Erosion can be described as the process by which the Earth’s surface material becomes decomposed and worn away as a result of naturally occurring forces driven by such variables as the sun as well as the Earth’s gravity and rotation. The surface materials subject to erosion include soils, rocks, rock formations and sedimentation. When these materials come into contact with the Earth’s forces, which include ocean currents, the flow of rivers, prevailing winds and precipitation, erosion can occur. Additional sources of erosion are chemical reactions between Earth’s surface materials and the adaptation of certain animal species through such processes as burrowing. Soil erosion, specifically, can result from human agriculture as well as deforestation and the deliberate removal of naturally occurring vegetation. For this reason, erosion’s most detrimental effects take place where the disintegration of fertile land is concerned. Despite the potentially devastating effects of erosion, particularly where soil is concerned, a degree of erosion is beneficial because it helps to distribute soil and sediment resources within certain ecosystems.
What Causes Erosion?
The process of erosion is driven by a variety of variables manifest as natural forces. Of these, water has powerful, direct effects on sediment and rocks. As a liquid, water can easily drive and transport sediment particles while eroding rocks with both those particles and its own mass. This is most clearly evident in the sediment distributions found in rivers and streams and in the indentations and grooves worn into rocks directly in contact with a regular flow of water. Water plays a significant role in the erosion of sloped formations, called gullies, composed of both soil and rocks. Water’s erosive effects in the form of ice occur as glacial movement transports rocks and sediments. Water from glacial melting can further transport and erode soils while depositing rocks and larger debris that may be present in the ice. Naturally occurring streams or rivulets combined with rainfall expedite the effects of gully erosion, transporting sediments while exposing and eroding larger rocks that once lay beneath the sediment. Critical to erosion in this instance, however, is the force of gravity. By exerting a downward force on both water sources and sedimentation, gravity speeds up the erosion process and can, by itself, result in erosion.
Gravity Causes Erosion
Gravity constantly exerts a downward pressure, and sloped formations such as hills and gullies are most susceptible to its erosive effects. The extent to which gravity behaves as an eroding force in and of itself relies heavily upon both the incline of a particular area experiencing erosion as well as the mass and compaction of the soil and rocks. Imperfections, such as cracks in a region of compacted soil and rocks, may result in quicker erosion because the weight of large chunks of rock and soil debris can break away, falling farther and faster due to greater momentum than individual rocks and loose soil. The effect of gravity as an erosive force is evident in large rocks and debris frequently found at the foot of hillsides and at the bottom of gullies.
Wind Causes and Increase in Erosion
Wind speed determines the speed at which the removal of soil occurs. Low wind speeds are more likely to affect the finely-textured soil particles, whereas higher wind speeds begin to remove more coarsely-textured soil particles. To this extent, wind erosion is also manifest in the weathering of hills and rocks. As wind carries soil particles within it, any objects which lay directly in its path become vulnerable to abrasion by the wind as well as by the traveling soil particles. This process is often referred to as “sand blasting”.
Certain Soil Properties Cause Erosion To Happen Easier
The properties of soil affect its susceptibility to wind erosion. Variables including, but not limited to, deforestation, the presence of chemicals, construction and public works, and agricultural activities all contribute to making soil less cohesive. Though such human industrial and agricultural activities play a significant role, incidence of wind erosion is dependent upon a number of variables related to the climate of a region. These variables include temperature, wind speed, humidity, and incidence of precipitation. Though each may vary independently from one another, the overall magnitude of these variables helps to determine the extent to which wind erosion occurs. Wind erosion is characteristic of dry regions such as deserts. Prevailing wind currents are powerful enough to carry soil and dust particles any number of distances. To this extent, the effects of wind erosion depend on the speed of the wind as well as the size of the soil particles. In drier regions, the soil tends to erode more quickly because moisture content behaves as an adhesive. As wind erodes soil, it also erodes hills and rockstructures that might lie in its path. The abrasive action of wind-born soil compounds the effects of wind erosion on such structures. This is evident in the buildup and diminishing of sand dunes as well as in the smoothed-out and worn areas of rock formations present in such dry regions.
Cohesiveness of Soil and How it Affects Erosion
The cohesiveness of soil depends upon how fine or coarse its particles are in combination with the presence of moisture. Additionally, the presence of vegetation serves to add further cohesion to soil due to root structures. The effect of human activities on soil under these conditions always increases the vulnerability of soil to wind erosion through the artificial displacement of soil. Construction work, agricultural production, and deforestation all lower the cohesiveness of soil. Such activities remove soil layers, exposing more moist layers below the ground. The soil from beneath the surface becomes broken up and, consequently, less compact. This causes moisture loss. In addition, construction and agriculture work often involves the use of chemicals which, environmentally harmful or not, become absorbed by the soil. Such agents remove further moisture from the soil.
Aridity or Soil Dryness Can Increase Erosion
The most important climatic variable which determines the susceptibility of soil to wind erosion is dryness, or aridity. A dry, arid climate is chiefly characterized by a lack of moisture in the form of humidity and precipitation. Under the circumstances of moisture, soil is more cohesive and less vulnerable to being moved by wind. In a dry climate, the soil is dry and incohesive, which lends it to being easily eroded by the wind. Given a constant wind speed, the ease with which soil erodes is inversely proportional to the size of individual soil particles. Small particles are light and are transported by wind farther than more coarse particles, which are heavier. The occurrence of wind erosion under the appropriate climatic conditions can be best exemplified by the “Dust Bowl” of the American mid-west during the early- to mid-1930s. The “Dust Bowl” was a period of severe drought during which the majority of the agricultural land of the Great Plains experienced a series of dust storms. These dust storms, ultimately, resulted in the erosion of parched soil which no longer constituted arable farm land. Though it was later determined that excessive crop planting and over-dependence on rain contributed greatly to the devastating effects of this period, the climatic conditions for such a catastrophe were all present. First, the lack of rain combined with heat resulted in a dry, or arid, climate. Second, the dryness parched the soil such that it lacked cohesion. Lastly, the winds which caused the dust storms were so strong that both fine- and coarse-textured soil became easily displaced.