How Water Erodes Land

Erosion is the process of moving weathered rock and soil from one place to another. Moving water is the most powerful force of erosion on Earth. It shapes our land every single day by carrying away soil, sand, and rocks.

When rain falls on hills and slopes, it doesn't just soak into the ground. The water flows downhill, and as it moves, it picks up and carries soil particles with it. This process is called runoff. You can see evidence of runoff after a rainstorm when you notice muddy puddles, small channels carved in dirt, or soil washed onto sidewalks and streets.

Streams and rivers are even more powerful than rainwater. As water flows in a channel, it carries sand, mud, and pebbles downstream. The faster the water moves, the more material it can carry and the bigger the pieces it can move. A slow, gentle stream might only carry tiny particles of clay. But a fast-moving river can push rocks as big as basketballs!

Over many years, rivers carve deeper and wider into the land. The Grand Canyon was created by the Colorado River cutting through rock for millions of years. Even more dramatic, flash floods can move enormous amounts of soil and rock in just minutes, completely changing the shape of the land.

Interesting Fact: The Mississippi River carries about 500 million tons of sediment to the ocean every year—that's enough soil and sand to fill a line of dump trucks stretching from New York to Los Angeles!