The Heard Island and McDonald Islands are an Australian external territory and volcanic group of barren Antarctic islands, about two-thirds of the way from Madagascar to Antarctica. The group's overall size is 372 square kilometres in area and it has 101.9 kilometres of coastline. Discovered in the mid-19th century, they have been territories of Australia since 1947 and contain the only two active volcanoes in Australian territory. The summit of one, Mawson Peak, is higher than any mountain on the Australian mainland. They lie on the Kerguelen Plateau in the Indian Ocean.
The islands are among the most remote places on Earth: they are located approximately 4,099 kilometres southwest of Perth, 3,845 kilometresi) southwest of Cape Leeuwin, Australia, 4,200 kilometres southeast of South Africa, 3,830 kilometres southeast of Madagascar, 1,630 kilometres north of Antarctica, and 450 kilometres southeast of the Kerguelen Islands. The islands are currently uninhabited.
Heard Island, by far the largest of the group, is a 368-square-kilometre bleak and mountainous island located at 53°06′00″S 73°31′00″E. Its mountains are covered in glaciers (the island is 80% covered with ice) and dominated by Mawson Peak, a 2,745-metre high complex volcano which forms part of the Big Ben massif. A July 2000 satellite image from the University of Hawaii's Institute of Geophysics and Planetology (HIGP) Thermal Alert Team, University of Hawai'i showed an active 2-kilometre long and 50–90 metres wide lava flow trending south-west from the summit of Big Ben.
The McDonald Islands are located 44 kilometres to the west of Heard Island at 53°02′20″S 72°36′04″E. The islands are small and rocky. They consist of McDonald Island (186 metres high), Flat Island (55 metres high) and Meyer Rock (170 metres high). They totall approximately 2.5 square kilometres in area, where McDonald Island is 1.13 square kilometres large. Mawson Peak is one of only 2 active volcanoes in Australian territory, the other being McDonald Island. There is a small group of islets and rocks about 10 kilometres north of Heard Island, consisting of Shag Islet, Sail Rock, Morgan Island and Black Rock. They total about 1.1 square kilometres in area. The volcano on McDonald Island, after being dormant for 75,000 years, became active in 1992 and has erupted several times since. The most recent eruption is thought to have been on 10 August 2005.
The islands have an Antarctic climate, tempered by their maritime setting. The weather is marked by low seasonal and daily temperature ranges, persistent and generally low cloud cover, frequent precipitation and strong winds. Snowfall occurs throughout the year. Monthly average temperatures at Atlas Cove (at the northwestern end of Heard Island) range from 0.0 to 4.2 °C, with an average daily range of 3.7 to 5.2 °C in summer and -0.8 to 0.3 °C in winter. The winds are predominantly westerly and persistently strong. At Atlas Cove, monthly average wind speeds range between around 26 to 33.5 km/h. Gusts in excess of 180 km/h have been recorded. Annual precipitation at sea level on Heard Island is in the order of 1,300 to 1,900 mm; rain or snow falls on about 3 out of 4 days.
Heard Island and the McDonald Islands have no ports or harbours; ships must anchor offshore.
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