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Journal ArticleDOI

A model of degassing for Stromboli volcano

TL;DR: In this article, the authors used the MultiGAS technique to provide the best documented record of gas plume discharges from Stromboli volcano to date, and showed that Strombolian's gases are dominated by H2O (48−98−mol); mean, 80%), and by CO2 (2−50−mol%; mean, 17%) and SO2 (0.2−14−mol; mean, 3%).
About: This article is published in Earth and Planetary Science Letters.The article was published on 2010-06-15 and is currently open access. It has received 144 citations till now. The article focuses on the topics: Strombolian eruption & Volcanic Gases.

Summary (4 min read)

1. Introduction

  • This, combined with recent developments in H2O–CO2 micro-analysis in silicate materials and the refinement of thermodynamic saturation codes, now opens the way to more detailed inspection of degassing processes.
  • Here, the authors report on the first MultiGAS measurements including H2O of the volcanic gas plume of Stromboli, an active basaltic volcano in Southern Italy (Fig. 1).
  • This combined volcanic gas-melt inclusion-thermodynamic approach finally leads to thorough characterization of degassing processes at Stromboli volcano, with general implications for all basaltic volcanism.

2. Stromboli volcano

  • The persistent Strombolian activity, for which the volcano is famous, began after the 3rd–7th centuries AD, and since then has continued without significant breaks or variations (Rosi et al., 2000).
  • Explosive activity is associated with a continuous “passive” streaming of gas from the crater area and with active degassing (“puffing”) originating from discrete small gas bursts, every 1–2 s. During the lava effusion, a paroxysmal eruption also occurred (on 15 March), which erupted a significant amount of basaltic pumice (Landi et al., 2009).
  • During July–December 2008 (the period over which the volcanic gas measurements are reported here), the volcano showed its typical activity, with rhythmic Strombolian explosions of variable energy at an average frequency of 10–15 events/h (see open-file reports at www.ct.ingv.it).
  • On September 7, December 6 and 17, three slightly more energetic events occurred.

3. Technique

  • The volcanic gas measurements reported here were carried out from July to December 2008, using the permanent MultiGAS installed on the summit of Stromboli by Istituto Nazionale di Geofisica and Vulcanologia (Sezione di Palermo).
  • Signals from both sensors were captured every 9 s from a data-logger board, which also enabled data logging and storage.
  • Because the instrument is located ∼150 m S–SE of the crater terrace (Fig. 1), plume gas sensing was only possible when moderate to strong winds from the northern quadrants blew on the island.
  • In contrast when the plume was gently lofting, rising vertically, or being dispersed north, the MultiGAS consistently detected the typical H2O (13,000– 18,000 ppm), CO2 (∼380 ppm), and SO2 (b0.1 ppm) concentrations in background air, and the cycle was considered null (e.g., no ratio was calculated from the data).

4.1. Raw data and calculation of volcanic gas composition

  • Fig. 2 shows an example of 1-cycle acquisition from the permanent MultiGAS at Stromboli.
  • From the raw plume concentration data (in ppm), the volcanic gas plume H2O/SO2 and H2O/CO2 ratios were derived by calculating the gradients of the best-fit regression lines in H2O vs. SO2 and H2O vs. CO2 scatter plots (Fig. 3), as previously reported for Etna (Shinohara et al., 2008).
  • This assumes that contributions from undetected species (e.g., H2, H2S, HCl) are relatively minor.
  • Visual observations and cross correlations of their dataset with seismic and thermal signals (available at http://www.ct.ingv.it) indicated that such short-term variations (generally lasting less than 2 min) systematically occurred soon after individual Strombolian bursts.
  • When the wind was particularly strong and explosive activity high, this syn-explosive gas phase, known to be compositionally distinct from the quiescent plume (Burton et al., 2007b), eventually reached the instrument (a few seconds after the explosion) before being diluted (and homogenised) within the bulk plume.

