Mount St. Helens reawakens
Article first published online: 3 JUN 2011
©2005. American Geophysical Union. All Rights Reserved.
Eos, Transactions American Geophysical Union
Volume 86, Issue 3, pages 25–29, 18 January 2005
How to Cite
2005), Mount St. Helens reawakens, Eos Trans. AGU, 86(3), 25–29, doi:10.1029/2005EO030001., , , , and (
- Issue published online: 3 JUN 2011
- Article first published online: 3 JUN 2011
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Following 18 years of relative quiescence, Mount St. Helens volcano (MSH) became restless and began erupting again during September–December 2004.
On 23 September, the U.S. Geological Survey's (USGS) David A. Johnston Cascades Volcano Observatory (CVO) and the Pacific Northwest Seismograph Network (PNSN) at the University of Washington detected the onset of a shallow earthquake swarm beneath the 1980–1986 lava dome. The Mount St. Helens Emergency Response Plan defines three alert levels that differ from normal background activity: Level 1, Notice of Volcanic Unrest (unusual activity detected); Level 2, Volcano Advisory (eruption likely but not imminent); and Level 3, Volcano Alert (eruption imminent or in progress).