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

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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. ??2006 Nature Publishing Group.

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Publication type Article
Publication Subtype Journal Article
Title Dynamics of seismogenic volcanic extrusion at Mount St Helens in 2004-05
Series title Nature
DOI 10.1038/nature05322
Volume 444
Issue 7118
Year Published 2006
Language English
Publisher Nature Publications
Contributing office(s) Volcano Hazards Program
Description 5 p.
First page 439
Last page 443
Country United States
State Washington
Other Geospatial Mount St Helens
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