Notes

Water that has frozen into ice can change the landscape, too. Over time, ice and snow in cold regions, such as near the poles or near the top of tall mountains, can build up to form huge masses of moving ice and snow called glaciers Opens in modal popup window.

Gravity causes glaciers to move slowly over the land. As they move, they can pick up rocks and soil from the ground and carry them over long distances. Although much of the material carried by glaciers is small, they can carve out U-shaped valleys and other unique land features. Many parts of the world used to be under glaciers and show evidence of glacial erosion.

Winds can pick up and carry small rock pieces for thousands of miles. For example, scientists have found dust from African deserts on the islands of Hawaii. Global winds carried these dust particles to there. In general, winds can carry only small particles over such long distances. Strong winds can carry larger rock pieces, but only over shorter distances. The particles carried by winds can act like sandpaper, wearing away wood, rock, and even metal.

Erosion is an important natural process that has been happening for years. The movement of soil and rock from place to place helps transport important nutrients over the earth's surface. However, erosion can also cause problems for people. For example, if the ground beneath a road or building erodes, the road or building can collapse. Although erosion is a natural process, people's actions can make erosion more or less likely to happen. For example, plant roots help hold soil in place. When people remove the plants from an area, erosion can increase because the soil moves more easily. In many areas, people are trying to reduce erosion to prevent damage to roads, buildings, and farmlands. One example of erosion's effect on people is a sinkhole.

People can use different methods to reduce erosion. One way is to build walls or barriers. A terrace is a sloped plane that is cut into a series of successively receding flat surfaces that resemble steps. Terraces are often used in farming. Graduated terrace steps are commonly used to farm hilly or mountainous terrain. Terraced fields both decrease erosion and surface runoff.