Overview Australia is a sovereign state located at (geodetic median point) in the
eponymous continent, within the loosely defined region of
Australasia /
Oceania in the
Southern Hemisphere of the Earth. Officially known as the
Commonwealth of Australia, its territory comprises a
mainland portion, the island state of
Tasmania (separate from the rest of the mainland by the
Bass Strait) and another
8,222 islands ranging from minor fringing islets to larger landmasses. This makes Australia the
sixth-largest country in the world by land area of jurisdiction, which comprises . Excluding Tasmania, Australian islands cover an area of .
Extreme points The points that are farther north, south, east or west than any other location in mainland Australia and Tasmania are as follows: • The northernmost point is in
Cape York Peninsula () • The southernmost point is in Tasmania Island in the
South East Cape () • The easternmost point is
Cape Byron, few kilometres east of
Byron Bay () • The westernmost point is Steep Point in
Shark Bay () Taking into account its extremities, the Australian landmass stretches approximately from its northernmost point to its southernmost point in Tasmania, and nearly from east to west. However, other sources refer to the Coastal Plains as the entire coastline of the mainland, outspreading beyond the east coast. This area is flat and has relatively high rainfall, making it suitable for human settlement and thus the most densely populated area in Australia. Towards the east, the flat land rises to the
Great Dividing Range which runs parallel to the east coast from the tip of the
Cape York Peninsula in Queensland almost south to the
Grampians in Victoria. This separates rivers flowing to the west and north from those flowing to the Pacific. This region, known as the Eastern Highlands, are made up of a series of mountains in the south topped by
Mount Kosciuszko and
volcanic plugs, ash domes and flow remnants further north. The Commonwealth of Australia is located in the lowest continent in the world with an average elevation of only ; around 86.77% of the country's surface (excluding islands) does not exceed an altitude of . Mainland Australia's highest point is Mount Kosciuszko ( high), located within the
Australian Alps, while the highest point on Australian sovereign territory is
Mawson Peak on
Heard Island, which is high and forms the summit of an active volcano called
Big Ben.
Regions The Australian continental landmass consists of six distinct landform divisions. These are: • The Eastern Highlands—including the Great Dividing Range, the fertile
Brigalow Belt strip of grassland behind the east coast, and the Eastern Uplands • The Eastern alluvial Plains and Lowlands—the Murray Darling basin covers the southern part; also includes parts of the
Lake Eyre basin and extends to the
Gulf of Carpentaria • The South Australian Highlands—including the Flinders Range,
Eyre Peninsula, and
Yorke Peninsula • The Western Plateau—including the
Nullarbor Plain • The Central Deserts • Northern Plateau and Basins—including the
Top End Geology Components Australia's onshore geology is divided into five principal provinces:
Archaean to
Paleoproterozoic cratons, Palaeo to
Mesoproterozoic orogenic belts, Meso to
Neoproterozoic sedimentary basins,
Paleozoic rocks of the Tasman
Foldbelt, and
Mesozoic rocks of the
Great Artesian Basin. The country contains some of the oldest geological features in the world, with the oldest known rocks dating from more than 3000 million years ago and rare
zircon crystals dating back 4400 million years. Other regions, however, are geologically much younger, shaped by volcanic activity that continued until only a few thousand years ago. Geomorphologist
Charles Rowland Twidale has estimated that between 10% and 20% of Australia's present-day landscapes developed during the Mesozoic Era, when the continent was part of Gondwana.
Geologic history Australia is located on the lowest, flattest, and oldest continental landmass on Earth. Most of the country's topography is a result of prolonged erosion by wind and water, and its shape is the product of tectonic Earth movements and long-term changes in sea level. These geological forces such as the
tectonic uplift of mountain ranges and clashes between tectonic plates occurred mainly in its early prehistory, when it was still a part of
Gondwana. The breakup of Gondwana began around 165 million years ago, though the separation of the
Australian plate was a slow process. In fact, Australian plate, along with Antarctica, was one of the last major continental plates of Gondwana to separate, doing so about 45 million years ago. During the
Pleistocene (2.6 million to 11,700 years ago), Australia was part of
Sahul, a
paleocontinent that included the landmasses of Australia and
New Guinea, as well as the land bridges that once connected them.
Geologic activity and its movement directions Most of Australia lies near the centre of the
continent's namesake tectonic plate, making it one of the most geologically stable landmasses on Earth. Although the country contains the
Newer Volcanics Province—a volcanic field in the southeast that has been dormant for about 5,000 years—significant volcanic activity is rare. The only currently active volcanoes under Australian jurisdiction are found about southwest of Perth, on
Heard Island and the nearby
McDonald Islands. Earthquakes occur regularly, though most are minor and cause no damage; major events exceeding magnitude 6 typically happen about once every five years.
Hydrology Surface water and the endorheic basin that discharge in it As being situated in the driest inhabited continent, Australia has few large, fast-flowing rivers or permanent lakes. Many rivers experience highly irregular flow patterns, with prolonged periods of low discharge followed by occasional years of flooding. About half of Australia's rivers
drain inland, often terminating in ephemeral
salt lakes. The country's natural freshwater lakes occur mainly along the coast as lakes or lagoons, while inland water bodies are typically wetlands or saline lakes located in the arid interior.
Glacial lakes and volcanic crater lakes are found primarily in Tasmania The nation also contains about 758
estuaries, most of which are located in tropical and subtropical regions.
Rainfall Australia's rainfall regime is highly variable, with low mean annual rainfall over most of the continent and heavy seasonal falls in the tropics, concentric around the continent's extensive arid core. The effects of this varied rainfall pattern and Australia's drainage system can result in parts of the continent being in drought, but inundated by water from rainfall thousands of kilometres away. Rainfall generally increases towards the coast as proximity to both
moisture sources and reliable rain-producing weather systems improves. Elevation also has an important influence on rainfall, with the mountain areas of northeastern Queensland, southeastern Australia and western Tasmania receiving higher rainfall totals. On average, only 9% of Australia's rainfall is converted to
surface runoff, and about 2% percolates through the ground to recharge
groundwater. Continental Australia is divided into
drainage divisions, which are subdivided into water regions and then into river basins. The drainage divisions depict where water flows across the continent and identify the major hydrological basins. Due to Australia's high variation in rainfall and streamflow, large reservoirs have been built in its main river basins to ensure reliable supply; in fact, the national per-person surface-water storage capacity in 2018 was about 3.25 ML, relatively high compared to other countries. Groundwater also plays a significant role as a supply for drinking water, industry, farming and other primary industries in the many regions where it is the only reliable water source. == Oceanography ==