Science Fair Project Encyclopedia
The Amazon River (occasionally River Amazon; Spanish: Río Amazonas, Portuguese: Rio Amazonas) of South America is one of the longest two rivers on Earth, the Nile River in Africa being the other. The Amazon has by far the greatest total flow of any river, carrying more water than the Mississippi, Nile, and Yangtze Rivers combined. It also has the largest drainage area of any river system.
The quantity of fresh water released to the Atlantic Ocean is enormous: 6.5 million cubic feet per second (184,000 m³/s) in the rainy season. Indeed, the Amazon is responsible for a fifth of the total volume of fresh water entering the oceans worldwide. It is said that 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 main river (which is usually between one and six miles wide) is navigable for ocean steamers as far as Iquitos, 2300 miles (3,700 km) from the sea, and 486 miles (780 km) higher up for smaller vessels, 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 6,915,000km² (2,722,000 mile²), 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; and, after a course of about 7200 km (4800 miles) through the interior of Peru and across Brazil, it enters the Atlantic Ocean at the equator.
Source and upper reaches
The ultimate source of the Amazon has only recently been firmly established as a stream on a 5,597 metre (18,363 ft) peak called Nevado Mismi in the Peruvian Andes, roughly 160 km (100 miles) N.N.E. of Lima. The mountain was first suggested as the source in 1971 but this was not confirmed until 2001. The stream from Nevado Mismi flows into Lake Lauricocha and then the Apurímac River. The Apurímac is a tributary of the Ucayali, which joins the Marañón to form the Amazon proper.
Below its confluence with the Huallaga, the river leaves Andean terrain and is instead surrounded by flood plain. From this point to the Ucayali, some 1500 miles (2,400 km), 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.
Main article: Amazon Rainforest
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, 1,000 miles (1600 km) from the Atlantic, is only 144 feet (44 m) 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 2000 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.
Seasonal rains give rise to extensive floods along the course of the Amazon and its tributaries. The average depth of the river in the height of the rainy season is 120 ft (40 m) and the average width can be nearly twenty-five miles. 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.
In the rainy season, the Amazon inundates the country throughout its course to the extent of several hundred thousand square miles, covering the flood-plain, called vargem . The flood-levels are, in some places, from 40 to 50 ft (12 to 15 m) higher than levels during the dry season. During the flood, the level at Iquitos is 20 ft (6 m); at Teffe, it is 45 ft (15 m); near Obidos, 35 ft (11 m); and at Para, 12 ft (4 m), above the low-water extreme seen during the dry season.
Towards the sea
The breadth of the Amazon in some places is as much as 4 to 6 miles (6 to 10 km) from one bank to the other. 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 15 ft (5 m) above low river, into almost numberless islands.
At the narrows of Óbidos, 400 miles (600 km) from the sea, the Amazon narrows, flowing in a single streambed, a mile (1.6 km) wide and over 200 ft (60 m). deep, through which the water rushes toward the sea at the speed of 4 to 5 mph (6 to 8 km/h).
From the village of Canaria at the great bend of the Amazon to the Negro 600 miles (1000 km) 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 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 Obidos, very little of which is from the northern slope of the valley. The drainage area of the Amazon basin above Óbidos is about 1,945,000 mile² (5 million km²), and, below, only about 423,000 mile² (1 million km²), or around 20%, exclusive of the 554,000 mile² (1.4 million km²) 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 150 miles (240 km) 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.
Mouth of the river
The width of the mouth of the river is usually measured from Cabo do Norte to Punto Patijoca , a distance of some 207 miles (330 km); but this includes the ocean outlet, 40 miles (60 km) 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 Marajo, an island about the size of Denmark lying in the mouth of the Amazon.
Following the coast, a little to the north of Cabo do Norte, and for 100 miles (160 km) 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 4 fathoms (7 m). The tidal bore starts with a roar, constantly increasing, and advances at the rate of from 10 to 15 mph (15 to 25 km/h, with a breaking wall of water from 5 to 12 ft (1.5 to 4 m) 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.
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 m.
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 Obidos in 1981.
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 very occasionally to attack fishermen.
The river also supports thousands of species of fish, as well as crabs and turtles.
The first ascent by a European of the river was made in 1638 by Pedro Teixeira, a Portuguese, who reversed the route of Orellana and reached Quito by way of the Napo River. He returned in 1639 with the two Jesuit fathers Acuna and Artieda , who had been delegated by the viceroy of Peru to accompany Texeira.
