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Tanaga

Photo of this volcano
  • Country
  • Landform (Volc Type)
  • Last Known Eruption
  • 51.885°N
  • 178.146°W

  • 1806 m
    5925 ft

  • 311080
  • Latitude
  • Longitude

  • Summit
    Elevation

  • Volcano
    Number

Most Recent Weekly Report: 12 July-18 July 2023 Citation IconCite this Report

AVO reported that earthquake activity near Tanaga had decreased in both rate and magnitude. The rate of earthquakes had been about three events per day during the previous three weeks, much lower than the 150 events per day recorded during the peak of the swarm in mid-March. Recent satellite images did not indicate any deformation on the island and no other signs of volcanic unrest had been detected. On 18 July the Volcano Alert Level was lowered to Normal (the lowest level on a four-level scale) and the Aviation Color Code was lowered to Green (the lowest color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)


Most Recent Bulletin Report: January 2006 (BGVN 31:01) Citation IconCite this Report

Weak, moderate depth seismicity

The Alaska Volcano Observatory (AVO) detected an increase in seismic activity beneath Tanaga beginning on 1 October 2005, with 15-68 earthquakes occurring daily. Previously, less than one earthquake had occurred per month since the seismic network was installed in 2003. The earthquakes were centered roughly 2 km NE of the summit at depths of 10-20 km below sea level. The largest event was M 1.7, with most earthquakes at M 0.5-1.5. Tanaga was at Concern Color Code Green on 5 October.

During 5-7 October, there was a marked increase in the rate of seismicity. The located earthquakes ranged in magnitude from 0.5 to 1.9 and ranged in depth from 6 to 12 km beneath the summit. In response, AVO raised the Concern Color Code to Yellow on 7 October. AVO reported that while the seismic activity represented a significant increase in rate, the size, depth, and character of the events were not indicative of imminent eruptive activity.

Elevated seismic activity below the young vents continued through 28 October 2005, although the rate of small earthquakes decreased slightly from the previous week. The activity that began on 1 October was at the highest level recorded since the seismic network was installed in 2003, so the Concern Color Code remained at Yellow. An unusual seismic signal on 17 October that persisted for several minutes may have been a landslide or small phreatic explosion, but satellite images detected no airborne ash. Beginning on 24 October, AVO observed weak, nearly continuous volcanic tremor in the vicinity of Takawangha volcano of the Tanaga volcano cluster. This was the first recorded tremor of this type. The daily number of small earthquakes continued to diminish from its peak in early October, but stayed above background levels.

AVO reported on 25 November 2005 that for several weeks seismicity beneath young volcanic vents on Tanaga Island decreased significantly from levels recorded in early October. Satellite images showed no anomalous temperatures or evidence of ash emissions. AVO reported that, based on the decrease in earthquake counts and frequency of tremor episodes, the likelihood of an eruption had diminished. Therefore, AVO downgraded the Concern Color Code to Green. According to AVO, the most recent eruptive activity at Tanaga was a lava flow observed in 1914.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of the U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.

Weekly Reports - Index


2023: March | July
2021: March | April
2005: October | November


12 July-18 July 2023 Citation IconCite this Report

AVO reported that earthquake activity near Tanaga had decreased in both rate and magnitude. The rate of earthquakes had been about three events per day during the previous three weeks, much lower than the 150 events per day recorded during the peak of the swarm in mid-March. Recent satellite images did not indicate any deformation on the island and no other signs of volcanic unrest had been detected. On 18 July the Volcano Alert Level was lowered to Normal (the lowest level on a four-level scale) and the Aviation Color Code was lowered to Green (the lowest color on a four-color scale).

