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Originally published in Science Express on 14 October 2004
Science 12 November 2004:
Vol. 306. no. 5699, pp. 1167 - 1169
DOI: 10.1126/science.1103869
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Reports

Geochemical Precursors to Volcanic Activity at Mount St. Helens, USA

Kim Berlo,1* Jon Blundy,1 Simon Turner,1,2 Kathy Cashman,3 Chris Hawkesworth,1 Stuart Black4

The importance of the interplay between degassing and crystallization before and after 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 element (lithium) and short-lived radioactive isotope (lead-210 and radium-226) data show that ascending magma stalled within the conduit, leading to the accumulation of volatiles and the formation of lead-210 excesses, which signals the presence of degassing magma at depth.

1 Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Rd, Bristol BS8 1RJ, United Kingdom.
2 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, UK.

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

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