4.2. The H2O–CO2–SO2 composition of Stromboli's plume

  • As such, they resemble quite closely the typical composition of volcanic gases from arc-settings, though sharing with nearby Etna (Shinohara et al., 2008) a characteristic of CO2-enrichment (most volcanic gases from arc basaltic volcanoes have N90% H2O; Shinohara, 2008).
  • The most striking feature of the dataset is the large spread of plume compositions observed in only 6 months of observations.

5. Discussion

  • The striking range of volcanic gas compositions at Stromboli suggest dynamic magma degassing processes at this open-vent volcano.
  • This deep source area also supported the idea of a separate ascent of gas and melt in the shallow (less than 2.7 km) plumbing system, as also proposed for other basaltic systems (Edmonds and Gerlach, 2007).
  • The authors measurements here extend further the conclusions of Burton et al. (2007b): the temporal variability of the composition of the bulk plume requires the existence of a complex degassing regime in which a separate gas ascent plays a key role (Pichavant et al., 2009).
  • Visual observations suggest that the bulk Stromboli's plume is essentially contributed by both quiescent gas release from the magma ponding at the crater terrace' open vents, and by small bursts of over-pressurised gas pockets at the magma-free atmosphere (Harris and Ripepe, 2007).
  • Finally, comparison between modelled and observed volcanic gas compositions (Section 5.3) offers new clues on volcanic degassing processes, and on the structure of the magmatic plumbing system of Stromboli.

5.1. Melt inclusion record of magma ascent and degassing

  • There is consensus (Bertagnini et al., 2008) that two magma types are involved in the present-day Stromboli's activity.
  • The persistent behaviour of the volcano implies that a supply of deeply derived magmas must occur not only prior to/during a paroxysm, but also during the normal Strombolian activity (yet at a slower rate).
  • This has three main implications and consequences: (i) first, de-hydration of a magma can be caused by fluxing with deep-rising CO2-rich gas (Spilliaert et al., 2006), a fact which is suggestive of the presence of a magma ponding zone at 2–4 km bsv, where CO2-rich gas bubbles accumulate to contents N5 wt. % (Métrich et al., 2010).
  • The contrasting compositions, volatile contents, and depth of storage of LP and HP magmas (Table 2) imply that the magmatic gas phases in equilibrium with (and separated from) these two magma types are inevitably different, as calculated below.

5.2. Numerical modelling

  • Volatile contents in MIs (Table 2) are used here to initialize model calculations of volatile partitioning between the magmatic gas phase and the melt, which the authors performed using the code described in Moretti and Papale (2004).
  • The authors utilised the code to perform two sets of complementary calculations.
  • LP runs were initialised with the input parameters summarised in Table 2.
  • Themodel results are critically dependent on the choice of the total (exsolved+dissolved) magma CO2 content: four sets of LP runs were thus carried out at different CO2 contents (0.2, 2, 5 or 20%, respectively), to account for the presence of a non-negligible (but poorly constrained) fraction of CO2-rich gas bubbles at reservoir conditions.
  • The highest entrapment pressure (∼100 MPa) derived from volatile contents in MIs (Table 2) was taken as the starting pressure of their simulations, followed by step-wise pressure decrease in first closed-system to then opensystem conditions.

5.2.1. Model results, and comparison with natural data

  • The outputs of model calculations are, for each run and at each pressure, the equilibrium volatile compositions of coexisting melt and vapour phases.
  • The authors model results are qualitatively similar to the pressure-related model degassing trends presented by Allard (2010) (see his Fig. 3), which were yet based on the use of different saturation model and assumptions.
  • As such, the volatile compositions of glass embayments may reflect gas-melt interactions within the CO2-rich intermediate (2–4 km deep) magma ponding zone (cfr. 5.1).
  • Modelled dissolved sulphur contents (Fig. 7b) are also consistent with MI record, and again support a mechanism of progressive increase of the CO2TOT/H2OTOT ratio from trends 1 to 4.
  • The authors note however that some of the richest CO2 volcanic gas data are consistent with model gas compositions calculated at P=100–120 MPa in the LP model run 1 (CO2TOT=0.2 wt.%; Fig. 8).

