Editing Amazon River (section)

== Course ==
=== Origins ===
{{main|Source of the Amazon River}}
[[File:Amazon origin at Mismi.jpg|thumb|left|upright|The Amazon was thought to originate from the Apacheta cliff in [[Arequipa]] at the [[Nevado Mismi]], marked only by a wooden cross.]]
[[File:The Source of the Amazon River.jpg|thumb|upright=1.3|Nevado Mismi, formerly considered to be the source of the Amazon]]
[[File:Río Marañón 03245.JPG|thumb|[[Marañón River]] in Peru]]

<!--see talk page re most distant source. 15 November 2015-->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,<ref name=Palkiewicz>{{cite web |url=http://www.palkiewicz.com/ekspedycje/index.php?p=zrodl_amaz |title=Source of the Amazon River Identificated (Jacek Palkiewicz) |publisher=Palkiewicz.com |date=19 November 1999 |access-date=13 February 2011 |url-status=live |archive-url=https://web.archive.org/web/20070312092613/http://www.palkiewicz.com/ekspedycje/index.php?p=zrodl_amaz |archive-date=12 March 2007}}</ref> 2001,<ref>{{cite magazine |url=http://news.nationalgeographic.com/news/2000/12/1221amazon.html |last=Smith |first=Donald |title=Explorers Pinpoint Source of the Amazon (National Geographic News) |magazine=National Geographic |date=21 December 2000 |access-date=15 July 2017 |archive-url=https://web.archive.org/web/20171101075405/https://news.nationalgeographic.com/news/2000/12/1221amazon.html |archive-date=1 November 2017}}</ref> 2007,<ref name=bbc-amazon>{{cite news |title=Amazon river 'longer than Nile' |work=BBC News |url=http://news.bbc.co.uk/2/hi/6759291.stm |access-date=3 August 2010 |date=16 June 2007 |url-status=live |archive-url=https://web.archive.org/web/20100926054938/http://news.bbc.co.uk/2/hi/6759291.stm |archive-date=26 September 2010 |df=dmy-all}}</ref> and 2008,<ref name=inpe>{{cite web |title=Studies from INPE indicate that the Amazon River is 140&nbsp;km longer than the Nile |publisher=Brazilian National Institute for Space Research |url=http://www.inpe.br/ingles/news/news_dest29.php |access-date=3 August 2010 |archive-url=https://web.archive.org/web/20110411011122/http://www.inpe.br/ingles/news/news_dest29.php |archive-date=11 April 2011}}</ref> where various authors identified the snowcapped {{cvt|5597|m|sp=us}} [[Nevado Mismi]] peak, located roughly {{cvt|160|km|sp=us}} west of [[Lake Titicaca]] and {{cvt|700|km|sp=us}} southeast of [[Lima]], as the most distant source of the river. From that point, Quebrada [[Carhuasanta]] emerges from Nevado Mismi, joins Quebrada Apacheta and soon forms Río Lloqueta which becomes Río Hornillos and eventually joins the [[Apurímac River|Río Apurímac]].

A 2014 study by Americans James Contos and Nicolas Tripcevich in ''[[Area (journal)|Area]]'', a peer-reviewed journal of the [[Royal Geographical Society]], however, identifies the most distant source of the Amazon as actually being in the [[Mantaro River|Río Mantaro]] drainage.<ref name="ContosTripcevich" /> 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 from [[Lake Junin|Lago 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 the [[International Scale of River Difficulty|class 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&nbsp;km farther upstream compared to Mt. Mismi in the Apurímac drainage, and thus the maximal length of the Amazon river is about 80&nbsp;km longer than previously thought. Contos continued downstream to the ocean and finished the first complete descent of the Amazon river from its newly identified source (finishing November 2012), a journey repeated by two groups after the news spread.<ref>{{cite web |url=http://blog.geographydirections.com/2014/04/03/redefining-the-upper-amazon-river |last=Contos |first=James (Rocky) |title=Redefining the Upper Amazon River |website=Geography Directions |date=3 April 2014 |access-date=15 July 2017 |url-status=live |archive-url=https://web.archive.org/web/20170312152411/https://blog.geographydirections.com/2014/04/03/redefining-the-upper-amazon-river/ |archive-date=12 March 2017}}</ref>

After about {{cvt|700|km|mi}}, the Apurímac then joins Río Mantaro to form the Ene, which joins the Perene to form the Tambo, which joins the [[Urubamba River]] to form the Ucayali. After the confluence of Apurímac and Ucayali, the river leaves Andean terrain and is surrounded by [[floodplain]]. From this point to the confluence of the Ucayali and the Marañón, some {{cvt|1600|km|sp=us}}, the forested banks are just above the water and are inundated long before the river attains its maximum flood stage.{{sfn|Church|1911|p=789}} The low river banks are interrupted by only a few hills, and the river enters the enormous [[Amazon rainforest]].

