AVO reported that a small phreatic explosion at Great Sitkin was recorded by the seismic network at 1105 on 11 August. The event was preceded by small local earthquakes. Cloudy satellite images prevented views of the volcano during 12-14 August. The Aviation Color Code remained at Yellow and the Volcano Alert Level remained at Advisory.
Source: US Geological Survey Alaska Volcano Observatory (AVO)
Small phreatic explosions in June and August 2018; ash deposit on snow near summit
Episodic recent and historic volcanic activity has been reported at Great Sitkin, located about 40 km NE of the community of Adak in the Aleutian Islands. Prior to the recent 2018 activity, the last confirmed eruption in 1974 produced at least one ash cloud that likely exceeded an altitude of 3 km (figures 1 and 2). This eruption extruded a lava dome that partially destroyed an existing dome from a 1945 eruption. Most recently, a small steam explosion was reported on 10 June 2018. In response, the Alaska Volcano Observatory (AVO) raised the Aviation Color Code (ACC) to Yellow (Advisory) from the previous Green (Normal).
AVO had previously reported that a seismic swarm had been detected beginning in late July 2016 and continuing through December 2017. Steam from the crater was also observed during this time period, in late November 2017 (figure 2). The seismicity was characterized by earthquakes typically less than magnitude 1.0 and at depths from near the summit to 30 km below sea level. Most earthquakes were in one of two clusters, beneath the volcano's summit or just offshore the NW coast of the island. Possible explosion signals were observed in seismic data on 10 January and 21 July 2017, but no confirmed emissions were observed locally or detected in infrasound data or satellite imagery.
The most recent eruption at Great Sitkin produced a small steam explosion which was detected in seismic data at 1139 local time on 10 June 2018 (figure 3). The explosion was followed by seismic activity which began diminishing after 24 hours, and by 15-16 June had returned to background levels.
![]() |
Figure 3. View of Great Sitkin steaming on 10 July 2018. Photographed from Adak Island, Alaska, approximately 40 km SW. Photo by Alain Beauparlant; image courtesy of AVO/USGS (color corrected). |
Due to heavy cloud cover on 10 June 2018, satellite views were obscured. Subsequent satellite data collected on 11 June showed an ash deposit on the surface of the snow extending to about 2 km SW from a vent in the summit crater (figure 4). Minor changes in the vicinity of the summit crater were observed from satellite data, including possible fumaroles north of the main crater. On 17 June an aerial photograph showed minor steaming at the vent (figure 5).
Another small phreatic explosion was observed in seismic data at 1105 local time on 11 August. Small local earthquakes preceded the event but were not recorded following the explosion. The event is similar to three other phreatic explosions that have occurred over the past 2 years.
Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: https://avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA (URL: http://dggs.alaska.gov/).
2018: January
| June
| August
2017: November
2002: May
AVO reported that a small phreatic explosion at Great Sitkin was recorded by the seismic network at 1105 on 11 August. The event was preceded by small local earthquakes. Cloudy satellite images prevented views of the volcano during 12-14 August. The Aviation Color Code remained at Yellow and the Volcano Alert Level remained at Advisory.
Source: US Geological Survey Alaska Volcano Observatory (AVO)
AVO reported that after the brief explosion at Great Sitkin on 10 June seismicity gradually declined to background levels. On 27 June AVO lowered the Volcano Alert Level to Normal and the Aviation Color Code to Green.
Source: US Geological Survey Alaska Volcano Observatory (AVO)
AVO reported continuing low-level unrest at Great Sitkin during 20-26 June; seismic activity remained at or near background levels. A recently analyzed satellite image acquired on 11 June, one day after short-duration explosive event was recorded, showed a minor ash deposit on the snow extending 2 km from a vent in the summit crater. The Aviation Color Code remained at Yellow and the Volcano Alert Level remained at Advisory.
Source: US Geological Survey Alaska Volcano Observatory (AVO)
AVO reported that satellite images captured after the short-lived steam explosion at Great Sitkin on 10 June indicated minor changes in the summit crater, characterized by possible new fumaroles in the N part of the main crater and slightly more vigorous steaming at pre-existing fumaroles. Seismicity declined to background levels during 15-16 June.
