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Aniakchak

Photo of this volcano
  • United States
  • Alaska Peninsula Volcanic Arc
  • Caldera | Caldera
  • 1931 CE
  • Country
  • Volcanic Province
  • Landform | Volc Type
  • Last Known Eruption
  • 56.88°N
  • 158.17°W

  • 1341 m
    4400 ft

  • 312090
  • Latitude
  • Longitude

  • Summit
    Elevation

  • Volcano
    Number

Most Recent Weekly Report: 25 October-31 October 2023 Citation IconCite this Report

AVO reported that on 26 October strong winds in areas NW of Aniakchak and E of Port Heiden dispersed unconsolidated ash up to 0.9 km (3,000 ft) a.s.l. to the NW. The ash cloud was visible in satellite images and in Port Heiden webcam views. The Volcano Alert Level remained at Normal (the lowest level on a four-level scale) and the Aviation Color Code remained at Green (the lowest level on a four-color scale). Equipment failed on 30 October, so AVO could no longer seismically monitor the volcano at an adequate level and determine if activity was at a typical background level. Both the Volcano Alert Level and the Aviation Color Code were changed to Unassigned.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

Weekly Reports - Index


2023: February | March | April | August | October
2022: June
2021: July


25 October-31 October 2023 Citation IconCite this Report

AVO reported that on 26 October strong winds in areas NW of Aniakchak and E of Port Heiden dispersed unconsolidated ash up to 0.9 km (3,000 ft) a.s.l. to the NW. The ash cloud was visible in satellite images and in Port Heiden webcam views. The Volcano Alert Level remained at Normal (the lowest level on a four-level scale) and the Aviation Color Code remained at Green (the lowest level on a four-color scale). Equipment failed on 30 October, so AVO could no longer seismically monitor the volcano at an adequate level and determine if activity was at a typical background level. Both the Volcano Alert Level and the Aviation Color Code were changed to Unassigned.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


16 August-22 August 2023 Citation IconCite this Report

On 17 August AVO reported that number of earthquakes beneath Aniakchak and the measurable uplift of the ground surface in the caldera had declined to background levels. The Aviation Color Code was lowered to Green (the lowest level on a four-color scale) and the Volcano Alert Level was lowered to Normal (the lowest level on a four-level scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)


12 April-18 April 2023 Citation IconCite this Report

On 13 April AVO issued an Information Statement about the ongoing unrest at Aniakchak. Measurements of the earthquake rate in the ongoing swarm were disrupted by a partial network outage that began on 4 March and reduced the ability to detect smaller earthquakes. Earthquake activity continued to be above background levels with a M 3.3 on 6 April as the largest recent event. In addition to the earthquake swarm, high rates of deformation were detected in radar data. A zone of uplift centered within the W side of the caldera was first detected between 4 and 27 February. The ground uplift rates were about 4 cm per week during February-March and about 3 cm per week during 23 March-4 April. These uplift rates are at the high end of those observed for restless volcanoes worldwide.

Seismic and deformation data suggested that magma was intruding beneath the caldera at a depth of 3-4 km below sea level. AVO noted that unrest at calderas such as Aniakchak sometimes lasts for many months or even years and could be variable . If an eruption were to occur, it could be after a period of months or years and would likely be preceded by additional signals that would allow AVO to provide advance warning. Aniakchak has a local monitoring network consisting of six seismometers, a web camera, and an infrasound sensor, as well as with satellite remote sensing data and regional infrasound and lightning networks. AVO recently installed an additional seismic station and web camera in Port Heiden, 26 km NW. The Aviation Color Code remained at Yellow (the second lowest level on a four-color scale) and the Volcano Alert Level remained at Advisory (the second lowest level on a four-level scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)


1 March-7 March 2023 Citation IconCite this Report

AVO reported that the earthquake swarm at Aniakchak was ongoing with 120 earthquakes located during 25 February-3 March. Magnitudes were as high as M3.1 and several earthquakes had magnitudes between M2 and M3. The earthquakes were located at shallow depths (less than 5 km) and below the S part of the caldera and to the E of the volcano. Daily, small, shallow earthquakes with magnitudes as high as M2.7 were recorded during 4-7 March. The Aviation Color Code remained at Yellow (the second lowest level on a four-color scale) and the Volcano Alert Level remained at Advisory (the second lowest level on a four-level scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)


22 February-28 February 2023 Citation IconCite this Report

On 22 February AVO raised the Aviation Color Code for Aniakchak to Yellow (the second lowest level on a four-color scale) and the Volcano Alert Level to Advisory (the second lowest level on a four-level scale) due to a recent increase in the number of earthquakes and a shallowing of those events. Background seismicity was generally characterized as deep (more than 15 km below sea level) long-period events occurring at a rate of about four events per month. Beginning in October 2022 the rate increased, and the earthquakes were located at depths less than 9 km below sea level. The earthquake rate further increased on 31 January and was sustained with dozens of earthquakes detected per day, including a M 3.7 earthquake recorded on 17 February.

