazon enters Brazil with only one-fifth of the flow it finally discharges into theAtlantic Ocean, yet already has a greater flow at this point than the discharge of any other river in the world.[31][32] It has a recognized length of 6,400 km (4,000 miles) but according to some reports its length varies from 6,575–7,062 km (4,086–4,388 mi).[33][34][35]
The Amazon was initially known byEuropeans as theMarañón, and thePeruvian part of the river is still known by that name, as well as the Brazilian state ofMaranhão, which contains part of the Amazon. It later became known as Rio Amazonas inSpanish andPortuguese.[citation needed]
The name Rio Amazonas was reportedly given after native warriors attacked a 16th-century expedition byFrancisco de Orellana. The warriors were led by women, reminding de Orellana of theAmazon warriors, a tribe of women warriors related toIranianScythians andSarmatians[36][37] mentioned inGreek mythology.The word Amazon itself may be derived from theIranian compound * ha-maz-an- "(one) fighting together"[38] orethnonym* ha-mazan- "warriors", a word attested indirectly through a derivation, a denominal verb inHesychius of Alexandria's gloss"ἁμαζακάραν· πολεμεῖν. Πέρσαι" ("hamazakaran: 'to make war' in Persian"), where it appears together with theIndo-Iranian root* kar- "make" (from whichSanskritkarma is also derived).[39]
Other scholars[who?] claim that the name is derived from theTupi wordamassona, meaning "boat destroyer".[40][citation needed]
Geological studies suggest that for millions of years, the Amazon River flowed in the opposite direction – from east to west. Eventually theAndes Mountains formed, blocking its flow to thePacific Ocean and causing it to switch directions to its current mouth in theAtlantic Ocean.[41]
Old drawing (from 1879) ofArapaima fishing at the Amazon River. The arapaima has been on Earth for at least 23 million years.[42]
During what manyarchaeologists called theformative stage, Amazonian societies were deeply involved in the emergence ofSouth America's highlandagrarian systems. Thetrade withAndean civilizations in the terrains of theheadwaters in theAndes formed an essential contribution to the social and religious development of higher-altitude civilizations like theMuisca andIncas. Early human settlements were typically based on low-lying hills or mounds.
Shell mounds were the earliest evidence of habitation; they represent piles of human refuse and are mainly dated between 7500 BC and 4000 BC. They are associated with ceramic age cultures; no preceramic shell mounds have been documented so far byarchaeologists.[43] Artificial earth platforms for entire villages are the second type of mounds. They are best represented by theMarajoara culture. Figurative mounds are the most recent types of occupation.
There is ample evidence that the areas surrounding the Amazon River were home to complex and large-scale indigenous societies, mainlychiefdoms who developed towns and cities.[44]Archaeologists estimate that by the time theSpanish conquistador De Orellana traveled across the Amazon in 1541, more than 3 million indigenous people lived around the Amazon.[45]: 24–25 Thesepre-Columbian settlements created highly developed civilizations. For instance, pre-Columbianindigenous people on the island ofMarajó may have developed social stratification and supported a population of 100,000 people. To achieve this level of development, the indigenous inhabitants of theAmazon rainforest altered the forest'secology by selective cultivation and the use of fire. Scientists argue that by burning areas of the forest repeatedly, the indigenous people caused the soil to become richer in nutrients. This created dark soil areas known asterra preta de índio ("Indian dark earth").[45]: 25 Because of the terra preta, indigenous communities were able to make land fertile and thus sustainable for the large-scale agriculture needed to support their large populations and complex social structures. Further research has hypothesized that this practice began around 11,000 years ago. Some say that its effects onforest ecology and regional climate explain the otherwise inexplicable band of lower rainfall through theAmazon basin.[45]: 25
Many indigenous tribes engaged in constantwarfare. According toJames S. Olson, "TheMunduruku expansion (in the 18th century) dislocated and displaced theKawahíb, breaking the tribe down into much smaller groups ... [Munduruku] first came to the attention ofEuropeans in 1770 when they began a series of widespread attacks on Brazilian settlements along the Amazon River."[46]
In March 1500,SpanishconquistadorVicente Yáñez Pinzón was the first documentedEuropean to sail up the Amazon River.[47]Pinzón called the streamRío Santa María del Mar Dulce, later shortened toMar Dulce, literally,sweet sea, because of its freshwater pushing out into the ocean. AnotherSpanish explorer,Francisco de Orellana, was the firstEuropean to travel from the origins of the upstream river basins, situated in theAndes, to the mouth of the river. In this journey, Orellana baptized some of the affluents of the Amazonas likeRio Negro,Napo andJurua.The name Amazonas is thought to be taken from the native warriors that attacked this expedition, mostly women, that reminded De Orellana of the mythical femaleAmazon warriors from the ancientHellenic culture in Greece (see alsoOrigin of the name).
