Aniakchak National Monument and Preserve, National monument and preserve in Lake and Peninsula, United States

Aniakchak National Monument and Preserve centres on the 6-mile (9.7 km) wide Aniakchak Crater, a caldera formed about 3,700 years ago when a roughly 7,000-foot mountain collapsed into its magma chamber. The rim high point, Aniakchak Peak, stands at about 4,380 feet, while the caldera floor near the outlet of Surprise Lake lies at about 1,055 feet. Inside are Surprise Lake, source of the Aniakchak River, Vent Mountain from the 1931 eruption, and the Gates, the cleft where the river leaves the caldera.

Mount Aniakchak, originally about 7,000 feet tall, collapsed into its magma chamber roughly 3,700 years ago, leaving a 6-mile-wide caldera about 3,300 feet deep. The region stayed virtually unexplored until the 1920s, when oil exploration brought reports of an undescribed volcano. A moderate 1931 eruption formed Vent Mountain and drew enough publicity to spur protection; President Jimmy Carter proclaimed the monument on December 1, 1978, and the Alaska National Interest Lands Conservation Act set the final monument and preserve boundaries on December 2, 1980.

The name Aniakchak comes from the Unangax language. The area is managed for subsistence use: Alaska Natives may hunt and fish within the monument and preserve, while sport hunting is allowed only in the preserve. The Aniakchak River, draining Surprise Lake through the Gates, is run by rafters and kayakers.

Access is by floatplane to Surprise Lake inside the crater, though fog often prevents landings, or by boat or plane to coastal towns followed by an overland traverse; a road from Port Heiden reaches only the outer caldera flanks. There are no permanent facilities and no visitor registration is required. Drop-offs and pick-ups may be delayed for long periods by weather.

The National Park Service recorded only 100 recreational visits in 2017, the lowest count of any unit in the system; a German-language source gives 199 registered visitors for 2023. Most arrivals land a floatplane on Surprise Lake, and fog often prevents landing, so a trip can end before it starts.