Amazon River

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Amazon
Apurímac, Ene, Tambo, Ucayali, Amazonas, Solimões
 Mouth of the Amazon River
Mouth of the Amazon River
Countries Peru, Colombia, Ecuador, Brazil
Length 6,400 km (3,977 mi)
Watershed 7,050,000 km² (2,722,020 mi²)
Discharge mouth
 - average 219,000 /s (7,733,912 ft³/s)
Source Apurímac
 - location Nevado Mismi, Peru
 - coordinates 15°31′05″S, 71°45′55″W
 - elevation 5,170 m (16,962 ft)
Mouth
 - location Atlantic Ocean, Brazil
 - elevation m (0 ft)
Major tributaries
 - left Marañón, Japurá, Rio Negro
 - right Purús, Madeira, Tapajós, Xingú, Tocantins
 Map showing the course of the Amazon, selected tributaries, and the approximate extent of its drainage area
Map showing the course of the Amazon, selected tributaries, and the approximate extent of its drainage area
This article is about the river. For other uses, see Amazon (disambiguation)

The Amazon River or River Amazon (Portuguese: Rio Amazonas; Spanish: Río Amazonas) of South America is the largest river in the world by volume, with greater total river flow than the next eight largest rivers combined, and the largest drainage basin in the world. Because of its vast dimensions it is sometimes called The River Sea. Most sources regard the Amazon as the second longest river; however, some sources disagree. The Amazon has been measured by different geographers as being anywhere between 6,259 kilometres (3,889 mi) and 6,712 kilometres (4,171 mi) long. The Nile River in Africa is reported to be anywhere from at 5,499 kilometres (3,417 mi) to 6,690 kilometres (4,157 mi).

The area covered by the water of the River and its tributaries more than triples over the course of a year. In an average dry season 110,000 square kilometres (42,000 mi²) of land are water-covered, while in the wet season the flooded area of the Amazon Basin rises to 350,000 square kilometres (135,000 mi²).[citation needed] At its widest point the Amazon River can be 11 kilometres (7 mi) wide during the dry season, but during the rainy season when the Amazon floods the surrounding plains it can be up to 40 kilometres (25 mi) wide.

A satellite image of the mouth of the Amazon River, looking south
A satellite image of the mouth of the Amazon River, looking south

The quantity of fresh water released by the Amazon to the Atlantic Ocean is enormous: up to 300,000 m³ per second in the rainy season. The Amazon is responsible for a fifth of the total volume of fresh water entering the oceans worldwide. Offshore of the mouth of the Amazon, potable water can be drawn from the ocean while still out of sight of the coastline, and the salinity of the ocean is notably lower a hundred miles out to sea.

The Amazon estuary is over 325 kilometres (202 mi) wide. The main river (which is between approximately one and six miles wide) is navigable for large ocean steamers to Manaus, 1,500 kilometres (930 mi) upriver from the mouth. Smaller ocean vessels of 3,000 tons[1] and 5.5 metres (18 ft) draft can reach as far as Iquitos, Peru, 3,600 kilometres (2,240 mi) from the sea. Smaller riverboats can reach 780 kilometres (485 mi) higher as far as Achual Point. Beyond that, small boats frequently ascend to the Pongo de Manseriche, just above Achual Point.

The Amazon drains an area of some 6,915,000 square kilometres (2,670,000 mi²), or some 40 percent of South America. It gathers its waters from 5 degrees north latitude to 20 degrees south latitude. Its most remote sources are found on the inter-Andean plateau, just a short distance from the Pacific Ocean.

The Amazon has changed its course several times. In early Cenozoic times, before the uplifting of the Andes, it flowed westward.[2]

Contents

[edit] Source and Upper Amazon

The Amazon originates from a cliff at the Nevado Mismi, with a sole sign of a wooden cross.
The Amazon originates from a cliff at the Nevado Mismi, with a sole sign of a wooden cross.

The Upper Amazon comprises a series of major river systems in Peru (many of which originate in Ecuador) that flow north and south into the Marañón and Amazon. Among others, these include the following rivers: Morona; Pastaza; Nucuray; Urituyacu; Chambira; Tigre; Nanay; Napo; Huallaga; and Ucayali. Originating in the snow-crested Andes high above Lake Lauricocha in central Peru, the headstream of the Marañón River rises in the glaciers in what is known as the Nevado de Yarupa. Rushing through waterfalls and gorges in an area of the high jungle called the pongos, the Marañón River flows about 1,000 miles (1,600 km) from west-central to northeast Peru before it combines with the Ucayali River, just below the provincial town of Nauta, to form the mighty Amazon River. The primary tributaries of the Marañón River are--from south to north--the Crisnejas, Chamayo, Urtcubamba, Cenepa, Santiago, Moroña, Pastaza, Huallaga, and Tiger Rivers (Cavero-Egusquiza 1941:49-51).