Gonzalo Pizarro set off in 1541 to explore east ofQuito into the South American interior in search ofEl Dorado, the "city of gold" andLa Canela, the "valley ofcinnamon".[48] He was accompanied by his second-in-commandFrancisco de Orellana. After 170 km (106 mi), theCoca River joined theNapo River (at a point now known asPuerto Francisco de Orellana); the party stopped for a few weeks to build a boat just upriver from this confluence. They continued downriver through an uninhabited area, where they could not find food. Orellana offered and was ordered to follow the Napo River, then known asRío de la Canela ("Cinnamon River"), and return with food for the party. Based on intelligence received from a captive native chief named Delicola, they expected to find food within a few days downriver by ascending another river to the north.
De Orellana took about 57 men, the boat, and some canoes and left Pizarro's troops on 26 December 1541. However, De Orellana missed the confluence (probably with theAguarico) where he was searching supplies for his men. By the time he and his men reached another village, many of them were sick from hunger and eating "noxious plants", and near death. Seven men died in that village. His men threatened to mutiny if the expedition turned back to attempt to rejoin Pizarro, the party being over 100 leagues downstream at this point. He accepted to change the purpose of the expedition to discover new lands in the name of the king of Spain, and the men built a larger boat in which to navigate downstream. After a journey of 600 km (370 mi) down the Napo River, they reached a further major confluence, at a point near modernIquitos, and then followed the upper Amazon, now known as the Solimões, for a further 1,200 km (746 mi) to its confluence with the Rio Negro (near modernManaus), which they reached on 3 June 1542.
Regarding the initial mission of finding cinnamon, Pizarro reported to the king that they had found cinnamon trees, but that they could not be profitably harvested. True cinnamon (Cinnamomum Verum) is not native to South America. Other related cinnamon-containing plants (of the familyLauraceae) are fairly common in that part of the Amazon and Pizarro probably saw some of these. The expedition reached the mouth of the Amazon on 24 August 1542, demonstrating the practical navigability of the Great River.
In 1560, another Spanishconquistador,Lope de Aguirre, may have made the second descent of the Amazon. Historians are uncertain whether the river he descended was the Amazon or theOrinoco River, which runs more or less parallel to the Amazon further north.
Portuguese explorerPedro Teixeira was the first European to travel up the entire river. He arrived in Quito in 1637, and returned via the same route.[49]
From 1648 to 1652, Portuguese BrazilianbandeiranteAntónio Raposo Tavares led an expedition fromSão Paulo overland to the mouth of the Amazon, investigating many of its tributaries, including the Rio Negro, and covering a distance of over 10,000 km (6,200 mi).
In what is currently in Brazil, Ecuador, Bolivia, Colombia, Peru, and Venezuela, severalcolonial and religious settlements were established along the banks of primary rivers and tributaries for trade, slaving[citation needed] , andevangelization among the indigenous peoples of the vast rainforest, such as theUrarina. In the late 1600s, Czech Jesuit FatherSamuel Fritz, an apostle of the Omagus established some forty mission villages. Fritz proposed that theMarañón River must be the source of the Amazon, noting on his 1707 map that the Marañón "has its source on the southern shore of a lake that is calledLauricocha, nearHuánuco." Fritz reasoned that the Marañón is the largest river branch one encounters when journeying upstream, and lies farther to the west than any other tributary of the Amazon. For most of the 18th–19th centuries and into the 20th century, the Marañón was generally considered the source of the Amazon.[50]
Henry Walter Bates was most famous for his expedition to the Amazon (1848–1859).
Early scientific, zoological, and botanical exploration of the Amazon River and basin took place from the 18th century through the first half of the 19th century.
TheCabanagem revolt (1835–1840) was directed against the white ruling class. It is estimated that from 30% to 40% of the population ofGrão-Pará, estimated at 100,000 people, died.[52]
The population of the Brazilian portion of the Amazon basin in 1850 was perhaps 300,000, of whom about 175,000 were Europeans and 25,000 were slaves. The Brazilian Amazon's principal commercial city, Pará (now Belém), had from 10,000 to 12,000 inhabitants, including slaves. The town of Manáos, now Manaus, at the mouth of the Rio Negro, had a population between 1,000 and 1,500. All the remaining villages, as far up asTabatinga, on the Brazilian frontier of Peru, were relatively small.[53]
On 6 September 1850, EmperorPedro II of Brazil sanctioned a law authorizing steam navigation on the Amazon and gave the Viscount of Mauá (Irineu Evangelista de Sousa) the task of putting it into effect. He organised the "Companhia de Navegação e Comércio do Amazonas" in Rio de Janeiro in 1852; in the following year it commenced operations with four small steamers, theMonarca ('Monarch'), theCametá, theMarajó and theRio Negro.[53][54]
At first, navigation was principally confined to the main river; and even in 1857 a modification of the government contract only obliged the company to a monthly service between Pará and Manaus, with steamers of 200 tons cargo capacity, a second line to make six round voyages a year between Manaus and Tabatinga, and a third, two trips a month between Pará and Cametá.[53] This was the first step in opening up the vast interior.