5.3. A model of degassing for Stromboli volcano

  • The authors model calculations above provide a quantitative background for interpreting the source processes controlling the time-changing composition of Stromboli's volcanic gases.
  • In the most extreme conditions, the CO2-rich gas bubbles may be thought to be sourced by the deep (7–11 km deep) LP magma storage zone; though partial gas-melt reequilibration at shallower depths (and particularly upon gas bubble accumulation within — before leakage from — the intermediate 2– 4 km deep magma ponding zone) cannot be ruled out.
  • Secondly, there is supporting evidence at Stromboli for that continuous magma convection takes place within the shallow (b1 km) dyke system (Harris and Stevenson, 1997).
  • The shallow convective overturning of the HPmagma obviously gives rise to a second source of volatiles: degassing of dissolved volatiles in the ascending HP magma will produce gas bubbles which pressure-dependent compositional evolution is best described by curves 5 and 6 in Fig.

6. Conclusions

  • The MultiGAS volcanic gas observations presented here show that, in spite of the relatively uniform activity and petrology of erupted solid materials, Stromboli shares with other basaltic volcanoes an exceptional variability in gas compositions.
  • The mechanisms controlling such time-changing nature of Stromboli's gas emissions have been explored by combining gas measurements with the MI record of volatile abundance in magmas, and by contrasting natural compositions with model results derived with an equilibrium saturation code.
  • From this, the authors propose that the compositional features of Stromboli's quiescent and syn-explosive gas emissions result from themixing of gases persistently sourced by (i) degassing of dissolved volatiles in the porphyric magma filling the upper (b1 km) dyke-conduit system; and (ii) CO2-rich gas bubbles, originated at depth (at depths N4 km, or PN100 MPa) in the plumbing system.
  • The proposed mixing mechanism is constrained by independent petrologic and model data, and it is geologically straightforward since it only requires a persistent but time-modulated source of deep gas bubbles; this however does not exclude that additional control mechanisms on volcanic gas composition might be at work.
  • The authors conclude however that, since magma fluxing by a free CO2-rich vapour phase is a recurrent process, the proposed degassing mechanism is probably a key to interpret volcanic gas observations at many basaltic volcanoes.

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01 Jan 2007
TL;DR: In this article, the authors propose that access to coordination numbers greater than 2 promotes protolytic cleavage of the Hg-C bond and the liberation of RH at elevated temperatures.
Abstract: t )HgMe} + and {(Hmim Bu t )HgEt} + are stable under comparable conditions; pro- tolytic cleavage and liberation of RH are none- theless observed at elevated temperatures (Scheme 3) (40). The lower reactivity of {(Hmim Bu t )HgR} + relative to (Tm Bu t )HgR sup- ports the proposal that access to coordination numbers greater than 2 promotes protolytic cleav- age of the Hg-C bond (41). In support of this suggestion, addition of Hmim Bu t to a mixture of {(Hmim Bu t )HgEt}(BF4) and PhSH causes elimina- tion of ethane at room temperature, an observation consistent with the formation of a higher-coordinate species {(Hmim Bu t )nHgEt} + that is more suscep- tible to Hg-C protolytic cleavage than is two- coordinate {(Hmim Bu t )HgEt} + (42). In view of the low reactivity of two- coordinate {(Hmim Bu t )HgR} + toward PhSH, we attribute the high reactivity of (Tm Bu t )HgMe and

