Erosion is the natural process where the earth and its soils are broken down by wind and water. As a result of this natural process, channels, gulleys, canyons and many other natural geological phenomena are created over hundreds or thousands of years. According to National Geographic, erosion by wind and water are responsible not only for small scale geological features, but also large-scale ones such as the Grand Canyon.
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As water falls onto a geological feature, such as a mountain, gravity pulls the water down, coalescing it into one or more places where it naturally encounters the least resistance on its way down to lower elevations. The natural pathway that water takes from places of higher elevation to lower elevations also causes the soils and rocks along that pathway to erode into features such as stream channels or small canyons, which may take several decades or hundreds of years. In large weather events, flash floods can dramatically cause quick changes in the landscape.
Another major contributor to erosion is the wind, especially in desert environments with mountains, where the winds can carry grains of sand at high speeds, hitting rock formations and degrading the rock. Over time, just as water can shape the earth's soils and rocks, wind can also change and shift Earth's geological formations; however, evidence of wind erosion is much more subtle than water-based erosion sites. One of the best examples of wind erosion is shifting sand dunes in deserts.
Although not technically considered erosion, primary succession does involve the breaking down of rocks over time; however, in this case, the rocks are broken down into soils by plants. Mosses and lichen are responsible for the initial stages of primary succession, where rocks are slowly broken down as these plants sink their root structures into the rock searching for water and minerals. Over time, enough rock is broken down into soil so that smaller plants or tree shoots can take root.
In urban development and community planning, the issue of erosion is of major importance due to the risk of freshwater ecosystems becoming easily contaminated by sediment runoff caused by erosion. Sediment runoff is the number one danger to the health of freshwater ecosystems, as the turbidity of the water becomes less clear and waterborne animals are not able to breathe. As a result, communities should seek to enact and enforce steep slope development ordinances and maintain a buffer zone between construction sites and freshwater sources.