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Peter J Wyllie - One of the best experts on this subject based on the ideXlab platform.
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Presentation of the Roebling Medal of the Mineralogical Society of America for 2002 to Werner Schreyer
American Mineralogist, 2003Co-Authors: Peter J WyllieAbstract:Mr. President, distinguished mineralogists, and guests, I was delighted when Werner Schreyer asked me to be his citationist, because I admire him for his scholarship, for his dogged pursuit of the perfect experiment seeking exquisite minerals, and for his application of Experimental mineralogy to petrological problems. Werner and I have had parallel lives in Experimental Petrology, following paths that have converged from time to time, and with each convergence has come growing respect and friendship. But as a schoolboy in the 1940s, I hated Werner Schreyer, and I’m sure that he hated me. We were receiving bombs from our respective air forces in Germany and England, and wartime propaganda is a powerful opinion-shaper. One of the exercises in my school’s Air Training Corps was aircraft recognition, identifying the silhouettes of German aircraft, and Werner probably was expert in the same exercise as a member of the “Hitlerjugend”.
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Experimental Petrology of upper mantle materials, processes and products
Journal of Geodynamics, 1995Co-Authors: Peter J WyllieAbstract:Experiments on rock materials and volatile components provide an array of phase equilibrium boundaries, giving the depth-temperature framework for the phase transitions experienced by rock masses as they move up or down within the Earth in response to the dynamic processes of mantle convection and plate tectonics. Sub-solidus phase transitions in mantle materials correlate well with upper mantle structure determined from seismic studies, but debate continues about whether there is a change in composition at some seismic boundaries. The interface at 650 km correlates with the transformation of most minerals into the perovskite structure, which may have significant effects on mantle dynamics. Recent research on mantle xenoliths has been concerned with extension of standard thermometers and barometers to higher pressures and their practical assessment, along with the development and refinement of new geothermobarometers. The Experimental partial melting of mantle peridotite has been elucidated by detailed studies of model systems and new Experimental techniques. Parameterization of the data makes prediction possible. The origin of MORBs involves a complex process of fractional fusion. Evidence from static olivine flotation experiments and shock wave compression experiments on molten komatiite indicates that the densities of mantle melts may exceed that of the residual rock at depths greater than 400 km, which would prohibit ascent of the magma. Recent investigations have identified many dense hydrous magnesian silicates (DHMS), stable through the upper mantle between ~ 300 and 650 km, and reaching the peridotite-volatile solidus curve through part of this interval. The near-solidus liquid composition in peridotite-CO_2-H_2O above ~ 2 GPa is carbonatitic (calcic dolomite), potentially a powerful agent for metasomatism. Experimental studies of trace element distributions between mantle minerals and carbonatitic liquids are beginning to permit quantification. Determination of the effect of reduced oxygen fugacity has introduced mantle scenarios with melting induced by redox changes There is indirect Experimental evidence that the solidus may terminate at a critical end-point at depths of a few hundred kilometers. Recent experiments related to subduction of oceanic crust include measurements of liquid composition from the melting of H_2O-undersaturated peridotite, the vapour-absent melting of amphibolite, and partial melting of pelagic clays. Much H_2O is expelled during subduction, but the current estimates of low temperatures support the deep subduction and longterm storage in the mantles of both H_2O and CO_2.
