Delayed, disequilibrium degassing in rhyolite magma: decompression experiments and implications for explosive volcanism

Mangan, Margaret T.; Sisson, T. W.

doi:10.1016/s0012-821x(00)00299-5

Cited by 275 publications

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“…Both distributions suggest 574 that the andesite underwent a single episode of bubble nucleation and growth, most likely due 575 to magma decompression and volatile exsolution, which is consistent with the higher bubble 576 number densities at smaller vesicle sizes (Mangan and Sisson, 2000). The steeper slope of the 577 size distribution (which is proportional to 1/Gτ) compared to the mafic inclusions, suggests 578 that bubble growth rates were much lower in the andesite, consistent with slow magma 579 decompression.…”

mentioning

confidence: 74%

Chapter 16 Pre-eruptive vapour and its role in controlling eruption style and longevity at Soufrière Hills Volcano

Edmonds

Humphreys

Hauri

et al. 2014

Memoirs

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Citation for published item:idmondsD wF nd rumphreysD wFgFF nd ruriD iF nd rerdD F nd dgeD qF nd wsonD rF nd veddenD F nd lilD wF nd frlyD tF nd eiuppD eF nd ghristopherD F nd qiudieD qF nd quidD F @PHIRA 9reEeruptive vpour nd its role in ontrolling eruption style nd longevity t oufri ere rills olnoF9D wemoirsFD QW F ppF PWIEQISF Further information on publisher's website: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Schmidt and Poli, 1999). The generation of mafic magmas in the "hot 52 zone" at the base of the arc crust is fundamentally controlled by the H 2 O content of the melts, 53 which act to "flux" the amphibolite crust and cause assimilation (Annen et al,. 2006). In 54 shallow storage areas, the exsolved fluid content of stored magma directly influences the 55 compressibility and hence response of the magma body to changes in pressure or volume, 56 ultimately determining magma ascent rates and eruption style, as well as eruption duration 57 and size (Huppert and Woods, 2002). The rate of crystallisation of magma in crustal 58 reservoirs is influenced by the opposing effects of fluxing by CO 2 -rich gases from depth, 59 which act to "freeze" the magma (Blundy et al., 2010), and new batches of incoming hot, 60 volatile-rich magma, which act to "defrost" it, by heating and transferring H 2 O-rich fluids 61 (e.g. Bachmann and Bergantz, 2006). Sulphur partitions into this fluid (e.g. Scaillet et al., 62 1998;Zajacz et al., 2012), further enhancing the proportion of vapour coexisting with the 63 magma prior to the eruption, and acting as a convenient tracer to measure in volcanic gases 64 (e.g. Gerlach et al., 2008). In the conduit, transitions between lava dome building and 65 explosive Vulcanian activity are controlled by finely-balanced feedbacks involving the 66 development of permeability during degassing, and the increase in viscosity and consequent 67 retardation of bubble growth caused by crystallisation and H 2 O exsolution from the melt 68 (Melnik and Sparks, 1999;Sparks et al., 2000;Melnik and Sparks, 2002; Clarke et al., 2007). 69 CarmichaelThe arc magma system is complex; petrological and geochemical evidence points to the 70 erupted porphyritic andesite being a hybrid, the result of perhaps countless recharge events by 71 internal energy associated with dissolved volatiles can be released into the magma chamber, 87 and this is a mechanism for inducing complex eruption cycles on long timescales for volatile-88 rich magmas (Huppert and Woods, 2002). One mechanism for this is the presence of a large 8...

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confidence: 74%

Chapter 16 Pre-eruptive vapour and its role in controlling eruption style and longevity at Soufrière Hills Volcano

Edmonds

Humphreys

Hauri

et al. 2014

Memoirs

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“…That growth causes the flow density to decrease, decompression rate to increase, and hence the flow to accelerate, possibly leading to an explosive eruption. Since the early work of Sparks (1978), bubble growth dynamics has been explored through increasingly complex numerical models (e.g., Barclay et al 1995;Lyakhovsky et al 1996;Proussevitch et al 1993a;Proussevitch and Sahagian 1998;Sparks et al 1994;Toramaru 1989; and experimental work (e.g., Gardner et al 1999;2000;Mangan and Sisson 2000).…”

Section: Introductionmentioning

confidence: 99%

Experimental constraints on degassing and permeability in volcanic conduit flow

2004

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This study assesses the effect of decompression rate on two processes that directly influence the behavior of volcanic eruptions: degassing and permeability in magmas. We studied the degassing of magma with experiments on hydrated natural rhyolitic glass at high pressure and temperature. From the data collected, we defined and characterized one degassing regime in equilibrium and two regimes in disequilibrium. Equilibrium bubble growth occurs when the decompression rate is slower than 0.1 MPa s -1 , while higher rates cause porosity to deviate rapidly from equilibrium, defining the first disequilibrium regime of degassing. If the deviation is large enough, a critical threshold of super-saturation is reached and bubble growth accelerates, defining the second disequilibrium regime. We studied permeability and bubble coalescence in magma with experiments using the same rhyolitic melt in open degassing conditions. Under these open conditions, we observed that bubbles start to coalesce at ~43 vol.% porosity, regardless of decompression rate. Coalescence profoundly affects bubble texture and size distributions, and induces the melt to become permeable. We determined coalescence to occur on a time scale (~180 s) independent of decompression rate. We parameterized and incorporated our experimental results into a 1D conduit flow model to explore the implications of our findings on eruptive behavior of rhyolitic melts with low crystal contents stored in the upper crust.Compared to previous models that assume equilibrium degassing of the melt during ascent, the introduction of disequilibrium degassing reduces the deviation from lithostatic pressure by ~ 25 %, the acceleration at high porosities (> 50 vol.%) by a factor 5, and the associated decompression rate by an order of magnitude. The integration of the time scale of coalescence to the model shows that the transition between explosive and effusive eruptive regimes is sensitive Burgisser and Gardner January 04 2 to small variations of the initial magma ascent speed, and that flow conditions near fragmentation may significantly be affected by bubble coalescence and gas escape.

