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Bulletin of Volcanology

, Volume 63, Issue 8, pp 545–556 | Cite as

Holocene geomagnetic secular variation recorded by volcanic deposits at Mount St. Helens, Washington

  • Jonathan T. Hagstrum
  • Richard P. Hoblitt
  • Cynthia A. Gardner
  • Thomas E. Gray
Research Article

Abstract

A compilation of paleomagnetic data from volcanic deposits of Mount St. Helens is presented in this report. The database is used to determine signature paleomagnetic directions of products from its Holocene eruptive events, to assign sampled units to their proper eruptive period, and to begin the assembly of a much larger database of paleomagnetic directions from Holocene volcanic rocks in western North America. The paleomagnetic results from Mount St. Helens are mostly of high quality, and generally agree with the division of its volcanic deposits into eruptive episodes based on previous geologic mapping and radiocarbon dates. The Muddy River andesite's paleomagnetic direction, however, indicates that it is more likely part of the Pine Creek eruptive period rather than the Castle Creek period. In addition, the Two-Fingers andesite flow is more likely part of the Middle Kalama eruptive period and not part of the Goat Rocks period. The paleomagnetic data from Mount St. Helens and Mount Hood document variation in the geomagnetic field's pole position over the last ~2,500 years. A distinct feature of the new paleosecular variation (PSV) record, similar to the Fish Lake record (Oregon), indicates a sudden change from rapid clockwise movement of the pole about the Earth's spin axis to relatively slow counterclockwise movement at ~800 to 900 years B.P.

Eruptive intervals Geomagnetic field Mount St. Helens Paleomagnetism Paleosecular variation 

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Copyright information

© Springer-Verlag 2001

Authors and Affiliations

  • Jonathan T. Hagstrum
    • 1
  • Richard P. Hoblitt
    • 2
  • Cynthia A. Gardner
    • 2
  • Thomas E. Gray
    • 3
  1. 1.US Geological Survey, 345 Middlefield Road, Mail Stop 937, Menlo Park, CA 94025USA
  2. 2.US Geological Survey, Cascades Volcano Observatory, 5400 MacArthur Blvd., Vancouver, WA 98661USA
  3. 3.State of Nevada, Division of Environmental Protection, 333 W. Nye Lane, Carson City, NV 89706USA

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