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Experimental Petrology: Earth Materials Science
1992Co-Authors: Peter J WyllieAbstract:Petrology is the science of rocks. Geologists map rocks in the field, and bring selected .samples back to the laboratory for detailed petrographic analysis, mineralogical study and chemical analysis. On the basis of these studies, existing hypotheses for the origin of the rocks are tested, or new hypotheses are erected. From examination of the rocks in field and laboratory, geologists then attempt to deduce their histories. Experimental Petrology involves further laboratory experiments which reproduce the conditions within the Earth during the generation and evolution of a rock or rock suite. This involves subjecting minerals and rocks, or their synthetic equivalents, to high pressures and temperatures under varied but precisely controlled conditions. Determination of the reactions which occur under the known conditions in the laboratory provides calibrations for the processes involved in formation of the rocks in nature, defining the actual conditions, and facilitating selection among competing hypotheses of origin. Furthermore, exploration of reactions under various conditions within the laboratory may reveal processes operating within the Earth which were previously unsuspected Experimental Petrology had its beginnings in adventurous experiments on minerals and rocks using furnaces or cannon barrels. It became a force in Earth sciences starting in the early 1900s with the systematic determination of high-temperature phase equilibria involving the crystallisation of synthetic silicate liquids, which included representatives of the common rock-forming minerals. These investigations brought the rigour of thermodynamics to the processes of partial melting of rocks and the crystallisation of magmas, and elucidated many problems in igneous Petrology. Only in the 1950s did phase equilibrium experiments with simultaneously maintained high temperatures and pressures become routine. At first the experiments reproduced conditions only within the continental crust, then during the 1960s the Experimental range was extended to high-pressure conditions within the mantle, equivalent to about 100 km depth. During the 1980s one type of large-volume apparatus reproduced conditions down to 650 km in the Earth, and a miniature device has reproduced conditions corresponding to 2000 km depth, not far short of the mantle-core boundary of the Earth. The equipment mentioned above is static, with samples being held at constant pressure and temperature as reactions occur in the samples. A dynamic Experimental approach reproduces conditions to the centre of the Earth; a sample is shattered by the passage of a shock wave, and its properties under extremely high pressures are measured during the last nanoseconds before its destruction.
Christina Widiwijayanti - One of the best experts on this subject based on the ideXlab platform.
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unprecedented pressure increase in deep magma reservoir triggered by lava dome collapse
Geophysical Research Letters, 2006Co-Authors: Barry Voight, R. S. J. Sparks, Alan T Linde, I S Sacks, G S Mattioli, Derek Elsworth, Dannie Hidayat, Peter E Malin, Eylon Shalev, Christina WidiwijayantiAbstract:[1] The collapse of the Soufriere Hills Volcano lava dome on Montserrat in July 2003 is the largest such event worldwide in the historical record. Here we report on borehole dilatometer data recording a remarkable and unprecedented rapid (∼600s) pressurisation of a magma chamber, triggered by this surface collapse. The chamber expansion is indicated by an expansive offset at the near dilatometer sites coupled with contraction at the far site. By analyzing the strain data and using added constraints from Experimental Petrology and long-term edifice deformation from GPS geodesy, we prefer a source centered at approximately 6 km depth below the crater for an oblate spheroid with overpressure increase of order 1 MPa and average radius ∼1 km. Pressurisation is attributed to growth of 1–3% of gas bubbles in supersaturated magma, triggered by the dynamics of surface unloading. Recent simulations demonstrate that pressure recovery from bubble growth can exceed initial pressure drop by nearly an order of magnitude.
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Unprecedented pressure increase in deep magma reservoir triggered by lava‐dome collapse
Geophysical Research Letters, 2006Co-Authors: Barry Voight, R. S. J. Sparks, Alan T Linde, I S Sacks, G S Mattioli, Derek Elsworth, Dannie Hidayat, Eylon Shalev, Peter Malin, Christina WidiwijayantiAbstract:[1] The collapse of the Soufriere Hills Volcano lava dome on Montserrat in July 2003 is the largest such event worldwide in the historical record. Here we report on borehole dilatometer data recording a remarkable and unprecedented rapid (∼600s) pressurisation of a magma chamber, triggered by this surface collapse. The chamber expansion is indicated by an expansive offset at the near dilatometer sites coupled with contraction at the far site. By analyzing the strain data and using added constraints from Experimental Petrology and long-term edifice deformation from GPS geodesy, we prefer a source centered at approximately 6 km depth below the crater for an oblate spheroid with overpressure increase of order 1 MPa and average radius ∼1 km. Pressurisation is attributed to growth of 1–3% of gas bubbles in supersaturated magma, triggered by the dynamics of surface unloading. Recent simulations demonstrate that pressure recovery from bubble growth can exceed initial pressure drop by nearly an order of magnitude.
