AUSTRALIA'S GEOGRAPHY

Australia is the world's smallest continent but the largest island and sixth-largest country. It is bounded by the Indian Ocean on the west and south, the Pacific Ocean on the east, and Arafura Sea in the north between Australia, Indonesia and New Guinea. With proportionately more desert land than any other continent, Australia has a low population density. The coastline length, estimated at 19,200 km, is remarkably short for so large an area, a result of the relative lack of indentation. Major inlets other than the Gulf of Carpentaria and the Great Australian Bight are few.

Australia is basically an extensive low plateau. It is the world's flattest continent and also one of the oldest. The continent was not affected by recent geological mountain-building forces, and all its land forms are highly eroded. The world's average elevation is 700m, three-quarters of Australia's land mass lies between 180m and 400m above sea level, with the highest point - Mount Kosciusko - only 2228m high.

Australia can be divided into three major physical regions: the vast Western Plateau, the Eastern Highlands, and the Great Artesian Basin.

Western Plateau consists of about 60 percent of the continent, more than 4,500,000 sq km of central and western Australia. The Western Plateau contains some of the world's oldest rocks and substantial mineral deposits. The flat, treeless Nullarbor Plain of south central Australia is the southern edge of the plateau. Erosion of the plateau's thick sandstones has produced mesas and buttes in Arnhem Land in the north and in the Kimberley and Pilbara regions of the northwest. In the centre of the continent rise the MacDonnell Ranges, carved out of ancient sediments and deformed by open folding. They culminate in Mount Zeil, at 1,150 m, the highest point in the Western Plateau. Ayers Rock is to the south of this area.

The Western Plateau is marked by aridity, and its desert and semidesert lands are extensive. The soils are generally thin and of little or no value for agriculture or grazing. Much of this area is covered with sand ridges. Sand-ridge country accounts for nearly a quarter of Australia's total land area. Other large portions of the continent's desert and semidesert country consist of gibber (stony desert), formed by the breakup of surface rocks.

The Eastern Highlands serve as a continental rim. These highlands, also known as the Great Dividing Range, are mainly plateau country and are separated from the discontinuous coastal plain by steep, erosional slopes. Elevations exceed 1,500 m in parts of the northern rim, but half the ground here is below 300 m. The New England Range and Blue Mountains to the south vary in height from 900 to 1,500 m. The Australian Alps in the extreme southeast reach more than 1,800 m and conclude with Mount Kosciusko in the Snowy Mountains. A detached and heavily glaciated portion of the Australian Alps occurs in Tasmania, where it exceeds 1,000 m in elevation. The Eastern Highlands form a major drainage divide of Australia. Off the tropical northeastern coast lies the Great Barrier Reef, the world's largest coral reef at 2,000 km long.

Great Artesian Basin lies between the Western Plateau and the Eastern Highlands. Most of the basin is less than 300 m in elevation and much of it less than 150 m. In the north is the Carpentaria Basin, which lies mostly beneath the sea (Gulf of Carpentaria). The vast Eyre Basin contains Lake Eyre, the shore of which is the continent's lowest point, 16 m below sea level. The Eyre Basin is almost separated from the Murray Basin on the south by the projection of high ground (actually worn mountains) in the Flinders, Mount Lofty, and Barrier Ranges. The overlap of the Simpson Desert from the Western Plateau to the interior basins somewhat blurs the physical distinction between the regions.

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