Alaska Volcano Observatory | Okmok Alaska Volcano Observatory 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 Okmok Description Current Activity Past Activity Images Maps Bibliography Prepare Ash Forecasting Facts Official Name: Mount Okmok Seismically Monitored: Yes Color Code: GREEN Alert Level: NORMAL Elevation: 1073m (3520ft) Latitude: 53.419 Longitude: -168.132 Smithsonian VNum: 311290 Pronunciation: Your browser does not support the audio element. Nearby Towns: Nikolski 45 mi (73 km) SW Unalaska 72 mi (117 km) NE Akutan 108 mi (174 km) NE False Pass 215 mi (347 km) NE Saint George 227 mi (365 km) NW Distance from Anchorage: 863 mi (1389 km) Subfeatures: Cone A Tulik Idak, Mt Jag Peak Cone B Cone C Cone D Cone E Cone F Cone G Cone H Cone I Cone J Kettle Cape Waist Tuya 1 Aslik Kidney Bean Idak cindercones Cinder Point Waist Tuya 2 Waist Tuya 3 Waist cone/flow 1 Waist cone/flow 2 Waist cone 3 Ahmanilix Description From Miller and others (1998) [1] : "Okmok Volcano occupies most of northeastern Umnak Island. The volcano, built on a base of Tertiary volcanic rocks, consists of three rock series: older flows and pyroclastic beds of a pre-caldera shield complex; pyroclastic deposits of two major caldera-forming eruptions; and a post-caldera field of small cones and lava flows that includes historically active vents within the caldera [2] "Construction of the pre-caldera volcano began in late Tertiary or early Quaternary time. Two whole-rock K-Ar analyses of a sample of basaltic lava are 1.7 and 2.1 +/- .2 m.y. [3] . Basaltic flows and pyroclastics compose most of the older rocks (unit Qbm); flows are more voluminous than pyroclastic deposits (see Byers, 1959 [2] , plate 41). Vent agglomerate is exposed in the walls of the younger caldera and tuffs and tuff-breccias occur further down the flanks. Flows and pyroclastic beds dip radially from the caldera at less than 5 degrees in most sectors, except for local steepening and reversal of dips at former vents. Such radial dips suggest that the older complex was a central volcano with parasitic vents. Domes and plugs of andesite and rhyolitic composition and basaltic lava flows (Byers, 1959 [2] , p. 312) mark minor vents that were active before caldera formation; these rocks are only slightly modified by erosion and are presumably early post-glacial in age. "Catastrophic pyroclastic eruptions resulted in the formation of 2 overlapping calderas (Byers, 1959 [2] , p. 274). The deposits, referred to as the Okmok Volcanics (Byers, 1959 [2] , p. 314), are mainly thick, non-sorted agglomerate at the caldera rim overlain by ash-flow tuffs, and airfall ash and pumice that cover the flanks of the volcano to the shoreline (unit Qov). Two arcuate ridges located about 1.5 km north and east of the main topographic basin are the remnants of the older caldera, which formed about 8200 years ago [4] . The topographic basin of the younger caldera is about 9.5 km in diameter; the maximum elevation of the rim is about 1070 m and the mean elevation of the floor, exclusive of areas underlain by post-caldera volcanic rocks, is about 370 m. The occurrence of 2 major ash-flow sheets, separated by a basalt flow and erosional unconformity, supports the two caldera-forming eruptions [5] . Miller and Smith (1987) [6] have reported a maximum C14 age of 2400 +/- 200 yr for the second and younger caldera-forming eruption. "Numerous small flows, plugs, and cinder cones on the flanks of Okmok Volcano are interbedded with or overlie the upper pars of the Okmok Volcanics (unit Qyv). Within the caldera, the oldest post-caldera deposits are brecciated pillow lavas and pyroclastic rocks that were deposited in a caldera lake. The lake attained a maximum depth of about 150 m and the upper surface reached an elevation of about 475 m, at which point it overtopped the low point of the caldera rim. A small shallow lake located near the outlet of the caldera is all that remains today. Three dissected tuff cones may have been produced by eruptions beneath the former caldera lake. Other cinder cones occur atop pillow lavas; such cones apparently breached the surface of the former lake. Cinder cones and associated lava flows that are younger than the caldera lake are identified by structures and textures characteristic of subaerial