The success of the venture called attention to the opportunities for economic exploitation of the Amazon, and a second company soon opened commerce on the Madeira, Purús, and Negro; a third established a line between Pará and Manaus, and a fourth found it profitable to navigate some of the smaller streams. In that same period, the Amazonas Company was increasing its fleet. Meanwhile, private individuals were building and running small steam craft of their own on the main river as well as on many of its tributaries.[53]
On 31 July 1867, the government of Brazil, constantly pressed by the maritime powers and by the countries encircling theupper Amazon basin, especially Peru, decreed the opening of the Amazon to all countries, but they limited this to certain defined points: Tabatinga – on the Amazon; Cametá – on the Tocantins; Santarém – on the Tapajós; Borba – on the Madeira, and Manaus – on the Rio Negro. The Brazilian decree took effect on 7 September 1867.[53]
Thanks in part to themercantile development associated withsteamboat navigation coupled with the internationally driven demand fornatural rubber, the Peruvian city ofIquitos became a thriving, cosmopolitan center of commerce. Foreign companies settled in Iquitos, from where they controlled the extraction of rubber. In 1851 Iquitos had a population of 200, and by 1900 its population reached 20,000. In the 1860s, approximately 3,000 tons of rubber were being exported annually, and by 1911 annual exports had grown to 44,000 tons, representing 9.3% of Peru's exports.[55] During therubber boom it is estimated that diseases brought by immigrants, such astyphus andmalaria, killed 40,000 native Amazonians.[56]
The first direct foreign trade with Manaus commenced around 1874. Local trade along the river was carried on by the English successors to the Amazonas Company—the Amazon Steam Navigation Company—as well as numerous small steamboats, belonging to companies and firms engaged in the rubber trade, navigating the Negro, Madeira, Purús, and many other tributaries,[53] such as the Marañón, to ports as distant asNauta, Peru.
By the turn of the 20th century, the exports of the Amazon basin wereIndia-rubber,cacao beans,Brazil nuts and a few other products of minor importance, such aspelts and exotic forest produce (resins, barks, wovenhammocks, prized birdfeathers, live animals) and extracted goods, such aslumber and gold.
Manaus, the largest city inAmazonas, as seen from aNASA satellite image, surrounded by the darkRio Negro and the muddy Amazon RiverCity of ManausFloating houses inLeticia,Colombia
Since colonial times, the Portuguese portion of the Amazon basin has remained a land largely undeveloped by agriculture and occupied by indigenous people who survived the arrival of European diseases.
Four centuries after the European discovery of the Amazon river, the total cultivated area in its basin was probably less than 65 km2 (25 sq mi), excluding the limited and crudely cultivated areas among the mountains at its extreme headwaters.[57] This situation changed dramatically during the 20th century.
Wary of foreign exploitation of the nation's resources, Brazilian governments in the 1940s set out to develop the interior, away from the seaboard where foreigners owned large tracts of land. The original architect of this expansion was presidentGetúlio Vargas, with the demand for rubber from the Allied forces in World War II providing funding for the drive.
In the 1960s, economic exploitation of the Amazon basin was seen as a way to fuel the "economic miracle" occurring at the time. This resulted in the development of "Operation Amazon", an economic development project that brought large-scale agriculture and ranching to Amazonia. This was done through a combination of credit and fiscal incentives.[58]
However, in the 1970s the government took a new approach with the National Integration Program (PIN). A large-scale colonization program saw families from northeastern Brazil relocated to the "land without people" in the Amazon Basin. This was done in conjunction with infrastructure projects mainly theTrans-Amazonian Highway (Transamazônica).[58]
The Trans-Amazonian Highway's three pioneering highways were completed within ten years but never fulfilled their promise. Large portions of the Trans-Amazonian and its accessory roads, such as BR-317 (Manaus-Porto Velho), are derelict and impassable in the rainy season. Small towns and villages are scattered across the forest, and because its vegetation is so dense, some remote areas are still unexplored.
