Australia

I

Introduction

Australia, island continent located between the Indian and South Pacific oceans south-east of Asia and forming, with the nearby island of Tasmania, the Commonwealth of Australia, a self-governing member of the Commonwealth of Nations. The continent is bounded on the north by the Timor Sea, the Arafura Sea, and the Torres Strait; on the east by the Coral Sea and the Tasman Sea; on the south by the Bass Strait and the Indian Ocean; and on the west by the Indian Ocean. The Commonwealth of Australia extends about 4,000 km (2,485 mi) from Cape Byron in the east to Western Australia, and about 3,700 km (2,300 mi) from Cape York in the north to Tasmania in the south. Its coastline measures some 36,735 km (22,826 mi). The area of Australia, including Tasmania, is 7,682,300 sq km (2,966,200 sq mi). The area of the continent alone is 7,614,500 sq km (2,939,974 sq mi), making Australia the smallest continent and one of the largest countries in the world.

The Commonwealth of Australia is made up of six states—New South Wales, Queensland, South Australia, Tasmania, Victoria, and Western Australia—and two territories—the Australian Capital Territory and the Northern Territory. Australia’s external dependencies are the Australian Antarctic Territory, Christmas Island, the Cocos Islands, the Territory of Heard and McDonald Islands, Norfolk Island, the Ashmore and Cartier Islands, and the Coral Sea Islands Territory. Canberra is the capital of Australia.

II

Land and Resources

The remotest of the settled continents, Australia is also the flattest and, except for Antarctica, the driest. The average elevation is about 300 m (987 ft) and only 6 per cent of its area is above 610 m (2,000 ft). The vast interior of Australia, known to white Australians as the Outback, is made up of plains and low plateaux, which are generally higher in the north-east. Low-lying coastal plains, averaging about 65 km (40 mi) in width, fringe the continent. The coastal plains in the east, south-east, and south-west are the most densely populated areas of Australia.

In the east the coastal plains are separated from the interior by the Great Dividing Range, or Eastern Highlands. This mountainous region averages approximately 1,220 m (4,000 ft) in height and runs parallel to the eastern coast from the Cape York Peninsula in the north to Victoria State in the south-east. Subdivisions of the range have many names, including, from north to south, the New England Range, the Blue Mountains, and the Australian Alps, including the Snowy Mountains. In Victoria, where the range extends westward, it is known as the Grampians, or by the name given by the indigenous Aborigines, Gariwerd. The highest peak in the Australian Alps, and the loftiest in Australia, is Mount Kosciusko (2,228 m/7,310 ft), in the Snowy Mountains of New South Wales. The Great Dividing Range continues into Tasmania, which was separated from the south-eastern tip of the continent by the shallow Bass Strait between 13,500 and 8,000 years ago when sea levels rose.

The Western Australian Shield occupies more than half of the continent, west of a line running north-south roughly from the eastern shore of Arnhem Land on the Bay or Gulf of Carpentaria to the Eyre Peninsula in the state of South Australia, and skirting to the west of the Simpson Desert in the interior. A huge plateau with an average elevation of between 305 and 460 m (1,000 and 1,500 ft), the shield is fractured into a number of distinct blocks. Some of the blocks have been raised to form uplands; others have been depressed, forming lowlands and basins. The lowlands include the Great Sandy Desert, the Gibson Desert, the Great Victoria Desert, and the Nullarbor Plain, which are located in the north-western, central, southern, and south-eastern shield areas respectively. The Nullarbor (from Latin, “no trees”) is an arid, virtually uninhabited limestone plateau. It is characterized by remarkable cave and tunnel systems which contain valuable geological information about ancient Australia.

The uplands include, in Western Australia state, the Hamersley and King Leopold ranges in the western and north-western coastal areas, and the Darling Range inland from Perth in the far south-west. The Macdonnell Ranges lie in the southern part of the Northern Territory, and the Stuart and Musgrave Ranges are located in the north of the state of South Australia. Erosion and weathering have created striking, isolated rock formations, called mesas or buttes, in many parts of the shield, including the Kimberleys and Pilbara districts of Western Australia and Arnhem Land in the Northern Territory.

Between the Western Australian Shield and the Great Dividing Range is the Great Artesian Basin region, an area of vast plains containing some of the most productive arable and range lands in Australia. It comprises three major basins: the Carpentaria, the Eyre, and the Murray basins. The rolling plains of the Carpentaria Basin form a narrow corridor running inland from the Bay of Carpentaria, between the Isa Highland on the north-eastern edge of the shield and the Great Dividing Range. The Eyre Basin lies to the south of the Carpentaria Basin, occupying almost 1.3 million sq km (500,000 sq mi) of the centre and north of the continent, in south-western Queensland, north-eastern South Australia, and north-western New South Wales. There are rolling plains in the north of the basin. Further into the arid interior, the land becomes flatter and changes into stony desert. There are sand dunes in the Simpson Desert, which lies to the north of Lake Eyre near the western edge of the basin. Lake Eyre, one of the largest of the salt lakes scattered through the interior, occupies the lowest part of the continent and many river systems drain into it. Uluru (Ayers Rock) lies to the west of Lake Eyre on the border between the Eyre Basin and the Western Australian Shield, in the centre of Australia. With a basal circumference of about 9 km (6 mi), and rising sharply from the surrounding plain to about 348 m (1,142 ft), Uluru is believed to be the largest monolith in the world.

