The Amazon River

English: Amazon River floating village neighborhood in Iquitos, Peru. Deutsch: Schwimmende Häusersiedlung auf dem Amazonas in Iquitos, Peru. Français : Amazone, Iquitos, Pérou. Español: Amazonas, Iquitos, Perú. (Photo credit: Wikipedia)

The Amazon River (US pron.: /ˈæməzɒn/ or UK /ˈæməzən/; Spanish & Portuguese: Amazonas) in South America is the second longest ^{[2][not in citation given]} river in the world and by far the largest by waterflow with an average discharge greater than the next seven largest rivers combined (not including Madeira and Rio Negro, which are tributaries of the Amazon). The Amazon, which has the largest drainage basin in the world, about 7,050,000 square kilometres (2,720,000 sq mi), accounts for approximately one-fifth of the world's total river flow.^[3][4]

 

In its upper stretches, above the confluence of the Rio Negro, the Amazon is called Solimões in Brazil; however, in Peru, Colombia and Ecuador, as well as the rest of the Spanish-speaking world, the river is generally called the Amazon downstream from the confluence of the Marañón and Ucayali rivers in Peru. The Ucayali-Apurímac river system is considered the main source of the Amazon, with as its main headstream the Carhuasanta glacial stream flowing off the Nevado Mismi mountain.

 

The width of the Amazon is 1.6 and 10 kilometres (1.0 and 6.2 mi) at low stage but expands during the wet season to 48 kilometres (30 mi) or more. The river enters the Atlantic Ocean in a broad estuary about 240 kilometres (150 mi) wide. The mouth of the main stem is 80 kilometres (50 mi).^[5] Because of its vast dimensions, it is sometimes called The River Sea. The first bridge in the Amazon river system (over the Rio Negro) opened on 10 October 2010 near Manaus, Brazil.

 

Drainage area

Main article: Amazon Basin

The Amazon Basin, the largest in the world, covers about 40% of South America, an area of approximately 7,050,000 square kilometres (2,720,000 sq mi). It drains from west to east, from Iquitos in Peru, across Brazil to the Atlantic. 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 locals often refer to it as "El Jefe Negro", referring to an ancient god of fertility.

 

The Amazon River and its tributaries are characterized by extensive forested areas that become flooded every rainy season. Every year the river rises more than 9 metres (30 ft), flooding the surrounding forests, known as várzea ("flooded forests"). The Amazon's flooded forests are the most extensive example of this habitat type in the world.^[6] In an average dry season, 110,000 square kilometres (42,000 sq mi) of land are water-covered, while in the wet season, the flooded area of the Amazon Basin rises to 350,000 square kilometres (140,000 sq mi).^[7]

 

The quantity of water released by the Amazon to the Atlantic Ocean is enormous: up to 300,000 cubic metres per second (11,000,000 cu ft/s) in the rainy season, with an average of 209,000 cubic metres per second (7,400,000 cu ft/s) from 1973 to 1990.^[8] The Amazon is responsible for about 20% of the Earth's fresh water entering the ocean.^[6] The river pushes a vast plume of fresh water into the ocean. The plume is about 400 kilometres (250 mi) long and between 100 and 200 kilometres (62 and 120 mi) wide. The fresh water, being lighter, flows on top of the seawater, diluting the salinity and altering the color of the ocean surface over an area up to 1,000,000 square miles (2,600,000 km²) 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.^[4]

 

The Atlantic has sufficient wave and tidal energy to carry most of the Amazon's sediments out to sea, thus the Amazon does not form a true delta. The great deltas of the world are all in relatively protected bodies of water, while the Amazon empties directly into the turbulent Atlantic.^[9]

There is a natural water union between the Amazon and the Orinoco basins, the so-called Casiquiare canal. The Casiquiare is a river distributary 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-called bifurcation.

