The Territory of Heard Island and McDonald Islands (abbreviated as HIMI) 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 in area and it has 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.