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Journal ArticleDOI
TL;DR: In this paper, the authors combine textural and chemical data acquired on large euhedral augite megacrysts from Roman era activity (Pizzo scoria cone, 2.4-1.8 ka) at Stromboli (Italy) to investigate the plumbing system prior to the onset of current steady-state activity.
Abstract: The magmatic architecture and physicochemical processes inside volcanoes influence the style and timescale of eruptions. A long-standing challenge in volcanology is to establish the rates and depths of magma storage and the events that trigger eruption. Magma feeder systems are remarkably crystal-rich, and the growth stratigraphy of minerals sampled by erupted magmas can reveal a wealth of information on pre-eruptive processes. Here we combine detailed textural and chemical data acquired on large (>5 mm), euhedral augite megacrysts from Roman era activity (Pizzo scoria cone, 2.4-1.8 ka) at Stromboli (Italy) to investigate the plumbing system prior to the onset of current steady-state activity. Our dataset includes novel laser ablation time-of-flight mass spectrometry (LA-ICP-TOFMS) maps, which rapidly visualise multi-element zoning patterns across entire megacryst sections. The clinopyroxene data are complemented with geochemical constraints on mineral and melt inclusions, and adhering glassy tephra. Megacrysts are sector and oscillatory zoned in trace elements, yet their major element compositions are relatively uniform and in equilibrium with shoshonite-buffered melts. Mild sector zoning documents dynamic crystallisation under conditions of low undercooling during magma residence and growth. Clinopyroxene-melt thermobarometric and hygrometric calibrations, integrated with thermodynamically derived equilibrium equations, accurately track the P-T-H2O path of magmas. The refined models return restricted crystallisation depths that are deeper than those reported previously for historical and current eruptions, but consistent with deep clinopyroxene-dominated crystallisation (≥10 km), resembling other water-rich alkaline mafic systems. Megacryst cores are overgrown by oscillatory zoned mantles recording continuous input of magma that failed to trigger eruption. Crystal rims are characterised by a mild increase in compatible transition metals Cr and Ni, and depletion in incompatible elements, indicative of pre-eruptive mafic replenishment and magma mixing. The volcanic system appears to have been dominated by protracted periods of replenishment, convection and crystal residence, punctuated by rapid megacryst evacuation and eruption upon arrival of more mafic magma (days-weeks). Since the inception of current steady-state activity, eruption-triggering melts have become appreciably more mafic, suggesting that intrusion of primitive magma may be a key driver of the steady-state regime.

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TL;DR: In this paper, a relazione tra le deformazioni del vulcano, le sovrapressioni del magma and l’instabilita dei fianchi de Stromboli stesso, during a periodo of acquisizione compreso tra 2009 and 2011, is presented.
Abstract: Deformazioni e instabilita di versante sul vulcano di Stromboli: integrazione tra i dati del GBInSAR e la modellazione analogica.Per capire la relazione tra le deformazioni del vulcano, le sovrapressioni del magma e l’instabilita dei fianchi del vulcano stesso, sono stati analizzati e comparati i risultati ottenuti con la modellizzazione analogica sperimentale ed i dati registrati dal sistema GBInSAR, posto sul fianco occidentale del vulcano di Stromboli, durante un periodo di acquisizione compreso tra il 2009 e il 2011. I modelli analogici riproducono quelli che sono i meccanismi d’innesco dei movimenti franosi sui fianchi del vulcano, come l’accumulo di materiale sul versante, in ambiente sia subaereo che subacqueo, o la presenza di dicchi intrusivi che determinano il fenomeno del bulging. L’analisi comparata derivata dai modelli analogici e dai dati di monitoraggio svela quelle che sono le relazioni tra le sovrapressioni nei condotti magmatici e le deformazioni registrate. I risultati fanno pensare che i movimenti superficiali osservati dal sistema GBInSAR rappresentino la risposta del vulcano di Stromboli ai cambiamenti di pressione nel condotto magmatico. I movimenti franosi osservati sulla Sciara del Fuoco sono fenomeni d’instabilita dove la componente gravitazionale produce un movimento costante sul versante, mentre i cambiamenti di pressione nel magma spiegano perche, certi particolari periodi siano caratterizzati da accelerazioni che inducono l’instabilita del fianco esterno dell’area craterica e della Sciara del Fuoco, portando infine anche allo sviluppo di movimenti franosi.

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Cites background from "A model of degassing for Stromboli ..."

  • ...This period was chosen because a large set of geochemical (Aiuppa et al., 2010), geophysical (Coppola et al....

    [...]

  • ...The increase in the CO2 soil-flux is a proxy for the closed to open-system degassing transition that occurs at certain depths (Burton et al., 2007b; Aiuppa et al., 2010)....

    [...]