Before the conquest of South America, the Río de las Amazonas had no general name; instead, indigenous peoples had names for the sections of the river they occupied, such as Paranaguazu , Guyerma , Solimões and others.
In the year 1500, Vicente Yañez Pinzon, in command of a Spanish expedition, became the first European to explore the river, exploring its mouth when he discovered that the ocean off the shore was fresh water. Pinzon called the river the Rio Santa Maria de la Mar Dulce, which soon became abbreviated to Mar Dulce, and for some years, after 1502, it was known as the Rio Grande.
Pinzon's companions called the river El Río Marañón. The word Marañón is thought by some to be of indigenous origin. This idea was first stated in a letter from Peter Martyr to Lope Hurtado de Mendoza in 1513. However, the word may also be derived from the Spanish word "maraña" — meaning a tangle, a snarl, which well represents the bewildering difficulties which the earlier explorers met in navigating not only the entrance to the Amazon, but the whole island-bordered, river-cut and indented coast of what is now the Brazilian state of Maranhão.
The name Amazon arises from a battle which Francisco de Orellana had with a tribe of Tapuyas where the women of the tribe fought alongside the men, as was the custom among the entire tribe. Orellana derived the name Amazonas from the ancient Amazons of Asia and Africa described by Herodotus and Diodorus.
For 350 years after the European discovery of the Amazon by Pinzon, the Portuguese portion of its basin remained an almost undisturbed wilderness, occupied by indigenous tribes split into countless fragments by their quest for food. Because of the difficulty of hunting and gathering food, the indigenous inhabitants probably had a population density no higher than one person to every 5 sq. miles of territory -
A few settlements on the banks of the main river and some of its tributaries had been founded by the Portuguese either for trade with the Indians or for evangelizing purposes. 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.
The principal commercial city, Para , 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 1000 to 1500 population. All the remaining villages, as far up as Tabatinga , on the Brazilian frontier of Peru, were very small.
On September 6 1850, the emperor, Dom Pedro II, sanctioned a law authorizing steam navigation on the Amazon, and gave Barao Maua (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 "Marajo" 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 Para and Manáos, with steamers of 200 tons cargo capacity, a second line to make six round voyages a year between Manaós 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 Para and Manáos; 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, 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 decree took effect on September 7, 1867.
Manáos (now Manaus), Para and Iquitos are now thriving commercial centres. The first direct foreign trade with Manáos was commenced about 1874. The local trade of the river was carried on by the English successors to the Amazonas Company - the Amazon Steam Navigation Company - as well as numerous small river steamers, belonging to companies and firms engaged in the rubber trade, navigating the Negro, Madeira, Purfis and many other streams. The principal exports of the valley were india-rubber, cacao, Brazil nuts and a few other products of very minor importance.
20th century concerns
Four centuries after the 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 rudely cultivated areas among the mountains at its extreme headwaters. 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 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 captial 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 Belem, 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.
The Amazon has over 1000 tributaries in total. Some of the more notable are:
Longest rivers in the Amazon system
- 6,762 km - Amazon, South America
- 3,379 km - Purus, Peru / Brazil, (2,948 km) (3,210 km)
- 3,239 km - Madeira, Bolivia / Brazil
- 2,820 km - Yapura, Colombia / Brazil
- 2,750 km - Tocantins, Brazil, (2,416 km) (2,640 km)
- 2,575 km - Araguaía, Brazil (tributary of Tocantins)
- 2,410 km - Juruá, Peru / Brazil
- 2,250 km - Negro, South America
- 2,100 km - Xingu, Brazil
- 1,900 km - Tapajós, Brazil
- 1,749 km - Guaporé , Brazil / Bolivia (tributary of Madeira)
- 1,575 km - Içá, South America
- 1,415 km - Marañón, Peru
- 1,300 km - Iriri , Brazil (tributary of Xingu)
- 1,240 km - Juruena , Brazil (tributary of Tapajós)
- 1,200 km - Tapajós, Brazil
- 1,130 km - Madre de Dios, Peru / Bolivia (tributary of Madeira)
- 1,100 km - Huallaga, Peru (tributary of Marañón)
- Amazon River and Amazon Rainforest virtual tour
- Information on the Amazon from Extreme Science
- Map of South America
- Pictures of the Amazon River
- Amazon River and rainforest photos and information
- An Amazon River web site
- Information and a map of the Amazon's watershed
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