Tanaga

Photo of this volcano
  • United States
  • Alaska
  • Stratovolcano(es)
  • 1914 CE
  • Country
  • Volcanic Region
  • Primary Volcano Type
  • Last Known Eruption
  • 51.885°N
  • 178.146°W

  • 1806 m
    5924 ft

  • 311080
  • Latitude
  • Longitude

  • Summit
    Elevation

  • Volcano
    Number

Most Recent Weekly Report: 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)


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


2005: October | November


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.

Eruptive History


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


Start Date Stop Date Eruption Certainty VEI Evidence Activity Area or Unit
1914 Unknown Confirmed 0 Historical Observations
1829 Unknown Confirmed   Historical Observations
[ 1791 Jun 7 ] [ Unknown ] Uncertain    
[ 1763 ] [ 1770 ] Uncertain    
1550 (?) Unknown Confirmed   Radiocarbon (uncorrected) Tanaga, Sajaka Two
1050 (?) Unknown Confirmed   Radiocarbon (uncorrected) Tanaga
0550 BCE ± 2500 years Unknown Confirmed   Tephrochronology Sajaka One
1050 BCE (?) Unknown Confirmed 0 Ar/Ar Sajaka One

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.

Photo Gallery


Broad Takawangha volcano (left), seen here from the east, is a 1449-m-high, youthful stratovolcano on northern Tanaga island with an ice-filled caldera. Numerous small post-caldera tephra cones are located within the caldera, as well as on its rim and flanks. The youngest cones are some of those in the caldera. No historical eruptions are known from Takawangha, in contrast to sharp-peaked Tanaga volcano (right), which occupies the NW tip of Tanaga Island.

Photo by Tom Edgarton, 1986 (U.S. Fish and Wildlife Service).
See title for photo information.
Tanaga volcano, the second largest volcanic center of the central Aleutians, is seen here from the SW with Cape Sajaka at the extreme left. The conical peak rising above the clouds (right center) is Tanaga; is the clouds to the left is Sajaka volcano. Most Holocene eruptions originated from the central peak, Tanaga volcano itself, which consists of two large cones constructed within a caldera whose 400-m-high rim is prominent to the SE.

Photo by Steve Ebbert (U.S. Fish and Wildlife Service).
See title for photo information.
Three peaks of the Tanaga volcanic complex, Sajaka, Tanaga, and East Tanaga (from left to right), are seen from the summit of Takawangha volcano. Tanaga volcano, the second largest volcanic center of the central Aleutians, is the central and highest of three youthful stratovolcanoes oriented along a roughly E-W line at the NW tip of Tanaga Island. The arcuate ridge at the lower left is part of the rim of an arcuate caldera formed by collapse of an ancestral Tanaga volcano during the Pleistocene.

Photo by Michelle Coombs, 2003 (Alaska Volcano Observatory, U.S. Geological Survey).
See title for photo information.

Smithsonian Sample Collections Database


There are no samples for Tanaga in the Smithsonian's NMNH Department of Mineral Sciences Rock and Ore collection.

Affiliated Sites