Photo of this volcano
Google Earth icon
  Google Earth Placemark
  • United States
  • Alaska
  • Caldera
  • 1931 CE
  • Country
  • Volcanic Region
  • Primary Volcano Type
  • Last Known Eruption
  • 56.88°N
  • 158.17°W

  • 1341 m
    4398 ft

  • 312090
  • Latitude
  • Longitude

  • Summit

  • Volcano

The Global Volcanism Program has no activity reports for Aniakchak.

The Global Volcanism Program has no Weekly Reports available for Aniakchak.

The Global Volcanism Program has no Bulletin Reports available for Aniakchak.

Geological Background

One of the most dramatic calderas of the Aleutian arc, the 10-km-wide Aniakchak caldera was formed around 3400 years ago during a voluminous eruption in which pyroclastic flows traveled more than 50 km north to the Bering Sea and also reached the Pacific Ocean to the south. At least 40 explosive eruptions have been documented from Aniakchak during the past 10,000 years, making it the most active volcano of the eastern Aleutian arc. A dominantly andesitic pre-caldera volcano was constructed above basement Mesozoic and Tertiary sedimentary rocks that are exposed in the caldera walls to elevations of about 610 m. The ice-free caldera floor contains many pyroclastic cones, tuff cones, maars, and lava domes. Surprise Lake on the NE side drains through The Gates, a steep-walled breach on the east side of the 1-km-high caldera rim. Vent Mountain and Half Cone are two long-lived vents on the south-central and NW caldera floor, respectively. The first and only confirmed historical eruption took place in 1931 from vents on the west and SW caldera floor.

Eruptive History

Summary of Holocene eruption dates and Volcanic Explosivity Indices (VEI).

Start Date Stop Date Eruption Certainty VEI Evidence Activity Area or Unit
[ 1951 Jun 25 ] [ 1951 Jun 25 ] Discredited    
[ 1942 ] [ Unknown ] Uncertain    
1931 May 1 1931 Jun 13 (in or after) Confirmed 4 Historical Observations West and SW caldera floor
1560 ± 50 years Unknown Confirmed 4 Radiocarbon (uncorrected) NW & S caldera floor (Half Cone, Vent Mtn)
1550 (?) Unknown Confirmed   Radiocarbon (uncorrected) SE caldera floor (New Cone)
1390 (?) Unknown Confirmed   Radiocarbon (uncorrected) NW caldera floor (Half Cone?)
1220 ± 150 years Unknown Confirmed   Tephrochronology NW caldera floor (Half Cone)
1050 (?) Unknown Confirmed   Tephrochronology Vent Mtn and other vents?
0700 ± 300 years Unknown Confirmed 0 Tephrochronology S & NW caldera floor (Vent Mtn & Half Cone)
0460 (?) Unknown Confirmed   Radiocarbon (uncorrected)
0200 Unknown Confirmed   Tephrochronology Northern & western caldera floor
0350 BCE (?) Unknown Confirmed   Radiocarbon (uncorrected)
1645 BCE ± 10 years Unknown Confirmed 6 Ice Core
2550 BCE ± 500 years Unknown Confirmed   Tephrochronology
5250 BCE ± 2700 years Unknown Confirmed 6 Tephrochronology

This compilation of synonyms and subsidiary features may not be comprehensive. Features are organized into four major categories: Cones, Craters, Domes, and Thermal Features. Synonyms of features appear indented below the primary name. In some cases additional feature type, elevation, or location details are provided.


Feature Name Feature Type Elevation Latitude Longitude
Blocky Cone Cone
Half Cone Cone
New Cone Cone
Vent Mountain Cone 1021 m


Feature Name Feature Type Elevation Latitude Longitude
Aniakchak Caldera


Feature Name Feature Type Elevation Latitude Longitude
Bolshoi Dome Dome
Pumice Dome Dome
Vulcan Dome Dome
West Dome Dome

Photo Gallery

Calderas are very large depressions that form by collapse. Many, like this 10-km-wide caldera that truncates Alaska's Aniakchak volcano, are created by very powerful explosive eruptions that empty a magma chamber beneath a volcano, causing it to collapse inward. Other calderas, such as those on Hawaiian volcanoes, are produced by collapse following major lava extrusion. Calderas often form incrementally, during widely spaced eruptions. Later activity can cover their floors with a wide variety of volcanic landforms.

Photo by M. Woodbridge Williams (National Park Service).
U.S. Geological Survey volcanologists on the rim of Vent Mountain, an intracaldera stratocone, look NW towards Half Cone, a prominent feature on the caldera floor and the source of the most-explosive post-caldera eruptions at Aniakchak. The aptly named Half Cone, whose SE side is missing, last erupted about 500 years ago. The NW caldera rim of Aniakchak caldera forms the skyline.

Photo by Christina Neal, 1992 (Alaska Volcano Observatory, U.S. Geological Survey).
This view looks south across the caldera from the north rim of Aniakchak. Surprise Lake and its outlet are visible at the upper left. The prominent dark peak on the skyline is Black Nose, a high-standing remnant of pre-caldera volcaniclastics. Hummocky ground in the distance against the caldera wall is a pumice-covered glacier and associated moraine. Surprise Lake once covered a much larger part of the caldera floor before catastrophically draining through a notch in the east caldera rim.