  • ...Paroxysmal explosions are generally anticipated by major changes in volcanic activity (Casagli et al., 2009; Aiuppa et al., 2010; Inguaggiato et al., 2011), and hence their occurrence can theoretically be forecasted....

    [...]

  • ..., 2008) and the occurrence of major explosions (Aiuppa et al., 2010; Di Traglia et al., 2012), which is defined here for simplicity as “major explosion-dominated periods”....

    [...]

  • ...batch and superficial degassing (Burton et al., 2007a; Aiuppa et al., 2010)....

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Journal ArticleDOI
TL;DR: In this paper, the state of knowledge on global volcanogenic Hg emissions to the atmosphere is reviewed and new data from seven active volcanoes (Poás, Rincón de la Vieja, Turrialba, Aso, Mutnovsky, Gorely and Etna) and two geothermal fields (Las Pailas and Las Hornillas).
Abstract: Abstract We review the state of knowledge on global volcanogenic Hg emissions to the atmosphere and present new data from seven active volcanoes (Poás, Rincón de la Vieja, Turrialba, Aso, Mutnovsky, Gorely and Etna) and two geothermal fields (Las Pailas and Las Hornillas). The variability of Hg contents (c. 4–125 ng m−3) measured in gaseous emissions reflects the dynamic nature of volcanic plumes, where the abundances of volatiles are determined by the physical nature of degassing and variable air dilution. Based on our dataset and previous work, we propose that an average Hg/SO2 plume mass ratio of c. 7.8×10−6 (±1.5×10−6; 1 SE, n=13) is best representative of open-conduit quiescent degassing. Taking into account the uncertainty in global SO2 emissions, we infer a global volcanic Hg flux from persistent degassing of c. 76±30 t a−1. Our data are derived from active volcanoes during non-eruptive periods and we do not have any direct constraint on the Hg flux during periods of elevated SO2 flux associated with large-scale effusive or explosive eruptions. This suggests that the time-averaged Hg flux from these volcanoes is even larger if the eruptive contribution is considered. Conversely, closed-conduit degassing and geothermal emissions contribute modest amounts of Hg.

53 citations


Cites methods from "A model of degassing for Stromboli ..."

  • ...Major volcanogenic species (H2O, CO2 and SO2) in volcanic plumes and fumaroles in tandem with Hg quantities have been measured at some locations (where logistics and weather conditions allowed) by using the MultiGAS analyser, a portable instrument previously described in Aiuppa et al. (2010, 2011)....

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References
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Journal ArticleDOI
TL;DR: Papale et al. as mentioned in this paper applied thermodynamic equilibrium between gaseous and liquid volatile components to model the volatile saturation surface in H 2 O−CO 2 -silicate melt systems.

491 citations


"A model of degassing for Stromboli ..." refers background or methods in this paper

  • ...b A note of caution should be spent on the application of the H2O–CO2 model (Papale et al., 2006) on shoshonitic composition....

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  • ...Standard deviations of model binary interaction terms showmaximum values for iron oxides, because they encompass all uncertainties on fO2 conditions within the calibration dataset (Papale et al., 2006)....