 

In 1500, Vicente Yáñez Pinzón was the first European to sail into the river.^[23] Pinzón called the river flow Río Santa María del Mar Dulce, later shortened to Mar Dulce (literally, sweet sea, because of its fresh water pushing out into the ocean). For 350 years after the first European encounter of the Amazon by Pinzón, the Portuguese portion of the basin remained an untended former food gathering and planned agricultural landscape occupied by the indigenous peoples who survived the arrival of European diseases. There is ample evidence for complex large-scale, pre-Columbian social formations, including chiefdoms, in many areas of Amazonia (particularly the inter-fluvial regions) and even large towns and cities.^[24] For instance the pre-Columbian culture on the island of Marajó may have developed social stratification and supported a population of 100,000 people.^[25] The Native Americans of the Amazon rain forest may have used Terra preta to make the land suitable for the large-scale agriculture needed to support large populations and complex social formations such as chiefdoms.^[25]

 

One of Gonzalo Pizarro's lieutenants, Francisco de Orellana, set off in 1541 to explore east of Quito into the South American interior in search of El Dorado and the "Country of Cinnamon".^[26] He was ordered to follow the Coca River and return when the river reached its confluence. After 170 km, the Coca River joined the Napo River (at a point now known as Puerto Francisco de Orellana), and his men threatened to mutiny if he followed his orders and the expedition turned back. On 26 December 1541, he accepted to change the purpose of the expedition to the conquest of new lands in the name of the King of Spain, and the forty-nine men built a larger boat in which to navigate downstream. After a journey of 600 km down the Napo River, constantly threatened by the Omaguas, they reached a further major confluence, at a point near modern Iquitos, and then followed what is now known as the Amazon River for a further 1,200 km to its confluence with the Rio Negro (near modern Manaus), which they reached on 3 June 1542.

 

This area around the Amazon was dominated by the Icamiaba natives, who were mistaken for fierce female warriors by the members of the expedition.^{[citation needed]} Orellana later narrated the belligerent victory of the Icamiaba “women” over the Spanish invaders to Charles V, Holy Roman Emperor, who, recalling the Amazons of Greek mythology, baptized the river Amazonas, the name by which it is still known in both Spanish and Portuguese. At the time, however, the river was referred to by the expedition as Grande Río ("Great River"), Mar Dulce ("Fresh Water Sea") or Río de la Canela ("Cinnamon River"). Orellana claimed that he had found great cinnamon trees there, in other words a source of one of the most important spices reaching Europe from the East. In fact, true cinnamon (Cinnamomum verum) is not native to South America. Other related cinnamon-containing plants (of the family Lauraceae) do occur, and Orellana may have observed some of these. The expedition continued a further 1,200 km to the mouth of the Amazon, which it reached on 24 August 1542, demonstrating the practical navigability of the Great River.

 

Underground river

Scientists have discovered the longest underground river in the world, in Brazil, running for a length of 6,000 km at a depth of nearly 4 km. It flows from the Andean foothills to the Atlantic coast in a nearly west-to-east direction like the Amazon River. The discovery was made public in August 2011^[35] meeting of the Brazilian Geophysical Society in Rio de Janeiro. The river, named Hamza after the discoverer, an Indian-born scientist Valiya Hamza who is working with the National Observatory at Rio, makes it the first and geologically unusual instance of a twin-river system flowing at different levels of the earth's crust in Brazil. If the slowing down of certain seismic waves caused by the damp spot helped uncover the underground ocean, the unusual temperature variation with depth measured in 241 inactive oil wells helped locate the subterranean river.

 

Except for the flow direction, the Amazon and the Hamza have very different characteristics. The most obvious ones are their width and flow speed. While the Amazon is 1 km to 100 km wide, the Hamza is 200 km to 400 km in width. But the flow speed is five meters per second in the Amazon and less than a millimeter per second speed in the Hamza.^[35]

 

Several geological factors have played a vital role in the formation and existence of these subterranean water bodies. The underground ocean, discovered in 2007, has been formed when the plate carrying the Pacific Ocean bottom gets dragged and ends up under the continental plate. Water at such depths would normally escape upwards but the unusual conditions that exist along the eastern Pacific Rim allow the moisture to remain intact. In the case of the Hamza, the porous and permeable sedimentary rocks behave as conduits for the water to sink to greater depths. East-west trending faults and the karst topography present along the northern border of the Amazon basin may have some role in supplying water to the river. If the impermeable rocks stop the vertical flow, the west to east gradient of the topography directs it to flow towards the Atlantic Ocean. Unlike the Hamza, the 153 km-long underground river in Mexico's Yucatán Peninsula and the 8.2 km-long Cabayugan River in the Puerto Princesa Subterranean River National Park in the Philippines have come into being thanks to the karst topography. Water in these places drills its way downward by dissolving the carbonate rock to form an extensive underground river system.