Elevated seismicity continued during 23-27 February at a variable rate. Dozens of earthquakes were recorded daily during 22-26 February, though more than one hundred small earthquakes (not all locatable) were detected during 24-25 February. Small earthquakes occurred at the rate of about 10 per hour during 26-28 February. AVO noted that there was no indication that an eruption of Aniakchak was imminent, or that one will occur. Increases in seismic activity have been detected previously at other similar volcanoes, with no subsequent eruptions.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


29 June-5 July 2022 Citation IconCite this Report

AVO reported that strong winds in a region NW of Aniakchak and E of Port Heiden resuspended ash and blew it NW on 30 June. A dense cloud of possible resuspended ash near ground levels was identified in Port Heiden webcam views. The altitude of the cloud was unknown, though the report noted that resuspended ash clouds typically do not rise above 5 km (16,400 ft) a.s.l. The cloud was not a result of volcanic activity; the Aviation Color Code and the Volcano Alert Level remained at Green and Normal, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


28 July-3 August 2021 Citation IconCite this Report

AVO reported that strong winds in a region N of Aniakchak and E of Port Heiden resuspended ash and blew it N on 2 August. A dense cloud of possible resuspended ash near ground levels was identified in Port Heiden webcam views. The cloud was also visible in satellite data drifting about 200 km N. The report noted that resuspended ash clouds typically do not rise above 5 km (16,400 ft) a.s.l. The cloud was not a result of volcanic activity; the Aviation Color Code and the Volcano Alert Level remained at Green and Normal, respectively.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


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

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.

Eruptive History

There is data available for 16 confirmed Holocene eruptive periods.

[ 1951 Jun 25 - 1951 Jun 25 ] Discredited Eruption

Pilot Everett Skinner observed extensive brown haze that reduced visibility at Port Heiden airport to under 1/3 km. Airport officials attributed the haze to an eruption of Aniakchak volcano (BVE). This event was determined by Cameron (2004, pers. comm.) to have been a result of resuspended ash.

[ 1942 ] Uncertain Eruption

Episode 1 | Uncertain Episode
1942 - Unknown Evidence from Unknown
 Decker (1971) listed a 1942? eruption not mentioned by Miller et al. (1998).

1931 May 1 - 1931 Jun 13 (in or after) Confirmed Eruption Max VEI: 4

Episode 1 | Eruption Episode West and SW caldera floor
1931 May 1 - 1931 Jun 13 (in or after) Evidence from Observations: Reported

List of 16 Events for Episode 1 at West and SW caldera floor

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Pyroclastic flow
   - - - -    - - - - Lava flow
   - - - -    - - - - Lava dome
   - - - -    - - - - Avalanche
   - - - -    - - - - Ash
   - - - -    - - - - Lapilli
   - - - -    - - - - Bombs
   - - - -    - - - - Pumice
   - - - -    - - - - Lightning
   - - - -    - - - - Earthquakes (undefined)
   - - - -    - - - - Fauna Kill Aquatic.
   - - - -    - - - - Property Damage
1931 May 1    - - - - VEI (Explosivity Index)
1931 May 11    - - - - VEI (Explosivity Index)
1931 May 20    - - - - VEI (Explosivity Index)

1540 ± 100 years Confirmed Eruption Max VEI: 4

Episode 1 | Eruption Episode NW & S caldera floor (Half Cone, Vent Mtn)
1540 ± 100 years - Unknown Evidence from Isotopic: 14C (calibrated)

List of 5 Events for Episode 1 at NW & S caldera floor (Half Cone, Vent Mtn)

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Pyroclastic flow
   - - - -    - - - - Lava flow
   - - - -    - - - - Pumice
1540 ± 100 years    - - - - VEI (Explosivity Index) VEI 4

1470 ± 20 years Confirmed Eruption  

Episode 1 | Eruption Episode SE caldera floor (New Cone)
1470 ± 20 years - Unknown Evidence from Isotopic: 14C (calibrated)

List of 1 Events for Episode 1 at SE caldera floor (New Cone)

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion

1370 ± 55 years Confirmed Eruption  

Episode 1 | Eruption Episode NW caldera floor (Half Cone)
1370 ± 55 years - Unknown Evidence from Isotopic: 14C (calibrated)

