What causes a river to flow backwards?

Related questions

1. Why Saraswati River is invisible?
2. What is the slowest river in the world?
3. What are the oldest rivers in the world?
4. Where do rivers flow fastest?
5. Is there a waterfall that flows up?
6. What film is river flows in you from?
7. What rivers flow south?
8. Do any rivers flow uphill?
9. What rivers flow backwards?
10. How can you tell the age of a river?

Tags

1. #rivers
2. #amazon
3. #reversed
4. #brought
5. #millions
6. #america
7. #years
8. #mountains
9. #erosion
10. #begins
11. #south
12. #andes
13. #became
14. #collection
15. #western
16. #growth
17. #about
18. #theory
19. #their
20. #larger
21. #basin
22. #course
23. #river
24. #change