The most distant source of the Amazon has only recently been firmly established as a glacial stream on a snowcapped 5,597 m (18,363 ft) peak called Nevado Mismi[3] in the Peruvian Andes, roughly 160 km (100 mi) west of Lake Titicaca and 700 km (430 mi) southeast of Lima. The mountain was first suggested as the source in 1971 but this was not confirmed until 2001. The waters from Nevado Mismi flow into the Quebradas Carhuasanta and Apacheta, which flow into the Río Apurímac which is a tributary of the Ucayali which later joins the Marañón to form the Amazon proper. Formally, though, the union of the Ucayali and the Marañón form the Río Amazonas, which changes its name to Solimões on the triple frontier between Peru, Colombia and Brazil, and later changes its name back to the Amazon only after it meets the Rio Negro near Manaus.

After the confluence of Río Apurímac and Ucayali, the river leaves Andean terrain and is instead surrounded by flood plain. From this point to the Marañón, some 1,600 km (990 mi), the forested banks are just out of water, and are inundated long before the river attains its maximum flood-line. The low river banks are interrupted by only a few hills, and the river enters the enormous Amazon Rainforest.

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".

[edit] Amazonian Rainforest

Amazon rainforest
Amazon rainforest
Main article: Amazon Rainforest

From the east of the Andes, the Amazon Rainforest begins. It is the largest rainforest in the world and is of great ecological significance, as its biomass is capable of absorbing enormous amounts of carbon dioxide. Conservation of the Amazon Rainforest has been a major issue in recent years.

The rainforest is supported by the extremely wet climate of the Amazon basin. The Amazon, and its hundreds of tributaries, flow slowly across the landscape, with an extremely shallow gradient sending them towards the sea: Manaus, 1,600 km (1,000 mi) from the Atlantic, is only 44 m (144 ft) above sea level.

The biodiversity within the rainforest is extraordinary: the region is home to at least 2.5 million insect species, tens of thousands of plants, and some 2,000 birds and mammals. One fifth of all the world's species of birds can be found in the Amazon rainforest.

The diversity of plant species in the Amazon basin is the highest on Earth. Some experts estimate that one square kilometre may contain over 75,000 types of trees and 150,000 species of higher plants. One square kilometre of Amazon rainforest can contain about 90,000 tons of living plants.

[edit] Flooding

A NASA satellite image of a flooded portion of the river.
A NASA satellite image of a flooded portion of the river.

The average depth of the river in the height of the rainy season is 40 m (131 ft) and the average width can be nearly 25 mi (40 km)[citation needed]. It starts to rise in November, and increases in volume until June, then falls until the end of October. The rise of the Negro branch is not synchronous; the rainy season does not commence in its valley until February or March. By June it is full, and then it begins to fall with the Amazon. The Madeira rises and falls two months earlier than the Amazon.

[edit] Towards the sea

The breadth of the Amazon in some places is as much as 6 km (4 mi) to 10 km (6 mi) from one bank to the other[citation needed]. At some points, for long distances, the river divides into two main streams with inland and lateral channels, all connected by a complicated system of natural canals, cutting the low, flat igapo lands, which are never more than 5 m (16 ft) above low river, into many islands.

At the narrows of Óbidos, 600 km (370 mi) from the sea, the Amazon narrows, flowing in a single streambed, 1.6 km (1 mi) wide and over 60 m (197 ft) deep, through which the water rushes toward the sea at the speed of 6 km/h (4 mi/h) to 8 km/h (5 mi/h).

The Amazon near Manaus
The Amazon near Manaus

From the village of Canaria at the great bend of the Amazon to the Negro 1,000 km (600 mi) downstream, only very low land is found, resembling that at the mouth of the river. Vast areas of land in this region 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. At Óbidos, a bluff 17 m (56 ft) above the river is backed by low hills. The lower Amazon seems to have once been a gulf of the Atlantic Ocean, the waters of which washed the cliffs near Óbidos.

Only about 10% of the water discharged by the Amazon enters the mighty stream downstream of Óbidos, very little of which is from the northern slope of the valley. The drainage area of the Amazon basin above Óbidos is about 5 million km² (2 million mile²), and, below, only about 1 million km² (400,000 mile²), or around 20%, exclusive of the 1.4 million km² (600,000 mile²) of the Tocantins basin.

