Amazon River

The Amazon River (UK: /ˈæməzən/, US: /ˈæməzɒn/; Portuguese: rio Amazonas, Spanish: río Amazonas) in South America is the largest river by discharge volume of water in the world, and the second-longest or longest river system in the world, a title which is disputed with the Nile.

The headwaters of the Apurímac River on Nevado Mismi in Peru had been considered, for nearly a century, the Amazon basin's most distant source until a 2014 study found it to be the headwaters of the Mantaro River on the Cordillera Rumi Cruz in Peru. The Mantaro and Apurímac rivers join, and with other tributaries form the Ucayali River, which in turn meets the Marañón River upstream of Iquitos, Peru, forming what countries other than Brazil consider to be the main stem of the Amazon. Brazilians call this section the Solimões River above its confluence with the Rio Negro forming what Brazilians call the Amazon at the Meeting of Waters (Portuguese: Encontro das Águas) at Manaus, the largest city on the river.

The Amazon River has an average discharge of about 215,000–230,000 cubic meters per second—approximately 6,591–7,570 cubic kilometers per year, greater than the next seven largest independent rivers combined. The Amazon represents 20% of the global riverine discharge into oceans. The Amazon basin is the largest drainage basin in the world, with an area of approximately 7,000,000 square kilometers. The Amazon enters Brazil with only one-fifth of the flow it finally discharges into the Atlantic Ocean, yet already has a greater flow at this point than the discharge of any other river in the world.

Etymology

The Amazon River was first called the Marañón by Europeans, and this name is still used in Peru and in the Brazilian state of Maranhão. Later, it became known as Rio Amazonas in Spanish and Portuguese.

The name Rio Amazonas came from an event where native warriors, led by women, attacked an expedition led by Francisco de Orellana in the 1500s. The women warriors reminded him of the Amazon warriors from ancient Greek mythology. The word "Amazon" may come from an old Iranian word meaning "fighting together" or "warriors."

History

Geological history

Geological studies suggest that for millions of years, the Amazon River flowed in the opposite direction – from east to west. Eventually the Andes Mountains formed, blocking its flow to the Pacific Ocean and causing it to switch directions to its current mouth in the Atlantic Ocean.

Pre-Columbian era

During what many archaeologists called the formative stage, Amazonian societies were deeply involved in the emergence of South America's highland agrarian systems. The trade with Andean civilizations in the terrains of the headwaters in the Andes formed an essential contribution to the social and religious development of higher-altitude civilizations like the Muisca and Incas. Early human settlements were typically based on low-lying hills or mounds.

Shell mounds were the earliest evidence of habitation; they represent piles of human refuse and are mainly dated between 7500 BC and 4000 BC. There is ample evidence that the areas surrounding the Amazon River were home to complex and large-scale indigenous societies, mainly chiefdoms who developed towns and cities. By the time the Spanish conquistador De Orellana traveled across the Amazon in 1541, more than 3 million indigenous people lived around the Amazon.

Arrival of Europeans

In March 1500, Spanish conquistador Vicente Yáñez Pinzón was the first documented European to sail up the Amazon River. Pinzón called the stream Río Santa María del Mar Dulce, later shortened to Mar Dulce, literally, sweet sea, because of its freshwater pushing out into the ocean. Another Spanish explorer, Francisco de Orellana, was the first European to travel from the origins of the upstream river basins, situated in the Andes, to the mouth of the river.

Exploration

Gonzalo Pizarro set off in 1541 to explore east of Quito into the South American interior in search of El Dorado, the "city of gold" and La Canela, the "valley of cinnamon". He was accompanied by his second-in-command Francisco de Orellana. The expedition reached the mouth of the Amazon on 24 August 1542, demonstrating the practical navigability of the Great River.

Scientific exploration

Early scientific, zoological, and botanical exploration of the Amazon River and basin took place from the 18th century through the first half of the 19th century.

• Charles Marie de La Condamine explored the river in 1743.
• Alexander von Humboldt, 1799–1804
• Johann Baptist von Spix and Carl Friedrich Philipp von Martius, 1817–1820
• Georg von Langsdorff, 1826–1828
• Henry Walter Bates and Alfred Russel Wallace, 1848–1859
• Richard Spruce, 1849–1864

Post-colonial exploitation and settlement

The Cabanagem revolt (1835–1840) was directed against the white ruling class. The population of the Brazilian portion of the Amazon basin in 1850 was perhaps 300,000.