=== The Upper Amazon or Solimões ===
[[File:Amazonas, Iquitos - Leticia, Kolumbien (11472506936).jpg|thumb|Amazon River near [[Iquitos]], Peru]]

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 the ''[[Solimões]] das Águas''. The river systems and flood plains in Brazil, Peru, Ecuador, Colombia, and Venezuela, whose waters drain into the ''Solimões'' and its tributaries, are called the "Upper Amazon".

The Amazon proper runs mostly through Brazil and Peru, and is part of the border between Colombia and Peru. It has a series of major tributaries in [[Colombia]], [[Ecuador]] and [[Peru]], some of which flow into the [[Marañón River|Marañón]] and [[Ucayali]], and others directly into the Amazon proper. These include rivers [[Putumayo River|Putumayo]], [[Caquetá River|Caquetá]], [[Vaupés River|Vaupés]], [[Rio Negro (Amazon)|Guainía]], [[Morona]], [[Pastaza River|Pastaza]], Nucuray, Urituyacu, [[Chambira River|Chambira]], [[Tigre River|Tigre]], [[Nanay River|Nanay]], [[Napo River|Napo]], and [[Huallaga River|Huallaga]].

At some points, the river divides into [[anabranch]]es, or multiple channels, often very long, with inland and lateral [[Stream channel|channels]], all connected by a complicated system of natural canals, cutting the low, flat ''igapó'' lands, which are never more than {{cvt|5|m|sp=us}} above low river, into many islands.{{sfn|Church|1911|p=788}}

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.{{sfn|Church|1911|p=789}}

=== The Lower Amazon ===
[[File:Manaus Encontro das aguas 10 2006 103 8x6.jpg|thumb|[[Meeting of Waters]]; the [[confluence]] of [[Rio Negro (Amazon)|Rio Negro]] (blue) and [[Solimões|Rio Solimões]] (sandy) near [[Manaus]], Brazil]]
[[File:Rio Solimoes and Rio Negro.JPG|thumb|Water samples of the [[Solimões]] (right) and [[Rio Negro (Amazon)|Rio Negro]] (left)]]

The Lower Amazon begins where the darkly colored waters of the Rio Negro meets the sandy-colored [[Solimões|Rio Solimões]] (the upper Amazon), and for over {{cvt|6|km|sp=us}} these waters [[Meeting of Waters|run side by side without mixing]]. At Óbidos, a bluff {{cvt|17|m|sp=us}} above the river is backed by low hills. The lower Amazon seems to have once been a [[bay|gulf]] 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 {{cvt|5000000|km2|sp=us}}, and, below, only about {{cvt|1000000|km2|sp=us}} (around 20%), exclusive of the {{cvt|1400000|km2|sp=us}} of the Tocantins basin.{{sfn|Church|1911|p=789}} The [[Tocantins River]] enters the southern portion of the [[Amazon delta]].

In the lower reaches of the river, the north bank consists of a series of steep, table-topped hills extending for about {{cvt|240|km|sp=us}} from opposite the mouth of the Xingu as far as [[Monte Alegre, Pará|Monte Alegre]]. These hills are cut down to a kind of [[Terrace (agriculture)|terrace]] which lies between them and the river.{{sfn|Church|1911|p=788}}

On the south bank, above the Xingu, a line of low bluffs bordering the floodplain extends nearly to [[Santarém, Brazil|Santarém]] 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.{{sfn|Church|1911|pp=788–89}}

=== Mouth ===
[[File:Amazon-river-delta-NASA.jpg|thumb|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. The [[Pará River|Pará]] and the Amazon are connected by a series of river channels called ''furos'' near the town of [[Breves, Pará|Breves]]; between them lies [[Marajó]], the world's largest combined river/sea island.

If the Pará river and the Marajó island ocean frontage are included, the Amazon [[estuary]] is some {{cvt|325|km|sp=us}} wide.<ref name=guo /> In this case, the width of the mouth of the river is usually measured from Cabo Norte, the cape located straight east of [[Pracuúba]] in the Brazilian state of [[Amapá]], to Ponta da Tijoca near the town of [[Curuçá]], in the state of [[Pará]].