In the lower reaches of the river, the north bank consists of a series of steep, table-topped hills extending for about 240 km (149 mi) from opposite the mouth of the Xingu as far as Monte Alegre. These hills are cut down to a kind of terrace which lies between them and the river.

Monte Alegre reaches an altitude of several hundred feet. On the south bank, above the Xingu, an almost-unbroken line of low bluffs bordering the flood-plain extends nearly to Santarem, in a series of gentle curves before they bend to the south-west, and, abutting upon the lower Tapajos, merge into the bluffs which form the terrace margin of the Tapajos river valley.

[edit] Mouth of the river

Mouth of the Amazon River
Mouth of the Amazon River

The width of the mouth of the river is usually measured from Cabo do Norte to Punto Patijoca, a distance of some 330 km (207 mi); but this includes the ocean outlet, 60 km (40 mi) wide, of the Para river, which should be deducted, as this stream is only the lower reach of the Tocantins. It also includes the ocean frontage of Marajó, an island lying in the mouth of the Amazon.

[edit] Tidal bore

Following the coast, a little to the north of Cabo do Norte, and for 160 kilometres (99 mi) along its Guiana margin up the Amazon, is a belt of half-submerged islands and shallow sandbanks. Here the tidal phenomenon called the bore, or pororoca, occurs, where the depths are not over 7 metres (23 ft). The tidal bore starts with a roar, constantly increasing, and advances at the rate of from 15 km/h (9 mi/h) to 25 km/h (16 mi/h), with a breaking wall of water from 1.5 m (5 ft) to 4 m (13 ft) high. The bore is the reason the Amazon does not have a delta; the ocean rapidly carries away the vast volume of silt carried by the Amazon, making it impossible for a delta to grow. It also has a very large tide sometimes reaching 20 feet (6 m) and has become a popular spot for river surfing.[1]

Amazon River at dawn
Amazon River at dawn

[edit] Wildlife

The waters of the Amazon support a diverse range of wildlife. Along with the Orinoco, the river is one of the main habitats of the Boto, also known as the Amazon River Dolphin. The largest species of river dolphin, it can grow to lengths of up to 2.6 metres (9 ft).

Also present in large numbers are the notorious Piranha, carnivorous fish which congregate in large schools, and may attack livestock and even humans. Although many experts believe their reputation for ferocity is unwarranted, a school of piranha was apparently responsible for the deaths of up to 300 people when their boat capsized near Óbidos in 1981.[citation needed] However, only a few species attack humans, and many are solely fish-eaters, and do not school.

The Anaconda snake 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. Anacondas have been known to occasionally attack fishermen.

The river also supports thousands of species of fish, as well as crabs and turtles.

[edit] The Colonial Encounter & Amazonia

During what many archaeologists call the formative period, Amazonian societies were deeply implicated in the emergence of South America's highland agrarian systems, and possibly contributed directly to the social and religious fabric constitutive of the Andean civilizational orders[2].

For 350 years after the European discovery of the mighty Amazon by Pinzon, the Portuguese portion of the basin remained a virtually undisturbed wilderness, occupied by Indigenous peoples. While there is ample evidence for large-scale, pre-Columbian social formations, including chiefdoms, in many areas of Amazonia (particularly the inter-fluvial regions) the former indigenous inhabitants probably had relatively low population densities.

In what is currently Brazil, Ecuador, Bolivia, Colombia, Peru, and Venezuela a number of colonial and religious settlements were established along the banks of primary rivers and tributaries for the purpose of trade, slaving and evangelization among the putatively savage indigenous peoples of the vast rain forest.

The total population of the Brazilian portion of the Amazon basin in 1850 was perhaps 300,000, of whom about two-thirds comprised by Europeans and slaves, the slaves amounting to about 25,000. In Brazil, the principal commercial city, Para (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 from 1,000 to 1,500 population. All the remaining villages, as far up as Tabatinga, on the Brazilian frontier of Peru, were relatively small.

On September 6, 1850, the emperor, Dom Pedro II, sanctioned a law authorizing steam navigation on the Amazon, and gave Barão de Mauá (Irineu Evangilista de Sousa) the task of putting it into effect. He organized the "Compania de Navigacao e Commercio do Amazonas" at Rio de Janeiro in 1852; and in the following year it commenced operations with three small steamers, the Monarch, the Marajó and Rio Negro.

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 Para and Cameta. 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, Purus 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.

On July 31 1867 the government of Brazil, constantly pressed by the maritime powers and by the countries encircling the upper Amazon basin, especially Peru, decreed the opening of the Amazon to all flags; but limited this to certain defined points: Tabatinga—on the Amazon; Cameta—on the Tocantins; Santarem—on the Tapajos; Borba—on the Madeira and Manáos—on the Rio Negro. The Brazilian decree took effect on 7 September 1867.

