Australian Deserts

By: David Cook, Photography by: David Cook


Australia’s desert systems aren’t as extensive as some might think, but they are still a significant contributor to our nation’s persona.

Australia is often seen, especially by those from overseas, as a place of vast deserts – an arid landscape of vast sand seas, rolling sandhills stretching to the horizon in all directions until you reach the coast. Yet for all except a few tiny locations those misconceptions couldn’t be further from the truth.- Strzelecki Track

There is no weather station in Australia that receives an average annual rainfall below 100mm, and formal deserts occupy just 35 percent of the mainland landscape, and less than that if you take into account Tasmania and our surrounding islands. And even then, most of that area has some form of vegetation and most of our deserts are defined by low or scattered scrub.

However, another 35 percent of Australia is classified as semi-arid, making this the driest inhabited continent on Earth. Only Antarctica is drier.

A MOVING LANDMASS

The principal reason for the extent of arid and semi-arid regions in Australia is the continent’s location.

 Bore Track

Beginning about 60 million years ago, Australia separated from Antarctica as one of the final major moves in the breakup of the supercontinent Gondwana. The northward drift of our landmass has continued at a rate of about 7cm per year ever since, and has gradually shifted us into a zone where a Mediterranean climate is dominant. This is a zone repeated both north and south of the Equator where deserts are more common. It's seen in North Africa and the Middle East, around the Mediterranean, across central Asia and into China and the southern United States and Mexico in the Northern Hemisphere, and across parts of Southern Africa, Australia and central South America in the Southern Hemisphere.

 Bore Track In Australia’s case, this saw the formation of stony deserts, starting about two to four million years ago, coinciding with the formation of the northern ice cap and its associated drying of global climates. Though the landscape remained well vegetated, lake and river levels remained high and existing sand dunes remained stable and were well vegetated. By this time, the climacic patterns had probably settled into one very similar to today's.

A cooling of sea surface temperatures about the time of the repeated waves of peak glaciation through the Ice Ages, starting about 22,000 years ago, saw a reduction in rainfall levels and a loss of denser vegetation. In some cases this was exacerbated by fire regimes introduced by early human interactions with the landscape, as well as the formation of extensive dune fields. With falling lake levels, these became clay and gypsum based to the south and east of such areas, and sand-based in other areas.

Studies by the University of Wollongong indicate that this appears to be a process that is still continuing. The deeper reds of the sand dunes of the Simpson Desert – cased by an iron coating of the individual grains – imply a much greater age than the pale yellow sands of the Strzelecki and Tirari deserts.- Strzelecki Track

CLIMATE CHANGE

Uniquely, the current rise in global temperatures has resulted in a benefit for some areas. The deserts in northern Western Australia are receiving a considerable increase in rain. In the past 50 years, rainfall at Giles, near the conjunction of WA, the Northern Territory and South Australia, has doubled. Some areas in the Pilbara have experienced an increase in annual rainfall of as much as 300mm. And this is a trend  in many of our desert areas across the north and west, even as rainfall in the south and east becomes more unpredictable and, at times, transient. Bore Track

This is good news in some ways, as agriculture in these regions is blossoming – literally – but it is also changing the patterns of pests, with wild dogs and insects increasing but feral camel numbers decreasing as they move to drier regions.

While this is generally good news for farmers it doesn’t necessarily mean an automatic boost for all plants in arid regions as they have evolved to tolerate cyclical wet and dry periods and have long ago 'learned' to expect a dry spell following rain.

VEGETATION

North of the Tropic of Capricorn, the vegetation of arid and desert Australia is typically grasslands, while south of this mulga woodlands dominate, determined by poor quality soils, fire regimes and local rainfall. The latter, dominated by Acacia species, are estimated to occupy 20 percent of the continent.

Along the usually dry streams the major plants are river red gums, usually as the single dominant tree along larger channels and mixed with other trees species on small stream channels.

Of great interest to travellers are the desert flowers with explode into life at certain seasons and in responses to rainfall pulses.

AUSTRALIA'S 10 LARGEST DESERTS

DESERT

STATE(S)

AREA

% AGE OF AUST

Great Victoria Desert WA/SA 348,750sqm

4.5%

Great Sandy Desert WA 267,250sqm 3.5%
Tanami Desert WA/NT 184,500sqm 2.4%
Simpson Desert NT/QLD/SA 176,500sqm

2.3%

Gibson Desert WA 156,000sqm

2.0%

Little Sandy Desert WA 111,500sqm

1.5%

Strzelecki Desert SA/QLD/NSW 80,250sqm 1.0%
Sturt Stony Desert SA/QLD/NSW 29,750 km2

0.3%

Tirari Desert SA 15,250sqm 0.2%
Pedirka Desert SA 1250sqm 0.016%

 

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