- Written by Nadia O'Carroll
For dust storms to occur the ground must have fine, loose, dry particles of dust or soil and the weather conditions must feature strong dry surface winds and vertical turbulence. These conditions exist in arid or semi-arid regions. Although dust storms are a natural phenomena in dryland areas, their frequency and intensity are predicted to increase due to human activities. Deforestation, over-grazing, agriculture and development cause desertification, a process where topsoil is exposed and blown away creating a desert. The worldwide use of 4WD vehicles offroad in desert areas is beginning to contribute to this too. Many desert surfaces have been stabilised over thousands of years by a layer of lichen, algae or gravel when this protective layer is breached the soil is exposed.
If a soil particle is not held by moisture, vegetation or soil structure, when the force of the wind passes over it, it will vibrate, then leap upwards. If the wind is moving quickly enough, the particle remains suspended in the air and is lifted higher, to altitudes of 3,000 metres, depending on the atmospheric stability above. Friction causes static electricity and this accelerates the process.
Dust storms have global environmental implications. It is now possible to track dust storms, a dust cloud from China went around the world in 13 days, the pathways and trajectories of dust storms can be diverse. Dust storms transport huge volumes of soil – in 2002 a major dust storm in Australia had a dust load of estimated at 4.8 million tonnes, and was depositing dust in the Tasman Sea at rate of approximately 75,000 tonnes of dust per hour.
Once in the atmosphere dust clouds can reflect and absorb radiation from the sun but their role in climate modelling is not yet fully understood.
The dust clouds contain a wide variety of materials – minerals, quartz, chemicals, pollen, soils, pollutants as well as microorganisms such as fungal spores, viruses and bacteria. There is a potential for pathogens to be transported and it is believed that microbes from dust blown from Africa has damaged coral reefs in the Carribean.
Dust storms are damaging, yet they can also be beneficial to the environment by redistributing nutrients such as iron and nitrogen to forests and oceans. They can also have a great impact on the amount of air particle concentration, in Sydney the rate of micrograms per cubic metre increased from the usual 20 to 15,400 during the dust storm.
The dust that blew across the East Coast was predominantly reddish due to its high iron content, but the colour of the haze varied from red, pink, orange, and yellow to grey. This is because the size and uniformity of the dust particles reflect and scatter the wavelengths of sunlight in complicated patterns
As the dust storm follows its pathway across the Tasman, some of the New Zealand snowfields will have a dusting of red added this year.