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Journal ArticleDOI
TL;DR: The abundances of CO2, H2O, S and halogens dissolved in basaltic magmas are strongly variable because their solubilities and ability to be fractionated in the vapor phase depend on several parameters such as pressure, temperature, melt composition and redox state as mentioned in this paper.
Abstract: The abundances of CO2, H2O, S and halogens dissolved in basaltic magmas are strongly variable because their solubilities and ability to be fractionated in the vapor phase depend on several parameters such as pressure, temperature, melt composition and redox state. Experimental and analytical studies show that CO2 is much less soluble in silicate melts compared to H2O (e.g., Javoy and Pineau 1991; Dixon et al. 1995). As much as 90% of the initial CO2 dissolved in basaltic melts may be already degassed at crustal depths, whereas H2O remains dissolved because of its higher solubility such that H2O contents of basaltic magmas at crustal depths may reach a few percents. Most subduction-related basaltic magmas are rich in H2O (up to 6–8 wt%; Sisson and Grove 1993; Roggensack et al. 1997; Newman et al. 2000; Pichavant et al. 2002; Grove et al. 2005) compared to mid-ocean ridge basalts (<1 wt%; Sobolev and Chaussidon 1996; Fischer and Marty 2005; Wallace 2005). During magma movement towards the surface, exsolution of major volatile constituents (CO2, H2O) causes gas bubble nucleation, growth, and possible coalescence that exert a strong control on the dynamics of magma ascent and eruption (Anderson 1975; Sparks 1978; Tait et al. 1989). Gas bubbles have the ability to move faster than magma (Sparks 1978), particularly in low viscosity basaltic magmas. Bubble accumulation, coalescence and foam collapse give rise to differential transfer of gas slugs and periodic gas bursting (Strombolian activity; Jaupart and Vergniolle 1988, 1989) or periodic lava fountains (Vergniolle and Jaupart 1990; Philips and Wood 2001) depending on magma physical properties and ascent rate. It is also thought that strombolian and lava …

340 citations


"A model of degassing for Stromboli ..." refers background in this paper

  • ...These limitations have long precluded the acquisition of robust and systematic volcanic gas datasets at openvent volcanoes, thus making degassing processes easier to probe by studying volatile contents in silicate melt inclusions (MIs) (Blundy and Cashman, 2008; Métrich and Wallace, 2008)....

    [...]

Journal ArticleDOI
TL;DR: In this article, the authors decipher the origin and mechanisms of the second eruption from the composition and volatile (H2O, CO2, S, Cl) content of olivine-hosted melt inclusions in explosive products from its south flank vents.
Abstract: [1] Two unusual, highly explosive flank eruptions succeeded on Mount Etna in July August 2001 and in October 2002 to January 2003, raising the possibility of changing magmatic conditions. Here we decipher the origin and mechanisms of the second eruption from the composition and volatile (H2O, CO2, S, Cl) content of olivine-hosted melt inclusions in explosive products from its south flank vents. Our results demonstrate that powerful lava fountains and ash columns at the eruption onset were sustained by closed system ascent of a batch of primitive, volatile-rich (≥4 wt %) basaltic magma that rose from ≥10 km depth below sea level (bsl) and suddenly extruded through 2001 fractures maintained opened by eastward flank spreading. This magma, the most primitive for 240 years, probably represents the alkali-rich parental end-member responsible for Etna lavas' evolution since the early 1970s. Few of it was directly extruded at the eruption onset, but its input likely pressurized the shallow plumbing system several weeks before the eruption. This latter was subsequently fed by the extrusion and degassing of larger amounts of the same, but slightly more evolved, magma that were ponding at 6–4 km bsl, in agreement with seismic data and with the lack of preeruptive SO2 accumulation above the initial depth of sulphur exsolution (∼3 km bsl). We find that while ponding, this magma was flushed and dehydrated by a CO2-rich gas phase of deeper derivation, a process that may commonly affect the plumbing system of Etna and other alkali basaltic volcanoes.

310 citations


"A model of degassing for Stromboli ..." refers background in this paper

  • ...This has three main implications and consequences: (i) first, de-hydration of a magma can be caused by fluxing with deep-rising CO2-rich gas (Spilliaert et al., 2006), a fact which is suggestive of the presence of a magma ponding zone at 2–4 km bsv, where CO2-rich gas bubbles accumulate to contents…...

    [...]

  • ...(i) first, de-hydration of a magma can be caused by fluxing with deep-rising CO2-rich gas (Spilliaert et al., 2006), a fact which is suggestive of the presence of a magma ponding zone at 2–4 km bsv, where CO2-rich gas bubbles accumulate to contents N5 wt....

    [...]

