Mount Aniakchak

Aniakchak Caldera
Mount Aniakchak caldera
Highest point
Elevation	1,341 m (4,400 ft)
Coordinates	56°53′N 158°09′W / 56.88°N 158.15°W / 56.88; -158.15[1]
Geography
Aniakchak Caldera Location in Alaska
Location	Aniakchak National Monument and Preserve, Alaska, US
Parent range	Aleutian Range
Topo map	USGS Chignik D-1
Geology
Mountain type	Caldera (Stratovolcano)
Volcanic arc/belt	Aleutian Arc
Last eruption	May to June 1931
U.S. National Natural Landmark
Designated	November 1967

Mount Aniakchak (Russian: Аниакчак) is a volcano on the western Alaska Peninsula. Part of the Aleutian Volcanic Arc, it was formed by the subduction of the oceanic Pacific Plate under the North American Plate. Aniakchak is a 10 kilometers (6.2 mi) wide caldera with a break to the northeast. The caldera contains Surprise Lake and many volcanic cones, maars and craters, including Vent Mountain. The volcano has erupted mainly calc-alkaline rocks ranging from basalt to rhyolite.

Activity began in the Pleistocene. Aniakchak is one of the most active volcanoes in Alaska and underwent several significant caldera-forming eruptions. The largest eruption is known as Aniakchak II and took place in 1628/1627 BCE. During this eruption, pyroclastic flows swept all the flanks of the volcano and caused a tsunami in Bristol Bay. Tephra from the eruption rained down over Alaska, with noticeable deposits being left as far as northern Europe. The eruption depopulated the central Alaska Peninsula and caused cultural changes in Alaska. Together with other volcanic eruptions at that time, Aniakchak II may have caused climatic anomalies. The present-day caldera formed during this eruption. A lake formed in the caldera, which drained in one of the largest known floods of the Holocene. Many lava domes and cones were emplaced within the caldera after the Aniakchak II eruption, with some events depositing ash over Alaska.

The last eruption took place in 1931. It was intense, forming a new crater in the caldera and causing ash fallout over numerous towns in Alaska. The volcano is monitored by the Alaska Volcano Observatory (AVO). The area around the volcano is the Aniakchak National Monument and Preserve, maintained by the National Park Service.