How do rivers keep running for thousands of years?

Question

To my understanding, a river’s source is fueled by snow and rain, but is it enough to keep it running for that long? Afterall the source doesn’t get rain/snow 24/7 so wouldn’t bigger rivers drain the source in a matter of weeks instead of many hundreds of years?

In: Planetary Science

Answer 1

|is it enough to keep it running for that long?
Demonstrably, yes, it is.

Rivers don’t just have one source. They have tributaries, which can gather rain water from enormous amounts of land. That’s why rivers start out small, and get larger and larger as they approach the ocean.

Consider [this image of the Mississippi basin](https://www.mvd.usace.army.mil/portals/52/siteimages/P1_new.jpg). That river is gathering rain from almost half of America.