"Australia - Down Under" Australia by Adeline_Foo

The total land area of Australia is approximately 7,692,030 square kilometres and lies between the latitudes of 10 degrees 41 minutes South and 43 degrees 39 minutes South and between the longitudes 113 degrees 09 minutes East and 153 degrees 39 minutes East. The distance by latitudinal measurement from North to South is 3,180 kilometres whilst the longitudinal destance East to West is approximately 4,000 kilometres.

Unlike Europe and some parts of North America for instance Australia is a relatively flat and dry Continent as it is scientifically accepted that much of the land formation within Australia occurred up to millions of years ago whilst in other Continents such formation can be measured in tens of thousands of years.

Much of the centre of Australia is flat, but there are numerous ranges (e.g. Macdonnels, Musgrave) and some individual mountains of which Uluru (Ayers Rock) is probably the best known. The area was worn to a plain, the plain uplifted and then eroded to form the modern ranges on today's plain. In looking at Uluru, one remarkable thing is not so much how it got there, but that so much has been eroded from all around to leave it there.

In South Australia there are the ranges of (Mt Lofty, Flinders Ranges) and hills (such as the Adelaide Hills), with the down faulted blocks occupied by sea (e.g. Spencer Gulf) or lowlands including the lower Murray Plains.

In the East there is a gentle rise to highest part around Mt Kosciuszko (2,228 metres).

Between 55 and 10 million years ago, Australia drifted across the surface of the earth as a plate, moving north from a position once adjacent to Antarctica. There have been many changes in the climate of Australia in the past, but oddly these do not seem to be due to changing latitude (associated with global scale plate movements). Even when Australia was close to the South Pole, the climate was relatively warm and wet, and this persisted for a long time despite changes in latitude. It was probably under this climate that the deep weathered, iron-rich profiles that characterise much of Australia were formed.

Today a large part of Australia is arid or semi-arid. The dunes are mostly fixed now. Stony deserts or gibber plains are areas without a sand cover and occupy a larger area than the dune fields. Salt lakes occur in many low positions, in places following lines of ancient drainage. They are often associated with lunettes, dunes formed on the downwind side of lakes. Many important finds of Aboriginal prehistory have been made in lunettes. Despite the prevalence of arid conditions today, real aridity seems to be geologically young, with no dunes or salt lakes older than a million years.

The broad shape of Australia has been influenced over long periods by earth movements associated with large tectonic processes. However, much of the detail has been carved by river erosion. A significant number of Australia's rivers, like the Diamantina River, drain inland. While they may be eroding their valleys near their highland sources, their lower courses are filling up with alluvium, and the rivers often end in salt lakes which are dry for most of the time. Other rivers reach the sea, and have dissected a broad near-coast region into plateaus, hills and valleys. Many of the features of the drainage pattern of Australia have a very long history, and some individual valleys have maintained their position for hundreds of millions of years.

The offshore shape of Australia, revealed in isobath contours, results mainly from the pattern of break-up of the super-continent of which Australia was once a part. In some areas, such as the Great Australian Bight, there is a broad continental shelf bounded by a steeper continental slope. In other areas, like south-east New South Wales around Merimbula and much of the Tasmanian coastline, the continental shelf is very narrow, sometimes coming to within 20 nautical miles of the coast.

The Queensland coast is bounded by a broad plateau on which the Great Barrier Reef has grown in only the last two million years.