Source: US Geological Survey Alaska Volcano Observatory (AVO)
Seismicity at Great Sitkin was elevated during the previous five days, though at 1139 on 10 June a seismic signal indicating a possible short-lived steam explosion prompted AVO to raise the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory. No infrasound signal associated with the event was detected, and no volcanic clouds rose about the meteorological cloud deck at 2.4 km (8,000 ft) a.s.l.
Source: US Geological Survey Alaska Volcano Observatory (AVO)
On 18 January AVO reported that seismicity at Great Sitkin had declined over the past two months to near background levels. In addition, no significant activity was observed in satellite data during this time period and no steam plumes were noted. AVO lowered the Aviation Color Code and Volcano Alert Level to Green/Normal.
Source: US Geological Survey Alaska Volcano Observatory (AVO)
AVO reported that during 28 November-5 December low-level unrest continued at Great Sitkin. Nothing noteworthy was identified in seismic data nor in partly cloudy to cloudy satellite images. The Aviation Color Code remained at Yellow and the Volcano Alert Level remained at Advisory.
Source: US Geological Survey Alaska Volcano Observatory (AVO)
Recent observations of a robust steam plume and a period of gradually increasing seismicity over several months at Great Sitkin prompted AVO to raise the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory on 22 November. On 19 November local observers photographed a light-colored vapor plume rising about 300 m above the vent and drifting 15-20 km S. A satellite image acquired on 21 November showed steam continuously jetting from a small fumarole on the W side of the 1974 lava flow within the summit crater, and at least one area where snow and ice had been melted.
Seismicity had fluctuated but increased overall since July 2016, most notably in June 2017. The seismic activity was characterized by earthquakes less than M 1, and occurred either just below the summit or just offshore the NW cost of the island, 30 km below sea level. Possible explosion signals were recorded in seismic data on 10 January and 21 July 2017, but there were no confirmed emissions.
Source: US Geological Survey Alaska Volcano Observatory (AVO)
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)
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.
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.
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.
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/).
Small phreatic explosions in June and August 2018; ash deposit on snow near summit
Episodic recent and historic volcanic activity has been reported at Great Sitkin, located about 40 km NE of the community of Adak in the Aleutian Islands. Prior to the recent 2018 activity, the last confirmed eruption in 1974 produced at least one ash cloud that likely exceeded an altitude of 3 km (figures 1 and 2). This eruption extruded a lava dome that partially destroyed an existing dome from a 1945 eruption. Most recently, a small steam explosion was reported on 10 June 2018. In response, the Alaska Volcano Observatory (AVO) raised the Aviation Color Code (ACC) to Yellow (Advisory) from the previous Green (Normal).
AVO had previously reported that a seismic swarm had been detected beginning in late July 2016 and continuing through December 2017. Steam from the crater was also observed during this time period, in late November 2017 (figure 2). The seismicity was characterized by earthquakes typically less than magnitude 1.0 and at depths from near the summit to 30 km below sea level. Most earthquakes were in one of two clusters, beneath the volcano's summit or just offshore the NW coast of the island. Possible explosion signals were observed in seismic data on 10 January and 21 July 2017, but no confirmed emissions were observed locally or detected in infrasound data or satellite imagery.
The most recent eruption at Great Sitkin produced a small steam explosion which was detected in seismic data at 1139 local time on 10 June 2018 (figure 3). The explosion was followed by seismic activity which began diminishing after 24 hours, and by 15-16 June had returned to background levels.
![]() |
Figure 3. View of Great Sitkin steaming on 10 July 2018. Photographed from Adak Island, Alaska, approximately 40 km SW. Photo by Alain Beauparlant; image courtesy of AVO/USGS (color corrected). |
Due to heavy cloud cover on 10 June 2018, satellite views were obscured. Subsequent satellite data collected on 11 June showed an ash deposit on the surface of the snow extending to about 2 km SW from a vent in the summit crater (figure 4). Minor changes in the vicinity of the summit crater were observed from satellite data, including possible fumaroles north of the main crater. On 17 June an aerial photograph showed minor steaming at the vent (figure 5).