Thanks in part to the mercantile development associated with steam boat navigation, coupled with the internationally driven demand for natural rubber (1880-1920), Manáos (now Manaus), Para (Brasil), and Iquitos, Peru became thriving, cosmopolitan centers of commerce and spectular—albeit illusory—modern "urban growth". This was particularly the case for Iquitos during its late 19th and early 20th century Rubber Bonanza zenith when this dynamic boom-town was known abroad as the St. Louis of the Amazon.

The first direct foreign trade with Manáos was 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, Purfis and many other tributaries, such as the Marañón to ports as distant as Nauta, Peru.

By the turn of the 20th century, the principal exports of the Amazon Basin were india-rubber, cacao, Brazil nuts and a few other products of minor importance, such as pelts and exotic forest produce (resins, barks, woven hammocks, prized bird feathers, live animals, etc.) and extracted goods (lumber, gold, etc.).

[edit] 20th century concerns

Four centuries after the European discovery of the Amazon river, the total cultivated area in its basin was probably less than 25 square miles (65 km²), excluding the limited and crudely cultivated areas among the mountains at its extreme headwaters. This situation changed dramatically during the 20th century.

Manaus, the largest city on the Amazon, as seen from a NASA satellite image, surrounded by the muddy Amazon River and the dark Negro River.
Manaus, the largest city on the Amazon, as seen from a NASA satellite image, surrounded by the muddy Amazon River and the dark Negro River.

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 President Getúlio Vargas, the demand for rubber from the Allied forces in World War II providing funding for the drive.

The construction of the new capital Brasilia in the interior in 1960 also contributed to the opening up of the Amazon basin. A large scale colonization program saw families from north-eastern Brazil relocated to the forests, encouraged by promises of cheap land. Many settlements grew along the road from Brasilia to Belém, but rainforest soil proved difficult to cultivate.

Still, long-term development plans continued. Roads were cut through the forests, and in 1970, the work on Trans-Amazon highway network began. The network's three pioneering highways were completed within ten years, connecting all the major cities of the Brazilian Amazon interior.

Cattle farming became a major impetus in deforestation, with military governments in the 1960s and 1970s heavily subsidising the creation of large ranches. By the 1980s the rate of destruction of the rainforest was dizzying, and it is estimated that over a fifth of the total area of the rainforest has now been clearcut. The preservation of the remaining forest is becoming an ever more prominent concern.

[edit] Major tributaries

The Amazon has over 1,000 tributaries in total. Some of the more notable:

  

[edit] Longest rivers in the Amazon system

  1. 6,387 km (3,969 mi) - Amazon, South America
  2. 3,379 km (2,100 mi) - Purus, Peru / Brazil, (2,948 km) (3,210 km)[citation needed]
  3. 3,239 km (2,013 mi) - Madeira, Bolivia / Brazil
  4. 2,820 km (1,752 mi) - Yapura, Colombia / Brazil
  5. 2,750 km (1,709 mi) - Tocantins, Brazil, (2,416 km) (2,640 km)[citation needed]
  6. 2,575 km (1,600 mi) - Araguaia, Brazil (tributary of Tocantins)
  7. 2,410 km (1,498 mi) - Juruá, Peru / Brazil
  8. 2,250 km (1,398 mi) - Negro, South America
  9. 2,100 km (1,305 mi) - Xingu, Brazil
  10. 1,900 km (1,181 mi) - Tapajós, Brazil
  11. 1,749 km (1,087 mi) - Guaporé, Brazil / Bolivia (tributary of Madeira)
  12. 1,575 km (979 mi) - Içá (Putumayo), South America
  13. 1,415 km (879 mi) - Marañón, Peru
  14. 1,300 km (808 mi) - Iriri, Brazil (tributary of Xingu)
  15. 1,240 km (771 mi) - Juruena, Brazil (tributary of Tapajós)
  16. 1,200 km (746 mi) - Tapajós, Brazil
  17. 1,130 km (702 mi) - Madre de Dios, Peru / Bolivia (tributary of Madeira)
  18. 1,100 km (684 mi) - Huallaga, Peru (tributary of Marañón)

[edit] References

  1. ^ Amazon uk.encarta.msn.com. Retrieved 1 October 2006.
  2. ^ BBC News - Science/Nature - "Amazon river 'switched direction'." Published 24 October 2006. Retrieved 25 October 2006.
  3. ^ Explorers Pinpoint Source of the Amazon

[edit] External links

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