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Published Online October 14, 2004
Science DOI: 10.1126/science.1103869

Reports

Submitted on August 10, 2004
Accepted on October 1, 2004

Geochemical Precursors to Volcanic Activity at Mount St. Helens USA

Kim Berlo 1*, Jon Blundy 1, Simon Turner 2, Kathy Cashman 3, Chris Hawkesworth 1, Stuart Black 4

1 Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Rd, Bristol BS8 1RJ, United Kingdom.
2 Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Rd, Bristol BS8 1RJ, United Kingdom; GEMOC, Department of Earth and Planetary Sciences, Macquarie University, Sydney, NSW 2109, Australia.
3 Department of Geological Sciences, 1272 University of Oregon, Eugene, OR 97403-1272, USA.
4 Department of Archaeology, School of Human and Environmental Sciences, University of Reading, Whiteknights, PO Box 227, Reading RG6 6AB, United Kingdom.

* To whom correspondence should be addressed.
Kim Berlo , E-mail: Kim.Berlo{at}bristol.ac.uk

The importance of the interplay between degassing and crystallization preceding and following the eruption of Mount St. Helens (Washington, USA) in 1980 is well established. Here, we show that degassing occurred over a period of decades to days before eruptions and that the manner of degassing, as deduced from geochemical signatures within the magma, was characteristic of the eruptive style. Trace elements (Li) and short-lived radioactive isotope (210Pb, 226Ra) data show that ascending magma stalled within the conduit leading to accumulation of volatiles and the formation of 210Pb excesses, signaling the presence of degassing magma at depth.


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Science. ISSN 0036-8075 (print), 1095-9203 (online)