Michel Pichavant - One of the best experts on this subject based on the ideXlab platform.
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Experimental Constraints on the Formation of Silicic Magmas
Elements, 2016Co-Authors: Bruno Scaillet, Francois Holtz, Michel PichavantAbstract:A rich history of Experimental Petrology has revealed the paths by which silicic igneous rocks follow mineral–melt equilibria during differentiation. Subdividing these rocks by ‘molar Al versus Ca + Na + K’ illustrates first-order differences in mineralogy and gives insight into formation mechanisms. Peraluminous magmas, formed by partial melting of sediments, largely owe their attributes and compositions to melting reactions in the protoliths, whereas most metaluminous felsic magmas record both continental and mantle inputs. Peralkaline rhyolites are mainly derived from either protracted crystallization or small degrees of partial melting of basalt, with only a marginal crustal contribution. Most silicic magmas hold 3–7 wt% H2Omelt, which is inversely correlated with pre-eruptive temperature (700 °C to >950 °C) but unrelated to their reduced/oxidized state.
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Limestone assimilation and the origin of CO2 emissions at the Alban Hills (Central Italy): Constraints from Experimental Petrology
Journal of Volcanology and Geothermal Research, 2007Co-Authors: Giada Iacono Marziano, Fabrice Gaillard, Michel PichavantAbstract:Abstract The Alban Hills volcanic region (20 km south of Rome, in the Roman Province) emitted a large volume of potassic magmas (> 280 km 3 ) during the Quaternary. Chemical interactions between ascending magmas and the ∼ 7000–8000-m-thick sedimentary carbonate basement are documented by abundant high temperature skarn xenoliths in the eruptive products and have been frequently corroborated by geochemical surveys. In this paper we characterize the effect of carbonate assimilation on phase relationships at 200 MPa and 1150–1050 °C by Experimental Petrology. Calcite and dolomite addition promotes the crystallization of Ca-rich pyroxene and Mg-rich olivine respectively, and addition of both carbonates results in the desilication of the melt. Furthermore, carbonate assimilation liberates a large quantity of CO 2 -rich fluid. A comparison of Experimental versus natural mineral, glass and bulk rock compositions suggests large variations in the degree of carbonate assimilation for the different Alban Hills eruptions. A maximum of 15 wt.% assimilation is suggested by some melt inclusion and clinopyroxene compositions; however, most of the natural data indicate assimilation of between 3 and 12 wt.% carbonate. Current high CO 2 emissions in this area most likely indicate that such an assimilation process still occurs at depth. We calculate that a magma intruding into the carbonate basement with a rate of ∼ 1 – 2 · 10 6 m 3 /year, estimated by geophysical studies, and assimilating 3–12 wt.% of host rocks would release an amount of CO 2 matching the current yearly emissions at the Alban Hills. Our results strongly suggest that current CO 2 emissions in this region are the shallow manifestation of hot mafic magma intrusion in the carbonate-hosted reservoir at 5–6 km depth, with important consequences for the present-day volcanic hazard evaluation in this densely populated and historical area.
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Limestone assimilation and the origin of CO2 emissions at the Alban Hills (Central Italy): constraints from Experimental Petrology.
