Geologic map of Okmok Volcano

Larsen, J.F.Neal, C.A.Schaefer, J.R.Nye, C.J.2023Geologic map of Okmok VolcanocsvReport of InvestigationRI 2023-1Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveys63 p., 4 sheetshttps://doi.org/10.14509/31015Geologic map of Okmok Volcano, Report of Investigation 2023-1, provides 40Ar/39Ar and radiocarbon geochronology data from Okmok Volcano and its eruptive products. Okmok Volcano is one of 54 historically active volcanoes in the Alaska-Aleutian volcanic arc that stretches across southern mainland Alaska and the Aleutian Islands. Okmok Volcano dominates the northeastern portion of Umnak Island, which is 100 km southwest of Unalaska/Dutch Harbor and 1,400 km southwest of Anchorage. Okmok Volcano is one of the most frequently active volcanoes in the Aleutian volcanic arc. In 1998, the Alaska Volcano Observatory (AVO) began a multi-year effort to expand geophysical monitoring in the central Aleutians Islands, including at Okmok Volcano. These data support the development of a modern geologic map of Okmok Volcano and related investigation of its eruptive history and hazards. The analytical data tables associated with this report are provided in digital format as comma-separated value (CSV) files. They are available from the DGGS website: http://doi.org/10.14509/31015.This data describes the nature and character of samples from a past eruption to aid in the discussion of spatial and temporal patterns of Alaska volcanism. In addition, the work supports improvements to eruption scenario forecasts and hazard response.>Appendix A 40Ar/39Ar Ages of Okmok lavas: Field station locations and 40Ar/39Ar ages of Okmok lavas >Appendix B Radiocarbon ages: Field station locations and radiocarbon ages used to interpret Okmok Volcano geologic map units >Appendix C Stations and samples: Field station locations of samples discussed in this report19982023ground conditionCompleteNone planned-168.399980-167.75316053.56239053.280010ISO 19115 Topic CategorygeoscientificInformationAlaska Division of Geological & Geophysical Surveys40Ar/39ArAshfallCalderaDGGSFumarole ChemistryGeochemical DataGeochemistryGeochronologyGeologicGeologic HazardsGeologic MapGeologyGisGlacialHazardsHelicopter SurveyLava FlowMorainesOutcrop SamplesPumiceRadiocarbon AgesRadiocarbon DatingRhyoliteRock GlaciersScoriaSubductionVolcanicVolcanic ArcVolcanic AshVolcanic EruptionVolcanic RocksVolcaniclastic DepositsVolcaniclasticsVolcanoesAlaska Division of Geological & Geophysical SurveysAleutian IslandsBering SeaColorado CreekCrater CreekDutch HarborJag PeakMount RecheshnoiMount VsevidofOkmokOkmok CalderaOkmok Hot SpringsOkmok VolcanoOkmok, MountPacific OceanReindeer CreekTulikUmnak IslandAlaska Division of Geological & Geophysical SurveysCrater Creek BasaltWalker, J.D., Geissman, J.W., Bowring, S.A, and Babcock, L.E., comp., 2012, Geologic Time Scale v. 4.0: Geological Society of AmericaHolocenePleistoceneThis report, map, and/or dataset is available directly from the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (see contact information below).Any hard copies or published datasets utilizing these datasets shall clearly indicate their source. If the user has modified the data in any way, the user is obligated to describe the types of modifications the user has made. The user specifically agrees not to misrepresent these datasets, nor to imply that changes made by the user were approved by the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys. The State of Alaska makes no express or implied warranties (including warranties for merchantability and fitness) with respect to the character, functions, or capabilities of the electronic data or products or their appropriateness for any user's purposes. In no event will the State of Alaska be liable for any incidental, indirect, special, consequential, or other damages suffered by the user or any other person or entity whether from the use of the electronic services or products or any failure thereof or otherwise. In no event will the State of Alaska's liability to the Requestor or anyone else exceed the fee paid for the electronic service or product.Alaska Division of Geological & Geophysical SurveysMetadata Managermailing and physical

