Trying to imagine the vastness of the River Amazon is almost as difficult as trying to comprehend infinity – the mind reels at its staggering immensity. With its countless tributaries, the Amazon drains an area of South America almost the size of Australia and is deep enough for ocean-going ships to sail inland from the Atlantic to Iquitos in Peru – half the river’s length. It disgorges ten times more water into the sea than the Mississippi in the USA.
The Amazon crosses virtually the entire continent. Its most far-flung tributaries begin in glacier-fed lakes high in the Peruvian Andes, just 120 miles (190km) from the Pacific. Thundering down from the mountains, the tributaries carve out dramatic gorges in the eastern slopes, churning up clay that turns the water the colour of milky waters. There are also black-water tributaries, whose water is coloured by decomposed plant matter from the swamps they drain, yet very clear. As the gradients slacken, the rushing water slows to a more stately pace before reaching the plain below – the immense Amazon basin.
Tropical rainforest in the Amazon basin covers an area nearly twice the size of India, with hardly any ground more than 650ft (200m) high once it has left the mountains. Melting snow in the Andes and heavy rains bring flooding for much of the year. An extent of the forest the size of Iceland, known as the varzea, is inundated to a depth of around 30ft (9m) for months, and some parts, the igapos, are underwater most of the time.
Most of the time, too, the forest is hot, wet and sticky, with temperatures around 33 °C (91°F ) by day and 23 °C (73°F ) by night. Near Manaus in Brazil – 750 miles (1200km) from the Atlantic – is the wedding of the waters, where the black-water River Negro, here 3 miles (5km) wide, converges with the white-water mainstream. To the Brazilians, the Amazon proper begins at this confluence – they call the river upstream from here the Solimoes.
So flat are the Amazon’s lower reaches that the river is tidal for 600 miles (966km) inland from the Atlantic, as far as Obidos. Before it finally discharges into the ocean, it forms a massive maze of channels, along with two other rivers (Tocantins and Para) that join it on the south side. Overall, the mouth spans some 200 miles (320km); two of its channels are separated by Marajo Island – the size of Switzerland.
Nowhere in the world has a larger variety of plants than the Amazon. Trees towering to 200ft (60m) shade out the sunlight, so that in the dry forest the floor is often barely more than a carpet of rotting vegetation. In the flooded forest, shrubs and trees have buttressed roots to help them survive. In all parts, the storeyed canopy of branches bursts with life – lianas. Orchids and bromeliads vie for holds in the upper branches that also shelter creatures such as monkeys, sloths, hummingbirds, macaws, huge butterflies and innumerable bats.
Caymans and river turtles live in the water, as do water-dwelling mammals such as manatees and botos (freshwater dolphins). Land animals include jaguars, jaguarondis, peccaries, tapirs, capybaras and armadillos. There are around 2500 species of fish and more than 1600 species of bird.
Some parts of the Amazon rainforest are preserved, including the Amazonians National Park that borders the River Tapajos in Brazil and covers almost 4000sq miles (10,000sq km). But if deforestation continues at the present rate, this vast forest – which totals a one-a third of the world’s tropical rainforest – which totals one-third of the world’s tropical rainforest – will have virtually disappeared by the end of the 21st century.