Mount St. Helens a decade after the 1980 eruptions: magmatic models, chemical cycles, and a revised hazards assessment

Pallister, John S.; Hoblitt, Richard P.; Crandell, Dwight Raymond; Mullineaux, Donal Ray

doi:10.1007/bf00278003

Cited by 115 publications

(73 citation statements)

References 55 publications

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“…Estimates of conduit diameter N of 20 þ 5 m have been made by observations [1] and indirectly from magma ascent velocities estimated from amphibole reaction rims [21]. A chamber depth of 7.2 km was estimated by Pallister [22]. We take a nucleation density of 10 14 m 33 to be consistent with observations of microphenocrysts abundance by Cashman and Blundy [8] 312 m/s.…”

Section: Case Studiesmentioning

confidence: 89%

Periodic behavior in lava dome eruptions

Бармин

Melnik

Sparks

2002

Earth and Planetary Science Letters

150

136

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Lava dome eruptions commonly display fairly regular alternations between periods of high activity and periods of low or no activity. The time scale for these alternations is typically months to several years. Here we develop a generic model of magma discharge through a conduit from an open-system magma chamber with continuous replenishment. The model takes account of the principal controls on flow, namely the replenishment rate, magma chamber size, elastic deformation of the chamber walls, conduit resistance, and variations of magma viscosity, which are controlled by degassing during ascent and kinetics of crystallization. The analysis indicates a rich diversity of behavior with periodic patterns similar to those observed. Magma chamber size can be estimated from the period with longer periods implying larger chambers. Many features observed in volcanic eruptions such as alternations between periodic behaviors and continuous discharge, sharp changes in discharge rate, and transitions from effusive to catastrophic explosive eruption can be understood in terms of the non-linear dynamics of conduit flows from open-system magma chambers. The dynamics of lava dome growth at Mount St. Helens (1980^1987) and Santiaguito (1922^2000) was analyzed with the help of the model. The best-fit models give magma chamber volumes of V0.6 km 3 for Mount St. Helens and V65 km 3 for Santiaguito. The larger magma chamber volume is the major factor in explaining why Santiaguito is a long-lived eruption with a longer periodicity of pulsations in comparison with Mount St. Helens. ß

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Section: Case Studiesmentioning

confidence: 89%

Periodic behavior in lava dome eruptions

Бармин

Melnik

Sparks

2002

Earth and Planetary Science Letters

150

136

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“…A change from gas-rich scoriacious dome textures to gas-poor smooth dome textures between 1980 and 1986 is evidence for progressively more degassing within the conduit with time [Anderson and Fink, 1990]. Further contributing to an increase in viscosity, the silica content of the extruded domes increased between 1980 and 1986 [Pallister et al, 1992]. The 2004 eruption at MSH also had high multiplet efficiency that coincided with the extrusion of solidified and highly degassed spines that formed up to 1 km below the vent .…”

Section: Physical Controls On the Development Of Multipletsmentioning

confidence: 99%

Multiplets: Their behavior and utility at dacitic and andesitic volcanic centers

Thelen¹,

Malone²,

West³

2011

J. Geophys. Res.

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[1] Multiplets, or groups of earthquakes with similar waveforms, are commonly observed at volcanoes, particularly those exhibiting unrest. Using triggered seismic data from the 1980-1986 Mount St. Helens (MSH) eruption, we have constructed a catalog of multiplet occurrence. Our analysis reveals that the occurrence of multiplets is related, at least in part, to the viscosity of the magma. We also constructed catalogs of multiplet occurrence using continuous seismic data from the 2004 eruption at MSH and 2007 eruption at Bezymianny Volcano, Russia. Prior to explosions at MSH in 2004 and Bezymianny in 2007, the multiplet proportion of total seismicity (MPTS) declined, while the average amplitudes and standard deviations of the average amplitude increased. The life spans of multiplets (time between the first and last event) were also shorter prior to explosions than during passive lava extrusion. Dome-forming eruptions that include a partially solidified plug, like MSH (1983MSH ( -1986MSH ( and 2004MSH ( -2008, often possess multiplets with longer life spans and MPTS values exceeding 50%. Conceptually, the relatively unstable environment prior to explosions is characterized by large and variable stress gradients brought about by rapidly changing overpressures within the conduit. We infer that such complex stress fields affect the number of concurrent families, MPTS, average amplitude, and standard deviation of the amplitude of the multiplets. We also argue that multiplet detection may be an important new monitoring tool for determining the timing of explosions and in forecasting the type of eruption.Citation: Thelen, W., S. Malone, and M. West (2011), Multiplets: Their behavior and utility at dacitic and andesitic volcanic centers,

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“…It appears that during the past 2200 years, the compositional range of magma erupted during a given eruptive period has become more restricted towards dacite with time (cf. Pallister et al, 1992 ) are greater than those produced during the Goat Rocks (0.5 km 3 ) and current (<0.5 km 3 ) eruptive periods (Carey et al, 1989;Criswell, 1989).…”

Section: Major Elementsmentioning

confidence: 99%

The origin of Mount St. Helens andesites

Smith

Leeman

1993

Journal of Volcanology and Geothermal Research

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Eruption of these magmatic variants within the same eruptive phase implies the existence of different petrogenetic lineages, and that the plumbing system is sufficiently complex to simultaneously isolate and preserve numerous magma batches. It is unlikely that any of the andesites (or dacites) are derived by fractional crystallization of the recognized basaltic variants. Formation of the andesites simply by contamination (or assimilation-fractional crystallization) of basaltic magma is also improbable. More plausibly, the andesites represent mixing between basaltic and dacitic end-member magmas, each of which may be somewhat heterogeneous or vary in composition with time. In this model, efficient mixing must occur in some parts of the magma plumbing system, while some conduits or storage reservoirs must be effectively isolated.

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Mount St. Helens a decade after the 1980 eruptions: magmatic models, chemical cycles, and a revised hazards assessment

Cited by 115 publications

References 55 publications

Periodic behavior in lava dome eruptions

Periodic behavior in lava dome eruptions

Multiplets: Their behavior and utility at dacitic and andesitic volcanic centers

The origin of Mount St. Helens andesites

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