Source: US Geological Survey Alaska Volcano Observatory (AVO)


15 March-21 March 2023 Citation IconCite this Report

AVO reported that earthquake activity near Tanaga had decreased in both rate and magnitude from the peak of the swarm recorded during 9-11 March. More than 800 earthquakes, including multiple M2 and above events, were detected beneath Tanaga Island at depths less than 9 km below sea level during 11-17 March. The decline in activity decreased the potential for an eruption, so AVO lowered the Volcano Alert Level to Advisory (the second lowest level on a four-level scale) and the Aviation Color Code to Yellow (the second lowest color on a four-color scale) on 16 March. The Volcano Alert Level and Aviation Color Code for Takawangha (8 km E) were also lowered to the same level. Several M 2 and higher earthquakes were detected during 17-18 March, in addition to numerous smaller events. Earthquake activity persisted through 20 March.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


8 March-14 March 2023 Citation IconCite this Report

AVO reported that earthquake activity near Tanaga began to increase on 4 March with events up to the M2 range and located 9-18 km deep. Seismicity again increased around 1330 on 7 March and by 2045 earthquakes were occurring at a rate of 2-3 per minute. AVO raised the Aviation Color Code 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). The seismicity was sustained during 8-9 March and had shallowed to depths less than about 6 km, indicating increased potential for an eruption. AVO raised the Volcano Alert Level to Watch and the Aviation Color Code to Orange, the highest levels, at 1719 on 9 March. Seismicity was also elevated at Takawangha, 8 km E; both volcanoes are located on Tanaga Island. It was uncertain which volcano would erupt, if an eruption were to occur, so the Volcano Alert Level and Aviation Color Code for Takawangha were also raised to the same level. Earthquakes beneath Tanaga Island occurred at a rate of up to several per minute, with the largest event during 8-9 March, a M3.9, located under Tanaga Volcano. Earthquakes beneath Tanaga and Takawangha occurred at a rate of up to several events per minute during 10-11 March and at a slightly reduced rate during 12-14 March. The earthquakes had magnitudes up to around 4.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


1 March-7 March 2023 Citation IconCite this Report

At 2215 on 7 March AVO raised the Aviation Color Code for Tanaga to Yellow and the Volcano Alert Level to Advisory due to increased seismicity. Earlier that afternoon, starting at about 1330, seismicity began to increase and by around 2045 earthquakes were occurring at a rate of 2-3 per minute. The events were located at shallow depths and the largest events were M2-3.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


14 April-20 April 2021 Citation IconCite this Report

AVO reported that communication was reestablished with two seismic stations on Tanaga, making a total of four operational stations. On 19 April AVO changed both the Aviation Color Code and the Volcano Alert Level to Green and Normal, respectively, reflecting the resumption of seismically monitoring unrest.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


31 March-6 April 2021 Citation IconCite this Report

AVO reported a loss of operation and communication with all but two seismic stations on Tanaga, likely caused by snow cover. Both the Aviation Color Code and the Volcano Alert Level were changed to Unassigned, reflecting the inability to locate earthquakes to detect unrest. Monitoring will continue with the remaining seismic stations, regional infrasound networks, lightning detection, and satellite images.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


23 November-29 November 2005 Citation IconCite this Report

AVO reported on 25 November that for several weeks seismicity beneath young volcanic vents on Tanaga Island decreased significantly from levels recorded in early October. Satellite images of the island showed no anomalous temperatures or evidence of ash emissions. AVO reported that based on the decrease in earthquake counts and frequency of tremor episodes, the likelihood of an eruption had diminished. Therefore, AVO downgraded the Concern Color Code from Yellow to Green.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


26 October-1 November 2005 Citation IconCite this Report

Elevated seismicity below young volcanic vents on Tanaga Island continued during 21-28 October. Beginning on 24 October, AVO observed weak, nearly continuous volcanic tremor in the vicinity of Takawangha volcano of the Tanaga volcano cluster. This was the first time that tremor of this sort had been observed in the volcanic cluster since the seismic network was installed in 2003. The daily number of small earthquakes continued to diminish from its peak in early October, but stayed above background levels. Tanaga remained at Concern Color Code Yellow.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


19 October-25 October 2005 Citation IconCite this Report

Elevated seismic activity below young volcanic vents on Tanaga Island continued during 14-21 October, although the rate of small earthquakes reduced in comparison to peak values during early October. An unusual, several minute-long seismic signal on 17 October may have been a landslide or small phreatic explosion, but satellite images detected no airborne ash. The activity that began at Tanaga on 1 October was at the highest level recorded since the seismic network was installed in 2003, so the Concern Color Code remained at Yellow.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