Another small phreatic explosion was observed in seismic data at 1105 local time on 11 August. Small local earthquakes preceded the event but were not recorded following the explosion. The event is similar to three other phreatic explosions that have occurred over the past 2 years.
Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: https://avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA (URL: http://dggs.alaska.gov/).
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.
Synonyms |
Great Sitchin | Sitchin | Chetkin | Belaya | Bolshoi Sitkin |
|
|
There is data available for 15 Holocene eruptive periods.
Start Date | Stop Date | Eruption Certainty | VEI | Evidence | Activity Area or Unit |
---|---|---|---|---|---|
2018 Jun 10 | 2018 Aug 11 | Confirmed | 1 | Historical Observations | |
[ 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 |
There is no Deformation History data available for Great Sitkin.
There is no Emissions History data available for Great Sitkin.
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. The maps database originated over 30 years ago, but was only recently updated and connected to our main database. We welcome users to tell us if they see incorrect information or other problems with the maps; please use the Contact GVP link at the bottom of the page to send us email.
There are no samples for Great Sitkin in the Smithsonian's NMNH Department of Mineral Sciences Rock and Ore collection.
DECADE Data | The DECADE portal, still in the developmental stage, serves as an example of the proposed interoperability between The Smithsonian Institution's Global Volcanism Program, the MAGA Database, and the EarthChem Geochemical Portal. The Deep Earth Carbon Degassing (DECADE) initiative seeks to use new and established technologies to determine accurate global fluxes of volcanic CO2 to the atmosphere, but installing CO2 monitoring networks on 20 of the world's 150 most actively degassing volcanoes. The group uses related laboratory-based studies (direct gas sampling and analysis, melt inclusions) to provide new data for direct degassing of deep earth carbon to the atmosphere. |
WOVOdat
Single Volcano View Temporal Evolution of Unrest Side by Side Volcanoes |
WOVOdat is a database of volcanic unrest; instrumentally and visually recorded changes in seismicity, ground deformation, gas emission, and other parameters from their normal baselines. It is sponsored by the World Organization of Volcano Observatories (WOVO) and presently hosted at the Earth Observatory of Singapore. |
Large Eruptions of Great Sitkin | Information about large Quaternary eruptions (VEI >= 4) is cataloged in the Large Magnitude Explosive Volcanic Eruptions (LaMEVE) database of the Volcano Global Risk Identification and Analysis Project (VOGRIPA). |
MIROVA | Middle InfraRed Observation of Volcanic Activity (MIROVA) is a near real time volcanic hot-spot detection system based on the analysis of MODIS (Moderate Resolution Imaging Spectroradiometer) data. In particular, MIROVA uses the Middle InfraRed Radiation (MIR), measured over target volcanoes, in order to detect, locate and measure the heat radiation sourced from volcanic activity. |
MODVOLC Thermal Alerts | Using infrared satellite Moderate Resolution Imaging Spectroradiometer (MODIS) data, scientists at the Hawai'i Institute of Geophysics and Planetology, University of Hawai'i, developed an automated system called MODVOLC to map thermal hot-spots in near real time. For each MODIS image, the algorithm automatically scans each 1 km pixel within it to check for high-temperature hot-spots. When one is found the date, time, location, and intensity are recorded. MODIS looks at every square km of the Earth every 48 hours, once during the day and once during the night, and the presence of two MODIS sensors in space allows at least four hot-spot observations every two days. Each day updated global maps are compiled to display the locations of all hot spots detected in the previous 24 hours. There is a drop-down list with volcano names which allow users to 'zoom-in' and examine the distribution of hot-spots at a variety of spatial scales. |
EarthChem | EarthChem develops and maintains databases, software, and services that support the preservation, discovery, access and analysis of geochemical data, and facilitate their integration with the broad array of other available earth science parameters. EarthChem is operated by a joint team of disciplinary scientists, data scientists, data managers and information technology developers who are part of the NSF-funded data facility Integrated Earth Data Applications (IEDA). IEDA is a collaborative effort of EarthChem and the Marine Geoscience Data System (MGDS). |