Many settlements grew along the road from Brasília to Belém with the highway and National Integration Program, however, the program failed as the settlers were unequipped to live in the delicate rainforest ecosystem. This, although the government believed it could sustain millions, instead could sustain very few.[59]
With a population of 1.9 million people in 2014, Manaus is the largest city on the Amazon. Manaus alone makes up approximately 50% of the population of the largest Brazilian state ofAmazonas. The racial makeup of the city is 64%pardo (mulatto and mestizo) and 32%white.[60]
Although the Amazon river remains undammed, around 412 dams are in operation on the Amazon's tributary rivers. Of these 412 dams, 151 are constructed over six of the main tributary rivers that drain into the Amazon.[61] Since only 4% of the Amazon's hydropower potential has been developed in countries like Brazil,[45]: 35 more damming projects are underway and hundreds more are planned.[62] After witnessing the negative effects of environmental degradation, sedimentation, navigation and flood control caused by theThree Gorges Dam in the Yangtze River,[45]: 279 scientists are worried that constructing more dams in the Amazon will harm its biodiversity in the same way by "blocking fish-spawning runs, reducing the flows of vital oil nutrients and clearing forests".[62] Damming the Amazon River could potentially bring about the "end of free flowing rivers" and contribute to an "ecosystem collapse" that will cause major social and environmental problems.[61]
The Amazon was thought to originate from the Apacheta cliff inArequipa at theNevado Mismi, marked only by a wooden cross.Nevado Mismi, formerly considered to be the source of the AmazonMarañón River in Peru
The most distant source of the Amazon was thought to be in the Apurímac river drainage for nearly a century. Such studies continued to be published even as recently as 1996,[63] 2001,[64] 2007,[25] and 2008,[65] where various authors identified the snowcapped 5,597 m (18,363 ft)Nevado Mismi peak, located roughly 160 km (99 mi) west ofLake Titicaca and 700 km (430 mi) southeast ofLima, as the most distant source of the river. From that point, QuebradaCarhuasanta emerges from Nevado Mismi, joins Quebrada Apacheta and soon forms Río Lloqueta which becomes Río Hornillos and eventually joins theRío Apurímac.
A 2014 study by Americans James Contos and Nicolas Tripcevich inArea, a peer-reviewed journal of theRoyal Geographical Society, however, identifies the most distant source of the Amazon as actually being in theRío Mantaro drainage.[28] A variety of methods were used to compare the lengths of the Mantaro river vs. the Apurímac river from their most distant source points to their confluence, showing the longer length of the Mantaro. Then distances fromLago Junín to several potential source points in the uppermost Mantaro river were measured, which enabled them to determine that the Cordillera Rumi Cruz was the most distant source of water in the Mantaro basin (and therefore in the entire Amazon basin). The most accurate measurement method was direct GPS measurement obtained by kayak descent of each of the rivers from their source points to their confluence (performed by Contos). Obtaining these measurements was difficult given theclass IV–V nature of each of these rivers, especially in their lower "Abyss" sections. Ultimately, they determined that the most distant point in the Mantaro drainage is nearly 80 km farther upstream compared to Mt. Mismi in the Apurímac drainage, and thus the maximal length of the Amazon river is about 80 km longer than previously thought. Contos continued downstream to the ocean and finished the first complete descent of the Amazon from its newly identified source (finishing November 2012), a journey repeated by two groups after the news spread.[66]
After about 700 km (430 mi), the Apurímac then joins Río Mantaro to form the Ene, which joins the Perene to form the Tambo, which joins theUrubamba River to form the Ucayali. After the confluence of Apurímac and Ucayali, the river leaves Andean terrain and is surrounded byfloodplain. From this point to the confluence of the Ucayali and the Marañón, some 1,600 km (990 mi), the forested banks are just above the water and are inundated long before the river attains its maximum flood stage.[53] The low river banks are interrupted by only a few hills, and the river enters the enormousAmazon rainforest.
Although the Ucayali–Marañón confluence is the point at which most geographers place the beginning of the Amazon River proper, in Brazil the river is known at this point as theSolimões das Águas. The river systems and flood plains in Brazil, Peru, Ecuador, Colombia, and Venezuela, whose waters drain into theSolimões and its tributaries, are called the "Upper Amazon".
At some points, the river divides intoanabranches, or multiple channels, often very long, with inland and lateralchannels, all connected by a complicated system of natural canals, cutting the low, flatigapó lands, which are never more than 5 m (16 ft) above low river, into many islands.[67]
From the town of Canaria at the great bend of the Amazon to the Negro, vast areas of land are submerged at high water, above which only the upper part of the trees of the sombre forests appear. Near the mouth of the Rio Negro to Serpa, nearly opposite the river Madeira, the banks of the Amazon are low, until approaching Manaus, they rise to become rolling hills.[53]
The Lower Amazon begins where the darkly colored waters of the Rio Negro meets the sandy-coloredRio Solimões (the upper Amazon), and for over 6 km (3.7 mi) these watersrun side by side without mixing. At Óbidos, a bluff 17 m (56 ft) above the river is backed by low hills. The lower Amazon seems to have once been agulf of the Atlantic Ocean, the waters of which washed the cliffs near Óbidos.
