When dust storms descend

By Karen McGhee 20 December 2010
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Dust storms are nothing new to Australia, despite the alarm felt by Sydneysiders when a red haze descended.

RECKON IT WAS dusty in Sydney ‘cos you couldn’t see the [Centre-point] Tower? Sheesh – you should have been here!” said long-time Broken Hill resident Doug Banks, after the so-called Red Dawn dust storm engulfed the NSW capital in late September.

The severity of the spring event was certainly unusual for Australia’s east coast. But in western NSW, closer to the inland source of the airborne dirt, it was part of a particularly nasty start to the annual dust season. “Last time I saw it that bad was 1967,” said Doug, who operates one of 27 DustWatch Australia recording stations in NSW.

Sydney dust storm – a red haze

Sydneysiders woke to an apocalyptic red haze on the morning of 23 September: it reduced visibility to a few hundred metres and wreaked havoc on road and air transport and respiratory health. However, by about 3 p.m. the day before in Broken Hill, the same dust storm had turned the world “absolutely pitch black: you couldn’t even see your hand in front of you,” Doug recalled. “[Car] headlights couldn’t illuminate anything because it was like they were shining off a solid wall of dirt.” At the storm’s peak, wind was gusting up to 90 km/h through Broken Hill, swirling thousands of tonnes of topsoil from central Australia through the air. To venture outside was to literally be “sandblasted”.

Our ancient, arid and often windy continent inevitably produces a lot of dust. In fact, Australia is acknowledged as the Southern Hemisphere’s biggest source of the stuff. Globally, the massive Lake Eyre Basin – which spans much of inland Queensland, part of western NSW and large chunks of NT and SA – is the planet’s eighth biggest source of dust. The top dust spot is the southern Sahara Desert, in northern Africa.

Dust storms caused both by nature and humans

DUST STORMS ARE perhaps the worst manifestations of soil erosion, both natural and human-induced. And there are now also a lot of unanswered climate-change queries surrounding them: will they become more prevalent? What’s the effect on the global climate of all that material circulating?

“The unusual thing about [the Red Dawn dust storm] was that it hit Sydney,” observed Dr John Leys, a scientist with the NSW Department of Environment, Climate Change and Water. “That’s 5.5million people who had no idea so many people go through this experience on a regular basis.”

John and Professor Grant McTainsh, of Griffith University, Queensland, were the co-founders of DustWatch Australia. It’s now understood – thanks to researchers such as John and Grant and a growing band of Australian scientists with interest in the movements and consequences of wind-blown dust – that these events aren’t a recent or unusual phenomenon. Australia’s climate and landform have combined to create well-worn and mostly predictable dust paths that emanate from the continent’s dry geographical heartland, and these have operated for millennia. We know that these storms are often more severe during periods of drought and that they tend to be seasonal. In northern NSW and Queensland, drier winters lead to a peak in dust-storm activity during spring and early summer. But in southern NSW and Victoria, wetter winters suppress dust-storm activity until summer.

Australian dust travels far and wide

It’s also clear that during the past 150 years poor land-management practices have undoubtedly exacerbated some dust storms. We also have evidence that Aussie dust travels a very long way. Dust laden with iron from September’s storms, for example, reached the snowfields of New Zealand’s Southern Alps and turned them pink. Lake Eyre dust that has been found in ice-core samples from the Antarctic proves that such events have occurred for many thousands of years. There’s also increasing speculation that the iron and nutrients that blow into the oceans around Australia could be a crucial nutritional supplement that fuels phytoplankton blooms.

For Doug and other Broken Hill residents, the dust will finally settle when the rains eventually return to the arid heart. Until then, each time a wind from the west starts howling they’ll close the windows and doors, use wet, rolled-up towels to plug any gaps and simply wait it out.