Only two of the world’s continents lie entirely within the Southern Hemisphere: Australia and Antarctica. Australia lies relatively close to the equator, while Antarctica is situated about the South Geographic Pole.
Antarctica is almost entirely covered by an ice sheet. At its thickest the ice is over 4 km deep, and beneath it there is a hidden landscape of mountains, valleys and plains. This dome-shaped ice sheet has been formed by the accumulation of snow over hundreds of thousands of years. The ice generally flows from the centre of the continent towards the surrounding ocean, and the Antarctic has thousands of glaciers extending into the sea. Great pieces of ice break away at the coast and drift away as icebergs. Huge icebergs, some larger than the Australian Capital Territory, have been observed, although normally they are several hundred metres to several kilometres in length.
During the winter months it becomes so cold that the sea surrounding Antarctica freezes for hundreds of kilometres offshore. This ice breaks up to form pack-ice which, under the action of winds and currents, is constantly changing form and distribution.
While the ice comprises about 98% of Antarctica’s surface, there are areas of bare rock, the greatest rock exposures being in the Antarctic Peninsula and the Transantarctic Mountains. The most significant ice-free areas of the Australian Antarctic Territory (AAT) are the Bunger Hills and the Vestfold Hills near Davis.
Except for coastal peaks, only the highest Antarctic mountains show above the icecap, some by only a few hundred metres. The highest point is the Vinson Massif at 5140 m above sea-level. The extensive Prince Charles Mountains inland of Mawson and the Transantarctic Mountains in the Eastern Sector contain the highest peaks in the AAT. The AAT also contains the world’s largest glacier, the Lambert Glacier.
The Southern Ocean, which surrounds Antarctica, consists of the southernmost parts of the Atlantic, Indian and Pacific Oceans. In the sub-Antarctic, between 50°S and 60°S, there are many small islands. Some of them, like Australia’s Heard Island, are almost completely capped by glaciers, while others, such as Macquarie Island, are ice-free and have no permanent snow cover.