Only about 10% of the Amazon's water enters downstream of Óbidos, very little of which is from the northern slope of the valley. The drainage area of the Amazon basin above Óbidos city is about 5,000,000 km2 (1,900,000 sq mi), and, below, only about 1,000,000 km2 (390,000 sq mi) (around 20%), exclusive of the 1,400,000 km2 (540,000 sq mi) of the Tocantins basin.[53] TheTocantins River enters the southern portion of theAmazon delta.
In the lower reaches of the river, the north bank consists of a series of steep, table-topped hills extending for about 240 km (150 mi) from opposite the mouth of the Xingu as far asMonte Alegre. These hills are cut down to a kind ofterrace which lies between them and the river.[67]
On the south bank, above the Xingu, a line of low bluffs bordering the floodplain extends nearly toSantarém in a series of gentle curves before they bend to the southwest, and, abutting upon the lower Tapajós, merge into the bluffs which form the terrace margin of the Tapajós river valley.[68]
Satellite image of the mouth of the Amazon River, from the north looking south
Belém is the major city and port at the mouth of the river at the Atlantic Ocean. The definition of where exactly the mouth of the Amazon is located, and how wide it is, is a matter of dispute, because of the area's peculiar geography. ThePará and the Amazon are connected by a series of river channels calledfuros near the town ofBreves; between them liesMarajó, the world's largest combined river/sea island.
If the Pará river and the Marajó island ocean frontage are included, the Amazonestuary is some 325 km (202 mi) wide.[69] In this case, the width of the mouth of the river is usually measured from Cabo Norte, the cape located straight east ofPracuúba in the Brazilian state ofAmapá, to Ponta da Tijoca near the town ofCuruçá, in the state ofPará.
A more conservative measurement excluding the Pará river estuary, from the mouth of theAraguari River to Ponta do Navio on the northern coast ofMarajó, would still give the mouth of the Amazon a width of over 180 km (112 mi). If only the river's main channel is considered, between the islands of Curuá (state of Amapá) and Jurupari (state of Pará), the width falls to about 15 km (9.3 mi).
The plume generated by the river's discharge covers up to 1.3 million km2 and is responsible for muddy bottoms influencing a wide area of the tropical north Atlantic in terms of salinity, pH, light penetration, and sedimentation.[30]
There are nobridges across the entire width of the river.[70] This is not because the river would be too wide to bridge; for most of its length, engineers could build a bridge across the river easily. For most of its course, the river flows through the Amazon Rainforest, where there are very few roads and cities. Most of the time, the crossing can be done by aferry. TheManaus Iranduba Bridge linking the cities of Manaus and Iranduba spans theRio Negro, the second-largest tributary of the Amazon, just before their confluence.
While debate as to whether the Amazon or theNile is the world's longest river has gone on for many years, the historic consensus of geographic authorities has been to regard the Amazon as the second longest river in the world, with the Nile being the longest. However, the Amazon has been reported as being anywhere between 6,275 km (3,899 mi) and 6,992 km (4,345 mi) long.[6] It is often said to be "at least" 6,400 km (4,000 mi) long.[5] The Nile is reported to be anywhere from 5,499 to 7,088 km (3,417 to 4,404 mi).[6] Often it is said to be "about" 6,650 km (4,130 mi) long.[24] There are several factors that can affect these measurements, such as the position of the geographical source and the mouth, the scale of measurement, and the length measuring techniques (for details see alsoList of rivers by length).[6][7]
In July 2008, theBrazilian Institute for Space Research (INPE) published a news article on their webpage, claiming that the Amazon River was 140 km (87 mi) longer than the Nile. The Amazon's length was calculated as 6,992 km (4,345 mi), taking the Apacheta Creek as its source. Using the same techniques, the length of the Nile was calculated as 6,853 km (4,258 mi), which is longer than previous estimates but still shorter than the Amazon. The results were reached by measuring the Amazon downstream to the beginning of the tidal estuary ofCanal do Sul and then, after a sharp turn back, following tidal canals surrounding the isle of Marajó and finally including the marine waters of theRío Pará bay in its entire length.[65][27] According to an earlier article on the webpage ofthe National Geographic, the Amazon's length was calculated as 6,800 km (4,200 mi) by a Brazilian scientist. In June 2007, Guido Gelli, director of science at theBrazilian Institute of Geography and Statistics (IBGE), told London'sTelegraph Newspaper that it could be considered that the Amazon was the longest river in the world.[26] However, according to the above sources, none of the two results was published, and questions were raised about the researchers' methodology. In 2009, apeer-reviewed article, was published, concluding that the Nile is longer than the Amazon by stating a length of 7,088 km (4,404 mi) for the Nile and 6,575 km (4,086 mi) for the Amazon, measured by using a combination of satellite image analysis and field investigations to the source regions.[6]According to theEncyclopædia Britannica, the final length of the Amazon remains open to interpretation and continued debate.[5][27]