12 October-18 October 2005 Citation IconCite this Report

Elevated seismic activity below young volcanic vents on Tanaga Island continued during 7-14 October, although the rate of small earthquakes reduced slightly in comparison to the previous week. The activity that began at Tanaga on 1 October was at the highest level recorded since the seismic network was installed in 2003, so the Concern Color Code remained at Yellow.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


5 October-11 October 2005 Citation IconCite this Report

AVO detected an increase in seismic activity beneath Tanaga beginning on 1 October, with 15-68 earthquakes occurring daily. Previously, less than one earthquake had occurred per month since the seismic network was installed in 2003. The earthquakes were centered roughly 2 km NE of the volcano's summit at depths of 10-20 km below sea level. The largest event was M 1.7, with most earthquakes between M 0.5-1.5. Tanaga was at Concern Color Code Green on 5 October. During 5-7 October, there was a marked increase in the rate of seismicity. The located earthquakes ranged in magnitude from 0.5 to 1.9 and ranged in depth from 6 to 12 km beneath the volcano's summit. In response to the observed changes in seismic activity, AVO raised the Concern Color Code to Yellow on 7 October. AVO reported that while the seismic activity represented a significant increase in rate, the size, depths and character of the events were not indicative of imminent eruptive activity.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


Bulletin Reports - Index

Reports are organized chronologically and indexed below by Month/Year (Publication Volume:Number), and include a one-line summary. Click on the index link or scroll down to read the reports.

01/2006 (BGVN 31:01) Weak, moderate depth seismicity




Information is preliminary and subject to change. All times are local (unless otherwise noted)


January 2006 (BGVN 31:01) Citation IconCite this Report

Weak, moderate depth seismicity

The Alaska Volcano Observatory (AVO) detected an increase in seismic activity beneath Tanaga beginning on 1 October 2005, with 15-68 earthquakes occurring daily. Previously, less than one earthquake had occurred per month since the seismic network was installed in 2003. The earthquakes were centered roughly 2 km NE of the summit at depths of 10-20 km below sea level. The largest event was M 1.7, with most earthquakes at M 0.5-1.5. Tanaga was at Concern Color Code Green on 5 October.

During 5-7 October, there was a marked increase in the rate of seismicity. The located earthquakes ranged in magnitude from 0.5 to 1.9 and ranged in depth from 6 to 12 km beneath the summit. In response, AVO raised the Concern Color Code to Yellow on 7 October. AVO reported that while the seismic activity represented a significant increase in rate, the size, depth, and character of the events were not indicative of imminent eruptive activity.

Elevated seismic activity below the young vents continued through 28 October 2005, although the rate of small earthquakes decreased slightly from the previous week. The activity that began on 1 October was at the highest level recorded since the seismic network was installed in 2003, so the Concern Color Code remained at Yellow. An unusual seismic signal on 17 October that persisted for several minutes may have been a landslide or small phreatic explosion, but satellite images detected no airborne ash. Beginning on 24 October, AVO observed weak, nearly continuous volcanic tremor in the vicinity of Takawangha volcano of the Tanaga volcano cluster. This was the first recorded tremor of this type. The daily number of small earthquakes continued to diminish from its peak in early October, but stayed above background levels.

AVO reported on 25 November 2005 that for several weeks seismicity beneath young volcanic vents on Tanaga Island decreased significantly from levels recorded in early October. Satellite images showed no anomalous temperatures or evidence of ash emissions. AVO reported that, based on the decrease in earthquake counts and frequency of tremor episodes, the likelihood of an eruption had diminished. Therefore, AVO downgraded the Concern Color Code to Green. According to AVO, the most recent eruptive activity at Tanaga was a lava flow observed in 1914.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of the U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.

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 6 confirmed Holocene eruptive periods.