eruption. The documented eruption of 1945 occurred at a cinder cone near the southwest caldera wall [2] [7] ; this cone may have been the site of all historical activity of Okmok volcano. Hot springs and fumaroles occur both within Okmok caldera and at Hot Springs cove, 20 km to the southwest." Name Origin Delanora Grey (2003) offers some insights into the name history of Mount Okmok: 'In Bergsland's (1994) Aleut Dictionary, the name Umnak ("Unmax") is said to perhaps be a derivative of "una", meaning "out there on the sea." Alternatively, Orth (1967), who got much of his information from Geoghegan (1944), reports that the name comes from "umnaqs" meaning "fish line." The origin of the name Okmok is unknown; it was called Unmagim Anatuu by the natives, meaning "the stout one of Umnak" (Bergsland, 1994). Tulik Volcano was called "Ismax" according to Bergsland, but Orth says the Aleut name "Tuliq" was reported by the U.S.Army Corps of Engineers in 1942 and means "crack or fissure." It is interesting to note that the name Tanak ("Tanaxsiqax", as in Cape Tanak) translates as "made into land" (Bergsland, 1994), as the shoreline along the cape was extended outward by approximately 2 km during the first outburst flood from the caldera between 1560 and 1010 BP (Wolfe and Beget, 2002). The author prefers this interpretation to Orth's (1967) report that the cape was named from the Unangam Tunuu "tanaq" meaning "lace."' 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 Umnak and Bogoslof Islands, Aleutian Islands, Alaska , 1959 Byers, F. M. Jr., 1959, Geology of Umnak and Bogoslof Islands, Aleutian Islands, Alaska: in Investigations of Alaskan volcanoes, U.S. Geological Survey Bulletin 1028-L, p. 267-369, 5 sheets, scale 1 at 1:63,360, 1 at 1:96,000, and 1 at 1:300,000. full-text PDF 3.5 MB plate 39 PDF 2.2 MB plate 40 PDF 3.9 MB plate 41 PDF 5.6 MB plate 48 PDF 85 KB table 3 PDF 149 KB [3] Palaeosecular variation of the geomagnetic field in the Aleutian Islands, Alaska , 1972 Bingham, D. K., and Stone, D. B., 1972, Palaeosecular variation of the geomagnetic field in the Aleutian Islands, Alaska: The Geophysical Journal of the Royal Astronomical Society, v. 28, n. 4, p. 317-335. [4] Late-Quaternary geomorphic processes: effects on the ancient Aleuts of Umnak Island in the Aleutians , 1975 Black, R. F., 1975, Late-Quaternary geomorphic processes: effects on the ancient Aleuts of Umnak Island in the Aleutians: Arctic, v. 28, n. 3, p. 159-169. [5] Two caldera-forming eruptions on Umnak Island, eastern Aleutian Islands , 1975 Miller, T.P., and Smith, R.L., 1975, Two caldera-forming eruptions on Umnak Island, eastern Aleutian Islands: The United States Geological Survey in Alaska: Accomplishments during 1975: U.S. Geological Survey Circular 733, p 45. [6] Late Quaternary caldera-forming eruptions in the eastern Aleutian arc, Alaska , 1987 Miller, T. P., and Smith, R. L., 1987, Late Quaternary caldera-forming eruptions in the eastern Aleutian arc, Alaska: Geology, v. 15, n. 5, p. 434-438. full-text PDF 2.5 MB [7] Exploring Aleutian volcanoes , 1948 Robinson, G. D., 1948, Exploring Aleutian volcanoes: National Geographic Magazine, v. 94, n. 4, p. 509-528. Current Activity No new updates for Okmok volcano since January 29, 2026, 5:55 pm. Recent Updates Resuspended ash observed from multiple sources on Unmak Island. Okmok Volcano aviation color code and alert level remain at GREEN/NORMAL Jan 29th, 2026 05:55:41 PM Local monitoring network restored. Color code / alert level now GREEN/NORMAL. Sep 10th, 2025 12:23:50 PM Major network outage due to power system degradation. Jan 28th, 2025 05:01:57 PM Change in pattern of ground deformation; Aviation Color Code and Volcanic Alert Level remain at GREEN/Normal Dec 10th, 2021 02:02:42 PM Recent ground deformation data showed evidence for possible shallow magma intrusion; no other signs of unrest observed. Dec 8th, 2021 04:19:20 PM Webcams Okmok [OKCF, 2247 ft] Okmok [OKIF, 717 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) 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 Okmok 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: 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: 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 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.