The Amazon basin, the largest in the world, covers about 40% of South America, an area of approximately 7,050,000 square kilometres (2,722,020 sq mi). It drains from west to east, fromIquitos in Peru, across Brazil to the Atlantic. It gathers its waters from5 degrees north latitude to20 degrees south latitude. Its most remote sources are found on the inter-Andean plateau, just a short distance from thePacific Ocean.[71]
The Amazon River and its tributaries are characterised by extensive forested areas that become flooded every rainy season. Every year, the river rises more than 9 m (30 ft), flooding the surrounding forests, known asvárzea ("flooded forests"). The Amazon's flooded forests are the most extensive example of this habitat type in the world.[72] In an averagedry season, 110,000 km2 (42,000 sq mi) of land are water-covered, while in thewet season, the flooded area of the Amazon basin rises to 350,000 km2 (140,000 sq mi).[69]
The quantity of water released by the Amazon to the Atlantic Ocean is enormous: up to 300,000 m3/s (11,000,000 cu ft/s) in the rainy season, with an average of 209,000 m3/s (7,400,000 cu ft/s) from 1973 to 1990.[73] The Amazon is responsible for about 20% of the Earth'sfresh water entering the ocean.[72] The river pushes a vast plume of fresh water into the ocean. The plume is about 400 km (250 mi) long and between 100 and 200 km (62 and 124 mi) wide. The fresh water, being lighter, flows on top of the seawater, diluting thesalinity and altering the colour of the ocean surface over an area up to 2,500,000 km2 (970,000 sq mi) in extent. For centuries ships have reported fresh water near the Amazon's mouth yet well out of sight of land in what otherwise seemed to be the open ocean.[32]
Despite this, the Atlantic has sufficient wave and tidal energy to carry most of the Amazon'ssediments out to sea, thus the Amazon does not form a significantriver delta. The great deltas of the world are all in relatively protected bodies of water, while the Amazon empties directly into the turbulent Atlantic.[29]
There is a natural water union between the Amazon and theOrinoco basins, the so-calledCasiquiare canal. The Casiquiare is a riverdistributary of the upper Orinoco, which flows southward into the Rio Negro, which in turn flows into the Amazon. The Casiquiare is the largest river on earth that links two major river systems, a so-calledbifurcation.
NASA satellite image of a flooded portion of the river
Not all of the Amazon's tributaries flood at the same time of the year. Many branches begin flooding in November and might continue to rise until June. The rise of the Rio Negro starts in February or March and begins to recede in June. The Madeira River rises and falls two months earlier than most of the rest of the Amazon river.
The depth of the Amazon betweenManacapuru andÓbidos has been calculated as between 20 and 26 m (66 and 85 ft). At Manacapuru, the Amazon's water level is only about 24 m (79 ft) abovemean sea level. More than half of the water in the Amazon downstream of Manacapuru is below sea level.[82] In its lowermost section, the Amazon's depth averages 20 to 50 m (66 to 164 ft), in some places as much as 100 m (330 ft).[83]
The main river is navigable for large ocean steamers toManaus, 1,500 km (930 mi) upriver from the mouth. Smaller ocean vessels below 9000 tons and with less than 5.5 m (18 ft)draft can reach as far asIquitos, Peru, 3,600 km (2,200 mi) from the sea. Smaller riverboats can reach 780 km (480 mi) higher, as far as Achual Point. Beyond that, small boats frequently ascend to thePongo de Manseriche, just above Achual Point in Peru.[67]
Annual flooding occurs in late northern latitude winter at high tide when the incoming waters of theAtlantic are funnelled into the Amazon delta. The resultingundulartidal bore is called thepororoca, with a leading wave that can be up to 7.6 m (25 ft) high and travel up to 800 km (500 mi) inland.[84][85]
The Amazon River originated as a transcontinental river in theMiocene epoch between 11.8 million and 11.3 million years ago and took its present shape approximately 2.4 million years ago in the EarlyPleistocene.