1914 Confirmed Eruption Max VEI: 0

Episode 1 | Eruption Episode
1914 - Unknown Evidence from Observations: Reported

List of 2 Events for Episode 1

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Lava flow
1914    - - - - VEI (Explosivity Index)

1829 Confirmed Eruption  

Episode 1 | Eruption Episode
1829 - Unknown Evidence from Observations: Reported

List of 2 Events for Episode 1

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

[ 1791 Jun 7 ] Uncertain Eruption

Episode 1 | Eruption Episode
1791 Jun 7 - Unknown Evidence from Unknown

List of 1 Events for Episode 1

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Volcanic "smoke"

[ 1763 - 1770 ] Uncertain Eruption

Episode 1 | Eruption Episode
1763 - 1770 Evidence from Unknown

1550 (?) Confirmed Eruption  

Episode 1 | Eruption Episode Tanaga, Sajaka Two
1550 (?) - Unknown Evidence from Isotopic: 14C (uncalibrated)

List of 2 Events for Episode 1 at Tanaga, Sajaka Two

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

1050 (?) Confirmed Eruption  

Episode 1 | Eruption Episode Tanaga
1050 (?) - Unknown Evidence from Isotopic: 14C (uncalibrated)

List of 2 Events for Episode 1 at Tanaga

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

0550 BCE ± 2500 years Confirmed Eruption  

Episode 1 | Eruption Episode Sajaka One
0550 BCE ± 2500 years - Unknown Evidence from Correlation: Tephrochronology

List of 4 Events for Episode 1 at Sajaka One

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Explosion
   - - - -    - - - - Pyroclastic flow
   - - - -    - - - - Avalanche
   - - - -    - - - - Edifice Destroyed Collapse/avalanche

1050 BCE (?) Confirmed Eruption Max VEI: 0

Episode 1 | Eruption Episode Sajaka One
1050 BCE (?) - Unknown Evidence from Isotopic: Ar/Ar

List of 2 Events for Episode 1 at Sajaka One

Start Date End Date Event Type Event Remarks
   - - - -    - - - - Lava flow
1050 BCE ± 1000 years    - - - - VEI (Explosivity Index)
Deformation History

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


Deformation during 2005 Oct - 2005 Nov [Uplift; Observed by InSAR]

Start Date: 2005 Oct Stop Date: 2005 Nov Direction: Uplift Method: InSAR
Magnitude: 5.000 cm Spatial Extent: 16.00 km Latitude: 52.000 Longitude: -178.000

Remarks: Concurrent with October 17 seismic event. Deformation centered between Tanaga and Takawangha volcanoes

Figure (see Caption)

Selected deformation interferograms of Tanaga Island for the following time periods: a September 10, 2005?October 15, 2005 (Envisat track 373), b July 2, 2005?August 26, 2006 (Envisat track 373), c November 3, 2005?July 6, 2006 (Envisat track 144), d August 25, 2005? November 3, 2005 (Envisat track 144), e September 1, 2004? September 6, 2006 (Envisat track 022), and f August 25, 2005? August 10, 2006 (Envisat track 144). All but (c) span the October?November 2005 earthquake swarm, which escalated during October 1?7 and declined to near background level by late November. Deformation fringes are absent in (c), which spans an 8-month period following the peak of the swarm. Black ellipses in (b) (d), and (f) outline an area of anomalous fringes that might correspond to a landslide-like signal noted on seismic records for October 17, 2005. A full cycle of colors (i.e., one interferometric fringe) represents 2.83 cm of surface displacement along the satellite- to-ground LOS

From: Lu and Dzurisin 2014.


Reference List: Lu and Dzurisin 2014.

Full References:

Lu Z, Dzurisin D, 2014. InSAR imaging of Aleutian volcanoes: monitoring a volcanic arc from space. Springer-Verlag Berlin Heidelberg. https://doi.org/10.1007/978-3-642-00348-6

Emission History

There is no Emissions History data available for Tanaga.

