The Amazon River: Origins, Course, and Characteristics

The Origins of the Amazon River

The Amazon River, renowned for its vastness, has its origins steeped in scientific inquiry and debate. Traditionally, the Nevado Mismi, a snow-capped peak in Arequipa, Peru, was cited as the river's furthest source. This assertion was supported by studies up until 2008, which pinpointed the Nevado Mismi as the starting point of the Amazon. However, a groundbreaking study in 2014 by James Contos and Nicolas Tripcevich, published in the journal 'Area,' proposed a new source—the Río Mantaro drainage. Their research, which included precise GPS tracking during a kayak expedition, suggested that the Mantaro's source extends the Amazon's length by an additional 80 kilometers beyond the Nevado Mismi, thus revising the understanding of the river's true origin.

The Course of the Amazon River

The Amazon River embarks on its monumental journey at the confluence of the Apurímac and the Río Mantaro, forming the Ene River. This river then merges with the Perene to create the Tambo, which in turn joins the Urubamba River, culminating in the Ucayali. The Ucayali then flows into the Amazon Basin, marking the transition from the Andean highlands to the expansive Amazon rainforest. The river meanders through the rainforest, its banks subject to seasonal flooding, with the terrain predominantly flat except for occasional hills. Along its course, the Amazon is fed by a multitude of tributaries from Peru, Colombia, and Ecuador, which contribute to its remarkable volume and width.

The Upper Amazon and Its Tributaries

The Upper Amazon, also known as the Solimões, is a region encompassing the river systems and floodplains within Brazil, Peru, Ecuador, Colombia, and Venezuela. The Amazon River itself, flowing mainly through Brazil and Peru, also delineates part of the Colombia-Peru border. It receives water from several significant tributaries, such as the Putumayo, Caquetá, Vaupés, and Guainía, which join either the Marañón and Ucayali or enter the Amazon directly. The river's path is characterized by anabranches and a complex network of natural canals, forming numerous islands within the flooded igapó forests.

The Lower Amazon and Its Estuary

The Lower Amazon is marked by the meeting of the Rio Negro's dark waters with the sandy-hued Rio Solimões, where they flow alongside each other for over six kilometers without mixing. The lower reaches of the river are believed to have been an ancient gulf of the Atlantic Ocean, as suggested by the presence of cliffs near Óbidos. The Amazon's estuary is expansive, with the Pará River and the oceanic front of Marajó island contributing to its breadth, which spans up to 325 kilometers when these features are included. The estuary's influence extends into the tropical north Atlantic, affecting the region's salinity, pH, light penetration, and sedimentation patterns.

The Amazon River's Bridgeless Span and Contested Length

The Amazon River, despite its enormity, has no bridges crossing its full width. This absence is not due to technical challenges, as engineering solutions exist, but rather because the river traverses the sparsely populated Amazon Rainforest, where infrastructure such as roads and cities is minimal. The length of the Amazon has been a topic of debate among geographers, with some considering it the world's second-longest river after the Nile. The Amazon's length has been reported to range from 6,275 to 6,992 kilometers, while the Nile's length varies between 5,499 and 7,088 kilometers. These discrepancies arise from different methodologies for identifying the source and mouth, the scale of measurement, and the techniques used to measure length. In 2008, the Brazilian Institute for Space Research (INPE) posited that the Amazon might be 140 kilometers longer than the Nile. However, this claim, among others, remains contested, and the precise length of the Amazon continues to be a subject of ongoing scientific exploration and debate.