The Amazon reverses and flows east
A river that had drained toward the Pacific is turned around by the rising Andes and cuts to the Atlantic.
- When
- —
- Duration
- 1.5 million years
- Known to
- ± 1 million years
- Era
- Miocene, Cenozoic
Before the Andes reached full height, drainage in northern South America ran west and north. As the mountains rise, the Pebas wetland fills and eventually spills eastward, and by around 10 to 9 million years ago a transcontinental river is delivering Andean sediment to the equatorial Atlantic. The Amazon is the direct result of a mountain range: the largest river on Earth by discharge exists because plate collision on one side of a continent reversed the slope of the other.