The Amazon River is the second longest river in the world, slightly shorter than the Nile River (4,258 miles or 6,853 km), although some experts contend that the two rivers are so close in length (since measuring methods vary and there is still some dispute over their true sources) that it is difficult to say which river is actually longer.
The modern Amazon and its tributaries occupy a vast system of drowned valleys that have been filled with alluvium. With the rise in sea level that followed the melting of the Pleistocene glaciers, the steep-sided canyons that had been eroded into the Pliocene surface during the period of lower sea levels were gradually flooded. In the upper part of the basin—in eastern Colombia, Ecuador, Peru, and Bolivia—more-recent outwash from the Andes has covered many of the older surfaces.
There are more than 1,000 tributaries of the Amazon that flow into it from the Guiana Highlands, the Brazilian Highlands, and the Andes. Six of these tributaries—the Japurá (Caquetá in Colombia), Juruá, Madeira, Negro, Purus, and Xingu rivers—are each more than 1,000 miles (1,600 km) long; the Madeira River exceeds 2,000 miles (3,200 km) from source to mouth. The largest oceangoing ships can ascend the river 1,000 miles to the city of Manaus, Brazil, while lesser freight and passenger vessels can reach Iquitos, Peru, 1,300 miles (2,090 km) farther upstream, at any time of year.
Credit : Britannica
Picture Credit : Google