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“…Similarly, the conversion of pressure^volume expansion work into kinetic energy is dramatically apparent during the eruption of H 2 O-rich magma from shallow crustal magma bodies characteristic of explosive volcanism. Extreme supersaturation accompanying magma decompression leads to rapid vesiculation and, for volatile volume fraction (P) exceeding V0.5^0.7, magma fragmentation during ascent and explosive eruption (e.g., Burnard, 1999;Mangan and Sisson, 2000;Martel et al, 2000). Knowledge of the rheological properties of magmatic mixtures^across the range of qualities from a dilute emulsion to large-porosity foams^is essential to better constrain the behavior of magma during decompression, ascent, eruption, and emplacement on Earth and other planetary bodies (e.g., Kie¡er et al, 2000).…”

Section: Introductionmentioning

confidence: 99%

Shear viscosity of rhyolite-vapor emulsions at magmatic temperatures by concentric cylinder rheometry

Stein

Spera

2002

Journal of Volcanology and Geothermal Research

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The viscosity of natural rhyolitic melt from Lipari, Aeolian Islands and melt-bubble emulsions (30^50 vol% porosity) generated from Lipari rhyolite have been measured in a concentric cylinder rheometer at temperatures and shear rates in the range 925^1150 ‡C and 10 33^1 0 31:2 s 31 , respectively, in order to better understand the dependence of emulsion shear viscosity on temperature and shear rate in natural systems. Bubble-free melt exhibits NewtonianÂ rrhenian behavior in the temperature range 950^1150 ‡C with an activation energy of 395 þ 30 kJ/mol; the shear viscosity is given by log R m = 38.320+20624/T. Suspensions were prepared from natural rhyolite glass to which small amounts of Na 2 SO 4 were added as a 'foaming agent'. Reasonably homogeneous magmatic mixtures with an approximate log-normal distribution of bubbles were generated by this technique. Suspension viscosity varied from 10 6:1 to 10 8:37 Pa s and systematically correlates with temperature and porosity in the shear stress range (10 4:26^1 0 5:46 Pa) of the experiments. The viscosity of melt-bubble emulsions is described in terms of the relative viscosity, R r = R e / R m where R e is the emulsion viscosity and R m is the viscosity of melt of the same composition and temperature. The dependence of relative viscosity on porosity for magmatic emulsions depends on the magnitude of the capillary number CarG/(cr 31 b R 31 m ), the ratio of viscous forces acting to deform bubbles to interfacial forces resisting bubble deformation. For inviscid bubbles in magmatic flows three regimes may be identified. For Ca 6 0.1, bubbles are nearly spherical and relative viscosity is an increasing function of porosity. For dilute systems, R r = 1+P given by the classical result of Taylor [Proc. R. Soc. London A 138 (1932) 41^48]. For Ca in the range 0.1 6 Ca 6 10, emulsions behave as power law fluids and the relative viscosity depends on shear rate (or Ca) as well as porosity. At high Ca (Ca s 10) an asymptotic regime is reached in which relative viscosity decreases with increasing porosity and is independent of Ca. Our experiments were carried out for 30 6 Ca 6 925 in order to quantify the maximal effect of bubbles in reducing the viscosity of magmatic emulsions relative to single-phase melt at identical conditions of shear rate and temperature. The viscosity of a 50 vol% emulsion is a factor of five smaller than that of melt alone. Rheometric measurements obtained in this study are useful in constraining models of magma transport and volcanic eruption mechanics relevant to transport of volatile-saturated magma in the crust and upper mantle. ß 2002 Elsevier Science B.V. All rights reserved.Keywords: magmatic emulsion; magma rheology; melts and bubbles; relative viscosity 0377-0273 / 02 / $^see front matter ß 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 7 -0 2 7 3 ( 0 1 ) 0 0 2 6 0 -8

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Delayed, disequilibrium degassing in rhyolite magma: decompression experiments and implications for explosive volcanism

Cited by 275 publications

References 29 publications

Chapter 16 Pre-eruptive vapour and its role in controlling eruption style and longevity at Soufrière Hills Volcano

Chapter 16 Pre-eruptive vapour and its role in controlling eruption style and longevity at Soufrière Hills Volcano

Experimental constraints on degassing and permeability in volcanic conduit flow

Shear viscosity of rhyolite-vapor emulsions at magmatic temperatures by concentric cylinder rheometry

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