Great Sitkin

Photo of this volcano
  • United States
  • Alaska
  • Stratovolcano
  • 1974 CE
  • Country
  • Volcanic Region
  • Primary Volcano Type
  • Last Known Eruption
  • 52.076°N
  • 176.13°W

  • 1740 m
    5707 ft

  • 311120
  • Latitude
  • Longitude

  • Summit
    Elevation

  • Volcano
    Number

Most Recent Weekly Report: 29 May-4 June 2002 Citation IconCite this Report


On 27 and 28 May, AVO recorded anomalous seismicity at Great Sitkin. The seismicity consisted of two periods of seismic tremor on 27 May (lasting for 20 and 55 minutes) and two earthquake swarms on 28 May (beginning at 0406 and 1328). The earthquake swarms each began with a relatively large event (ML (local magnitude) 2.2 and ML 4.3) followed by tens to hundreds of smaller aftershocks, most located 5-6 km SE of the crater at depths of 0-5 km. Both the tremor and the earthquake swarms represent significant changes from what is considered to be normal, "background" seismicity at Great Sitkin. However, aftershocks declined significantly overnight, and no tremor episodes were detected after the 27th. There were neither signs of surface volcanic activity on satellite imagery nor ground-level reports of anomalous activity. Great Sitkin remained at Concern Color Code Green.

Source: US Geological Survey Alaska Volcano Observatory (AVO)


Most Recent Bulletin Report: June 2002 (BGVN 27:06) Citation IconCite this Report


Abnormal tremor and earthquake swarms in May 2002

On 27 and 28 May the Alaska Volcano Observatory (AVO) detected anomalous seismicity at Great Sitkin, a volcano located 1,895 km SW of Anchorage, Alaska. On 27 May two periods of seismic tremor lasted for 20 and 55 minutes and on 28 May earthquake swarms began at 0306 and 1228. The earthquake swarms each began with a relatively large event (ML 2.2 and ML 4.3) followed by tens to hundreds of smaller aftershocks, most located 5-6 km SE of the crater at depths of 0-5 km. Both the tremor and earthquake swarms represent significant changes from background seismicity at Great Sitkin. However, aftershocks declined significantly overnight, and seismicity returned to background levels with a lack of recorded tremor since 27 May. Satellite imagery showed no signs of surface volcanic activity, and no reports of anomalous activity were received by AVO.

Information Contacts: Tom Murray and John Eichelberger, Alaska Volcano Observatory (AVO) (URL: http://www.avo.alaska.edu/).

Weekly Reports - Index


2002: May


29 May-4 June 2002 Citation IconCite this Report


On 27 and 28 May, AVO recorded anomalous seismicity at Great Sitkin. The seismicity consisted of two periods of seismic tremor on 27 May (lasting for 20 and 55 minutes) and two earthquake swarms on 28 May (beginning at 0406 and 1328). The earthquake swarms each began with a relatively large event (ML (local magnitude) 2.2 and ML 4.3) followed by tens to hundreds of smaller aftershocks, most located 5-6 km SE of the crater at depths of 0-5 km. Both the tremor and the earthquake swarms represent significant changes from what is considered to be normal, "background" seismicity at Great Sitkin. However, aftershocks declined significantly overnight, and no tremor episodes were detected after the 27th. There were neither signs of surface volcanic activity on satellite imagery nor ground-level reports of anomalous activity. Great Sitkin remained at Concern Color Code Green.

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.

02/1974 (CSLP 27-74) Explosive activity and light-colored plume

09/1974 (CSLP 27-74) Lava dome still growing, overspilling crater rim

06/2002 (BGVN 27:06) Abnormal tremor and earthquake swarms in May 2002




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


February 1974 (CSLP 27-74)


Explosive activity and light-colored plume

Card 1804 (22 February 1974) Explosive activity and light-colored plume

The following was cabled from the Geophysical Institute on 22 February 1974. "Explosive activity was observed at 1855 local time from Adak, 48 km WSW of Great Sitkin volcano. An earthquake originating at the volcano of Richter magnitude 2.6 occurred at the time of onset. An estimated 10,000-foot light-colored plume was reported over the summit at dusk. Since that time bad weather has obscured the island."

Information Contacts: J. Kienle and D.B. Stone, Geophysical Institute, University of Alaska, Fairbanks AK; Dale Glover, NOAA, Adak AK.


