ANIAKCHAK NATIONAL MONUMENT AND PRESERVE

formerly Aniakchak National Monument, national monument and preserve in southwestern Alaska, U.S., on the southern shore of the Alaska Peninsula. Proclaimed a national monument in 1978, the area underwent boundary and title changes in 1980. Aniakchak is a great dry caldera in the volcanically active Aleutian Mountains that last erupted in 1931. The crater, with an average diameter of about 6 miles (10 km), includes lava fields and cinder cones. Surprise Lake, the outlet of which cascades through a 1,500-foot (450-metre) rift in the crater wall, forms the Aniakchak River. The monument and preserve cover an area of 942 square miles (2,440 square km).