Petrologic constraints on the decompression history of magma prior to Vulcanian explosions at the Soufrière Hills volcano, Montserrat

Clarke, A. B.; Stephens, Susanna L.; Teasdale, Rachel; Sparks, R. S. J.; Diller, K.

doi:10.1016/j.jvolgeores.2006.11.007

Cited by 114 publications

(123 citation statements)

References 49 publications

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“…showed how the variety within these explosions could be modelled as variants on a tripartite conduit layering: a dense, stiff cap; a transition zone of heterogeneous vesicularity; and a lower, homogeneous, low-porosity zone. The volume density of plagioclase microlites is inferred to show a sharp transition at about 700 m depth, consistent with the base of the stiff cap or plug (Clarke et al 2007). Giachetti et al (2010) showed that detailed textural analysis of vesicles could be used to recognize populations of bubbles formed by explosions, and to understand nucleation mechanisms and decompression rates.…”

Section: Explosive Variety and Mechanismsmentioning

confidence: 71%

“…Amphibole rims related to decompression can be applied to infer magma ascent speeds Rutherford & Devine 2003) and the results are in broad agreement with similar studies at Mount St Helens, with ascent speeds of less than a few millimetres per second producing well-developed reaction rims. The compositions of microlites of plagioclase have been used to infer the pressures in explosively erupted clasts derived from magma in the conduit just prior to Vulcanian eruptions (Clarke et al 2007). Secondary ion mass spectrometry depth profiling of plagioclase crystals has also demonstrated an increase in conduit temperatures during Vulcanian explosions (Genareau et al 2009).…”

Section: Petrologymentioning

confidence: 99%

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Chapter 1 An overview of the eruption of Soufrière Hills Volcano, Montserrat from 2000 to 2010

Wadge

Voight

Sparks

et al. 2014

Memoirs

139

119

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Abstract:The 1995-present eruption of Soufrière Hills Volcano on Montserrat has produced over a cubic kilometre of andesitic magma, creating a series of lava domes that were successively destroyed, with much of their mass deposited in the sea. There have been five phases of lava extrusion to form these lava domes: -March 1998-July 2003 August 2005-April 2007July 2008-January 2009 and October 2009-February 2010. It has been one of the most intensively studied volcanoes in the world during this time, and there are long instrumental and observational datasets. From these have sprung major new insights concerning: the cyclicity of magma transport; low-frequency earthquakes associated with conduit magma flow; the dynamics of lateral blasts and Vulcanian explosions; the role that basalt-andesite magma mingling in the mid-crust has in powering the eruption; identification using seismic tomography of the uppermost magma reservoir at a depth of 5.5 . 7.5 km; and many others. Parallel to the research effort, there has been a consistent programme of quantitative risk assessment since 1997 that has both pioneered new methods and provided a solid evidential source for the civil authority to use in mitigating the risks to the people of Montserrat.At the time of writing (January 2013), the Soufrière Hills Volcano (SHV) is in its 17th year of eruption, placing it with a select group of very long-lived eruptions from silicic volcanoes. Within the Caribbean plate, only two other silicic volcanoes have had longer-lived historical extrusive eruptions: Santiaguito, Guatemala (1922( -present: Harris et al. 2003 and Arenal, Costa Rica (1968 -present: Wadge et al. 2006). As with both of these volcanoes, SHV has not extruded lava continuously for the whole eruption, but has erupted intermittently. In fact, it has been extruding lava for a cumulative total of only 8.5 years out of 17. So in what sense can we consider this a single eruption rather than a series of shorter ones? The longest gaps between extrusive phases have been about 2-3 years (July 2003-August 2005 February 2010-present). However, during the pauses between extrusion at SHV, there have been many indications that the volcanic system remains active. These have included inflation of the island's surface, the release of volatiles in quantities similar to those seen during lava extrusion, swarms of low-frequency seismicity, explosions and the production of ash. This suggests that there are processes within the system responsible for producing alternating extrusive and non-extrusive states. Melnik & Sparks (2005) showed theoretically how non-linear response to relatively minor perturbations of the magmatic system can result in such behaviour.Recognition of the long-term continuity of the eruption process has direct consequences for the tasks of monitoring and estimating the risks posed by the volcano. It means that the Montserrat Volcano Observatory (MVO) must monitor the volcano continuously, even during periods of relative quiescence and apparent inactivity. The probabil...

