As the name suggests, wind is the transport agent in “wind erosion”. The speed of the wind must surpass a threshold in order to initiate sediment movement. This speed is referred to as the “Friction Threshold Velocity”. Larger particles (>90 μm) are usually the first particles to move, hopping along the soil surface. Each time a large particle bounces off the soil surface more sediment is released, a bit like an avalanche. This bombardment by the larger particles releases finer particles into the airstream. The smaller the particle the lighter it is and therefore the higher it can be held aloft. It is this fine fraction which is called dust (<20 μm) and can travel greater distance. Australian dust has been tracked to New Zealand and Antarctica. The dust fraction also has the highest content of organic matter and clays; this represents large sources of nutrients. Therefore wind erosion is responsible for the depletion of nutrients at source (where the dust came from) and potentially an enrichment of nutrients at sink (where the dust was deposited). Marine studies have found that dust is an important source of iron, an essential nutrient missing from pelagic food webs.
Study of water erosion is aided by the necessity of water to flow downhill. Water carrying sediment will flow down a channel. This channel will have a measurable cross section and flow rate making it relatively easy to calculate how much sediment has been transported and from where the sediment came from. Wind however does not have such boundaries. Spatially a wind event could encompass one paddock to paddocks from across the entire eastern Australian continent. Measurement of how “deep” (height) of the dust plume is difficult, relying on meteorological studies or observations by pilots. As such calculation of sediment loss and sediment source areas caused by wind erosion is problematic.
The atmospheric characteristics of each dust event help characterise the event. Meteorological measurements identify what weather systems produced the event, the possible extent and the probable direction in which the dust will travel. Regular meteorological observations build up a picture of the controlling forces at a local scale.