The Heard Island glaciers covered 79 percent of Heard Island itself, in 1947, covering 288 km2; by 1988, this had decreased by 11 percent to 257 km2. The glaciers fall under the Antarctic Environmental Gradient, which spans 30 degrees of latitude and includes a range of macro-climatic zones from cool temperate islands to the frigid and arid Antarctic continent. Glaciers extend from 2745 m to sea level, with ice up to 150 m deep.