Unique Facts About South & Central America: : The Amazon River

Unique Facts- South America

The Amazon River

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 than the Mississippi, Nile, and Yangtze rivers combined. It also has the largest drainage area of any river system. It may be correctly stated that the Nile is the longest river, while the Amazon is the strongest.

The quantity of fresh water released to the Atlantic Ocean is enormous: 184,000 m³ per second (6.5 million ft³/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 large ocean steamers to Manaus. Smaller ocean vessels of 3,000 tons and 5.5 m (18 ft) draft can reach as far as Iquitos, 3,700 km (2,300 miles) from the sea. Smaller riverboats can reach 780 km (486 mi) higher as far as Achual Point. Beyond that, small boats frequently ascend to the Pongo de Manseriche, just above Achual Point.

Mouth of the Amazon seen from space, looking south.(Photo courtesy of NASA)

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 7,200 km (4,800 mi) through the interior of Peru and across Brazil, it enters the Atlantic Ocean at the equator.

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 2,400 km (1,500 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.

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 40 m (120 ft) 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.

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.

The abundance of water in the Amazon basin is due to the fact that much of this lies in the region below the Intertropical convergence zone, where rainfall is at a maximum. Also, the basin lies in the Trade Wind zone, where moisture from the Atlantic is pushed westwards, and eventually forced to rise over the Andes, the second tallest mountain range on Earth, where the moist air cools and precipitates water. This combination creates more rainfall over a large river basin than anywhere else on the planet.

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 12 to 15 m (40 to 50 ft) higher than levels during the dry season. During the flood, the level at Iquitos is 6 m (20 ft); at Teffe, it is 15 m (45 ft); near Obidos, 11 m (35 ft); and at Para, 4 m (12 ft), above the low-water extreme seen during the dry season.

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.

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.

Amazon River Interior

(photo courtesy NASA Goddard Space Flight Center's Laboratory for Terrestrial Physics)

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 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.