List of 2 Events for Episode 1 at NW caldera floor (Half Cone)

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Pumice

1280 ± 145 years Confirmed Eruption  

Episode 1 | Eruption Episode NW caldera floor (Half Cone)
1280 ± 145 years - Unknown Evidence from Isotopic: 14C (calibrated)

List of 2 Events for Episode 1 at NW caldera floor (Half Cone)

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Tephra

1190 ± 30 years Confirmed Eruption  

Episode 1 | Eruption Episode NW caldera floor (Half Cone)
1190 ± 30 years - Unknown Evidence from Isotopic: 14C (calibrated)

List of 3 Events for Episode 1 at NW caldera floor (Half Cone)

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Lava flow
   - - - -    - - - - Pumice

1120 ± 80 years Confirmed Eruption  

Episode 1 | Eruption Episode East-central caldera (Surprise Cone)
1120 ± 80 years - Unknown Evidence from Isotopic: 14C (calibrated)

List of 2 Events for Episode 1 at East-central caldera (Surprise Cone)

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Lapilli

1050 (?) Confirmed Eruption  

Episode 1 | Eruption Episode Vent Mtn and other vents?
1050 (?) - Unknown Evidence from Correlation: Tephrochronology

List of 2 Events for Episode 1 at Vent Mtn and other vents?

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Lahar or Mudflow

0700 ± 250 years Confirmed Eruption Max VEI: 0

Episode 1 | Eruption Episode S & NW caldera floor (Vent Mtn & Half Cone)
0700 ± 250 years - Unknown Evidence from Correlation: Tephrochronology

List of 2 Events for Episode 1 at S & NW caldera floor (Vent Mtn & Half Cone)

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Lava flow
0700 ± 300 years    - - - - VEI (Explosivity Index)

0460 (?) Confirmed Eruption  

Episode 1 | Eruption Episode
0460 (?) - Unknown Evidence from Isotopic: 14C (uncalibrated)

List of 2 Events for Episode 1

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Lava flow

0200 ± 255 years Confirmed Eruption  

Episode 1 | Eruption Episode Northern & western caldera floor
0200 ± 255 years - Unknown Evidence from Correlation: Tephrochronology

List of 2 Events for Episode 1 at Northern & western caldera floor

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Lava dome

0370 BCE ± 210 years Confirmed Eruption  

Episode 1 | Eruption Episode
0370 BCE ± 210 years - Unknown Evidence from Isotopic: 14C (calibrated)

List of 2 Events for Episode 1

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Pumice

1645 BCE ± 10 years Confirmed Eruption Max VEI: 6 (?)

Episode 1 | Eruption Episode
1645 BCE ± 10 years - Unknown Evidence from Sidereal: Ice Core

List of 8 Events for Episode 1

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion extremely violent or catastrophic
   - - - -    - - - - Pyroclastic flow
   - - - -    - - - - Ash
   - - - -    - - - - Bombs
   - - - -    - - - - Pumice
   - - - -    - - - - Caldera Explosion
   - - - -    - - - - Tsunami
1645 BCE ± 10 years    - - - - VEI (Explosivity Index)

2550 BCE ± 500 years Confirmed Eruption  

Episode 1 | Eruption Episode
2550 BCE ± 500 years - Unknown Evidence from Correlation: Tephrochronology

List of 1 Events for Episode 1

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion

5930 BCE ± 240 years Confirmed Eruption  

Episode 1 | Eruption Episode Black Nose Pumice
5930 BCE ± 240 years - Unknown Evidence from Isotopic: 14C (calibrated)

List of 3 Events for Episode 1 at Black Nose Pumice

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Pyroclastic flow
   - - - -    - - - - Pumice

6300 BCE ± 1250 years Confirmed Eruption Max VEI: 6 (?)

Episode 1 | Eruption Episode
6300 BCE ± 1250 years - Unknown Evidence from Correlation: Tephrochronology

List of 4 Events for Episode 1

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Pyroclastic flow
   - - - -    - - - - Caldera Explosion. Uncertain.
5250 BCE ± 1000 years    - - - - VEI (Explosivity Index)
Deformation History

There is data available for 1 deformation periods. Expand each entry for additional details.


Deformation during 1992 - 2010 [Subsidence; Observed by InSAR]

Start Date: 1992 Stop Date: 2010 Direction: Subsidence Method: InSAR
Magnitude: Unknown Spatial Extent: Unknown Latitude: Unknown Longitude: Unknown

Remarks: Variable rates of subsidence are observed at Aniakchak.

