-Plate Tectonics
Some 15 million years ago, the Amazon River flowed westward into the Pacific Ocean. When the South American plate moved into another tectonic plate, the Andes Mountains slowly rose up and blocked the flow of the river. As the river system backed up, freshwater lakes were formed, and the environment of the Amazon basin changed drastically. Then about 10 million years ago the river found its way eastward towards the Atlantic.
Some 15 million years ago, the Amazon River flowed westward into the Pacific Ocean. When the South American plate moved into another tectonic plate, the Andes Mountains slowly rose up and blocked the flow of the river. As the river system backed up, freshwater lakes were formed, and the environment of the Amazon basin changed drastically. Then about 10 million years ago the river found its way eastward towards the Atlantic.