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Studies by the U.S. Geological Survey in Alaska, 2004
U.S. Geological Survey
Professional Paper 1709-D

Argon Geochronology of Late Pleistocene to Holocene Westdahl Volcano, Unimak Island, Alaska

By Andrew T. Calvert, Richard B. Moore, and Robert G. McGimsey


photo of volcano summit area covered in snow
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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For questions about the content of this report, contact Andrew Calvert

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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Maintained by: Michael Diggles
Created: November 29, 2005
Last modified: May 2, 2006 (mfd)