Understanding the Process of Wind Erosion

Every year, millions of tonnes of fertile topsoil disappear – not washed away by rain, but lifted and carried off by the wind. Wind erosion is far more than just dust blowing around on a dry day. It is a structured, sequential process that begins the moment wind velocity crosses a critical threshold and ends only when particles are finally deposited, sometimes hundreds or even thousands of kilometres from where they started. Understanding exactly how this process unfolds – from the first movement of a soil grain to its eventual settling – is essential for anyone working in soil and water conservation or agricultural land management.

Wind erosion as a three-phase process 🔗

According to the USDA Agricultural Research Service, wind erosion consists of three distinct phases: initiation of soil particle movement (detachment), transportation of soil particles, and deposition. Each phase is governed by specific physical forces, and each has direct consequences for soil health and agricultural productivity. Colorado State University Extension notes that wind erosion damages soil by physically removing the most fertile components – clays, silts, and organic matter – lowering water-holding capacity and degrading soil structure, which ultimately reduces crop production.

Phase 1: Initiation – how wind gets soil moving 🔗

Soil particles do not move the instant any breeze passes over them. Movement begins only when wind velocity reaches a specific minimum, known as the threshold velocity. Global Road Technology explains that for each specific soil type and surface condition, there is a minimum velocity required to move soil particles, and once that threshold is crossed, the quantity of soil moved depends on particle size, adhesion between particles, and the wind velocity itself.

Research published through the USDA-ARS shows that at 15 cm above the ground, the threshold velocity for small soil grains ranging from 0.1 to 0.15 mm in diameter is approximately 12-14 metres per hour. The USDA Natural Resources Conservation Service (NRCS) further specifies that winds are considered erosive when they reach 13 miles per hour (about 21 km/h) at 1 foot above the ground, or approximately 18 miles per hour at a height of 30 feet.

The nature of the soil surface plays a significant role here. Colorado State University Extension points out that erosive wind energy increases by a factor equal to the velocity cubed – meaning even a small rise in wind speed results in a disproportionately large increase in erosive force. A rough or cloddy surface, or one protected by vegetation, requires stronger winds to initiate particle movement. On a bare, smooth, dry field, the threshold is crossed far more easily.

Once the wind force against soil particles becomes sufficient to overcome gravitational force, detachment occurs. The USDA-ARS notes that once detached, moving particles may collide with and dislodge other particles, setting off a chain reaction across the soil surface.

Wind turbulence plays a critical role in this initiation phase. The NRCS Wind Erosion Overview describes wind erosion as a complex process involving detaching, transporting, sorting, abrading, avalanching, and depositing of soil particles, with turbulent winds blowing over erodible soils being the fundamental driver.

Phase 2: Transportation – three modes of soil movement 🔗

Once particles are detached, wind transports them in one of three ways, determined primarily by particle size and wind speed. The University of Nebraska-Lincoln’s PASSEL resource identifies these three modes as suspension, saltation, and surface creep, each carrying different fractions of the total eroded soil.

Saltation – the dominant transport mechanism 🔗

Saltation is the most significant of the three processes in terms of volume. According to the USDA Southwest Climate Hub’s Dust Mitigation Handbook, individual particles or aggregates ranging from 0.1 to 0.5 mm in diameter lift off the surface at a steep angle of 50 to 90 degrees and follow distinct trajectories under the combined influence of air resistance and gravity. They return to the surface at much shallower impact angles of 6 to 14 degrees from the horizontal. Upon impact, they either rebound or embed themselves – and in both cases, they initiate movement in other particles, creating what is described as an avalanching effect.

Most saltation occurs within 12 inches (about 30 cm) above the soil surface, and the length of a typical saltating particle’s trajectory is roughly ten times its maximum height. Wikipedia’s article on Aeolian processes notes that saltation likely accounts for 50-70% of total deflation. The PASSEL resource from the University of Nebraska-Lincoln places this figure even higher, at 50 to 90% of total soil movement by wind, depending on conditions.

Saltating particles also act as abrasive agents – the Southwest Climate Hub describes them as “abrading bullets” that remove protective soil crusts and break down clods, progressively making the surface more erodible. This is also related to a process called attrition, where the repeated bouncing and collision of particles in flight gradually breaks them into finer fragments, making them increasingly susceptible to suspension.

Suspension – the long-distance carrier 🔗

Queensland Government’s wind erosion resource defines suspension as the movement of very fine particles – less than 0.1 mm in diameter – that are lifted into the atmosphere either by direct wind force or through impact with saltating particles. These particles include very fine sand grains, clay particles, and organic matter.

Once airborne, these particles are fully entrained in the wind and can travel extraordinary distances. Global Road Technology explains that particles around 0.01 mm may travel hundreds of kilometres, while particles as fine as 0.001 mm can travel thousands of kilometres – with documented cases of Australian soil being transported to New Zealand and beyond. Fine dust remains in suspension until either the wind subsides or it is washed out by rainfall.

Purdue University’s WEPP documentation notes that while soil can be blown at virtually any height, over 93% of all soil movement by wind takes place at or below one metre above the surface. Suspension, however, is the exception – these fine particles can be carried high into the atmosphere, making suspension the most visually dramatic and easily recognisable form of wind erosion, often manifesting as large-scale dust storms.