Journal of Volcanology and Geothermal Research, 2007Co-Authors: Giada Iacono-marziano, Fabrice Gaillard, Michel PichavantAbstract:The Alban Hills volcanic region (20 km south of Rome, in the Roman Province) emitted a large volume of potassic magmas (> 280 km3) during the Quaternary. Chemical interactions between ascending magmas and the ~7000-8000-m-thick sedimentary carbonate basement are documented by abundant high temperature skarn xenoliths in the eruptive products and have been frequently corroborated by geochemical surveys. In this paper we characterize the effect of carbonate assimilation on phase relationships at 200 MPa and 1150-1050°C by Experimental Petrology. Calcite and dolomite addition promotes the crystallization of Ca-rich pyroxene and Mg-rich olivine respectively, and addition of both carbonates results in the desilication of the melt. Furthermore, carbonate assimilation liberates a large quantity of CO2-rich fluid. A comparison of Experimental versus natural mineral, glass and bulk rock compositions suggests large variations in the degree of carbonate assimilation for the different Alban Hills eruptions. A maximum of 15 wt% assimilation is suggested by some melt inclusion and clinopyroxene compositions; however, most of the natural data indicate assimilation of between 3 and 12 wt% carbonate. Current high CO2 emissions in this area most likely indicate that such an assimilation process still occurs at depth. We calculate that a magma intruding into the carbonate basement with a rate of ~1-2•106 m3/year, estimated by geophysical studies, and assimilating 3-12wt% of host rocks would release an amount of CO2 matching the current yearly emissions at the Alban Hills. Our results strongly suggest that present CO2 emissions in this region are the shallow manifestation of hot mafic magma intrusion in the carbonate-hosted reservoir at 5-6 km depth, with important consequences for the present-day volcanic hazard evaluation in this densely populated and historical area.
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The viscosity of silicic magmas: a review from the viewpoint of Experimental Petrology.
1999Co-Authors: Bruno Scaillet, Alan Whittington, Michel PichavantAbstract:From the rheological standpoint any magma can be usefully considered as a three phases system made of a mixture of melt, crystal and bubbles of exsolved volatiles in varying proportions. The rheological behaviour of such a polyphased system will be the interplay of the dynamical response of each of these phases with respect to any applied stress. Decisive progress in the determination of the viscosity of hydrous silicate melts has been made in recent years and several empirical equations are now available. These may be valid over a rather large compositional range (e.g., Hess and Dingwell, 1996; Holtz et al., 1999) or apply to a more specific (yet widespread) group of granitic magmas (Scaillet et al., 1996 for peraluminous granites). These empirical formulations supersede the classical model of Shaw (1972), especially in the low melt water content range. In particular, these new data have shown that hydrous silicic melts are distinctly non-Arrhenian over large temperature ranges (i.e. > 1000°C) although notable exceptions do exist (ie hydrous peraluminous silicic magmas). However, granitic magmas sensu lato display fairly smaller melting/crystallization temperature intervals, typically 100-200°C, over which the temperature dependence of the melt viscosity can be considered as Arrhenian. The melt viscosity is also strongly dependent on the strain rate: at low strain rates, silicic melts display a newtonian behaviour, while at high strain rates, non-newtonian behaviour are observed, shear viscosities decreasing with increasing strain rates (Webb and Dingwell, 1990). The low strain rates prevailing in plutonic environments imply that the melt in magmas at depths obeys predominantly a Newtonian behaviour. However, magmas transported through dykes, be it from the source region or from the plumbing system of volcanoes, may well experience high strain rates at which the onset of non-newtonian behaviour is observed. Applications of the above empirical models to such cases will likely give a maximum value for the melt viscosity. The role of crystals on magma viscosity is still a subject of active research. Experiments carried out on model systems have shown that the Eintein-Roscoe equation satisfactorily reproduces the data for crystal contents < 30% in volume (e.g., Lejeune and Richet, 1995). Beyond, magma viscosities are generally observed to increase rapidly up