Alaska Volcano Observatory | Great Sitkin Alaska Volcano Observatory Home Volcanoes Webcams Webcams Ashcam GUI News Explore Data Explore Data References Webicorder Hazard Alert System Eruptions Geochem Locations Glossary Images Get Involved About AVO About AVO Staff Study Areas Alert Levels FAQ Great Sitkin Description Current Activity Past Activity Images Maps Bibliography Prepare Ash Forecasting Facts Official Name: Great Sitkin Volcano Seismically Monitored: Yes Color Code: ORANGE Alert Level: WATCH Elevation: 1740m (5708ft) Latitude: 52.0765 Longitude: -176.1109 Smithsonian VNum: 311120 Pronunciation: Your browser does not support the audio element. Nearby Towns: Adak 26 mi (42 km) SW Atka 81 mi (131 km) NE Nikolski 310 mi (499 km) NE Saint George 409 mi (659 km) NE Shemya Station 414 mi (667 km) NW Distance from Anchorage: 1167 mi (1878 km) Description From Miller and others (1998) [1] : "Great Sitkin Volcano occupies most of the northern half of Great Sitkin Island, a member of the Andreanof Islands group in the central Aleutian Islands. The volcano is roughly oval-shaped, 8 by 11 km at the base, with the long axis trending east-west. It is a composite structure consisting of the remains of an older, decapitated volcano and a younger parasitic cone that collapsed forming a small caldera (0.8 by 1.2 km) on the west flank [2] . The highest point on the island is apparently a remnant of the former central volcano's eastern rim. Most of the constructional surface of the cone has been deeply eroded. A steep-sided, recently emplaced dome (unit Qgd) occupies the center of the caldera at an elevation of 1220 m. The dome is 183 m high, 0.4 km wide, and 0.6 km long with a blocky, flat top. Five small plugs (unit Qa) are intruded into the northwest slope of the cone; three of the plugs are aligned in a northwest direction from the crater, and the remaining two are aligned north-northwest. "Rocks that comprise the main cone are named the Great Sitkin volcanics (unit Tgc), and consist of andesite and basalt lava flows interbedded with tuff beds [2] . Lava flows predominated on the upper part of the cone, which has undergone extensive glacial erosion; construction of the cone may have begun in late Tertiary or early Quaternary time and was apparently completed before the end of Pleistocene glaciation. Partial destruction of the cone's former peak was followed by a westward shift in eruptive activity. A parasitic cone was built and subsequently destroyed during caldera-forming eruptions of unknown age. Pumice, scoria, and rock fragments from this eruption blanket the island to depths of a few centimeters to more than 6 m. Overlying the pumice deposit on the northwest flank of the main cone is an ash deposit that was apparently erupted from a subsidiary vent located immediately northwest of the crater [2] . A glacially truncated, columnar jointed basalt flow occurs low on the south flank of the main cone near the head of Sitkin Creek (unit Tgs). This flow is the product of a flank eruption, the source of which is covered by pumice (Simons and Mathewson, 1955 [2] , p. 31). "Great Sitkin volcano is built upon the eroded remnants of a late Tertiary shield volcano, which forms more of the southern half of the island. The undeformed succession, termed the Sand Bay volcanics by Simons and Mathewson (1955) [2] , consists of pyroclastic rocks, mainly volcanic breccias, which are overlain by a sequence of andesite and basalt lava flows. The succession crops out in a gently dipping radial pattern suggesting a source near the present cone. "The Sand Bay volcanics unconformably overlie the Finger Bay volcanics, an older, highly altered and deformed sequence of lava flows, breccia, and tuff that form the rugged headlands along the southern and southeastern coasts. By correlation with nearby Adak Island, the Finger Bay volcanics are probably no younger than late Eocene in age, and may be as old as Cretaceous [3] ." Name Origin Great Sitkin Volcano is named for Great Sitkin Island. Bergsland (1994) says the Unanagan name for Great Sitkin means "defecator". Great Sitkin Island's Unangam Tunuu name was published by the Russians as "O[strov] Sitkhin." or "Sitkhin Island" (Sarychev, 1826). Dall (1880) called the island "Great Net Island" (Orth, 1971). References Cited [1] Catalog of the historically active volcanoes of Alaska, 1998 Miller, T. P., McGimsey, R. G., Richter, D. H., Riehle, J. R., Nye, C. J., Yount, M. E., and Dumoulin, J. A., 1998, Catalog of the historically active volcanoes of Alaska: U.S. Geological Survey Open-File Report 98-0582, 104 p. title page PDF 52 intro and TOC PDF 268 KB eastern part - Wrangell to Ukinrek Maars PDF 972 KB central part - Chiginagak to Cleveland PDF 2,463 KB western part - Carlisle to Kiska PDF 956 KB references PDF 43 KB [2] Geology of Great Sitkin Island, Alaska, 1955 Simons, F. S., and Mathewson, D. E., 1955, Geology of Great Sitkin Island, Alaska: in Investigations of Alaskan volcanoes, U.S. Geological Survey Bulletin 1028-B, p. 21-43, 1 sheet, scale 1:50,000. full-text PDF 659 KB plate 5 PDF 3 MB [3] Eocene age of the Adak 'Paleozoic(?)' rocks, Aleutian Islands, Alaska, 1970 Scholl, D. W., Greene, R. G., and