The continent of Australia has a land surface area of 7674 518 km2 lying between latitudes 11°S to 44°S and extending from 113°E to 154°E longitude. It has a generally low to moderate relief, average elevation 305 m, in the form of extensive plateau and broad sedimentary plains. The highest elevations occur in the Snowy mountains of the south-east, near the New South Wales–Victoria border and culminate in Mount Kosciusko (2442 m). The sedimentary plains of the interior are the result of downwarping of the basement complex and in some instances this has resulted in the land surface being below sea level; the surface of Lake Eyre is – 12m to – 13m below sea level.

The boundary of the Australasian lithospheric plate may be traced along the south-east Indian oceanic ridge from Amsterdam and St Paul Islands to a point south of New Zealand (Figure 7.1). It then passes east of New Zealand, the Kermadec Islands and Tonga. The northern boundary then extends from the vicinity of Fiji to the Bismarck archipelago and New Guinea. It continues north-westward along a line, clearly marked by the Java trench, as far as the Nicobar Islands. The western edge of the Australian plate is the Ninety East oceanic ridge, which separates it from ocean floor associated with the northward movement of the Indian plate.