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Section: Explosive Variety and Mechanismsmentioning

confidence: 71%

Section: Petrologymentioning

confidence: 99%

Chapter 1 An overview of the eruption of Soufrière Hills Volcano, Montserrat from 2000 to 2010

Wadge

Voight

Sparks

et al. 2014

Memoirs

139

119

View full text Add to dashboard Cite

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“…According to field observations, the porosity of lava domes typically ranges from 0 to 0.5 (e.g., Melnik and Sparks, 2002;Kueppers et al, 2005;Mueller et al, 2005). On the other hand, Clarke et al (2007) showed that the porosity in the subsurface region where the pressure is higher than about 10 MPa can be as large as 0.5-0.7, as was the case for the pre-explosion (dome growth) state of the 1997 events in Soufrière Hills Volcano, Montserrat (SHV). We discuss the mechanism for these observed porosity distributions to be generated on the basis of our simple formula, Eq.…”

Section: Geological Implicationsmentioning

confidence: 99%

A simple formula for calculating porosity of magma in volcanic conduits during dome-forming eruptions

Kozono

Koyaguchi

2010

Earth Planet Sp

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We present a simple formula for analyzing factors that govern porosity of magma in dome-forming eruptions. The formula is based on a 1-dimensional steady conduit flow model with vertical gas escape, and provides the value of the porosity as a function of magma flow rate, magma properties (viscosity and permeability), and pressure. The porosity for a given pressure depends on two non-dimensional numbers ε and θ . The parameter ε represents the ratio of wall friction force to liquid-gas interaction force, and is proportional to the magma viscosity. The parameter θ represents the ratio of gravitational load to liquid-gas interaction force and is inversely proportional to the magma flow rate. Gas escape is promoted and porosity decreases with increasing ε or θ . From the possible ranges of ε and θ for typical magmatic conditions, it is inferred that the porosity is primarily determined by ε at the atmospheric pressure (near the surface), and by θ at higher pressures (in the subsurface region inside the conduit). The porosity near the surface approaches 0 owing to high magma viscosity regardless of the magnitude of the magma flow rate, whereas the subsurface porosity increases to more than 0.5 with increasing magma flow rate.

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“…Highly porous edifice rock may constitute an effective means of passive outgassing during periods of eruptive quiescence; when subject to stress, however -for example as a result of shallow fluid migration (e.g. Denlinger and Hoblitt, 1999;Clarke et al, 2007) or deep-seated magma chamber deformation (e.g. Melnik and Sparks, 2005;Wadge et al, 2006) -its permeability will tend to decrease.…”

Section: Implications For Volcanologymentioning

confidence: 99%

“…Magma is a constantly developing multi-phase medium, and as it migrates through the crust, vesiculating and crystallising along the way, it can impart significant mechanical stress on the surrounding edifice rock (e.g. Sparks, 1997;Voight et al, 1998;Denlinger and Hoblitt, 1999;Clarke et al, 2007;Heimisson et al, 2015). Deeper in the crust, magma chamber deformation can pressurise conduit and dyke systems above, in turn displacing the edifice (e.g.…”

Section: Introductionmentioning

confidence: 99%

Inelastic compaction and permeability evolution in volcanic rock

2017

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Abstract. Active volcanoes are mechanically dynamic environments, and edifice-forming material may often be subjected to significant amounts of stress and strain. It is understood that porous volcanic rock can compact inelastically under a wide range of in situ conditions. In this contribution, we explore the evolution of porosity and permeability -critical properties influencing the style and magnitude of volcanic activity -as a function of inelastic compaction of porous andesite under triaxial conditions. Progressive axial strain accumulation is associated with progressive porosity loss. The efficiency of compaction was found to be related to the effective confining pressure under which deformation occurred: at higher effective pressure, more porosity was lost for any given amount of axial strain. Permeability evolution is more complex, with small amounts of stress-induced compaction ( < 0.05, i.e. less than 5 % reduction in sample length) yielding an increase in permeability under all effective pressures tested, occasionally by almost 1 order of magnitude. This phenomenon is considered here to be the result of improved connectivity of formerly isolated porosity during triaxial loading. This effect is then overshadowed by a decrease in permeability with further inelastic strain accumulation, especially notable at high axial strains (> 0.20) where samples may undergo a reduction in permeability by 2 orders of magnitude relative to their initial values. A physical limit to compaction is discussed, which we suggest is echoed in a limit to the potential for permeability reduction in compacting volcanic rock. Compiled literature data illustrate that at high axial strain (both in the brittle and ductile regimes), porosity φ and permeability k tend to converge towards intermediate values (i.e. 0.10 ≤ φ ≤ 0.20; 10 −14 ≤ k ≤10 −13 m 2 ). These results are discussed in light of their potential ramifications for impacting edifice outgassing -and in turn, eruptive activity -in active volcanoes.

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Petrologic constraints on the decompression history of magma prior to Vulcanian explosions at the Soufrière Hills volcano, Montserrat

Cited by 114 publications

References 49 publications

Chapter 1 An overview of the eruption of Soufrière Hills Volcano, Montserrat from 2000 to 2010

Chapter 1 An overview of the eruption of Soufrière Hills Volcano, Montserrat from 2000 to 2010

A simple formula for calculating porosity of magma in volcanic conduits during dome-forming eruptions

Inelastic compaction and permeability evolution in volcanic rock

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