Where it is and what it carries
The Antarctic Plate covers about 58.2 million km², nearly the same area as the African Plate. It carries all of Antarctica and a wide ring of Southern Ocean seafloor. Scattered volcanic islands also sit on it, including the Balleny Islands, Heard and McDonald Islands, Bouvet Island, Marion Island and Île Saint-Paul.
The continent has two very different halves. East Antarctica is an old, thick block of continental crust. West Antarctica is a collection of smaller crustal blocks, stretched by the West Antarctic Rift System, and much of its bedrock lies below sea level under the ice. The Transantarctic Mountains run along the boundary between the two halves.
A plate ringed by ridges
Almost every boundary of the plate is divergent. Its longest edge is the Southeast Indian Ridge, about 11,150 km of spreading ridge and transform faults where the Australian Plate moves away at about 6.8 cm/yr. The Pacific-Antarctic Ridge separates it from the Pacific Plate at about 7.3 cm/yr, reaching 9.5 cm/yr in places, the fastest relative motion on any of its boundaries. The Chile Rise and its transform faults divide it from the Nazca Plate at about 5.7 cm/yr.
On the Atlantic and Indian Ocean side the ridges are much slower. The Southwest Indian Ridge opens at about 1.2 cm/yr against the Somali Plate and about 1.4 cm/yr against the African Plate. The boundary with the South American Plate moves at about 1.8 cm/yr and includes a short subduction zone off southern Chile, where Antarctic seafloor sinks beneath the Andes. Near the Antarctic Peninsula, the plate meets the Scotia Plate at about 1.2 cm/yr and the Shetland Plate at about 1.0 cm/yr. It also touches the tiny Juan Fernandez Plate and Sandwich Plate.
How Antarctica became isolated
Antarctica sat at the heart of Gondwana. Africa and India split away first, followed much later by Australia and South America. When the last links opened south of Tasmania and at the Drake Passage, a current could flow all the way around the continent. Many scientists link that change to the growth of the Antarctic ice sheet about 34 million years ago.
Earthquakes and volcanoes
The dataset lists 77 earthquakes of magnitude 6.5 or larger on the plate since 1900, and 2 reached magnitude 8. The 1998 Balleny Islands earthquake (M8.1) struck inside the oceanic plate, far from a boundary, which makes it one of the largest intraplate quakes recorded. The 1942 Southwest Indian Ridge earthquake reached M8.0. Most other large events cluster in the Scotia Sea, including a M7.7 in 2013 and a M7.6 in 2003, and in the Drake Passage, where a M7.6 and a M7.5 struck in 2025.
The plate has 27 volcanoes in the dataset. Mount Erebus on Ross Island is the most active on the continent. Mount Melbourne in Victoria Land, Buckle Island in the Balleny group and the Hudson Mountains in West Antarctica are also listed. Heard Island and the McDonald Islands hold Australia’s only active volcanoes.