The Southwest Climate Hub notes that suspension increases progressively in the downwind direction, and on long, exposed fields can ultimately exceed the combined volume of soil moved by saltation and surface creep combined. It estimates that between 20% and more than 60% of eroding soil may be carried in suspension, depending on soil texture.

Surface creep – the slow roll of heavy particles 🔗

The largest particles involved in wind erosion – those ranging from 0.5 mm to 2 mm in diameter – are too heavy to be lifted off the ground but are set into rolling or sliding motion by the energy transferred from saltating particles. This process is called surface creep.

The Queensland Government explains that these particles move through surface creep wind erosion over only a few metres, colliding with and dislodging other particles as they roll. The NRCS notes that under high winds, the entire soil surface can appear to be moving slowly forward as particles are continuously pushed and rolled by the saltation flow. Surface creep typically accounts for 7 to 25% of total wind-eroded transport.

Research published via ResearchGate clarifies that surface creep generally involves particles approximately ½ to 1 millimetre in size – large enough to resist being lifted, but small enough to be pushed by wind. These rolling particles stop when the wind slows, when they are blocked by other particles, or when they settle into a sheltered location such as a furrow or vegetated patch.

The avalanching effect: how erosion intensifies downwind 🔗

One of the most important aspects of wind erosion that is often overlooked is how it accelerates along the length of an exposed field. The Southwest Climate Hub’s Dust Mitigation Handbook explains that as saltating particles accumulate downwind, they increase the frequency of surface impacts, which in turn breaks down clods and crusts and produces a progressively smoother, more erodible surface. This self-reinforcing cycle is known as the avalanching effect. The more erodible the soil, the shorter the distance over which this maximum erosion rate is reached.

This is why a small bare patch in an otherwise protected field can quickly become a major erosion source – once the process starts, it builds momentum rapidly in the downwind direction.

Phase 3: Deposition – where eroded soil ends up 🔗

The final phase of wind erosion is deposition, which occurs when wind velocity drops below the level needed to keep particles in motion. USDA-ARS describes deposition as occurring when gravitational force finally exceeds the forces keeping a particle airborne or in motion. Heavier particles – those moved by saltation and surface creep – are deposited first, settling in furrows, vegetated strips, ditches, fencerows, or behind windbreaks. Fine suspended particles, however, may not settle until they have travelled hundreds or thousands of kilometres.

Deposition is not merely the end of an erosion event – it has significant agricultural consequences. Soil deposited in unwanted areas can smother crops, block drainage systems, and reduce the fertility of receiving lands. Meanwhile, the source area – typically productive cropland – is left depleted of its finest, most nutrient-rich fractions: the clays, silts, and organic matter that were carried furthest by the wind.

Factors that influence the wind erosion process 🔗

Several interacting factors determine the intensity of wind erosion at any given location. The NRCS Wind Erosion Overview identifies the key influences as the erodibility of the soil surface, wind velocity and turbulence, the presence or absence of vegetative cover, field length in the direction of the prevailing wind, and surface roughness. Wherever the soil surface is loose and dry, vegetation is sparse or absent, and wind is sufficiently strong, erosion will occur unless active control measures are applied.

Global Road Technology specifically highlights soil moisture as one of the prime factors: when soil moisture decreases, the cohesive bonds between soil particles weaken, making individual grains far easier to detach and transport. Vegetation cover is equally critical – Wikipedia’s aeolian processes article notes that vegetation cover of as little as 15% is sufficient to eliminate most sand transport, demonstrating just how effective even sparse plant cover can be in interrupting the erosion process.

In India, Rama University’s Soil and Water Conservation Engineering lecture notes point out that wind erosion is most commonly observed in arid and semi-arid regions with inadequate precipitation – particularly Rajasthan and parts of Gujarat, Punjab, and Haryana – where loose, dry, finely granulated soils are exposed to high-velocity winds over flat, bare terrain.

What do you think? Given that saltation is responsible for triggering both suspension and surface creep, do you think managing the very first stage of particle detachment could be more effective than trying to control the later stages of transport? And considering that even 15% vegetation cover can significantly reduce wind erosion, what practical challenges do farmers in arid regions face in maintaining that minimum threshold of ground cover?

References

1. https://www.ars.usda.gov/ARSUserFiles/30200525/419PrinciplesofWinderosionanditscontrol.pdf
2. https://www.extension.colostate.edu/docs/pubs/crops/xcm180.pdf
3. https://globalroadtechnology.com/wind-erosion-types-factors-causes/
4. https://www.ars.usda.gov/ARSUserFiles/24758/11.%20A%20review%20of%20wind%20erosion%20models%20Data%20requirements%20processes%20and%20validity.pdf
5. https://efotg.sc.egov.usda.gov/references/public/TX/Wind_Erosion.pdf
6. https://passel2.unl.edu/view/lesson/5653c03d7cee/19
7. https://dust.swclimatehub.info/2.1
8. https://en.wikipedia.org/wiki/Aeolian_processes
9. https://www.qld.gov.au/__data/assets/pdf_file/0021/65217/wind-erosion.pdf
10. https://milford.nserl.purdue.edu/weppdocs/overview/wndersn.html
11. https://www.researchgate.net/figure/Soil-particles-can-move-through-saltation-creep-and-suspension_fig1_253553937
12. https://www.ramauniversity.ac.in/online-study-material/agriculture/agriculturec/iisemester/soilandwaterconservationengineering/lecture-11.pdf