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 118211-1 Basalt -- 15 Sep 2015
NMNH 118211-10 Basaltic andesite scoria -- 15 Sep 2015
NMNH 118211-11 Basaltic andesite lapilli tephra -- 15 Sep 2015
NMNH 118211-12 Basaltic andesite scoria -- 15 Sep 2015
NMNH 118211-13 Volcanic Ash -- 16 Sep 2015
NMNH 118211-14 Fine ash -- 16 Sep 2015
NMNH 118211-15 Lapilli tephra -- 16 Sep 2015
NMNH 118211-16 Basaltic andesite lapilli tephra -- 16 Sep 2015
NMNH 118211-17 Basalt Scoria -- 16 Sep 2015
NMNH 118211-18 Scoria -- 16 Sep 2015
NMNH 118211-19 Volcanic Ash -- 16 Sep 2015
NMNH 118211-2 Scoriaceous tephra -- 15 Sep 2015
NMNH 118211-20 Lapilli tephra -- 16 Sep 2015
NMNH 118211-21 Basalt lapilli tephra -- 16 Sep 2015
NMNH 118211-22 Tephra -- 16 Sep 2015
NMNH 118211-23 Basalt lapilli tephra -- 18 Sep 2015
NMNH 118211-24 Lapilli tephra -- 18 Sep 2015
NMNH 118211-25 Lapilli tephra -- 18 Sep 2015
NMNH 118211-26 Lapilli tephra -- 18 Sep 2015
NMNH 118211-27 Lapilli tephra -- 18 Sep 2015
NMNH 118211-28 Coarse ash -- 18 Sep 2015
NMNH 118211-29 Basaltic andesite lapilli tephra -- 18 Sep 2015
NMNH 118211-3 Lapilli tephra -- 15 Sep 2015
NMNH 118211-30 Scoriaceous tephra -- 18 Sep 2015
NMNH 118211-31 Basalt scoriaceous tephra -- 16 Sep 2015
NMNH 118211-32 Basaltic andesite pumiceous tephra -- 16 Sep 2015
NMNH 118211-33 Pumiceous tephra -- 16 Sep 2015
NMNH 118211-34 Basalt scoriaceous tephra -- 16 Sep 2015
NMNH 118211-35 Pumiceous tephra -- 16 Sep 2015
NMNH 118211-36 Scoriaceous tephra -- 17 Sep 2015
NMNH 118211-37 Scoriaceous tephra -- 17 Sep 2015
NMNH 118211-38 Pumiceous lapilli tephra -- 17 Sep 2015
NMNH 118211-39 Basaltic andesite pumiceous tephra -- 17 Sep 2015
NMNH 118211-4 Basalt scoriaceous tephra -- 15 Sep 2015
NMNH 118211-40 Basaltic andesite pumiceous tephra -- 17 Sep 2015
NMNH 118211-41 Basaltic andesite pumiceous tephra -- 17 Sep 2015
NMNH 118211-42 Basalt scoriaceous tephra -- 17 Sep 2015
NMNH 118211-43 Lapilli tephra -- 17 Sep 2015
NMNH 118211-44 Lapilli tephra -- 17 Sep 2015
NMNH 118211-45 Lapilli tephra -- 17 Sep 2015
NMNH 118211-46 Scoriaceous tephra -- 18 Sep 2015
NMNH 118211-47 Basalt scoriaceous tephra -- 18 Sep 2015
NMNH 118211-48 Lapilli tephra -- 18 Sep 2015
NMNH 118211-49 Lapilli tephra -- 18 Sep 2015
NMNH 118211-5 Basalt lapilli tephra -- 15 Sep 2015
NMNH 118211-50 Coarse ash -- 18 Sep 2015
NMNH 118211-51 Scoriaceous tephra -- 19 Sep 2015
NMNH 118211-52 Lapilli tephra -- 19 Sep 2015
NMNH 118211-53 Coarse ash -- 19 Sep 2015
NMNH 118211-54 Scoriaceous tephra -- 19 Sep 2015
NMNH 118211-6 Scoria -- 15 Sep 2015
NMNH 118211-7 Basaltic andesite pumiceous tephra -- 15 Sep 2015
NMNH 118211-8 Basaltic Andesite -- 15 Sep 2015
NMNH 118211-9 Basalt Scoria -- 15 Sep 2015
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