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  • 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.

Basic Data

Volcano Number

Last Known Eruption



1931 CE

1341 m / 4398 ft


Volcano Types

Pyroclastic cone(s)
Lava dome(s)

Rock Types

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

Tectonic Setting

Subduction zone
Continental crust (> 25 km)


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

Geological Summary

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.


The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography.

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.

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).

Smithsonian Sample Collections Database

The following 54 samples associated with this volcano can be found in the Smithsonian's NMNH Department of Mineral Sciences collections. Catalog number links will open a window with more information.

Catalog Number Sample Description
NMNH 117233-106 Pumice
NMNH 117233-107 Pumice
NMNH 117233-108 Pumice
NMNH 117233-109 Pumice
NMNH 117233-110 Pumice
NMNH 117233-111 Pumice
NMNH 117233-112 Pumice
NMNH 117233-113 Pumice
NMNH 117233-114 Pumice
NMNH 117233-115 Pumice
NMNH 117233-116 Pumice
NMNH 117233-117 Pumice
NMNH 117233-118 Pumice
NMNH 117233-119 Basalt
NMNH 117233-120 Pumice
NMNH 117233-121 Pumice
NMNH 117233-122 Tuff
NMNH 117233-123 Pumice
NMNH 117233-124 Pumice
NMNH 117233-125 Pumice
NMNH 117233-126 Pumice
NMNH 117233-127 Basalt
NMNH 117233-128 Dacite
NMNH 117233-131 Obsidian
NMNH 117233-132 Pumice
NMNH 117233-133 Pumice
NMNH 117233-134 Pumice
NMNH 117233-135 Pumice
NMNH 117233-136 Pumice
NMNH 117233-137 Pumice
NMNH 117233-138 Pumice
NMNH 117233-139 Andesite
NMNH 117233-140 Basalt
NMNH 117233-141 Basalt
NMNH 117233-143 Basalt
NMNH 117233-144 Basalt
NMNH 117233-145 Pumice
NMNH 117233-146 Pumice
NMNH 117233-147 Pumice
NMNH 117233-148 Pumice
NMNH 117233-149 Pumice
NMNH 117233-150 Pumice
NMNH 117233-151 Pumice
NMNH 117233-152 Pumice
NMNH 117233-153 Pumice
NMNH 117233-154 Pumice
NMNH 117233-155 Pumice
NMNH 117233-156 Pumice
NMNH 117233-157 Pumice
NMNH 117233-158 Basalt
NMNH 117233-159 Pumice
NMNH 117233-160 Pumice
NMNH 117233-193 Basalt
NMNH 117457-1 Obsidian

Affiliated Sites

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).
MODVOLC - HIGP MODIS Thermal Alert System Using infrared satellite Moderate Resolution Imaging Spectroradiometer (MODIS) data, scientists at the Hawai'i Institute of Geophysics and Planetology, University of Hawai'i, developed an automated system called MODVOLC to map thermal hot-spots in near real time. For each MODIS image, the algorithm automatically scans each 1 km pixel within it to check for high-temperature hot-spots. When one is found the date, time, location, and intensity are recorded. MODIS looks at every square km of the Earth every 48 hours, once during the day and once during the night, and the presence of two MODIS sensors in space allows at least four hot-spot observations every two days. Each day updated global maps are compiled to display the locations of all hot spots detected in the previous 24 hours. There is a drop-down list with volcano names which allow users to 'zoom-in' and examine the distribution of hot-spots at a variety of spatial scales.
MIROVA Middle InfraRed Observation of Volcanic Activity (MIROVA) is a near real time volcanic hot-spot detection system based on the analysis of MODIS (Moderate Resolution Imaging Spectroradiometer) data. In particular, MIROVA uses the Middle InfraRed Radiation (MIR), measured over target volcanoes, in order to detect, locate and measure the heat radiation sourced from volcanic activity.