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Learning About Erosion

Part 1 of 3:
Some Changes Occur Slowly.

Mountains do not pop up overnight. They are slowly lifted from beneath by gradual movements of rock beneath the surface. Mountains are made of rock, which is visible on the steepest slopes and hidden in other places by a thin layer of soil. Look at the appearance of each mountain in the pictures. From one day to another they look the same. Mountains do not change much from one year to the next. But what if you could see them again after a hundred years? A thousand years? How much would they change in a million years?

Over long periods of time, millions and millions of years, mountains rise, then disappear. They are gently lifted from below, and slowly worn down from above. If a mountain is lifted faster than it is worn down, it becomes higher. If it erodes faster than it grows, it loses height. Erosion goes on all the time, century after century, changing the shape of the mountain. When the rock underneath stops pushing up, erosion wears the mountain down.

Go back to introduction.	Go to part 2.