Some rivers have a lifetime of many thousands of years, but they eventually dry up. As a river flows over land, the water wears away, or erodes, the rock of the riverbed. Over time, the river levels out the land until it is flat, and then it stops flowing. Rivers also need a steady source of water, such as from a mountain’s rainwater or snowmelt, or from rainfall. Without it, they will dry up.
- Why do planes disappear in the Bermuda Triangle?
- What are coral reefs?
- What is an iceberg?
- What is the difference between an ocean, a sea, a gulf, and a bay?
- Why is the ocean salty?
- How much of Earth is covered with land and water?
- Where is the deepest hole?
- How are caves formed?
- Is there life on planets in other solar systems?
- Which planet might float on water?
- Which planets have rings?
- Is a day the same on all planets?
- Who named our planets?
- What is Planet X?
- Which planets are called the gas giants?
- Why isn’t Pluto a planet anymore?
- Which planets are the rocky planets?
- How many planets are there?
- What is a planet?
- What is an orbit?