Marlow, M. S., 1970, Eocene age of the Adak 'Paleozoic(?)' rocks, Aleutian Islands, Alaska: Geological Soceity of America Bulletin, v. 81, p. 3583-3592. Current Activity August 12, 2026, 1:25 pm Slow eruption of lava within the summit crater continues. Minor earthquakes were detected over the past day, likely associated with rockfall on the growing dome. No activity was observed in cloudy satellite and webcam images over the past day. The current eruption began in July 2021. Since then, lava flows have filled most of the summit crater and advanced into valleys below. There have been no explosions at Great Sitkin Volcano since an event in May 2021. The volcano is monitored using local seismic and infrasound sensors, satellite data, webcams, and regional infrasound and lightning networks. Recent Updates Slow eruption of lava within the summit crater continues. Aug 12th, 2026 01:25:34 PM Slow eruption of lava within the summit crater continues. Aug 11th, 2026 01:01:29 PM Slow eruption of lava within the summit crater continues. Aug 10th, 2026 01:15:54 PM Slow eruption of lava within the summit crater continues. Aug 9th, 2026 09:09:04 AM Slow eruption of lava within the summit crater continues. Aug 8th, 2026 09:53:21 AM Webcams Great Sitkin [GSCK, 1181 ft] Great Sitkin [GSIG, 1342 ft] Great Sitkin [WHIT, 620 ft] Webicorder Color Code Timeline An explanation of color codes and alert levels can be found here. Loading Past Activity... Loading Images... Loading Maps... Loading Bibliography... Before an eruption Sign up for volcanic activty alerts from the Volcano Notification System (US Geological Survey) Preliminary volcano-hazard assessment for Great Sitkin Volcano, Alaska Ashfall & Preparedness Information Ashfall impacts & preparedness (US Geological Survey) Volcanic health hazards & impacts (International Volcanic Health Hazards Network) Ash Alert! Pamphlet (AK Division of Homeland Security & Emergency Management) Volcanic Ashfall (AK Department of Environmental Conservation, Division of Air Quality) During and After an Eruption National Weather Service Ashfall Warnings are posted here when in effect Alaska Division of Homeland Security and Emergency Management Ted Stevens Airport Flight Status (Anchorage) Fairbanks Airport Flight Status Other Useful Links Citizen Science: Ashfall collection instructions Citizen Science: IS ASH FALLING? Report your observations (yes or no!) Ash Forecasting Mathematical models developed by the USGS forecast various aspects of how a volcanic ash plume will interact with wind—where, how high, and how fast ash particles will be transported in the atmosphere, as well as where ash will fall out and accumulate on the ground. AVO runs these models when a volcano is restless by assuming a reasonable hypothetical eruption, to provide a pre-eruptive forecast of areas likely to be affected. During an ongoing eruption, AVO will update the forecast with actual observations (eruption start time and duration, plume height) as they become available. View the current airborne ash cloud models for Great Sitkin Ashfall thickness forecast The Ash3d model was developed by the USGS to forecast how a volcanic ash plume will interact with wind and where ash will fall out and accumulate on the ground. AVO runs these models twice daily when a volcano is restless by assuming a reasonable hypothetical eruption altitude and duration. The map shows the model results of ashfall thickness for areas that are likely to be affected, if one were to occur. During an ongoing eruption, AVO will update the forecast with actual observations (eruption start time and duration, plume height) as they become available, and these plots will be automatically updated. The National Weather Service Anchorage Forecast Office will issue the official ashfall warning product and post them at weather.gov/afc THESE PRODUCTS MAY NOT BE CURRENT. During an actual eruption, see National Weather Service forecasts of ashfall:https://weather.gov/afc. Ashfall Forecast Click on the X on the graphic (upper right) to expand the map to show the map legend. Ashfall Start Time This map shows the modeled estimate of the time it would take for ashfall to begin following an eruption. It corresponds to the ashfall thickness forecast map shown above. This map uses the start time of either the twice-daily hypothetical model runs (time shown in the legend) or the actual eruption start time (if one were to occur). In the case of an actual eruption, the National Weather Service Anchorage Forecast Office will issue the official ashfall warning product that includes the ashfall start time and post them at weather.gov/afc THESE PRODUCTS MAY NOT BE CURRENT. During an actual eruption, see National Weather Service forecasts of ashfall:https://weather.gov/afc. Ashfall Start Times Forecast Click on the X on the graphic (upper right) to expand the map to show the map legend. USGS Volcano Notification Service Contact AVO Privacy Accessibility Information Quality FOIA This website is supported by the U.S. Geological Survey under Cooperative Agreement Grant G22AC00137 and G23AC00070. Mention of trade names or commercial products does not constitute their endorsement by the U.S. Geological Survey. ×