September 1974 (CSLP 27-74)


Lava dome still growing, overspilling crater rim

Card 1938 (30 September 1974) Lava dome still growing, overspilling crater rim

D. Glover reported that, on a helicopter inspection trip to the volcano on 22 February, he ". . . found that a large lava dome had been emplaced in the crater, with mostly steam and gas being emitted." Foul weather prevented observations on all but three occasions between then and 29 March. About one week after the eruption, he noted, through a high-power telescope, ". . . that the dome had been extruded a considerable extent, with some ash being emitted. Since then activity has decreased to steam and gas emissions."

In mid-September, her reported that he had ". . . only been able to observe Great Sitkin volcano by high-power telescope and a few times from aircraft. The lava dome appears to continue to extrude with minor lava flows spilling over the lip of the crater. The size of the dome is hard to estimate but it is probably close to 700 m in diameter and 200-300 m high. We have recently installed seismic instrumentation on the volcano but we have not noticed any unusual activity." In summary, it appears that, following the initial release of the pressure head of volatiles on 19 February a dome has been extruded in the caldera of Great Sitkin. The new dome appears to be about the size of that extruded in 1945. Further, the dome is still active, overspilling the lip of the caldera as it grows. The extrusion has been quiet, with little of no associated explosiveness.

Information Contacts: Dale Glover, NOAA Adak Observatory, FPO Seattle WA; Dan Shackleford, Villa Park CA.


June 2002 (BGVN 27:06) Citation IconCite this Report


Abnormal tremor and earthquake swarms in May 2002

On 27 and 28 May the Alaska Volcano Observatory (AVO) detected anomalous seismicity at Great Sitkin, a volcano located 1,895 km SW of Anchorage, Alaska. On 27 May two periods of seismic tremor lasted for 20 and 55 minutes and on 28 May earthquake swarms began at 0306 and 1228. The earthquake swarms each began with a relatively large event (ML 2.2 and ML 4.3) followed by tens to hundreds of smaller aftershocks, most located 5-6 km SE of the crater at depths of 0-5 km. Both the tremor and earthquake swarms represent significant changes from background seismicity at Great Sitkin. However, aftershocks declined significantly overnight, and seismicity returned to background levels with a lack of recorded tremor since 27 May. Satellite imagery showed no signs of surface volcanic activity, and no reports of anomalous activity were received by AVO.

Information Contacts: Tom Murray and John Eichelberger, Alaska Volcano Observatory (AVO) (URL: http://www.avo.alaska.edu/).

Eruptive History


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


Start Date Stop Date Eruption Certainty VEI Evidence Activity Area or Unit
[ 1987 Mar 18 ] [ Unknown ] Uncertain    
1974 Feb 19 1974 Sep 16 ± 15 days Confirmed 2 Historical Observations
[ 1953 May 11 ] [ 1953 May 14 ] Discredited    
1950 Nov 5 1950 Nov 29 Confirmed   Historical Observations
1949 Dec 30 1950 Jan 7 Confirmed 1 Historical Observations
[ 1946 Aug 14 ] [ Unknown ] Uncertain    
1945 Mar Unknown Confirmed 2 Historical Observations
1933 Nov Unknown Confirmed 2 Historical Observations
[ 1904 ] [ Unknown ] Uncertain    
[ 1829 ] [ Unknown ] Uncertain    
[ 1828 ] [ Unknown ] Uncertain    
1792 May 26 ± 5 days Unknown Confirmed   Historical Observations
[ 1784 ] [ Unknown ] Uncertain    
[ 1760 ] [ Unknown ] Uncertain    

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


Great Sitkin volcano in the Andreanof Islands of the central Aleutians is seen here rising to the NE across Sitkin Sound from Finger Bay on Adak Island. The volcano was constructed within the caldera of an older shield volcano, part of which forms the high snow-covered peak at the right. The 1740-m-high post-caldera cone of Great Sitkin volcano itself contains a small, 0.8 x 1.2 km ice-filled summit caldera, whose rim forms the irregular summit on the left horizon. In 1945, a 400-600-m wide lava dome was emplaced through a glacier filling this caldera.

Photo by Fred Zeillemaker, 1982 (U.S. Fish and Wildlife Service, courtesy of Alaska Volcano Observatory).
See title for photo information.
This September 1946 photo of Great Sitkin volcano from the east rim of the summit crater shows a steam plume rising above a lava dome emplaced in the crater in March 1945. The prominent fissures cutting the summit icecap were produced as the dome forced its way through the summit glacier. The oval-shaped blocky dome is formed of glassy basaltic rocks.

Photo courtesy of U.S. Geological Survey (published in USGS Bulletin 1028-B).
See title for photo information.

Smithsonian Sample Collections Database


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

Affiliated Sites