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University of Washington
Stratovolcanoes are prone to failure by their very nature and often fail catastrophically. Mount St. Helens, Washington and Bezymianny volcano, Russia had remarkably similar catastrophic eruptions including edifice failure in 1980 and 1956, respectively. The progression of activity afterward included explosions, discrete dome building and continuous dome building at both volcanoes. While the similarities morphologically and seismically are striking, the differences give clues to the individual processes at work under each volcano. In particular, the analysis of the continuous dome building phases at both volcanoes has led to two conclusions. The first, that the comparatively vigorous seismicity prior to extrusion of the 2004 dome at Mount St. Helens was due directly to the period of quiescence prior to the eruption. The second conclusion is that the vigorous seismicity that accompanied continuous extrusion at Mount St. Helens was caused by a bend in the conduit, which is supported by a compilation of earthquake locations and tilt. Because of the divergence in compositions between the two volcanoes during the latest phases of activity, it does not appear that Bezymianny is a good predictor of future activity at Mount St. Helens. Several volcanoes worldwide have also had edifice failures and are currently in more advance stages of rebuilding than Mount St. Helens and may be used as analogues for the range of expected behavior. Examples include Reventador, Guagua Pichincha, Tungurahua, Pacaya and Santiaguito.
Bogoyavlenskaya et. al, 1985, Catastrophic Eruptions of the Directed-Blast Type at Mount St. Helens, Bezymianny and Shiveluch Volcanoes, Journal of Geodynamics, vol. 3, iss 3-4, pp.189-218. Part 1 | Part 2
Moran et al., Seismicity associated with renewed dome building at Mount St. Helens, 2008, from: A Volcano Rekindled: The Renewed Eruption of Mount St. Helens 2004-2006, USGS Professional Paper, Chap. 2.
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