Wind erosion is a natural process where wind removes and transports soil, sand, and rock particles from one location to another. This phenomenon contributes to land degradation globally, impacting approximately 28% of the world’s land area and affecting about 430 million hectares of drylands. Understanding the mechanisms and factors involved in wind erosion is important for managing landscapes and mitigating its effects.
The Driving Force: Wind
Wind initiates erosion by exerting force on the soil surface. For particle movement to begin, wind must reach a specific speed known as the threshold velocity. This velocity can be around 13 miles per hour (mph) at one foot above the ground, or about 18 mph at a height of 30 feet. Stronger winds generate more force, increasing their capacity to detach and transport soil particles.
The duration of wind exposure also influences erosion, as prolonged winds can dry out the soil surface, making it more susceptible to movement. Wind turbulence, characterized by unpredictable changes in wind speed and direction, further enhances erosive power by creating eddies that lift particles from the surface.
How Soil Particles Move
Once the wind’s force overcomes the soil particles’ resistance, these particles move through three primary mechanisms.
Surface Creep
Surface creep involves larger, heavier particles, typically ranging from 0.5 to 2 millimeters in diameter, that are too heavy to be lifted into the air. These particles are rolled or slid along the ground by the direct force of the wind or by impacts from other moving particles. Surface creep usually moves particles only a few meters and accounts for about 5% to 25% of the total soil movement by wind.
Saltation
Saltation is the most significant mechanism, responsible for 50% to 90% of total soil movement, and involves medium-sized particles, generally between 0.05 and 0.5 millimeters. These particles are light enough to be lifted by the wind, travel a short distance in a hopping or bouncing motion, and then fall back to the surface. Upon impact, saltating particles often dislodge other particles, initiating further movement and contributing to an “avalanching” effect. Most saltating particles remain within 30 centimeters of the ground.
Suspension
Suspension occurs when very fine particles, less than 0.1 millimeters in diameter, are lifted high into the air by strong winds and turbulence. These minute particles, including fine sand, clay, and organic matter, can remain suspended for extended periods and travel vast distances, sometimes thousands of kilometers from their origin. This process is particularly noticeable during dust storms, where fine dust is carried high into the atmosphere.
Conditions That Influence Erosion
Beyond the direct force of wind, several environmental and land-surface conditions influence the susceptibility and severity of wind erosion.
Soil Type and Structure
Loose, dry, and sandy soils are more prone to erosion because their particles have less ability to bind together. Cohesive soils like loams, clay loams, and silt loams, with stable aggregates and higher organic matter content, are more resistant to particle detachment.
Vegetation Cover
Vegetation cover is a primary defense against wind erosion. Plants protect the soil surface from direct wind force, reduce wind speed at ground level, and hold soil particles in place with their root systems. Bare land, lacking this protective cover, is vulnerable to wind erosion; a 30% ground cover is often necessary to prevent it.
Surface Roughness and Topography
Uneven surfaces, such as those with ridges, depressions, or natural obstacles like rocks or small hills, create friction that reduces wind speed and can trap moving particles. Flat, smooth surfaces allow wind to flow unimpeded, increasing the potential for erosion.
Soil Moisture Content
Dry soil is more susceptible to erosion than moist soil. Water acts as a binding agent, holding soil particles together and increasing their resistance to wind forces. Conditions leading to dry soil, such as drought, can exacerbate wind erosion.
Visible Signs and Immediate Outcomes
Wind erosion leaves distinct, observable signs on the landscape and in the atmosphere.
Dust Plumes and Storms
One indicator is the formation of dust plumes and large-scale dust storms, where vast quantities of fine soil particles are lifted into the air, reducing visibility and impacting air quality. These storms can transport dust for hundreds or even thousands of miles.
Sand Drifts and Dunes
Accumulation of transported material forms sand drifts and dunes. These formations occur as saltating and creeping particles are deposited in areas where wind speed decreases or encounters obstacles.
Loss of Topsoil
The loss of fertile topsoil is a consequence, as the finer, nutrient-rich upper layers of soil are selectively removed, leaving behind less productive subsoil or coarser materials. This removal can decrease rooting depth for plants and reduce agricultural yields.
Abrasion
Abrasion is a visible result of wind erosion, where impacting soil particles can damage plants, structures, and even natural rock formations. This “sandblasting” effect can destroy young crops, expose plant roots, and contribute to the physical deterioration of infrastructure.