20th-century development

Since colonial times, the Portuguese portion of the Amazon basin has remained a land largely undeveloped by agriculture and occupied by indigenous people who survived the arrival of European diseases.

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

With a population of 1.9 million people in 2014, Manaus is the largest city on the Amazon. Manaus alone makes up approximately 50% of the population of the largest Brazilian state of Amazonas. The racial makeup of the city is 64% pardo (mulatto and mestizo) and 32% white.

Although the Amazon river remains undammed, around 412 dams are in operation on the Amazon's tributary rivers. Of these 412 dams, 151 are constructed over six of the main tributary rivers that drain into the Amazon. Since only 4% of the Amazon's hydropower potential has been developed in countries like Brazil, more damming projects are underway and hundreds more are planned. Scientists are worried that constructing more dams in the Amazon will harm its biodiversity in the same way by "blocking fish-spawning runs, reducing the flows of vital oil nutrients and clearing forests".

Course

Main article: Source of the Amazon River

The Amazon River has its most distant source in the Río Mantaro drainage. For a long time, people thought the source was in the Apurímac River near Nevado Mismi. But in 2014, scientists found that the Mantaro River is actually farther from the sea.

The Amazon River is made from several smaller rivers. The Apurímac and Mantaro rivers join to form the Ene River. This then joins others to become the Ucayali River. The Ucayali meets the Marañón River, and this is where most people say the Amazon River begins.

The Amazon River flows through Brazil and Peru, and forms part of the border between Colombia and Peru. It has many important tributaries, such as the Putumayo, Caquetá, Vaupés, Guainía, Morona, Pastaza, Napo, and Huallaga. In some places, the river splits into many channels, creating many islands.

The Amazon River ends at the Atlantic Ocean near the city of Belém. The exact place and width of the mouth are debated because of the area's unusual geography. Some measurements say the mouth is over 300 kilometers wide!

There are no bridges that cross the entire width of the Amazon River. This is mostly because the river flows through a rainforest with very few roads and cities. People usually cross by ferry. The Manaus Iranduba Bridge crosses the Rio Negro, a major tributary of the Amazon, connecting the cities of Manaus and Iranduba.

There has long been a debate about whether the Amazon or the Nile is the world's longest river. Different measurements give different results, and scientists are still discussing this today. Some say the Amazon is longer, while others say the Nile is longer.

Watershed

Main article: Amazon basin

The Amazon basin is the largest in the world, covering about 40% of South America. It stretches from Iquitos in Peru all the way across Brazil to the Atlantic Ocean. The basin gathers water from areas as far north as 5 degrees north latitude to as far south as 20 degrees south latitude.

The Amazon River and its tributaries flood huge forested areas each rainy season. During the wet season, the flooded area grows to 350,000 km². The Amazon releases a massive amount of water into the Atlantic Ocean—up to 300,000 m³ per second during the rainy season. This fresh water creates a large plume in the ocean, changing its color and diluting its saltiness over a wide area.

Discharge

The Amazon River has the largest amount of water flowing out of any river in the world. Scientists measured how much water flows out near the river’s mouth between 2003 and 2015, and found an average of 7,200 cubic kilometers of water each year. This is a lot of water — enough to fill many huge swimming pools!

We can also learn about the river’s water flow at different places along its path. For example, at places called Santarém, Óbidos, and Itacoatiara, scientists have measured how much water the Amazon River carries. Even at these spots farther upstream, the Amazon still moves a huge amount of water. The Amazon’s water flow can also be compared to other big rivers, like the Tocantins River.

Sediment load

The Amazon River carries a huge amount of sediment. At a gauge station called Óbidos, scientists measured the sediment load to be about 754 × 10⁶ tons each year, from 1996 to 2007. This shows just how powerful and important the Amazon River is for shaping the land around it.

Flooding

The Amazon River does not flood all at once. Some parts start flooding in November and keep rising until June. The Rio Negro begins to rise in February or March and starts to fall by June. The Madeira River has its flood season two months earlier than most of the Amazon.

Between Manacapuru and Óbidos, the Amazon River is between 20 and 26 metres deep. Near Manacapuru, the river is only about 24 metres above sea level, and more than half of the water below this point is actually below sea level. In its lowest part, the Amazon averages 20 to 50 metres deep, and in some places it can be as deep as 100 metres.