The proto-Amazon during theCretaceous flowed west, as part of a proto-Amazon-Congo river system, from the interior of present-day Africa when the continents were connected, forming westernGondwana. 80 million years ago, the two continents split. Fifteen million years ago, the maintectonic uplift phase of the Andean chain started. This tectonic movement is caused by the subduction of theNazca Plate underneath theSouth American Plate. The rise of the Andes and the linkage of the Brazilian andGuyana bedrock shields,[clarification needed] blocked the river and caused the Amazon Basin to become a vast inland sea. Gradually, this inland sea became a massive swampy, freshwater lake and the marine inhabitants adapted to life in freshwater.[86]
Eleven to ten million years ago, waters worked through thesandstone from the west and the Amazon began to flow eastward, leading to the emergence of the Amazon rainforest. Duringglacial periods, sea levels dropped and the great Amazon lake rapidly drained and became a river, which would eventually become the disputed world's longest, draining the most extensive area of rainforest on the planet.[87]
Paralleling the Amazon River is a large aquifer, dubbed theHamza River, the discovery of which was made public in August 2011.[88]
More than one-third of all known species in the world live in theAmazon rainforest.[93] It is the richest tropical forest in the world in terms ofbiodiversity.[94] In addition to thousands of species of fish, the river supports crabs, algae, and turtles.
Along with the Orinoco, the Amazon is one of the main habitats of theboto, also known as theAmazon river dolphin (Inia geoffrensis). It is the largest species ofriver dolphin, and it can grow to lengths of up to 2.6 m (8.5 ft). The colour of its skin changes with age; young animals are gray, but become pink and then white as they mature. The dolphins useecholocation to navigate and hunt in the river's tricky depths.[95] Theboto is the subject of a legend in Brazil about adolphin that turns into a man and seduces maidens by the riverside.[96]
Thetucuxi (Sotalia fluviatilis), also a dolphin species, is found both in the rivers of the Amazon basin and in the coastal waters of South America. TheAmazonian manatee (Trichechus inunguis), also known as "seacow", is found in the northern Amazon River basin and its tributaries. It is a mammal and a herbivore. Its population is limited to freshwater habitats, and, unlike other manatees, it does not venture into saltwater. It is classified as vulnerable by theInternational Union for Conservation of Nature.[97]
The Amazon and its tributaries are the main habitat of thegiant otter (Pteronura brasiliensis).[98] Sometimes known as the "river wolf," it is one of South America's top carnivores. Because of habitat destruction and hunting, its population has dramatically decreased. It is now listed on Appendix I of the Convention on International Trade in Endangered Species (CITES), which effectively bans international trade.[99]
Theanaconda is found in shallow waters in the Amazon basin. One of the world's largest species of snake, the anaconda spends most of its time in the water with just its nostrils above the surface. Species ofcaimans, that are related to alligators and other crocodilians, also inhabit the Amazon as do varieties of turtles.[100]
Characins, such as thepiranha species, are prey for thegiant otter, but these aggressive fish may also pose a danger to humans.Theneon tetra is one of the most popular aquarium fish.
The Amazonian fish fauna is the centre of diversity forneotropical fishes, some of which are popular aquarium specimens like theneon tetra and thefreshwater angelfish. More than 5,600 species were known as of 2011[update], and approximately fifty new species are discovered each year.[94]: 308 [45]: 27 Thearapaima, known in Brazil as thepirarucu, is a South American tropicalfreshwater fish, one of the largest freshwater fish in the world, with a length of up to 4.6 metres (15 ft).[101] Another Amazonian freshwater fish is thearowana (oraruanã in Portuguese), such as thesilver arowana (Osteoglossum bicirrhosum), which is a predator and very similar to the arapaima, but only reaches a length of 120 cm (47 in). Also present in large numbers is the notoriouspiranha, an omnivorous fish that congregates in large schools and may attack livestock. There are approximately 30 to 60 species of piranha. Thecandirú, native to the Amazon River, is a species of parasitic fresh watercatfish in the familyTrichomycteridae,[102] just one of more than 1200 species of catfish in the Amazon basin. Other catfish 'walk' overland on their ventral fins,[45]: 27–29 while thekumakuma (Brachyplatystoma filamentosum), akapiraiba or "goliath catfish", can reach 3.6 m (12 ft) in length and 200 kg (440 lb) in weight.[103]
