Dynamics of seismogenic volcanic extrusion at Mount St Helens in 2004–05

Richard M. Iverson (), Daniel Dzurisin (), Cynthia A. Gardner (), Terrence M. Gerlach, Richard G. LaHusen, Michael Lisowski, Jon J. Major, Stephen D. Malone, James A. Messerich, Seth C. Moran, John S. Pallister, Anthony I. Qamar, Steven P. Schilling and James W. Vallance
Additional contact information
Richard M. Iverson: Cascades Volcano Observatory
Daniel Dzurisin: Cascades Volcano Observatory
Cynthia A. Gardner: Cascades Volcano Observatory
Terrence M. Gerlach: Cascades Volcano Observatory
Richard G. LaHusen: Cascades Volcano Observatory
Michael Lisowski: Cascades Volcano Observatory
Jon J. Major: Cascades Volcano Observatory
Stephen D. Malone: University of Washington
James A. Messerich: Denver Federal Center
Seth C. Moran: Cascades Volcano Observatory
John S. Pallister: Cascades Volcano Observatory
Anthony I. Qamar: University of Washington
Steven P. Schilling: Cascades Volcano Observatory
James W. Vallance: Cascades Volcano Observatory

Nature, 2006, vol. 444, issue 7118, 439-443

Abstract: Abstract The 2004–05 eruption of Mount St Helens exhibited sustained, near-equilibrium behaviour characterized by relatively steady extrusion of a solid dacite plug and nearly periodic shallow earthquakes. Here we present a diverse data set to support our hypothesis that these earthquakes resulted from stick-slip motion along the margins of the plug as it was forced incrementally upwards by ascending, solidifying, gas-poor magma. We formalize this hypothesis with a dynamical model that reveals a strong analogy between behaviour of the magma–plug system and that of a variably damped oscillator. Modelled stick-slip oscillations have properties that help constrain the balance of forces governing the earthquakes and eruption, and they imply that magma pressure never deviated much from the steady equilibrium pressure. We infer that the volcano was probably poised in a near-eruptive equilibrium state long before the onset of the 2004–05 eruption.

Date: 2006
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DOI: 10.1038/nature05322

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