to reaching solid behaviour at around 60% vol crystals. Phase equilibria carried out on several granitic rocks have conclusively shown that granitic magmas arrive in a nearly molten state at their emplacement level, their load of crystals barely exceeding 10% (e.g. Clemens and Wall, 1981; Scaillet et al., 1995). This indicates that during extraction and ascent, the rheology of granitic magmas is mostly controlled by the melt properties. Crystallization paths calculated from those phase equilibria have shown that the crystal content is lower than 30% during 60-80% of the crystallization interval, a result of the eutectic-like crystallization of silicic magmas. Consequently, the viscosity increase arising from the increase in crystallinity hardly exceeds 1 order of magnitude during cooling, except at near solidus conditions. Melt viscosities of silicic magmas tightly cluster at 104.5 Pa s, irrespective of the temperature, melt water contents and the plutonic or volcanic nature (pre-eruptive conditions) of the rock. This shows that the fate of silicic magmas, whether volcanic or plutonic, is not due to fundamental differences in rheological properties. The fact that there are virtually no volcanic rocks with crystal contents higher than 50%, corresponding to magma viscosities of 106 Pa s, indicates that this is a fundamental rheological barrier, beyond which silicic magmas hardly move upward. Volcanic rocks having higher crystal content may have had their viscosity lowered by the presence of bubbles, at least in the low strain rate regime. The restored fluid contents of most volcanic rocks are, however, in the range 1-5 wt.% (eg, Wallace et al., 1995; Scaillet et al., 1998), which indicates that the rheological role of bubbles at depth is probably minor. Thus, although the relative rheological role of the melt, crystals and bubble can be expected to vary significantly among magmas, a general subdivision for crustally derived magmas can be proposed as follows: melt properties will be critical in determining whether a magma is extracted from its source; the crystal content will be instrumental in controlling the fluid dynamics of a magma chamber and the eruptability of the magma; bubbles will play a fundamental role in volcanic environments, that is only at very shallow levels. Still, aside from volcanic environments, a viscosity of 104.5 Pa s can be safely used for most intents and purposes, such as in numerical simulations of the fluid dynamics at work in silicic magma chambers. Clemens JC and VJ Wall, Can Mineral, 19, 111-131, 1981. Hess KU and, DB Dingwell, Am. Mineral., 81, 1297-1300, 1996. Holtz, F, J Roux, S Ohlhorst, H Beherens, and F Schulze, Am. Mineral, 84, 27-36, 1999. Lejeune AM, and P Richet, J. Geophys. Res., 100, 4215-4229, 1995. Scaillet, B., M Pichavant, and J. Roux, J. Petrol., 36, 664-706, 1995. Scaillet, B, F Holtz, and M Pichavant, J. Geophys. Res., 101, 27691-27699, 1996. Scaillet , B, B Clemente, BW Evans, and M Pichavant, J. Geophys. Res., 95, 15695-15701, 1998. Shaw, HR., Am. J. Sci., 272, 870-893, 1972. Wallace, P, AT Anderson, and AM Davis, Nature, 377, 612-616, 1995. Webb SL and DB Dingwell, J. Geophys. Res., 95, 15695-15701, 1990.
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Synthesis of fluorphlogopite single crystals. Applications to Experimental studies
European Journal of Mineralogy, 1995Co-Authors: Tahar Hammouda, Michel Pichavant, Pierre Barbey, Adrian BrearleyAbstract:We describe a practical method of synthesis of fluorphlogopite single crystals suited to common laboratoryconditions. The l-atm batch melting technique was adapted using starting compositions having a slight excessof fluorine, added as K2SiF6. The oxide-fluoride mixture was melted above the liquidus temperature and thencooled at a rate of a few degrees per hour between 1400 and 13OO°C. Large (millimetre- to centimetre-size), clearand detachable single crystals were obtained by adding a quench of the charge during the cooling stage. XRD,TEM and electron microprobe analyses confirm that the micas produced are mostly monoclinic IM polytypeshaving chemical compositions very close to the end-member fluorphlogopite. Heating experiments confirm thatmelting of fluorphlogopite is congruent. From both heating experiments and thermal analysis, the melting temperatureof fluorphlogopite is located at values ⩾ 1390°C. Synthetic fluor-mica single crystals are of practical interestas analytical standards, and for several applications in Experimental Petrology.
Piergiorgio Scarlato - One of the best experts on this subject based on the ideXlab platform.
