Lessons from deforming volcanoes
Whereas previous chapters are focused primarily on geodetic techniques, this one addresses specific applications of those techniques at a few well-studied volcanoes. Mount St. Helens, KTlauea, Yellowstone, and Long Valley illustrate the tremendous diversity in terms of style, duration, dimensions, and mechanisms of ground movements. That is not to say that these four examples encompass the full range of deformation observed at volcanoes worldwide, or that other examples would not serve equally well. Rather, I chose these four because I know them personally, having worked at each for at least several years, and because they have been studied thoroughly with a variety of monitoring techniques, including geodesy. Therefore, the geodetic results can be placed in a rich context of other information to help interpret the processes responsible for ground deformation and other symptoms of unrest.
KeywordsGlobal Position System Rift Zone United States Geological Survey Earthquake Swarm Summit Area
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- 1.A prolonged dome-building eruption at Mount St. Helens that began in September-October 2004 produced another dacite dome immediately south of the 1980s dome (Dzurisin etal., 2005). The eruption was continuing in March 2006.Google Scholar
- 2.The term ‘deviatoric stress’ is quoted here from the original literature. The current author is aware of the article by Engelder (1994) entitled ‘Deviatoric stressitis: A virus infecting the earth science community,’ which points out widespread misuse of the term and attempts to set the record straight. In this case, the intended meaning seems clear.Google Scholar
- 3.Other enormous submarine landslide deposits were discovered soon thereafter, including the 5,600 km3 Storegga Slide off the western coast of Norway (Bugge, 1983), which left evidence of a tsunami along the eastern coast of Scotland about 7,000 years ago (Dawson et al., 1988; Long et al., 1989). Masson (1996) and Masson et al. (2002) identified several large submarine landslides and associated deposits offshore the western Canary Islands, including the large ~15 ka E1 Golfo debris avalanche off the flank of E1 Hierro Volcano, and a 1,000 km3 slide offshore the Oratava and Icod valleys onTenerife from Las Cañadas Volcano (Watts and Masson, 1995).Google Scholar
- 4.M s refers to surface-wave magnitude, which is based on the amplitude of Rayleigh surface waves measured at a period near 20 s. Depending on how they were determined, earthquake magnitudes are expressed as local magnitude (Ml), body magnitude (M b, based on the amplitude of P body-waves), or moment magnitude (M w, based on the moment of the earthquake). Unless specified otherwise, earthquake magnitude M refers to local magnitude.Google Scholar
- 5.The activity in a remote part of Yellowstone National Park went unnoticed at the time, except possibly for a false report of smoke from the area on 3 July 1985. The new feature was discovered on 5 October 1986 by National Park Service geologists Roderick (Rick) Hutchinson and C. Craig-Hunter (Hutchinson, 1992).Google Scholar
- 8.Peak dynamic stresses accompanied the S-wave (secondary shear wave) and the crustal Love and Rayleigh waves, which have periods of 10 to 20 seconds and wavelengths of crustal dimensions (15–50 km) (Hill etal., 1995).Google Scholar