Author
Listed:
- 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)
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.
Suggested Citation
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, 2006.
"Dynamics of seismogenic volcanic extrusion at Mount St Helens in 2004–05,"
Nature, Nature, vol. 444(7118), pages 439-443, November.
Handle:
RePEc:nat:nature:v:444:y:2006:i:7118:d:10.1038_nature05322
DOI: 10.1038/nature05322
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