Australia’s outback is home to some of the country’s most extreme environments, but the deserts are also extremely varied in their shape, from vast salt pans and scrubby plains to rugged red-rock desert massifs and seas of sand dunes. Up north, the Top End, with its abundant seasonal rainfall, is another world altogether.
Deserts cover an estimated 18% of the Australian mainland, and up to one-third of the country’s mainland could technically qualify as desert based on rainfall levels alone. The Great Victoria Desert, in Western Australia and South Australia, is Australia’s largest at around 350,000 sq km, or nearly 5% of mainland Australia.
Parts of the Australian outback are among the world’s oldest land surfaces. Australia’s last great mountain-building events took place more than 300 million years ago, and it’s hard to believe that Uluru was once part of a mountain range that would have rivalled the Andes in height. Erosion and the relentless cycle of drought and flood have leached the nutrients away from Australia’s ancient soils and prevented the creation of new soils, resulting in the vast sandy plains of the Australian outback.
The Stuart Hwy passes through some of the lowest, flattest and driest parts of Australia, but there are numerous ranges and individual mountains scattered through the outback. At 1531m, Mt Zeil is not remarkable by world standards, but it is the highest mountain west of the Great Dividing Range. The rocky ranges of the outback provide important refuges for a diverse collection of plants and animals, and are significant in the ancient song lines and stories (accounts of the Dreaming which link into the law) of the traditional Aboriginal custodians of these areas.
In the outback you will also drive past huge salt pans or claypans that rarely fill with water. These may be dry for years, but when there is an abundance of rain they become important arid wetland systems: they hold water long after the surrounding landscape has dried out and are crucial to the survival of many plants and animals, especially those that require inundation during their life cycles. Lake Eyre, Australia’s largest lake, is the most obvious example.
Sand dunes are less visible than you might think out here – grasslands, desert scrub (including the ubiquitous spinifex grass) and salt pans are far more common. There are seas of sand dunes, but most tend to occur in the deserts’ more accessible reaches – the Simpson Desert, which extends across the Northern Territory, South Australia and Queensland, is estimated to be the world’s largest sand-dune desert and is home to what could the world’s longest parallel sand dunes.
The Top End
While spectacular geological formations are characteristics of the outback’s arid interior, it is the extensive river systems and wetlands that herald your arrival in the Top End. The sandstone escarpment and plateau of western Arnhem Land is a magnificent sight, but the life-sustaining floodplains at its base are just as impressive.
Kakadu and Arnhem Land are thought to be home to some of the oldest rocks on earth. Geologists estimate that the Arnhem Land plateau was formed a mind-boggling 1650 million years ago. For much of the period from 500 million to 140 million years ago, the region lay beneath the surface of a shallow sea, and it was the Arnhem Land Escarpment – visible across the region, but most easily at Nourlangie and Jim Jim Falls – that provided the cliff-bound shore.
For millions of years, the escarpment was a continuous body of rock, but the erosion by the sea’s waters gradually created the sandstone outliers that still ripple down into the interior today. The most obvious examples are Nourlangie and, further afield, Katherine Gorge.