In the year 1500, the Spanish navigator Vicente Yáñez Pinzón was sailing off the coast of South America, far out of sight of land, when his crew hauled up buckets of seawater and found it fresh enough to drink. He called the phenomenon the Mar Dulce — the sweet sea. What he had actually found was the mouth of the Amazon, a river so enormous that it pushes a plume of fresh water more than a hundred kilometres out into the Atlantic. The Amazon discharges on average around two hundred thousand cubic metres of water every second — roughly a fifth of all the river water that flows into the world's oceans, and more than the next several biggest rivers combined.
Everything about it is built on this scale. The Amazon basin sprawls across some seven million square kilometres — about forty per cent of South America — and drains parts of nine countries and territories, from the Andes to the Atlantic. At Manaus, a thousand kilometres from the sea, the river's level routinely rises and falls by around ten metres between seasons, drowning and revealing whole forests. Whether it is also the world's longest river is a genuinely open feud: the Amazon runs roughly 6,400 kilometres, and partisans of the Amazon and the Nile have traded the crown back and forth depending on where each river is deemed to begin. One superlative is beyond dispute: not a single bridge crosses the Amazon's main stem along its entire length. The famous bridge at Manaus spans the Rio Negro, a tributary — a distinction that has won and lost many a pub-quiz point.
The river beneath the river
In 2011, Brazilian scientists announced something stranger still: a second Amazon, four kilometres underground. Analysing temperature readings from more than two hundred disused oil boreholes drilled by Petrobras, a team led by the geophysicist Valiya Hamza inferred a vast, slow migration of water through deep porous rock, tracking the great river far above but spread over a front hundreds of kilometres wide. It was informally christened the Hamza, after its discoverer. Call it a river with caution, though — and quizmasters should: the Hamza creeps along at speeds better measured in metres per year than metres per second, and many hydrologists prefer to describe it as regional groundwater flow rather than a true river. Even so, the image endures: the world's mightiest river has a dark, sluggish twin sliding beneath it towards the same ocean.
The wave that runs the wrong way
Sometimes the Atlantic shoves back. Around the new and full moons, especially near the equinoxes, the incoming tide funnels into the Amazon's shallow mouth and rears up into a tidal bore — a wall of water that can stand metres high and roll upstream for tens of kilometres, snapping trees and tearing at the banks as it goes. Local Tupi speakers named it the pororoca, usually translated as "great roar": the wave announces itself with a rumble heard long before it arrives. Since the late 1990s surfers have treated it as a pilgrimage, riding a single wave for kilometres at a stretch — among the longest surfs ever recorded — while dodging debris in water the colour of milky tea.
The river's deep past holds one more reversal. Geologists studying the basin's sediments have concluded that the proto-Amazon once flowed in the opposite direction, westwards towards the Pacific, until the rise of the Andes walled off that exit and ponded the continent's water into vast wetlands; roughly ten million years ago the system tipped east and began carving today's route to the Atlantic. The modern river still carries souvenirs of its strangeness: pink river dolphins hunt in its flooded forests, and at the Meeting of the Waters near Manaus the black Rio Negro and the sandy Solimões run side by side for kilometres in the same channel, visibly refusing to mix. Even the forest's fertiliser is exotic — mineral dust blown across the Atlantic from the Sahara helps replenish the basin's phosphorus.
Stand at its mouth on the equator, where the channel is broken by an island roughly the size of Switzerland, and the word "river" starts to feel too small. The Amazon is less a line on the map than a fifth of the world's flowing water, briefly gathered in one place.
Quiz nuggets
- The Amazon discharges roughly a fifth of all river water entering the world's oceans — more than the next several largest rivers combined.
- The Hamza, named after geophysicist Valiya Hamza in 2011, is a vast groundwater flow about four kilometres beneath the Amazon, moving mere metres per year.
- The Amazon's tidal bore is called the pororoca, from a Tupi word usually translated as "great roar"; surfers ride it for kilometres upstream.
- No bridge crosses the Amazon's main stem; the Manaus bridge spans the Rio Negro, a tributary.
- In 1500 Vicente Yáñez Pinzón found fresh water in the open Atlantic off the Amazon's mouth and named it the Mar Dulce — the sweet sea.