Aniakchak National Monument and Preserve (ănēăkˈchăk) [key], on the Alaska Peninsula, SW Alaska. Located in the Aleutian Range, the monument (137,176 acres/55,556 hectares) and surrounding preserve (465,603 acres/188,569 hectares) feature the Aniakchak volcano (4,420 ft/1,347 m high), which last erupted in 1931. Aniakchak was proclaimed a U.S. national monument in 1978 and established as a national monument and preserve in 1980. The Aniakchak's caldera is c.6 mi (9.7 km) in diameter and contains Surprise Lake, the source of the 63-mi (101-km) Aniakchak Wild River. The surrounding preserve has many varieties of wildlife. See National Parks and Monuments, table.