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Summary of Holocene eruption dates and Volcanic Explosivity Indices (VEI).
|Start Date||Stop Date||Eruption Certainty||VEI||Evidence||Activity Area or Unit|
|[ 1845 ]||[ Unknown ]||Uncertain|
|[ 1831 Mar ]||[ 1831 May 6 ± 1 days ]||Uncertain|
|[ 1830 Nov ]||[ Unknown ]||Uncertain||2|
|[ 1825 Mar 10 ]||[ Unknown ]||Uncertain||4|
|[ 1795 ]||[ Unknown ]||Uncertain||3|
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.
|Issanakski | Sannak | Isannach | Ragged Jack | Isannachotski|
|Three prominent volcanoes are constructed along an E-W line on the eastern half of Unimak Island. The aptly named Roundtop volcano in the lower foreground is glacially eroded and has had no historical eruptive activity. In the 1930s warm springs were found on its slopes. The recent discovery of Holocene pyroclastic-flow deposits and a group of lava domes south of Roundtop indicate it is still an active volcano. The glacially dissected Isanotski volcano and the beautifully symmetrical Shishaldin volcano are the prominent peaks behind Roundtop.
Photo by Clayton and Marcia Brown, 1986 (courtesy of John Reeder, Alaska Div. Geology Geophysical Surveys).
|Three prominent stratovolcanoes are constructed along an E-W line on Unimak Island. Steaming Shishaldin, the highest of the three, rises to 2857 m in the foreground and is one of the most active volcanoes in the Aleutians. The dissected Isanotski volcano (right) has had reported eruptions of uncertain validity, and Roundtop volcano (center distance) has had Holocene eruptions, but no historical activity.
Photo by Clayton and Marcia Brown, 1987 (courtesy of John Reeder, Alaska Div. Geology & Geophysical Surveys).
|Glaciers drape the ruggedly dissected upper flanks of Isanotski volcano and its dramatic summit pinnacles. Isanotski, locally known as Ragged Jack, is at the center of an E-W-trending group of three volcanoes on Unimak Island. Four poorly documented historical eruptions were noted in the 18th and 19th centuries. Some or all of these eruptions, however, could have been from neighboring Shishaldin volcano, and historical eruptions of Isanotski must be considered unlikely, given the extreme degree of erosional dissection.
Photo courtesy of Alaska Volcano Observatory, 1994.
The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography. Discussion of another volcano or eruption (sometimes far from the one that is the subject of the manuscript) may produce a citation that is not at all apparent from the title.
Coats R R, 1950. Volcanic activity in the Aleutian Arc. U S Geol Surv Bull, 974-B: 35-47.
IAVCEI, 1973-80. Post-Miocene Volcanoes of the World. IAVCEI Data Sheets, Rome: Internatl Assoc Volc Chemistry Earth's Interior..
Miller T P, McGimsey R G, Richter D H, Riehle J R, Nye C J, Yount M E, Dumoulin J A, 1998. Catalogue of the historically active volcanoes of Alaska. U S Geol Surv Open-File Rpt, 98-582: 1-104.
Motyka R J, Liss S A, Nye C J, Moorman M A, 1993. Geothermal resources of the Aleutian arc. Alaska Div Geol Geophys Surv, Prof Rpt, no 114, 17 p and 4 map sheets.
Smith R L, Shaw H R, Luedke R G, Russell S L, 1978. Comprehensive tables giving physical data and thermal energy estimates for young igneous systems of the United States. U S Geol Surv Open-File Rpt, 78-925: 1-25.
Wood C A, Kienle J (eds), 1990. Volcanoes of North America. Cambridge, England: Cambridge Univ Press, 354 p.
|Large Eruptions of Isanotski||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).|
|WOVOdat||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.|
|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).|
|Smithsonian Collections||Search the Smithsonian's NMNH Department of Mineral Sciences collections database. Go to the "Search Rocks and Ores" tab and use the Volcano Name drop-down to find samples.|