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An island continent in the Southern Hemisphere with a total area of 2,941,526 mi2 (7,618,552 km2). It is bounded on the west by the Indian Ocean and on the east by the Pacific Ocean and the Tasman Sea. Numerous small and several large islands lie off the coast, including Tasmania and New Zealand. Australia is generally of remarkably low elevation and moderate relief. Three-fourths of the land mass lies between 600 and 1500 ft (180 and 450 m) in the form of a huge plateau. A cross section from east to west shows first a narrow belt of coastal plain, then the steep escarpments of the eastern face of the Great Dividing Range, stretching 1200 mi (1900 km) from the north of Queensland to the south of Victoria. The descent on the western slope of the Dividing Range is gradual until often elevation in the inland basins is below sea level, rising gradually again across the great plateau until the low ranges of western Australia fringing the plateau are reached, and beyond these lies another coastal plain. With the exception of the Gulf of Carpentaria and Cape York peninsula in the north and the Great Australian Bight in the south, there are few striking features in the configuration of the coast. Australia may conveniently be divided into three great structural and landform regions.

The region called East Australian Highlands consists of a narrow plain extending north and south along the eastern coast. Flanking the plain are the series of ranges and tablelands making up the Great Dividing Range. The East Australian Highlands is the best-watered region in Australia, and some of the river systems are of considerable size. On the flanks of the East Australian Highlands are Australia's  principal coal deposits—in the vicinity of Sydney and Newcastle and in the Bowen and Ipswich fields in Queensland. Petroliferous basins at Surat (Roma), flanking the divide in Queensland and off the coast of Victoria in Bass Strait, are Australia's most promising deposits of petroleum and natural gas.

The region known as the Interior Lowland Basins comprises a region of sedimentary rocks that occupy one-third of the continent between the western slope of the eastern highlands and the inner eastern margin of the ancient shield which forms the Western Plateau. Little land is over 500 ft (150 m), and some is below sea level. The rivers of the Murray-Darling Basin, draining the western slopes of the Great Dividing Range, have a marked seasonal variation in flow but never dry up in the lower reaches. South Australia's  shallow lakes are more often dry expanses of encrusted white salt than bodies of water—the result of low rainfall and high evaporation. In most parts of the region water from deep artesian wells is available.

The region known as the Western Plateau is the largest area, occupying almost three-fifths of the continent, and is a great shield of ancient rocks standing 750–1500 ft (225–450 m) high. Much of it is buried in desert sand, and only a few ridges of ancient mountains (such as the Macdonnel and Musgrave ranges) break the monotony of the plateau surface. Only in the southwestern corner of the continent and along the northwestern coast is rainfall sufficient to support a sclerophyll forest of eucalypts and a monsoon woodland, respectively. In the north, coastal rivers are of considerable size but change from flooded torrents after rains to a succession of water holes in dry seasons.

Tasmania is a small mountainous island lying 150 mi (240 km) southeast of Australia across Bass Strait, with a total area of 26,383 mi2 (68,332 km2). The island is structurally similar to the East Australian Highlands. The dominant feature is the central plateau, falling from a general level of 3500 ft (1070 m) in the northwest toward the southeast. A dense eucalyptus forest covers most of the island except along the wetter west coast, where beech forest predominates. The rivers have short, rapid courses with little seasonal variation in flow. New Zealand

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From McGraw-Hill Concise Encyclopedia of Environmental Science. The Content is a copyrighted work of McGraw-Hill and McGraw-Hill reserves all rights in and to the Content. The Work is © 2008 by The McGraw-Hill Companies, Inc.
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