Photo by Tom Miller, 1985 (Alaska Volcano Observatory, U.S. Geological Survey).
The Gates is a v-shaped notch in the 1-km-high eastern rim of Aniakchak caldera. Surprise Lake, now restricted to the NW part of the caldera floor, was once much larger. It is thought to have drained catastrophically through The Gates at the time of an eruption at Half Cone about 500 years ago.

Photo by Christina Neal, 1994 (Alaska Volcano Observatory, U.S. Geological Survey).
A geologist examines pyroclastic deposits (above hand) from a violent eruption of Half Cone less than 500 years ago. The Half Cone layers overlie dark gray phreatomagmatic deposits from Surprise tuff cone in Aniakchak caldera. The Half Cone eruption produced about 1 cu km of tephra, and resulted in truncation of the SE side of the cone.

Photo by Game McGimsey (Alaska Volcano Observatory, U.S. Geological Survey).
The primary 1931 eruption site is nestled against the NW wall of Aniakchak caldera. This crater, about 600 m across, was the site of intermittent explosions of pumice-lithic tephra over the course of several weeks in May and June, 1931. During the final phases of the eruption, a small lava flow and spatter field formed in the bottom of the crater. The 1931 eruption occurred along a fissure cutting through Vent Mountain and across the caldera floor to the west caldera wall.

Photo by Game McGimsey, 1992 (Alaska Volcano Observatory, U.S. Geological Survey).


The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography. Discussion of another volcano or eruption (sometimes far from the one that is the subject of the manuscript) may produce a citation that is not at all apparent from the title.

Coats R R, 1950. Volcanic activity in the Aleutian Arc. U S Geol Surv Bull, 974-B: 35-47.

Dreher S T, Eichelberger J C, Larsen J F, 2005. The petrology and geochemistry of the Aniakchak caldera-forming ignmbrite, Aleutian Arc, Alaska. J Petr, 46: 1747-1763.

Henning R A, Rosenthal C H, Olds B, Reading E (eds), 1976. Alaska's volcanoes, northern link in the ring of fire. Alaska Geog, 4: 1-88.

IAVCEI, 1973-80. Post-Miocene Volcanoes of the World. IAVCEI Data Sheets, Rome: Internatl Assoc Volc Chemistry Earth's Interior..

McGimsey R G, Waythomas C F, Neal C A, 1994. High strand and catastrophic draining of intracaldera Surprise Lake, Aniakchak volcano, Alaska. In: Till A B, Moore T E (eds) {Geologic Studies in Alaska by the U. S. Geological Survey in 1993}, U S Geol Surv Bull 2017: 59-71.

Miller T P, McGimsey R G, Richter D H, Riehle J R, Nye C J, Yount M E, Dumoulin J A, 1998. Catalogue of the historically active volcanoes of Alaska. U S Geol Surv Open-File Rpt, 98-582: 1-104.

Motyka R J, Liss S A, Nye C J, Moorman M A, 1993. Geothermal resources of the Aleutian arc. Alaska Div Geol Geophys Surv, Prof Rpt, no 114, 17 p and 4 map sheets.

Neal C A, McGimsey R G, Miller T P, Riehle J R, Waythomas C F, 2001. Preliminary volcano-hazard assessment for Aniakchak volcano, Alaska. U S Geol Surv Open-File Rpt, 00-519: 1-35.

Newhall C G, Dzurisin D, 1988. Historical unrest at large calderas of the world. U S Geol Surv Bull, 1855: 1108 p, 2 vol.

Smith R L, Shaw H R, Luedke R G, Russell S L, 1978. Comprehensive tables giving physical data and thermal energy estimates for young igneous systems of the United States. U S Geol Surv Open-File Rpt, 78-925: 1-25.

Smith W R, 1925. Aniakchak Crater, Alaska Peninsula.. U S Geol Surv Prof Pap, 132-J: 139-149.

Volcano Types

Pyroclastic cone(s)
Lava dome(s)

Tectonic Setting

Subduction zone
Continental crust (> 25 km)

Rock Types

Andesite / Basaltic Andesite
Basalt / Picro-Basalt
Trachyte / Trachyandesite
Trachyandesite / Basaltic trachy-andesite


Within 5 km
Within 10 km
Within 30 km
Within 100 km

Affiliated Databases

Large Eruptions of Aniakchak Information about large Quaternary eruptions (VEI >= 4) is cataloged in the Large Magnitude Explosive Volcanic Eruptions (LaMEVE) database of the Volcano Global Risk Identification and Analysis Project (VOGRIPA).
WOVOdat WOVOdat is a database of volcanic unrest; instrumentally and visually recorded changes in seismicity, ground deformation, gas emission, and other parameters from their normal baselines. It is sponsored by the World Organization of Volcano Observatories (WOVO) and presently hosted at the Earth Observatory of Singapore.
EarthChem EarthChem develops and maintains databases, software, and services that support the preservation, discovery, access and analysis of geochemical data, and facilitate their integration with the broad array of other available earth science parameters. EarthChem is operated by a joint team of disciplinary scientists, data scientists, data managers and information technology developers who are part of the NSF-funded data facility Integrated Earth Data Applications (IEDA). IEDA is a collaborative effort of EarthChem and the Marine Geoscience Data System (MGDS).
Smithsonian Collections Search the Smithsonian's NMNH Department of Mineral Sciences collections database. Go to the "Search Rocks and Ores" tab and use the Volcano Name drop-down to find samples.