A more conservative measurement excluding the Pará river estuary, from the mouth of the [[Araguari River (Amapá)|Araguari River]] to Ponta do Navio on the northern coast of [[Marajó]], would still give the mouth of the Amazon a width of over {{cvt|180.|km|sp=us}}. 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 {{cvt|15|km|sp=us}}.

The plume generated by the river's discharge covers up to 1.3 million km<sup>2</sup> and is responsible for muddy bottoms influencing a wide area of the tropical north Atlantic in terms of salinity, pH, light penetration, and sedimentation.<ref name="auto" />

=== Lack of bridges ===
There are no [[bridge]]s across the entire width of the river.<ref>{{cite web |url=http://encarta.msn.com/encyclopedia_761571466/Amazon_(river).html |title=Amazon (river) |publisher=Microsoft Encarta Online Encyclopedia |edition=2007 |access-date=12 August 2007 |archive-url=https://web.archive.org/web/20080306073804/http://encarta.msn.com/encyclopedia_761571466/Amazon_%28river%29.html |archive-date=6 March 2008}}</ref> 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 a [[ferry]]. The [[Manaus Iranduba Bridge]] linking the cities of Manaus and Iranduba spans the [[Rio Negro (Amazon)|Rio Negro]], the second-largest tributary of the Amazon, just before their confluence.

=== Dispute regarding length ===
[[File:Amazon River Taxi.jpg|thumb|River taxi in Peru]]
{{see also|Coastline paradox}}

While debate as to whether the Amazon or the [[Nile]] 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 {{cvt|6275|km|sp=us}} and {{cvt|6992|km|sp=us}} long.<ref name=liu-etal-river-length /> It is often said to be "at least" {{cvt|6575|km|sp=us}} long.<ref name=britannica-amazon /> The Nile is reported to be anywhere from {{cvt|5499|to|7088|km|sp=us}}.<ref name=liu-etal-river-length /> Often it is said to be "about" {{cvt|6650|km|sp=us}} long.<ref name=britannica-nile>{{cite encyclopedia |title=Nile River |encyclopedia=[[Encyclopædia Britannica]] |year=2010 |url=https://www.britannica.com/EBchecked/topic/415347/Nile-River |access-date=3 August 2010 |url-status=live |archive-url=https://web.archive.org/web/20150429130526/https://www.britannica.com/EBchecked/topic/415347/Nile-River |archive-date=29 April 2015 |df=dmy-all}}</ref> 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 also [[List of rivers by length]]).<ref name=liu-etal-river-length /><ref name=river-source />

In July 2008, the [[National Institute for Space Research|Brazilian Institute for Space Research (INPE)]] published a news article on their webpage, claiming that the Amazon River was {{cvt|140|km|sp=us}} longer than [[Nile|the Nile]]. The Amazon's length was calculated as {{cvt|6992|km|sp=us}}, taking the Apacheta Creek as its source. Using the same techniques, the length of the Nile was calculated as {{cvt|6853|km|sp=us}}, 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 of ''Canal do Sul'' and then, after a sharp turn back, following tidal canals surrounding the isle of Marajó and finally including the marine waters of the ''Río Pará'' bay in its entire length.<ref name=inpe /><ref name=britannica-amazon-length /> According to an earlier article on the webpage of [[National Geographic|the National Geographic]], the Amazon's length was calculated as {{cvt|6800|km|sp=us}} by a Brazilian scientist. In June 2007, [[Guido Gelli]], director of science at the [[Brazilian Institute of Geography and Statistics]] (IBGE), told London's [[The Daily Telegraph|Telegraph]] Newspaper that it could be considered that the Amazon was the longest river in the world.<ref name=Roach/> However, according to the above sources, none of the two results was published, and questions were raised about the researchers' methodology. In 2009, a [[Scholarly peer review|peer-reviewed]] article, was published, concluding that the Nile is longer than the Amazon by stating a length of {{cvt|7088|km|sp=us}} for the Nile and {{cvt|6575|km|sp=us}} for the Amazon, measured by using a combination of satellite image analysis and field investigations to the source regions.<ref name="liu-etal-river-length" />
According to the [[Encyclopædia Britannica]], the final length of the Amazon remains open to interpretation and continued debate.<ref name=britannica-amazon /><ref name=britannica-amazon-length />