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FairbanksAK99709-3707USA(907)451-5020(907)451-5050dggspubs@alaska.gov8 am to 4:30 pm, Monday through Friday, except State holidaysPlease view our website (https://www.dggs.alaska.gov) for the latest information on available data. Please contact us using the e-mail address provided above when possible.Geophysical Institute and the Alaska Division of Geological & Geophysical Surveys, currently Cooperative Agreement G19AC00171, and by USGS Volcano Hazards Program funding to the Alaska Volcano Observatory. We thank many geologists and geophysicists who provided their time, insights, and camaraderie at Fort Glenn in all kinds of weather, including Jim Beget, Deb Bergfeld, Alain Burgisser, Michelle Coombs, Cheryl Cameron, John Eichelberger, Jeff Freymueller, Rick Hazlett, Alexander Max Kaufman, David Lescinsky, Taryn Lopez, Doerte Mann, Steve McNutt, Michael Ort, and Guy Tytgat. Former undergraduate and graduate students who participated in the geology fieldwork at Okmok Volcano include a cohort from Pomona College and the University of Alaska Fairbanks: Leslie Almberg, Matt Patrick, Ben Finney, Delanora Grey, Ken Papp, Joel Unema, and Lily Wong. Reviews by Tim Orr, Julie Nolan, and Drew Downs provided helpful insight and are much appreciated. Bering Pacific Ranches Ltd. supported this work through lodging and logistics support. Access to Umnak Island was by charter flights or boat from the Port of Dutch Harbor. We thank Cliff Gill (Airborne Scientific), Don Graves (Miss Peppers), and Jimmer MacDonald (Miss Alyssa) for safe transport to Umnak Island in often challenging sea conditions. Maritime Helicopters and pilots Bill Springer, Rick Farrish, and Jon Combs made our work possible, providing efficient, safe, and professional transportation in the field area. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.Beget, J.E.Larsen, J.F.Neal, C.A.Nye, C.J.Schaefer, J.R.2005Preliminary volcano-hazard assessment for Okmok Volcano, Umnak Island, AlaskaReport of InvestigationRI 2004-3Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveys32 p., 1 sheet, scale 1:150,000https://doi.org/10.14509/7042Cameron, C.E.Mulliken, K.M.Crass, S.W.Schaefer, J.R.Wallace, K.L.2019Alaska Volcano Observatory geochemical database, version 2Digital Data SeriesDDS 8 v. 2Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveys22 phttps://doi.org/10.14509/30058Larsen, J.F.Neal, C.A.Schaefer, J.R.Kaufman, A.M.Lu, Zhong2015The 2008 phreatomagmatic eruption of Okmok Volcano, Aleutian Islands, Alaska: Chronology, deposits, and landform changesReport of InvestigationRI 2015-2Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveys53 phttps://doi.org/10.14509/29405Larsen, J.F.Schaefer, J.R.Cameron, C.E.2022Electron probe microanalytical data of minerals and glass from rock samples from Okmok volcano, AlaskaRaw Data FileRDF 2022-6Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveys13 phttps://doi.org/10.14509/30853Nye, C.J.Beget, J.E.Layer, P.W.Mangan, M.T.McConnell, V.S.McGimsey, R.G.Miller, T.P.Moore, R.B.Stelling, P.L.2018Geochemistry of some quaternary lavas from the Aleutian Arc and Mt. WrangellRaw Data FileRDF 2018-1Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveys29 phttps://doi.org/10.14509/29843Schaefer, J.R.200530-meter shaded relief image of Okmok Volcano, Umnak Island, AlaskaRaw Data FileRDF 2005-1Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveyshttps://doi.org/10.14509/7041Schaefer, J.R.Larsen, J.F.Unema, J.A.2012Digital elevation model (DEM) and shaded relief image of Okmok Caldera, 2010Raw Data FileRDF 2011-6Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveyshttps://doi.org/10.14509/23223The data tables provide calculated 2 sigma level uncertainty values for all ages and isotope ratios.Not applicableThis data releaase is complete.AVO staff used handheld GPS units to acquire location coordinates. Positional uncertainty reported by the GPS units was not recorded.Sample collection - A team of five geologists from AVO (UAF/GI and USGS partner agencies) conducted summer geologic fieldwork throughout Umnak Island from July 1998 to 2016.201640Ar/39Ar Analytical Techniques - Rocks were submitted for 40Ar/39Ar age dating to the geochronology laboratories at the University of Alaska Fairbanks (UAF) and the USGS in Menlo Park. For 40Ar/39Ar analysis at UAF, 12 samples were dated, with the data yielding the isochron ages provided in the digital data; all ages are quoted to the +/-1-sigma level and calculated using the decay constants of Steiger and Jager (1977). The USGS Menlo Park geochronology lab analyzed 17 groundmass samples separated by crushing, sieving, and magnetic techniques, with 14 samples yielding interpretable results. Uncertainties in 40Ar/39Ar ages are also reported at the one-sigma level unless otherwise noted and include propagated uncertainties in counting statistics and J values. Lab methods and age interpretation calculations are described in detail in the accompanying report.2017Radiocarbon Analytical Techniques - Radiocarbon dating (conventional and Accelerator Mass Spectrometer [AMS]) of organic material to constrain eruption ages was carried out using Beta Analytic and Geochron Laboratories. Datable material was found typically in soils beneath tephra fall or pyroclastic density current deposits on the lower flanks of the volcano. Dating of wood and carbonized vegetation found within surge deposits was also possible in several cases. All samples were hand-cleaned thoroughly to remove modern plant material before submission to the lab. Soil samples were treated before analysis in the lab by dispersion in water, and isolating organic matter using agitation and ultrasound. Modern rootlets were screened with a nylon filter, and the remaining clay and organic fraction were subject to both acid and alkali washes. The humic acid fraction was precipitated, filtered, dried, and combusted in O2 to produce CO2 for analysis. The ages of the two caldera-forming eruptions are well constrained by this method. A compilation of dates and laboratories is provided in the digital data.2017point0.0000010.000001decimal degreesNAD83GRS 806378137298.257222101AppendixA_OkmokArAr-data.csv, AppendixA_OkmokArAr-data-dictionary.csvField station locations and 40Ar/39Ar ages of Okmok lavasDGGSAppendix A 40Ar/39Ar Ages of Okmok lavasAppendixB_OkmokRadiocarbon-data.csv, AppendixB_OkmokRadiocarbon-data-dictionary.csvField station locations and radiocarbon ages used to interpret Okmok Volcano geologic map unitsDGGSAppendix B Radiocarbon agesAppendixC_StationsAndSamples.csv, AppendixC_StationsAndSamples-data-dictionary.csvField station locations of samples discussed in this reportDGGSAppendix C Stations and samplesAlaska Division of Geological & Geophysical SurveysMetadata Managermailing and physical

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FairbanksAK99709-3707USA(907)451-5020(907)451-5050dggspubs@alaska.gov8 am to 4:30 pm, Monday through Friday, except State holidaysFGDC Content Standard for Digital Geospatial MetadataFGDC-STD-001-1998If the user has modified the data in any way they are obligated to describe the types of modifications they have performed in the supporting metadata file. User specifically agrees not to imply that changes they made were approved by the Alaska Department of Natural Resources or Division of Geological & Geophysical Surveys.https://dggs.alaska.gov/metadata/dggs.extdggs metadata extensions