The Amazon River, located in South America, is renowned as the world’s largest river by discharge volume and is one of the longest river systems, competing with the Nile for this title. The exact source of the river has been debated: traditionally, the Apurímac River on Nevado Mismi was considered its most distant source, but a 2014 study identified the Mantaro River in Peru as the true origin. With an average discharge of 215,000 to 230,000 cubic meters per second, the Amazon surpasses the combined discharge of the next seven largest rivers and contributes about 20% of the world’s riverine discharge into the oceans. The Amazon basin, the world’s largest drainage basin, covers approximately 7 million square kilometers (2.7 million square miles) and stretches at least 6,400 kilometers (4,000 miles) from the Andes Mountains to the Atlantic Ocean. It spans parts of Brazil, Peru, Colombia, Ecuador, Bolivia, and a small area of Venezuela.
Geological origin
The Amazon River's geological history dates back to the Miocene epoch, roughly 11.8 to 11.3 million years ago. Originally part of a transcontinental river system flowing westward from Africa, it connected to South America as part of the supercontinent Gondwana. Around 80 million years ago, continental shifts altered its course. About 15 million years ago, the rise of the Andes Mountains, due to the collision of the Nazca Plate with the South American Plate, redirected the river, creating a vast inland sea in the Amazon Basin. This sea gradually transformed into a freshwater lake, adapting its marine life to new conditions. Around 11 to 10 million years ago, the river began carving its path through sandstone, leading to the formation of the Amazon rainforest. During glacial periods, the Amazon Lake drained rapidly due to falling sea levels, and the river emerged as one of the world’s longest rivers. The river’s modern journey begins high in the Peruvian Andes, at 5,598 meters (18,363 feet) above sea level, where it starts as the Carhuasanta. It flows eastward, merging with tributaries like the Apurímac, Ene, and Ucayali, eventually reaching the Atlantic Ocean. The Amazon descends gradually at a rate of 1.5 centimeters per kilometer (0.6 inches per mile) over its 6,400-kilometer (4,000-mile) length, and in some sections, it spans up to 10 kilometers (6.2 miles) wide, allowing large ships to navigate up to Iquitos, Peru.
Course of the river and its tributaries
For nearly a century, the Apurímac River was thought to be the Amazon’s farthest source, with studies up to the early 2000s identifying a peak near Lake Titicaca as this source. The river system begins with a stream from this peak, flowing into other streams to form the Apurímac. However, a 2014 study found that the true source is actually in the Río Mantaro drainage. This research showed that the farthest source is further than previously believed, making the Amazon about 80 kilometers (50 miles) longer. The Amazon’s course starts from the confluence of the Apurímac and Ucayali rivers, flows into the Marañón, and extends through the Amazon rainforest. The river predominantly flows through Brazil and Peru, with significant tributaries including the Putumayo, Caquetá, and Huallaga. In its lower reaches, where it meets the Rio Negro and Rio Solimões, the Amazon’s water often displays a striking color contrast due to differences in sediment content. The estuary is notably wide, stretching up to 325 kilometers (202 miles) when including the Pará River estuary and Marajó Island. The Amazon’s hydrological system features over 1,000 tributaries from various highlands and ranges. The river’s sedimentary axis includes two main landforms: the várzea (floodplain) and the terra firme (upland surfaces). Major blackwater tributaries like the Rio Negro contribute to the river’s dark color, while whitewater tributaries such as the Madeira River bring substantial sediment loads, forming islands like Tupinambarana. Other important tributaries include the Purus, Juruá, and Huallaga, which support diverse ecosystems throughout the basin.
Climate
The Amazon basin has a warm, rainy, and humid climate, with nearly equal day and night lengths at the Equator. Nights are cooler due to clear skies and rapid heat loss, making temperature changes between day and night more noticeable than seasonal variations. In Manaus, temperatures average in the low 80s°F (around 28°C) in September and mid-70s°F (about 24°C) in April, with high humidity year-round. Occasionally, cold air from the south can drop temperatures into the 50s°F (around 14°C), a local phenomenon known as a friagem. The region experiences a mix of heavy rains and sunny days with cool nights. Most rain comes from the Atlantic Ocean and forest evaporation. While the eastern and northwestern areas get rain throughout the year, the central region has a drier season from June to November. Manaus has faced severe droughts, such as in 2005, leading to lower river levels and shortages of water and transportation. The Andes Mountains to the west block much of the water vapor, resulting in higher rainfall on the eastern slopes and the highest precipitation in areas like the upper Putumayo near the Colombian border. Moving south, the climate shifts to that of west-central Brazil, with a distinct dry season during the Southern Hemisphere winter. Temperatures also drop significantly with higher elevation in the Andes.
Flora and fauna
The Amazon basin is a marvel of biodiversity, featuring a tropical rainforest with a vast variety of trees and plants. The forest is layered, with towering emergent trees reaching up to 60 meters (200 feet), a dense canopy below, and a rich undergrowth of shade-tolerant species. Surrounding ecosystems, such as montane cloud forests along the Andean fringe and savannas and heath forests in the south, support unique plant species suited to their environments. The fauna is equally diverse. The rivers are home to species like the Amazon river dolphin, Amazonian manatee, and giant otter, though many face threats from habitat destruction and hunting. The basin supports a range of reptiles, including the giant anaconda, and numerous fish species, including the arapaima and piranha.
History
In the pre-Columbian era, complex indigenous societies developed in the Amazon, engaging in advanced agricultural practices and urban development. Evidence suggests early inhabitants constructed shell mounds and artificial earth platforms, supporting large populations. They managed the forest ecology through practices like selective burning, creating nutrient-rich terra preta soil that facilitated sustainable agriculture. European exploration began in the early 16th century with figures like Vicente Yáñez Pinzón and Francisco de Orellana, who highlighted the river’s navigability and resource potential. The rubber boom of the late 19th and early 20th centuries spurred economic growth in cities like Iquitos but had devastating effects on indigenous populations through displacement and disease. In the 20th century, Brazilian development efforts, including the construction of the Trans-Amazonian Highway, aimed to integrate the region economically but faced challenges due to the difficult environment and unsustainable practices. Today, the Amazon is a blend of urbanization and ongoing environmental concerns, with major cities like Manaus playing key roles in the region’s economy while grappling with issues related to deforestation and resource exploitation.
Economy
Since World War II, countries in the Amazon Basin have prioritized economic development by constructing roads that link remote areas with more populated regions. These roadways have facilitated the exploitation of resources, including oil, timber, and illegal cocaine production since the 1980s. In addition to these activities, small-scale farming of crops such as rice, manioc, and corn has become widespread, with cleared lands also being used for cattle ranching. Valuable resources like timber and rubber continue to be harvested, but illegal activities, including unauthorized soybean farming, pose significant threats to protected areas and contribute to environmental degradation. Mining operations, particularly in Serra dos Carajás, have been economically beneficial yet detrimental to the environment, causing deforestation and pollution. Similarly, the Tucuruí hydroelectric plant, while providing energy, has faced substantial criticism for its environmental impact. Oil development has been concentrated primarily in the Andean regions, with limited exploration occurring in Brazil and Bolivia. The deforestation resulting from these activities has sparked global concerns due to its detrimental effects on climate regulation, biodiversity, and the livelihoods of indigenous communities. Despite efforts to monitor these changes, accurate assessments of deforestation remain challenging. Continued deforestation jeopardizes the rainforest’s capacity to absorb carbon dioxide, disrupts local ecosystems, and threatens indigenous ways of life.
Test your knowledge
What was traditionally considered the most distant source of the Amazon River before the 2014 study?
