Erosion is the process by which rocks and soil move from one location to another, either through water, wind, ice or gravity – or can even be hastened by activities such as farming, ranching or building cities that increase erosion rates.
Streams can be extremely effective erosional agents. They can transport fine sand and sediments quickly across their path, as well as erode bedrock surfaces.
Water
Water is an enormous force capable of eroding land. Erosion starts with raindrop impact, breaking apart soil aggregates and carrying away smaller particles that accumulate on surfaces such as lawns. Once in motion, flowing water transports these particles downstream where streams, rills and gullies form. Erosion occurs globally; however, its severity increases exponentially in regions with heavy and frequent rainfall.
Erosion can also be caused by natural processes, like weathering, which breaks down rock. Human activities like farming, ranching and building roads and cities may further accelerate erosion.
People who plow, hoe or plant crops alter soil structure in ways that make it more susceptible to erosion – making it looser and easier for washout or blowoff – which over time reduces productivity of the land while leading to landslides, flooding, loss of topsoil and even pollution of lakes, rivers and oceans from runoff from agriculture. Erosion accelerates desertification – turning fertile lands into dry, infertile ones.
Wind
Wind can create havoc in dry areas by dislodging soil particles and transporting them away (deflation), or by blowing sand away from its surface (abrasion). This effect is particularly prevalent in desert regions where plant life has diminished significantly and soil erosion by wind has increased dramatically.
Once soil becomes loose enough to be carried by wind, it can travel long distances over long distances, discharging its contents as the wind blows. Its speed depends on wind strength and slope of land downwind of where it originates from.
Wind erosion can be caused by various factors, including tillage, animal traffic and equipment movement across fields, field size and the presence of silt-, clay- and organic-matter deficient soils; those without clods – hard aggregates that resist wind movement – tend to be less vulnerable. Other preventative methods include building windbreaks, weighting down soil or increasing watering to make the soils heavier.
Ice
Ice, in the form of glaciers, can erode rocks. Glaciers are particularly active in frigid regions and high mountain regions where their movement creates spectacular landforms such as U-shaped valleys, hanging valleys, cirques, and aretes. Eroded material from glacial erosion is transported as glacial erratics, stratified drift, outwash plains, drumlins or drumlins before eventually depositing as varves into glacial lakes.
Glaciers erode by two processes: plucking and abrasion. Plucking occurs when rock and sediment attached to the bottom of a glacier are dislodged by its movement, carried away along its flow by plucking. Meanwhile, glacier movement grinds and scrapes away at bedrock beneath them, leaving behind scratches known as striations marks on its surface.
Erosion caused by ice is much more intense than erosion caused by wind or water; however, due to less sea ice preventing large waves from hitting Arctic shorelines and increasing coastal erosion. Therefore, Arctic regions are experiencing rapid changes both in erosion and deposition rates.
Vegetation
Plants and crop residues help decrease soil erosion by keeping its particles together and bound together, thus limiting displacement. Their roots also play an important part in keeping the ground together and bound, which reduces displacement. Their presence alters how water and wind interact with the soil, making it less vulnerable to erosion.
Speed of moving water impacts its level of erosion; for instance, currents of rivers flowing down steep hillsides tend to cause more soil loss than when moving at a steady rate through an open valley. Water speed may also help explain why meandering rivers or Oxbow lakes (those horseshoe-shaped lake structures) form.
Unfortunately, people’s pursuit of food and other agricultural products often leads them to clear land for cultivation, increasing erosion rates as the trees and grass that once stood on this space no longer hold onto soil which then washes into rivers or other bodies of water. Furthermore, this process can also cause pollution when polluted soil carries downstream to become part of lakes, rivers, or other bodies of water.