Amazon geography

From her source 5,597 meters high in the Peruvian mountains to her mouth at Belém, the Amazon travels some 6,448 km. A patchwork of tropical rainforests, montane forests, grasslands, and 15,000 tributaries decorate the 6,869,000 km2 of the Amazon basin.

The hydrology of the river depends little on gravity considering much of the Amazon basin is relatively flat. In fact from Iquitos to the mouth of the river there is only a mere 70 m drop in altitude giving the river only a 1 in 50,000 gradient. Instead, the hydrology depends primarily on the melting snow high in the Andes. When the sun warms the peaks, a good quantity of the melting snow is sent downhill causing waters to rise. In fact, seasonal flooding depends more on this supply of snow than it ever does of rainfall, which explain why there is a large increase in river levels but not in rain amounts.

Amazingly, these seasonal floods, which are so vital to the forests ecosystem and diversity, only cover 2% of the forest’s land. The rest remain terra firma (forests above flood levels) and depend on rainfall to determine their season. The river transforms this environment every year during these floods simply on a whim, chooses to eliminate a bank here, while creating new land a few miles a way. New islands, oxbow lakes, and sandbanks are formed wherever one looks. The flood also provides essential nutrients to the soil downstream. The banks are so pliable because they lack the rock foundations that make most other rivers relatively stable. Although this life of constant change may seem tumultuous at best, it is this ever-changing environment that allows for habitat variety and the Amazon’s wide species diversity.