Tanaga

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  • Country
  • Subregion Name
  • Primary Volcano Type
  • Last Known Eruption
  • 51.885°N
  • 178.146°W

  • 1806 m
    5924 ft

  • 311080
  • Latitude
  • Longitude

  • Summit
    Elevation

  • Volcano
    Number

23 November-29 November 2005

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)



 Available Weekly Reports


2005: October | November


23 November-29 November 2005

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

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

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

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

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)


Summary of 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

The following references are the sources used for data regarding this volcano. References are linked directly to our volcano data file. 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. Additional discussion of data sources can be found under Volcano Data Criteria.

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

Coats R R, 1956c. Reconnaissance geology of some western Aleutian islands, Alaska.. U S Geol Surv Bull, 1028-E: 83-100.

Coombs M L, McGimsey R G, Browne B L, 2007a. Preliminary volcano-hazard assessment for the Tanaga volcanic cluster, Tanaga Island, Alaska. U S Geol Surv, Sci Invest Rpt, 2007-5094: 1-35.

Coombs M L, White S M, Scholl D W, 2007b. Massive edifice failure at Aleutian arc volcanoes. Earth Planet Sci Lett, 256: 403-418.

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..

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.

Myers J D, 1994. The Geology, Geochemistry and Petrology of the recent Magmatic Phase of the Central and Western Aleutian Arc. Unpublished manuscript, unpaginated.

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.

Wood C A, Kienle J (eds), 1990. Volcanoes of North America. Cambridge, England: Cambridge Univ Press, 354 p.

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. Arcuate ridges to the east and south represent the rim of an arcuate caldera formed by collapse of an ancestral Tanaga volcano during the Pleistocene. Most Holocene eruptions originated from Tanaga volcano itself, which consists of two large cones, the western of which is the highest, constructed within a caldera whose 400-m-high rim is prominent to the SE. At the westernmost end of the Tanaga complex is conical Sajaka, a 1304-m-high double cone that may be the youngest of the three volcanoes. Sajaka One volcano collapsed during the late Holocene, producing a debris avalanche that swept into the sea, after which Sajaka Two cone was constructed within the collapse scarp.