Erosion

As already mentioned, sediment grains and chemical solutions are common products of erosion. Wind, water, ice, or gravity transport these products from their site of origin and lay them down elsewhere in a process known as deposition. Deposition, which occurs in large depressions known as basins, is considered to be a separate process from erosion.

Soil is also an erosional product. Soil is formed primarily by chemical weathering of loose sediments or bedrock along with varying degrees of biological activity, and the addition of biological material. Some soil materials may also have undergone a certain amount of transport before they were incorporated into the soil.

Another important product of erosion is the landscape that is left behind. Erosional landscapes are present throughout the world and provide some of our most majestic scenery. Some examples are mountain ranges such as the Rocky Mountains, river valleys like the Grand Canyon, and the rocky sea cliffs of Northern California. Anywhere that you can see exposed bedrock, or where there is only a thin layer of regolith or soil covering bedrock, erosion has been at work creating a landscape. In some places one erosional agent may be responsible for most of the work; in other locations a combination of agents may have produced the landscape. The Grand Canyon is a good example of what the combination of flowing river water and mass wasting can do.

In addition to producing sediment, chemical solutions, soil, and landscapes, erosion also has some rather negative impacts. Two of the most important of these concern the effect of erosion on soil productivity and slope stability.

Soils are vital to both plants and animals. Without soils plants cannot grow. Without plants, animals cannot survive. Unfortunately, erosion can have a very negative impact on soil productivity because it decreases soil fertility. Just as erosion can lead to the deposition of thick layers Dust storms, like this one, occur when soils not properly anchored by vegetation are subjected to dry conditions and winds. FMA Production. Reproduced by permission. of nutrient rich material, thereby increasing soil fertility, erosion can also remove existing soil layers. Soil forms very slowly—a 1-in (2.5-cm) thick soil layer typically takes 50-500 years to form. Yet an inch of soil or more can be eroded by a single rainstorm or windstorm, if conditions are right. Farming and grazing, which expose the soil to increased rates of erosion, have a significant impact on soil fertility worldwide, especially in areas where soil conservation measures are not applied. High rates of soil erosion can lead to crop loss or failure and in some areas of the world, mass starvation. On United States farmland, even with widespread use of soil conservation measures, the average rate of soil erosion is three to five times the rate of soil formation. Over time, such rates cut crop yields and can result in unproductive farmland.

Erosion is also a very important control on slope stability. Slopes, whether they are small hillsides or large mountain slopes, tend to fail (mass waste) due to a combination of factors. However, erosion is a significant contributor to nearly all slope failures. For example, in California after a drought has killed much of the vegetation on a hillside, the rains that signal the end of the drought lead to increased erosion. Eventually, due to the increased erosion, the slope may fail by some type of mass wasting, such as a mudflow or landslide.