Wind erosion and land degradation – An Overview

What is wind erosion? 

Wind Erosion is the natural process of transportation and deposition of soil by the wind. It is a common phenomenon occurring mostly in dry, sandy soils or anywhere the soil is loose, dry, and finely granulated. Wind erosion damages land and natural vegetation by removing soil from one place and depositing it in another. The main mechanism of wind erosion is wind propelling sand and dirt causing erosion.

Over time all the impacts of the loose sand on the rocks start to make the rocks chip away and erode. Wind erosion is obviously more common in windy areas. Let us take it back to earth science. Erosion is the action of surface processes such as wind that remove soil, rock, or dissolved material from one location on the Earth’s crust and then transports it to another location. Wind erosion can be caused by a light wind that rolls soil particles along the surface through to a strong wind that lifts a large volume of soil particles into the air to create dust storms. As wind erosion is the wind-forced entrainment, transportation, and deposition of soil particles it causes devastating global environmental degradation through the movement of fine nutrient-rich surface soil particles to water bodies, air, and other land surfaces. This in turn decreases cropland productivity and increases the risk to human life. Wind erosion also impairs soil properties such as structure, moisture content, and organic matter, and it is enhanced by the lack of vegetation on the soil surface.

In this article we delve deeper into understanding:

• Types of wind erosion. 
• Factors contributing to wind erosion.
• Causes of wind erosion. 

Learn more about Global Road Technology’s erosion control application here.

What are the types of wind erosion?

There are three types of wind erosion, namely

1. Surface creep
2. Saltation
3. Suspension

Surface creep in a wind erosion event, involves rolling across the surface of large particles ranging from 0.5 mm to 2 mm in diameter. This causes them to collide with, and dislodge other particles. Surface creep wind erosion results in these large particles moving only a few meters. Saltation occurs among middle-sized soil particles that range from 0.05 mm to 0.5 mm in diameter. Such particles are light enough to be lifted off the surface but are too large to become suspended. These particles move through a series of low bounces over the surface, causing an abrasion on soil surface and attrition which is the breaking of particles into smaller particles. Suspension involves tiny particles less than 0.1 mm in diameter being moved into the air by saltation, forming dust storms when taken further upwards by turbulence. These particles include very fine grains of sand, clay particles, and organic matter. However, not all dust ejected from the surface is carried in the air indefinitely. Larger dust particles (0.05 to 0.1 mm) may be dropped within a couple of kilometers of the erosion site. Particles of the order of 0.01 mm may travel hundreds of kilometers and 0.001 mm sized particles may travel thousands of kilometers. Near home examples, would include transportation of Australian soil to New Zealand and beyond. Fine dust may remain in suspension in the air until it is washed out by rainfall. 

Which factors contribute to wind erosion?

The factors that contribute to wind erosion include soil moisture and wind speed. That way the water molecules bind themselves together, and how they hold together in the soil is a very strong bond. This cohesiveness will be evident all the way up the column of soil if they are a good percentage of soil moisture. If soil moisture starts to fall, the water in the soil column will be less, the soil will be drier and more sensitive to wind erosion. Wind speed is always difficult to calculate with regards to its capabilities of causing wind erosion. The soil moisture will influence what the speed will have to be. The size of the soil particles at the surface will be a factor in the equation. How much ground cover is there? Is the field freshly prepared, nice, flat and level with nothing covering it? The form of mechanization used in a farming context plays party to the susceptibility to wind erosion. For example, has the farmer taken a disc across the field that he harvested his corn? Whether he has used the disc to loosen the soil and to cut up the stalks and root balls left after the harvest or has not removed them matters. Their presence becomes an impedance to wind speed. Lack of physical barriers separating fields to impede wind over a long distance contribute to wind erosion. Overall, having a closer look at the Universal Soil Loss Equation, soil moisture is one of the prime factors in the equation and wind speeds are not as one would theoretically say. However, in practice the different factors work in collaboration and synergy to contribute to wind erosion.           

What are the causes of wind erosion?

Wind erosion can be caused by activities that reduce ground cover below 50% and remove trees and scrub that act as windbreaks. Soil movement is initiated because of wind forces exerted against the surface of the ground. For each specific soil type and surface condition, there is a minimum velocity required to move soil particles. This is called the threshold velocity. Once the velocity is reached, the quantity of soil moved is dependent upon the particle size, the adhesion of the soil particles, and the wind velocity itself. Land clearing, over-grazing by livestock, and cropping are activities that leave the soil exposed to the wind. Drought causes greater wind erosion because less rain means lower vegetation growth and it is vegetation that binds the soil in place. Less moisture in the soil, makes it easier for soil particles to be blown away. All in all, drought will deteriorate soil, when the drought ends and the rains begin, the soils will not have any mechanisms with which to maintain composure, and they will be eroded swiftly and efficiently. Vegetation can agitate soil and many farming practices disturb the ground. The process of removing vegetation and ploughing land without properly preparing the site is often the main cause. Livestock such as goats, sheep, cattle, horses and ponies expose topsoil by eating grasses and shrubs. Although this helps the ecosystem, too much won’t be good for the land. Overgrazing can also destroy the soil structure by compaction of the soil by the animals, reducing infiltration and increasing susceptibility to wind erosion. Excessive logging is never good for the environment. Trees protect the ground from wind erosion and removing trees without replacing them will put the land area at risk from wind erosion.  

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REFERENCES 

• Principles of Wind Erosion and its Control – http://www.jnkvv.org/PDF/0704202017563554201706_07.pdf Retrieved 22/05/21
• Wind erosion – https://www.environment.nsw.gov.au/topics/land-and-soil/soil-degradation/wind-erosion. Retrieved 22/05/21