Journal ArticleDOI
TL;DR: In this article, the authors present some of the current petrological techniques that can be used for studying eruptive products and for constraining key magmatic variables such as pressure, temperature, and volatile content.
Abstract: Explosive volcanic eruptions constitute a major class of natural hazard with potentially profound economic and societal consequences. Although such eruptions cannot be prevented and only rarely may be anticipated with any degree of accuracy, better understanding of how explosive volcanoes work will lead to improved volcano monitoring and disaster mitigation. A major goal of modern volcanology is linking of surface-monitored signals from active volcanoes, such as seismicity, ground deformation and gas chemistry, to the subterranean processes that generate them. Because sub-volcanic systems cannot be accessed directly, most of what we know about these systems comes from studies of erupted products. Such studies shed light on what happens underground prior to and during eruptions, thereby providing an interpretative framework for post hoc evaluation of monitoring data. The aim of this review is to present some of the current petrological techniques that can be used for studying eruptive products and for constraining key magmatic variables such as pressure, temperature, and volatile content. We first review analytical techniques, paying particular attention to pitfalls and strategies for analyzing volcanic samples. We then examine commonly used geothermometry schemes, evaluating each by comparison with experimental data not used in the original geothermometer calibrations. As there are few mineral-based geobarometers applicable to magma storage regions, we review other methods used to determine pre-eruptive magma equilibration pressures. We then demonstrate how petrologically-constrained parameters can be compared to the contemporaneous monitoring record. These examples are drawn largely from Mount St. Helens volcano, for which there are abundant petrological and monitoring data. However, we emphasize that our approaches can be applied to any number of active volcanoes worldwide. Finally, we illustrate the application of these techniques to two different types of magmatic systems—large silicic magma chambers and small intermediate-composition magma storage regions—with particular focus on the combined evolution of melt …

301 citations


"A model of degassing for Stromboli ..." refers background in this paper

  • ...These limitations have long precluded the acquisition of robust and systematic volcanic gas datasets at openvent volcanoes, thus making degassing processes easier to probe by studying volatile contents in silicate melt inclusions (MIs) (Blundy and Cashman, 2008; Métrich and Wallace, 2008)....

    [...]

Journal ArticleDOI
13 Jul 2007-Science
TL;DR: Spectroscopic measurements performed during both quiescent degassing and explosions on Stromboli volcano are used to demonstrate that gas slugs originate from as deep as the volcano-crust interface (∼3 kilometers), where both structural discontinuities and differential bubble-rise speed can promote slug coalescence.
Abstract: Strombolian-type eruptive activity, common at many volcanoes, consists of regular explosions driven by the bursting of gas slugs that rise faster than surrounding magma. Explosion quakes associated with this activity are usually localized at shallow depth; however, where and how slugs actually form remain poorly constrained. We used spectroscopic measurements performed during both quiescent degassing and explosions on Stromboli volcano (Italy) to demonstrate that gas slugs originate from as deep as the volcano-crust interface (∼3 kilometers), where both structural discontinuities and differential bubble-rise speed can promote slug coalescence. The observed decoupling between deep slug genesis and shallow (∼250-meter) explosion quakes may be a common feature of strombolian activity, determined by the geometry of plumbing systems.

294 citations


"A model of degassing for Stromboli ..." refers background or result in this paper

  • ...Our measurements here extend further the conclusions of Burton et al. (2007b): the temporal variability of the composition of the bulk (quiescent) plume requires the existence of a complex degassing regime in which a separate gas ascent plays a key role (Pichavant et al., 2009)....

    [...]

  • ...To start with, MI determinations (cfr. 5.1) and gas measurements (Burton et al., 2007a,b, and this study) offer ample evidence for that the shallow Stromboli's plumbing system is fluxed by the ascent of CO2-rich gas bubbles....

    [...]

  • ...Transition from closed- to open-system conditions was fixed at 50 MPa (or ∼2 km bsv), the pressure at which vesicularity of the HP magma is thought to become high enough for gas percolation through a network of inter-connected bubbles to occur (Burton et al., 2007a)....

    [...]

  • ...Our data support further the earlier conclusions of Burton et al. (2007b), demonstrating that the synexplosive gas phase is significantly richer in CO2 (and poorer in H2O and SO2) than the bulk plume (Fig....

    [...]

  • ...%) fraction of CO2-rich gas bubbles at reservoir conditions (Burton et al., 2007a,b)....

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