Bulletin of Volcanology

, Volume 52, Issue 7, pp 545–550 | Cite as

A new tree-ring date for the “floating island” lava flow, Mount St. Helens, Washington

  • David K Yamaguchi
  • Richard P Hoblitt
  • Donald B Lawrence


Anomalously narrow and missing rings in trees 12 m from Mount St. Helens' “floating island” lava flow, and synchronous growth increases in trees farther from the flow margin, are evidence that this andesitic flow was extruded between late summer 1799 and spring 1800 a.d., within a few months after the eruption of Mount St. Helens' dacitic layer T tephra. For ease of reference, we assign here an 1800 a.d. date to this flow. The new date shows that the start of Mount St. Helens' Goat Rocks eruptive period (1800–1857 a.d.) resembled the recent (1980–1986) activity in both petrochemical trends and timing. In both cases, an initial explosive eruption of dacite was quickly succeeded by the eruption of more mafic lavas; dacite lavas then reappeared during an extended concluding phase of activity. This behavior is consistent with a recently proposed fluid-dynamic model of magma withdrawal from a compositionally zoned magma chamber.


Explosive Tephra Sedimentology Lava Flow Magma Chamber 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Springer-Verlag 1990

Authors and Affiliations

  • David K Yamaguchi
    • 1
    • 2
  • Richard P Hoblitt
    • 3
  • Donald B Lawrence
    • 4
  1. 1.Mountain Research StationUniversity of ColoradoBoulderUSA
  2. 2.Institute of Arctic and Alpine Research (INSTAAR)University of ColoradoBoulderUSA
  3. 3.Cascades Volcano ObservatoryUS Geological SurveyVancouverUSA
  4. 4.Department of Plant BiologyUniversity of MinnesotaSt. PaulUSA

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