Rivers
Rivers are a powerful force that can build islands, carve canyons, create waterfalls, provide electric power and drinking water, and give us many hours of enjoyment. Read through the slides to learn about rivers.
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Rivers usually flow into the ocean. Most areas of our country have a river. Some of these rivers are short, and some, such as the Mississippi River, are very long. The Mississippi River is the longest river in the United States; it is close to 3,900 km long.
Some rivers begin as tiny trickles of water from a lake. Other rivers begin as water bubbles up from under the ground. But most rivers begin when rain and snow fall on mountains and hills—as the snow melts it trickles down the mountainside to form tiny streams. Then many tiny streams join together to make bigger streams. Eventually these streams form a river.
As a fast-flowing river pushes hard against the soil on both sides of its banks, it loosens the sand, stones, and plants, and they are swept into the moving water. This wearing away of the ground is called erosion.
When the water in a river moves very slowly, it does not carry bits of rock, sand, and plants with it. Instead, these become sediment on the bottom of the river. When a lot of sediment falls to the bottom, it eventually builds up to form a new piece of land, which we call an island.
The land next to a river is called a flood plain because the water often spills over. The flood plain is the land that is flooded when the river water goes over its banks during heavy rains. A flood plain contains very good soil for growing crops.
An example of the power of a river can be seen in the Grand Canyon in Arizona. A canyon starts to form when a river erodes dry, rocky land. The water cuts a path that gets deeper and deeper over millions of years. Click the picture to the right to see a larger version image of the Grand Canyon.
