Wind erosion occurs when soil is detached from the Earth’s surface, transported by wind and then deposited in another location. It occurs when the force of the wind overcomes the adhesion of the soil particles.

Factors that influence wind erosion include:

• wind speed and duration.
• soil properties and particle size.
• vegetation cover.
• land management practices.

Wind erosion is a natural process, but can be affected by human activities which remove ground cover and expose more soil, such as farming, grazing animals, or construction.

Wind erosion can lead to loss of topsoil, resulting in reduced growing capacity, reduced water penetration of the soil, increased water run-off and drought vulnerability, dust storms, and desertification.

How far the soil moves depends on the wind speed, the properties of the soil and its moisture level. Light winds tend to move only fine/light soil particles, whilst heavier winds can move larger particles. Soil that is wet is more difficult to move, because its adherence is increased and it is heavier.

The wind moves soil in three different way.

1. Surface creep: Heavier particles roll or slide along the surface, pushed by the force of the wind. As they move they dislodge other soil particles. These larger particles tend to only move a few metres.
2. Saltation: Mid-sized particles, light enough to be lifted off the ground but too heavy to be suspended, bounce along the surface. As they bounce they abrade the surface further, and break into smaller particles themselves. These smaller particles might then be small enough to become suspended.
3. Suspension: Tiny particles, usually less than 0.1mm in diameter, are lifted off the ground and suspended in the air. They include very fine particles of sand, clay and organic matter. The larger of these particles (between 0.05-0.1mm) are usually deposited within a few kilometres of the erosion site. Particles around 0.01mm may be carried and deposited hundreds of kilometers away, and particles smaller than this can be carried thousands of kilometers from the original erosion site!

Wind is the movement of air over the surface of the Earth. Winds are driven by the heat from the Sun, which warms the air and causes it to rise. Where warm air rises, cool air flows in to take its place. This motion is felt on the Earth’s surface as wind. Wind is described in terms of its strength or speed and the compass direction from which it is blowing. Wind speed can be expressed in kilometres per hour, metres per second, knots, or as a force on the Beaufort wind force scale.

When weather forecasters describe the wind they usually include information about both its strength and direction. For example, a fresh south-westerly wind is a wind blowing from the south-west at an average speed of 30–39 kilometres per hour (the speed of a ‘fresh breeze’ on the Beaufort scale). The term ‘gusty’ is often used in weather reports to describe winds that have sudden increases above the average speed for short periods of time. Knowledge of wind strength is useful for recreational activities like sailing, the safety of people working in high places or at sea, and for forecasting the movement of pollution and smoke from bushfires to populated areas.

The Beaufort scale was developed by Naval officer Sir Francis Beaufort in 1806. Wind is classified into categories based on its speed, from calm (no wind) to hurricane force (wind speed over 118 kilometres per hour). Wind speed always increases with height above the ground, so wind speeds in the Beaufort scale are measured at a height of 10 metres above open, flat ground.

Soil is the loose material that covers most of the Earth’s land surface. 

The small particles are either sand, silt, or clay. The amount of sand, silt, or clay in a soil gives the soil its texture and determines how much air and water the soil can hold.

• Sand particles are relatively large, so sandy soil holds a lot of air and drains water freely. Sand makes the soil feel gritty.
• Silt particles are smaller than sand, so soil high in silt holds a moderate amount of water and air.
• Clay particles are the smallest, so clay-based soils hold a lot of water and little air. This can make it difficult for the roots of plants to take in oxygen. Clay makes the soil feel silky to the touch.

Loam is a combination of sand, silt, and clay and is the ideal soil for growing plants.

Humus (a Latin word meaning earth or ground) is the decomposed plant and animal matter in soil. It is important because it provides nutrients, contributes to water and air retention, and provides food and habitat for the microorganisms that live in the soil. Humus is stable, meaning it can't be decomposed any further. Organic matter that is still being broken down, or decomposing, is called compost.

Soil composition is different in different places. These differences can be seen in a very small distance, such as from one side of a garden or farm to the other, as well as from country to country. The differences depend on the type of rocky material and plant matter from which the soil was made and the kinds of organisms that live in, around, and on the soil.

Dirt is typically only made up of sand, clay or silt particles, but may also contain rocks. It is devoid of humus and compost, and because of this lacks the nutrients required for plant and animal life.