Figure (see Caption)

a Observed and b best-fit synthetic descending- track ERS interferograms of Aniakchak Caldera; ? marks location of best-fit Mogi source. c Time-series showing cumulative source-volume change based on modeling ERS and Envisat interferograms from track 086. Observed Envisat interferograms are averaged deformation-rate maps for 1992?2010. Synthetic interferograms were produced using a Mogi (1958) source at about 4 km depth beneath the center of Aniakchak Caldera. Areas lacking interferometric coherence are uncolored. A full cycle of colors (i.e., one interferometric fringe) represents 10 mm/year LOS surface displacement

From: Lu and Dzurisin 2014.


Reference List: Lu and Dzurisin 2014, Kwoun et al. 2006.

Full References:

Lundgren P, Lu Z, 2006. Inflation model of Uzon caldera, Kamchatka, constrained by satellite radar interferometry observations. Geophysical Research Letters, 33, L06301. https://doi.org/10.1029/2005GL025181

Emission History

There is no Emissions History data available for Aniakchak.

Photo Gallery

The 10-km-wide Aniakchak caldera is one of the most dramatic volcanoes on the Alaska Peninsula. It was formed about 3400 years ago during an eruption in which voluminous pyroclastic flows reached the Bering Sea, 80 km away. This view from the NE shows the largest post-caldera volcano, Vent Mountain (upper right) and Surprise Lake (lower right), which drains through The Gates (left center), a steep-walled notch in the 1-km-high eastern caldera rim. The only historical eruption of Aniakchak took place in 1931.

Copyrighted photo by Katia and Maurice Krafft, 1978.
Vent Mountain, a post-caldera volcano that rises 450 m above the caldera floor, is the largest of a variety of volcanic features on the floor of the 10-km-wide caldera. In addition to Vent Mountain, the most prominent post-caldera features are Half Cone, on the NW side and a 1931 vent near the west rim. Lava flows, tuff cones, maars, cinder cones, and lava domes are all found within Aniakchak caldera. This view from the SW shows the east caldera rim, with The Gates, a steep-walled notch in the east rim, at the upper left.

Copyrighted photo by Katia and Maurice Krafft, 1978.
Aniakchak is a 10-km-wide summit caldera containing numerous cones, lava domes, and lava flows on the caldera floor. The largest intra-caldera cone is Vent Mountain that reaches 430 m in height and has a diameter at the base of 2.5 km. At least 20 Holocene eruptions may have occurred before the Aniakchak II caldera-forming eruption.

Photo by M. Woodbridge Williams (National Park Service).
Volcanologists from the U.S. Geological Survey on the rim of the intra-caldera Vent Mountain at Aniakchak look NW towards Half Cone, a prominent feature on the caldera floor and the source of an explosive post-caldera eruption. 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. The prominent dark peak on the skyline (left) is Black Nose, a remnant of pre-caldera volcaniclastics. A pumice-covered glacier and associated moraine is in the distance against the caldera wall. 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 was once much larger but is now restricted to the NW part of the caldera floor. 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 km3 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 Aniakchak 1931 eruption site is against the NW caldera wall. This 600-m-wide crater produced 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 formed in the bottom of the crater. The fissure eruption cut through Vent Mountain and across the caldera floor to the western caldera wall.

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

Maps are not currently available due to technical issues.

The maps shown below have been scanned from the GVP map archives and include the volcano on this page. Clicking on the small images will load the full 300 dpi map. Very small-scale maps (such as world maps) are not included.

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, and may be availble for research (contact the Rock and Ore Collections Manager). Catalog number links will open a window with more information.

Catalog Number Sample Description Lava Source Collection Date
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 Aniakchak Ash Flow --
NMNH 117233-149 Pumice Aniakchak Ash Flow --
NMNH 117233-150 Pumice Aniakchak Ash Flow --
NMNH 117233-151 Pumice Aniakchak Ash Flow --
NMNH 117233-152 Pumice Aniakchak Ash Flow --
NMNH 117233-153 Pumice Aniakchak Ash Flow --
NMNH 117233-154 Pumice Aniakchak Ash Flow --
NMNH 117233-155 Pumice Aniakchak Ash Flow --
NMNH 117233-156 Pumice Aniakchak Ash Flow --
NMNH 117233-157 Pumice Aniakchak Ash Flow --
NMNH 117233-158 Basalt Aniakchak Ash Flow --
NMNH 117233-159 Pumice Aniakchak Ash Flow --
NMNH 117233-160 Pumice Aniakchak Ash Flow --
NMNH 117233-193 Basalt -- --
NMNH 117457-1 Obsidian -- --
External Sites