The Murray Basin runs inland from the Indian Ocean coasts of South Australia and Victoria into western New South Wales. It is bordered on the west by the Flinders and Mount Lofty ranges in South Australia, and on the east by the Australian Alps of the Great Dividing Range. The Murray Basin contains large areas of fossil sand dunes, and is generally arid; the western Murray Plains are a stony desert. In the east of the basin, however, there are extensive alluvial plains associated with the major tributaries of the Murray, the only permanent river to cross the interior.

The coastline of continental Australia is generally regular, with few bays or capes. The largest inlets are the Gulf of Carpentaria in the north and the Great Australian Bight in the south. The several fine harbours include those of Sydney, Hobart, Port Lincoln, and Albany. Tasmania has a more indented coastline, particularly in the south-east, where postglacial submergence has produced one of the finest drowned coastlines in the world.

The Great Barrier Reef, a World Heritage site, extends some 2,010 km (1,250 mi) along the eastern coast of Queensland from Cape York in the north to Bundaberg in the south. Made of coral, it is the world’s largest structure created by a living organism. The chain of reefs forms a natural breakwater for the passage of ships along the coast. See also Kosciusko National Park.

A

Geology

Australia was originally part of the ancient continent of Gondwana, which had earlier formed part of the supercontinent of Pangaea. Much of it is geologically ancient; the oldest known rock formations have been dated at between 3 and 4.3 billion years old. The great plateau of the Western Australian Shield is underlaid by a vast, stable shield of Precambrian metamorphic and igneous rocks, ranging in age from 570 million to 3.7 billion years. These form the core of the ancestral continent, which, with Antarctica, split off from Gondwana during the Jurassic period, less than 200 million years ago, and began to drift eastwards and northwards (see Plate Tectonics; Continent). Australia emerged as a separate continent about 100 million years ago, when Antarctica broke away and drifted southward. Australia is still moving, northward, away from Antarctica and is in the process of merging with Asia. Its life as a separate continent will be relatively short, in geological time.

The thick sedimentary rocks of the Great Dividing Range were deposited in a great north-south trending geosyncline during an interval that spanned most of the Palaeozoic era, ending some 245 million years ago. Compressive forces buckled these rocks at least twice during the era, forming mountain ranges and chains of volcanoes.

B

Rivers and Lakes

Two thirds of Australia is desert or semi-desert and experiences very high rates of evaporation; only about 10 per cent of rainfall survives as surface run-off to feed the rivers. As a result, permanent rivers are limited, with one exception, to the wetter eastern and south-western margins of the continent, and to Tasmania. The Great Dividing Range is the watershed for the eastern half of Australia. On its eastern flanks, permanent rivers flow to the Coral Sea and South Pacific Oceans; the most important are the Burdekin, the Fitzroy, and the Hunter. Of the rivers which flow westward from the Great Dividing Range across the interior, only the Murray is permanent. Fed by melting snow at its source in the Mount Kosciusko region, and by large tributaries like the Darling and Murrumbidgee rivers, the Murray gains enough volume to cross the dry plains which bear its name. It meets the sea on the south coast, east of Adelaide. The Murray-Darling-Murrumbidgee network is the most important river system in Australia. It drains more than 1.1 million sq km (415,000 sq mi) in Queensland, New South Wales, Victoria, and South Australia, and waters some of the country’s most important arable and grazing lands. Much of the network is also navigable during the wet season. The Murray forms most of the border between New South Wales and Victoria.

The other rivers of central Australia, like those of the western part of the continent, flood adjacent, low-lying land when it rains. At other times they are dry channels, or at best a series of water holes; the central plains region is sometimes known as the Channel Country. The Victoria, the Daly, and the Roper rivers drain a section of the Northern Territory. In Queensland the main rivers flowing north to the Gulf of Carpentaria are the Mitchell, the Flinders, the Gilbert, and the Leichhardt. Western Australia has few significant rivers. The most important are the Fitzroy, the Ashburton, the Gascoyne, the Murchison, and the Swan rivers.

The natural lakes of the interior of continental Australia are salinas, or salt lakes. Fed by ephemeral or intermittent streams and rivers, they receive water rarely and are normally reduced by evaporation to salt-encrusted swamp beds or salt pans. The large salinas in the centre and south of the Great Artesian Basin—lakes Eyre, Torrens, Frome, and Gairdner—are the remains of a vast inland sea which once extended south from the Gulf of Carpentaria.