While representing just 5% of the land surface, as a country located in Oceania according to holidaysort, Australia has a structure substantially the same as that of the continents. That is, it has an archaic shield, rigid and stable, originating from the fragmentation of Gondwana, formed by crystalline rocks (granite and gneiss) and morphologically marked by the remains of ancient Precambrian reliefs, which separate vast depression areas. These, since the Paleozoic, were invaded by the sea which left powerful sedimentations, even several thousand meters thick; they present all the successive levels, in some cases up to the Cenozoic, thereby demonstrating the substantial stability of Australia, at least in the central and western parts where there is no lack of volcanic, intrusive and effusive formations, linked to fractures suffered by the cratogenic mass. The instability was originally characteristic instead of the eastern section where, since the Paleozoic era, a large geosyncline (called Tasman) opened, whose evolution led to the birth of the mountain ranges that border E Australia. The orogeny dates back to the Hercynian phase and raised the paleozoic formations accumulated in the geosynclin, including those carboniferous layers that still constitute the surface level of the chain. This has undergone extensive smoothing processes, as evidenced by its mature forms, but in the Cenozoic it underwent a partial rejuvenation. The conformation of Australia is extremely simple. The vast central and western body is opposed for approx. 3000 km from N to S of the pads band called unitarily Great Dividing Range (Great Dividing Range), by the gentle shapes and constituted by a succession of plateaus (tablelands and highlands) or wide ridges divided by very open valleys. Only in the extreme southern section is the relief more vigorous, forming the so-called Australian Alps, which in Mount Kosciusko (2229 m) reach the maximum altitude of Australia; relatively high they are also the neighbors mountains Blue (Blue Mountains), where one finds the important coal deposits. The rest of Australia has predominantly horizontal lines; even the reliefs are actually vast penepian planes dominated by archaic remains of chains or isolated Inselberge. At the center of Australia are the Macdonnell and Musgrave mountains, on average 1500 m above sea level, which dominate the large depressions closed to the E by the Great Dividing Range (Murray River Basin and Great Artesian Basin), which reach Lake Eyre lowest altitude in Australia (–16 m). AW rise the Hamersley Mountains and other slight plateaus bordering the coastal basins of Perth and Carnarvon and, inland, the Gibson Desert and the Nullarbor Plain. Finally, the highlands of Kimberley (983 m) and Arnhem close inwards other depressions. The coasts, which extend for over 19,000 km, have various shapes: they are rectilinear and cliff-like in correspondence with the sedimentary basins (for example along the Great Australian Bay, Great Australian Bight, which corresponds to the current limit of the marine regression), articulated to N where alternate insular fragmentations (especially along the coasts of the seas of Timor and Arafura) and deep inlets, such as the Gulf of Carpentaria, closed pronounced by the peninsula of Cape York (Cape York peninsula). AE the coastal morphology is determined by the nearby relief, especially in the southern part, where there are some beautiful bays; the north-east coast, bathed by the tropical seas, is preceded and protected by the Great Barrier Reef (Great Barrier Reef) 2000 km long, unique example in the world for the vastness and singularity of the environment built by the coralligenic concretions up to 200 km away from the coast.
The poverty of hydrography is connected to the general dryness of the whole large central and western section. The only rivers are fed by the eastern and northern mountainous belt; the rivers on the external side are however very short given the proximity of the reliefs to the coast; those directed inwards, on the other hand, have a greater development. Australia’s main waterway is the Murray, which originates from the Australian Alps, with a very extensive basin (910,000 km²), the largest of the continent, which also includes that of its tributary Darling, 2720 km long, but with a poor flow and a very irregular regime. The Murray, which is 2575 km long, is instead relatively rich in water and its regime, now partly controlled by weirs in the upper part of the basin, is more regular; it thus feeds a vast agricultural region, which uses its waters for irrigation. AN of the Murray basin lies the Great Artesian Basin (Great Artesian Basin), wide depression area drains where numerous aquifers emerge which gather at the foot of the Great Dividing Range. The basin is crossed by temporary water courses (creeks), which are lost in salt lakes, the largest of which is the Eyre (9583 km²). The whole western part, very poor in rainfall and morphologically flat, also lacks temporary rivers and presents itself with vast succession of areic and endorheic areas, scattered with saline deposits.