Theelectric eel (Electrophorus electricus) and more than 100 species of electric fishes (Gymnotiformes) inhabit the Amazon basin. River stingrays (Potamotrygonidae) are also known. Thebull shark (Carcharhinus leucas), aeuryhaline species which can thrive in both salt and fresh water, has been reported as far as 4,000 km (2,500 mi) up the Amazon River atIquitos in Peru.[104]
The Amazon River serves as a vital lifeline for more than 47 million people in its basin and faces a multitude of challenges that threaten both its ecosystem and the indigenous communities dependent on its resources. According to the Office of theUnited Nations High Commissioner for Human Rights (OHCHR), theYanomami, a tribe of approximately 30,000, struggles to preserve their land, culture, and traditional way of life due to encroaching illegal gold miners,malnutrition, and malaria. Meanwhile, in 2022, the region's severedrought, has led to a devastating increase in water temperatures, reaching 39.1 degrees Celsius, causing the demise of 125 Amazon river dolphins.[106] This event displays the deteriorating environmental conditions and indicates the increasing vulnerability of the river's ecosystem. In recent years, the Amazon River has experienced historically low water levels, the lowest in over a century. Brazil, the primary custodian of this invaluable natural resource, grapples with the challenges of mitigating the effects of this drought on communities and ecosystems, further emphasizing the urgency of sustainable environmental management and conservation efforts.[107]
^The length of the Amazon River is usually said to be "at least" 6,400 km (4,000 mi),[5] but reported values lie anywhere between 6,275 and 7,025 km (3,899 and 4,365 mi).[6]The length measurements of many rivers are only approximations and differ from each other because many factors determine the calculated river length, such as the position of the geographical source and the mouth, the scale of measurement, and the length measuring techniques (for details see alsoList of rivers by length).[6][7]
^Multiannual average discharge 220,800–223,700 m3/s (7,800,000–7,900,000 cu ft/s)[9][17]
^(Period: 1971–2000) 173,272.6 m3/s (6,119,060 cu ft/s)[19](Period: 1928–1996) 176,177 m3/s (6,221,600 cu ft/s)[21](Period: 01/01/1997–31/12/2015) 178,193.9 m3/s (6,292,860 cu ft/s)[22]
^TheNile is usually said to be the longest river in the world, with a length of about 6,650 km (4,130 mi),[24] and the Amazon the second longest river in the world, with a length of at least 6,400 km (4,000 mi).[5] In 2007 and 2008, some scientists claimed that the Amazon has a length of 6,992 km (4,345 mi) and was longer than the Nile, whose length was calculated as 6,853 km (4,258 mi).[25][26] Apeer-reviewed article, published in 2009, states a length of 7,088 km (4,404 mi) for the Nile and 6,575 km (4,086 mi) for the Amazon, measured by using a combination of satellite image analysis and field investigations to the source regions.[6]According to theEncyclopædia Britannica, as of 2020, the length of the Amazon remains open to interpretation and continued debate.[5][27]
^"Amazon| Origin And Meaning Of Amazon By Online Etymology Dictionary". 2018. Etymonline.Com. Accessed 15 October 2018.[1]Archived 15 October 2018 at theWayback Machine.
^Lundberg, J.G. & B. Chernoff (1992). "A Miocene fossil of the Amazonian fish Arapaima (Teleostei, Arapaimidae) from the Magdalena River region of Colombia--Biogeographic and evolutionary implications".Biotropica.24 (1):2–14.Bibcode:1992Biotr..24....2L.doi:10.2307/2388468.JSTOR2388468.
^abcJianli, Chen; Byron, Tapley; Matt, Rodell; Ki-Weon, Seo; Clark, Wilson; Bridget K., Scanlon; Yadu, Pokhrel (2020). "Basin-Scale River Runoff Estimation From GRACE Gravity Satellites, Climate Models, and in Situ Observations: A Case study in the Amazon Basin".Water Resources Research.56 (10) e2020WR028032.Bibcode:2020WRR....5628032C.doi:10.1029/2020WR028032.S2CID224933962.
^Figueiredo, J.; Hoorn, C.; van der Ven, P.; Soares, E. (2009). "Late Miocene onset of the Amazon River and the Amazon deep-sea fan: Evidence from the Foz do Amazonas Basin".Geology.37 (7):619–22.Bibcode:2009Geo....37..619F.doi:10.1130/g25567a.1.S2CID70646688.
Garfield, Seth.In search of the Amazon: Brazil, the United States and the nature of a region (Duke University Press, 2013)online
Hecht, Susanna, et al. "The Amazon in motion: Changing politics, development strategies, peoples, landscapes, and livelihoods."Amazon Assessment Report 2021, Part II (2021): ch 14 pp 1–65.online, with long bibliography
Nugent, Stephen L.The rise and fall of the Amazon rubber industry: an historical anthropology (Routledge, 2017)online.
Schulze, Frederik, and Georg Fischer. "Brazilian history as global history."Bulletin of Latin American Research 38.4 (2019): 408–422.online
Wohl, Ellen (2011).The Amazon: Rivers of Blushing Dolphins. A World of Rivers. TheUniversity of Chicago Press.
Source:Wills, Fernando; et al. (2001).Nuestro patrimonio – 100 tesoros de Colombia [Our heritage – 100 treasures of Colombia] (in Spanish).El Tiempo. pp. 1–311.ISBN958-8089-16-6.
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