Macquarie Island is the only place on earth where rocks from the earth's mantle (6 km below the ocean floor) are being actively exposed above sea-level. That's essentially the process that formed tiny Macquarie Island, located in the Southern Ocean about halfway between New Zealand … Macquarie Island (34 km long x 5 km wide) is an oceanic island in the Southern Ocean, lying 1,500 km south-east of Tasmania and approximately halfway between Australia and the Antarctic continent. Macquarie Island is an Australian Subantarctic Island with an area of 12,875 hectares (31,814 acres). This makes it an important focus of geological study. The island lies in the southwest corner of the Pacific Ocean, … It is 34 kilometres (21 miles) long and up to 5 kilometres (3 miles) wide, and is located 1,500 kilometres (930 miles) south-east of Hobart, Tasmania. Macquarie rose from the mantle about one millimeter per year.