75% of the Australian continent is arid, receiving under 250mm (9.8”) rain per annum, the semi arid zone between 250 and 350mm. Despite this, Australia’s deserts are relatively high in biomass. For example the biomass of termites in northern Australia is greater than the biomass of all the cattle in Australia combined!
No other deserts in the world experience the capricious climate or the lack of soil nutrients as the Australian deserts. Rainfall is erratic, there are no predetermined wet or dry seasons, precipitation comes when it pleases, and sometimes the gap in-between events is measured in years, and when the drought breaks there are floods of biblical proportion. Denied the protection of an ice sheet during the numerous ice ages, Australian soils have been leeched of their nutrients and are depauperate. And yet when a traveller arrives in the arid zone for the first time they are astonished by the number of plants and trees -unique plants that have adapted over millions of years to the erratic and harsh climate.
Looking closely at the landscapes it is easy to see that they are mainly formed by water. In the eastern half of the arid zone great dry rivers stretch across the Lake Eyre Basin to terminate in the vast salt lake that is Lake Eyre - the sump of the continent - 15 metres below sea level. For years their dried muddy beds crackle in the sun, and then a flood event turns them into a watercourse to rival the Mississippi or the Danube as they disgorge into the lake, turning a playa into an inland sea. This eastern half of the arid zone dominated by Lake Eyre is a land of playas, claypans and rivers.
40% of the continent is made up of longitudinal dune fields and sand plains, which in turn make up 40% of the dunefields on earth. They are aeolian, made by wind. The early explorers gave these dunefields names, they called them deserts. These sand dunes sit on a sandy mantle that is only around 10metres deep, which is relatively shallow compared to say deserts like the Kalahari in Africa where the sand mantle is 100-200 metres in depth. Throughout the western desert regions there are numerous rockholes, soakages and wells that provided Aboriginals with the opportunity to range and survive on the scant food resources. The western deserts contrast dramatically with those of the Lake Eyre Basin.
The only named desert in Australia that is not a dunefield is the Gibson Desert, named by the colourful explorer Ernest Giles, who named it after his lost fellow expeditioner Alfred Gibson ‘…the first white man to fall victim to its horrors.’ |
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