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| Studies by the U.S. Geological Survey in Alaska, 2004 |
Summit area of Westdahl volcano located on the southwest part of Unimak Island in the eastern Aleutian Islands. Photograph by C. Zeillemaker, U.S. Fish and Wildlife Service, February 2, 1993. (from USGS DDS-40 ) |
| High-precision 40Ar/39Ar geochronology of selected lavas from Westdahl Volcano places time constraints on several key prehistoric eruptive phases of this large active volcano. A dike cutting old pyroclastic-flow and associated lahar deposits from a precursor volcano yields an age of 1,654±11 k.y., dating this precursor volcano as older than early Pleistocene. A total of 11 geographically distributed lavas with ages ranging from 47±14 to 127±2 k.y. date construction of the Westdahl volcanic center. Lava flows cut by an apparent caldera-rim structure yielded ages of 81±5 and 121±8 k.y., placing a maximum date of 81 ka on caldera formation. Late Pleistocene and Holocene lavas fill the caldera, but most of them are obscured by the large summit icecap. |
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Go to other chapters in this series: Haeussler, Peter J., and Galloway, John P., eds., 2005, Studies by the U.S. Geological Survey in Alaska, 2004: U.S. Geological Survey Professional Paper 1709.
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