Alaska, United States
Mount Aniakchak is a 3,400 year old volcanic caldera (about 10 kilometers in diameter) located in the Aleutian Range of Alaska, United States. The area around the volcano is the Aniakchak National Monument and Preserve, maintained by the National Park Service. In November 1967, Aniakchak Caldera was designated as a National Natural Landmark by the National Park Service.
Aniakchak is an extant volcano - at least ten lava flows have occurred since the formation of the caldera during a major eruption of VEI=6 in 1645 BC.; the most recent was in 1931.
Surprise Lake within the caldera is the source of the Aniakchak River, a National Wild River.