large wilderness area in southwestern Alaska, U.S., on the southern shore of the Alaska Peninsula, about 450 miles (720 km) south of Anchorage. Proclaimed a national monument in 1978, the area underwent boundary changes in 1980 when the national preserve was established. The monument covers an area of 214 square miles (554 square km), while the preserve covers an additional 725 square miles (1,878 square km).

Aniakchak is a great dry caldera in the central region of the volcanically active Aleutian Range; the volcano itself last erupted in 1931. The crater, with an average diameter of about 6 miles (10 km), includes lava fields, cinder cones, and, at its bottom, Surprise Lake. A 1,500-foot (450-metre) rift in the crater wall allows the lake's water to drain, the flow forming the Aniakchak River. Access to the area is by float plane; raft trips also are made on the Aniakchak, which is designated a national wild river.