Macquarie Island - Geography

Geography

Macquarie Island is an exposed portion of the Macquarie Ridge, and is located where the Australian plate meets the Pacific plate. It is the only place in the world where rocks from the mantle are actively exposed at sea level. Due to this it was made a UNESCO world heritage site in 1997.

The island has an approximate length of 34 km (21 mi) and a width of 5 km (3 mi), with an area of 128 km2 (49 sq mi). Near Macquarie Island are two small groups of minor islands, the Judge and Clerk Islets, 54°21′S 159°01′E / 54.35°S 159.017°E / -54.35; 159.017 (Judge and Clerk Islets), 14 km (9 mi) to the north, and 0.2 km2 (49 acres) in area, and the Bishop and Clerk Islets, 55°03′S 158°46′E / 55.05°S 158.767°E / -55.05; 158.767 (Bishop and Clerk Islets), 34 km (21 mi) to the south, and 0.6 km2 (150 acres) in area.

The island is in two main pieces of plateau of around 150–200 m (490–660 ft) elevation to the north and south, joined by a narrow isthmus close to sea level. The high points include Mount Elder on the north-east coastal ridge at 385 m (1,263 ft), and Mounts Hamilton and Fletcher in the south at 410 m (1,350 ft).

Macquarie Island lies atop a geographic feature named for the island, the Macquarie Ridge. This seafloor ridge is aligned along the eastern margin of the tectonic plate boundary between the Indo-Australian Plate and the Pacific Plate. The Bishop and Clerk Islets mark the southernmost point of Australia (including islands). In the 19th Century the phantom Emerald Island supposedly lay to the south of Macquarie Island.