Large ocean ships can travel up to Manaus, 1,500 kilometres from the mouth of the river. Smaller ships can go as far as Iquitos, Peru, 3,600 kilometres from the sea. Even smaller boats can go 780 kilometres further, reaching up to the Pongo de Manseriche.

Each year, in late winter in the northern hemisphere, high tides in the Atlantic send a powerful wave up the Amazon delta. This wave, called the pororoca, can be up to 7.6 metres high and travel 800 kilometres inland.

Geology

The Amazon River began as a transcontinental river in the Miocene epoch between 11.8 million and 11.3 million years ago and took its present shape about 2.4 million years ago in the Early Pleistocene.

Long ago, during the Cretaceous period, the area that would become the Amazon flowed westward as part of a river system connecting Africa and South America when the continents were joined. About 80 million years ago, the continents split apart. The rise of the Andes mountains blocked the river's path, turning the basin into a vast inland sea that eventually became a massive lake. Over time, this lake drained and transformed into the river we know today, helping create the Amazon rainforest. There is also a large hidden aquifer called the Hamza River that runs parallel to the Amazon.

Protected areas

The Amazon River flows through several protected areas that help keep its environment safe. These places are important because they protect plants, animals, and the water from being damaged. Many of these areas are watched over to make sure they stay healthy for all the living things there.

Flora and fauna

See also: Biodiversity of Colombia § Amazon natural region

See also the categories Flora of the Amazon and Trees of the Amazon rainforest

See also: Category:Fauna of the Amazon

More than one-third of all known species in the world live in the Amazon rainforest. It is the richest tropical forest in the world for plant and animal life. The river supports many kinds of fish, crabs, algae, and turtles.

Mammals

Along with the Orinoco, the Amazon is a home for the boto, also called the Amazon river dolphin (Inia geoffrensis). It is the largest river dolphin and can grow up to 2.6 m long. The tucuxi (Sotalia fluviatilis) is another dolphin found in the Amazon. The Amazonian manatee (Trichechus inunguis), known as a "seacow", lives only in freshwater and does not go into the ocean. The giant otter (Pteronura brasiliensis) is one of South America’s top hunters but its numbers have dropped due to habitat loss and hunting.

Reptiles

The anaconda lives in shallow waters of the Amazon. Caimans, which are like alligators, also live there along with many kinds of turtles.

Birds

See also: Category:Birds of the Amazon rainforest

Fish

The Amazon River has the most different kinds of fish in the world. Popular aquarium fish like the neon tetra and the freshwater angelfish come from here. The arapaima, one of the largest freshwater fish, can grow up to 4.6 metres long. The piranha is known for gathering in large groups. The candirú is a small parasitic catfish. The electric eel (Electrophorus electricus) can produce electric shocks to defend itself.

Butterflies

See also: List of butterflies of the Amazon River basin and the Andes

Microbiota

Freshwater microbes in the Amazon are still being studied. Recent research shows that important microbes include Actinomycetota, Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria and Thermoproteota.

Challenges

The Amazon River is very important to over 47 million people, but it faces many challenges that threaten both its environment and the local communities. Illegal gold miners have made it hard for the Yanomami, a tribe of about 30,000 people, to protect their land and culture. In 2022, a severe drought caused water temperatures to rise dramatically, reaching 39.1 degrees Celsius, which hurt many animals in the river. These problems show how important it is to take care of the Amazon and its resources carefully.

Major tributaries

The Amazon River has over 1,100 tributaries, twelve of which are longer than 1,500 km (930 mi). Some important ones include:

• Branco
• Casiquiare canal
• Caquetá
• Huallaga
• Putumayo (or Içá River)
• Javary (or Yavarí)
• Juruá
• Madeira
• Marañón
• Morona
• Nanay
• Napo
• Negro
• Pastaza
• Purús
• Tambo
• Tapajós
• Tigre
• Tocantins
• Trombetas
• Ucayali
• Xingu
• Yapura

The longest tributaries, sorted by length, include the Madeira River in Bolivia and Brazil at 3,250 km (2,019 mi), the Purús River in Peru and Brazil at 3,211 km (1,995 mi), and the Japurá or Caquetá River in Colombia and Brazil at 2,820 km (1,752 mi). Other notable long tributaries are the Tocantins River in Brazil at 2,639 km (1,640 mi) and the Juruá River in Peru and Brazil at 2,400 km (1,500 mi).