Australia
From Encyclopædia
Australia is the
world's smallest continent and sixth-largest country. With proportionately more
desert land than any other continent, Australia has a low population
density. Lying completely in the Southern Hemisphere, Australia is bounded by the Indian Ocean on the west and south and by the Pacific Ocean on the east. These oceans merge on the north in the Arafura Sea between Australia and
Indonesia and New Guinea, and on the south in the
Bass Strait. The coastline length, estimated at 19,200 km (12,000 mi), 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.A self-governing member of the
Commonwealth of Nations, Australia celebrated its bicentennial in 1988 (see
BICENTENNIAL, AUSTRALIAN). It is a federation of five mainland states (NEW SOUTH
Wales, QUEENSLAND, SOUTH AUSTRALIA, VICTORIA, WESTERN AUSTRALIA) and one island state (
Tasmania), as well as two territories (AUSTRALIAN CAPITAL
territory, NORTHERN
territory). The country's name derives form the Latin terra australis incognita, meaning "unknown southern land," which resulted from a confusion between Australia and Antarctica on early
world maps.In many ways Australia is unusual among continents. It lacks major relief features and has a high proportion of dry land. The continent's isolation from other landmasses accounts for its unique varieties of vegetation and animal life, and for the existence of a Paleolithic (Old Stone Age) culture among the Aborigines. Except for Antarctica, Australia was probably the last continent to be inhabited by man and the last to be explored and settled by Europeans. It is the only continent comprising a single
nation-state.Dutch
Explorers first sighted Australia in the early 17th century. Capt. James COOK explored the east coast in 1770 and claimed the land for
Great Britain. In 1778 the first settlement (SYDNEY) was founded at an excellent harbor on the southeast coast. British convicts played an important role in the early history of the
territory. The discovery of gold and other ores attracted immigrants, but Australia remained a primarily agricultural country until
world War II.Subsequent industrialization has been rapid, and today Australia ranks as one of the
world's most economically developed countries, although vast areas of the interior, known as the Outback, remain all but uninhabited. (See AUSTRALIA, HISTORY OF.)LAND AND RESOURCESAustralia is primarily a flat low-lying
plateau, with about 95% of the land standing less than 600 m (1,970 ft) above sea level. The continent was not affected by recent geological mountain-building forces, and all its landforms are highly eroded; Australia's mountains reach only 2,228 m (7,310 ft) in Mount KOSCIUSKO in southeastern New South
Wales.Physical RegionsAustralia can be divided into three major physical regions: the vast Western
plateau, the Eastern
Highlands, and the
Great Artesian Basin.Western
plateau. Some 60% of the continent--more than 4,500,000 sq km (1,740,000 sq mi) of
Central and western Australia--is the Western
plateau. About half of its area lies between 300 and 600 m (1,000 and 2,000 ft) above sea level. A major fault terminates the
plateau on the west, separating a strip of coastal lowland about 50 km (30 mi) wide from the interior. 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 center 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 (4,955 ft), 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. In clockwise order from the south, these
deserts include the GREAT VICTORIA, GIBSON, GREAT SANDY, SIMPSON, Tanami, and Arunta. Much of this area is covered with sand ridges. In
Central areas the dunes are live (that is, subject to realignment by the elements), but elsewhere they are dead and fixed by vegetation. The dune ridges are strikingly parallel outside sand-source areas, reaching heights as great as 30 m (100 ft) with separations as wide as 500 m (1,650 ft). 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.Eastern
Highlands. Uplands, to a width of about 500 km (300 mi), serve as an eastern 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 scarps. Elevations exceed 1,500 m (5,000 ft) in parts of the northern rim, but half the ground here is below 3?0 m (1,000 ft). The
New England Range and Blue Mountains to the south vary in height from 900 to 1,500 m (3,000 to 5,000 ft). The Australian Alps in the extreme southeast reach more than 1,800 m (6,000 ft) and culminate in 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 (3,000 ft) 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 (1,250 mi) long.
Great Artesian Basin. Between the Western
plateau and the Eastern
Highlands lie three interior basins, called the
Great Artesian Basin. Most of this area is less than 300 m (1,000 ft) in elevation and much of it less than 150 m (500 ft). 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, 15 m (49 ft) 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.Geological HistoryGeologically, Australia is part of the former southern supercontinent GONDWANALAND, which broke up some 160 million years ago, isolating Australia from the other landmasses of the Southern Hemisphere.The Western
plateau is a stable shield area and has extensive outcrops of Precambrian age rocks (3,000 to 570 million years old). Some Precambrian rocks are also incorporated in the northern half of the Eastern
Highlands. These rocks record at least two episodes of compression and mountain building: the first producing granitic masses and highly altered rocks; the second forming a trough (the
Adelaide geosyncline) along the eastern edge of the shield (from the site of the Flinders and Mount Lofty ranges, through the center, to the northwest coast). Parts of the Western
plateau have from time to time been submerged by shelf seas or have sagged into troughs. For example, the Canning Basin in the northwest is filled with sediments that are 600 to 250 million years old; the Eucla Basin in the south contains mainly
limestones that are less than 70 million years old.Thick sedimentation in a subsiding trough, now the site of the Eastern
Highlands, began some 600 to 500 million years ago, and continued in places until 250 million years ago. Between 400 and 275 million years ago, the trough was twice compressed; mountains were formed, and volcanic chains erupted. Volcanic outbreaks were repeated later throughout the region, especially 25 to 20 million years ago. Most of the volcanic fields are old enough for their cones to have been stripped
Down by erosion.
plateau basalts are also much broken by erosion. In the south of the mainland, however, volcanic activity persisted until less than a million years ago.Sagging basins in coastal areas subsequently collected sediment, much of it deltaic sand, which is now seen as thick sandstone formations. The major sags, however, were to form Australia's interior basins, which contain sediments dating from about 200 million years ago to the present day.ClimateThe climate of Australia varies with latitude. The northern part of the continent is tropical and influenced by the trade winds. The southern parts lie in the belt of westerly winds and have a more temperate climate. The vast center of the continent is arid and extremely hot during the summer (December to
march).The tropical region, and especially the northern coast, experiences a hot, wet (monsoonal) summer. The
average January temperature in
Darwin is 28 deg C (83 deg F), and the
average annual rainfall is 1,240 mm (59 in), nearly 80% of which falls between December and
march. In winter, hurricanes tend to develop over the
coral and Arafura seas, some f?llowing the path of the East Australian Current as far south as Sydney.Two parts of southern Australia have dry summers and mild, wet winters, resembling a Mediterranean climate. The southwest experiences hot, dry summers, dominated by subtropical high-
pressure systems.
average temperatures at PERTH are 23 deg C (74 deg F) in January and 13 deg C (55 deg F) in July; the
average annual rainfall is 900 mm (35 in). A similar climate affects an area around
Adelaide, where brush fires caused extensive damage during the unusually dry 1982-83 summer.
