0:00Here’s how most river valleys form: A stream
starts high in the mountains, and at first,
0:04its path to the ocean might be
a little bumpy. But as it flows,
0:07it picks up pebbles and dirt – and in the process
smooths out those bumps. The debris from the
0:12erosion can also build up its streambed by
filling in any dips in the river downstream.
0:17Ultimately, the processes of carving down and
building up tend to balance each other and they
0:21create a specific slope over time. And given
enough time, pretty much all rivers end up with
0:26vertical profiles that look like this.
Find out why in our full video below.