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Carbonate assimilation in magmas: A reappraisal based on Experimental Petrology
Lithos, 2010Co-Authors: Silvio Mollo, Mario Gaeta, Carmela Freda, Tommaso Di Rocco, Valeria Misiti, Piergiorgio ScarlatoAbstract:The main effect of magma-carbonate interaction on magma differentiation is the formation of a silica-undersaturated, alkali-rich residual melt. Such a desilication process was explained as the progressive dissolution of CaCO3 in melt by consumption of SiO2 and MgO to form diopside sensu stricto. Magma chambers emplaced in carbonate substrata, however, are generally associated with magmatic skarns containing clinopyroxene with a high Ca-Tschermak activity in their paragenesis. Data are presented from magma-carbonate interaction experiments, demonstrating that carbonate assimilation is a complex process involving more components than so far assumed. Experimental results show that, during carbonate assimilation, a diopside-hedenbergite-Ca-Tschermak clinopyroxene solid solution is formed and that Ca-Tschermak/diopside and hedenbergite/diopside ratios increase as a function of the progressive carbonate assimilation. Accordingly, carbonate assimilation reaction should be written as follows, taking into account all the involved magmatic components:. CaCO3solid + SiO2melt + MgOmelt + FeOmelt + Al2O3melt → (Di-Hd-CaTs)sssolid + CO2fluid. The texture of Experimental products demonstrates that carbonate assimilation produces three-phases (solid, melt, and fluid) whose main products are: i) diopside-hedenbergite-Ca-Tschermak clinopyroxene solid solution; ii) silica-undersaturated CaO-rich melt; and iii) C-O-H fluid phase. The silica undersaturation of the melt and, more importantly, the occurrence of a CO2-rich fluid phase, must be taken into account as they significantly affect partition coefficients and the redox state of carbonated systems, respectively. © 2009 Elsevier B.V. All rights reserved
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Carbonate assimilation in magmas: A reappraisal based on Experimental Petrology
Lithos, 2009Co-Authors: Silvio Mollo, Mario Gaeta, Carmela Freda, Tommaso Di Rocco, Valeria Misiti, Piergiorgio ScarlatoAbstract:TRIGS Project “Sixth Framework Programme of the European Commission and to the New and Emerging Science and Technology Pathfinder". Project FIRB MIUR “Development of innovative technologies for the environmental protection from natural events”.
Barry Voight - One of the best experts on this subject based on the ideXlab platform.
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unprecedented pressure increase in deep magma reservoir triggered by lava dome collapse
Geophysical Research Letters, 2006Co-Authors: Barry Voight, R. S. J. Sparks, Alan T Linde, I S Sacks, G S Mattioli, Derek Elsworth, Dannie Hidayat, Peter E Malin, Eylon Shalev, Christina WidiwijayantiAbstract:[1] The collapse of the Soufriere Hills Volcano lava dome on Montserrat in July 2003 is the largest such event worldwide in the historical record. Here we report on borehole dilatometer data recording a remarkable and unprecedented rapid (∼600s) pressurisation of a magma chamber, triggered by this surface collapse. The chamber expansion is indicated by an expansive offset at the near dilatometer sites coupled with contraction at the far site. By analyzing the strain data and using added constraints from Experimental Petrology and long-term edifice deformation from GPS geodesy, we prefer a source centered at approximately 6 km depth below the crater for an oblate spheroid with overpressure increase of order 1 MPa and average radius ∼1 km. Pressurisation is attributed to growth of 1–3% of gas bubbles in supersaturated magma, triggered by the dynamics of surface unloading. Recent simulations demonstrate that pressure recovery from bubble growth can exceed initial pressure drop by nearly an order of magnitude.
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Unprecedented pressure increase in deep magma reservoir triggered by lava‐dome collapse
Geophysical Research Letters, 2006Co-Authors: Barry Voight, R. S. J. Sparks, Alan T Linde, I S Sacks, G S Mattioli, Derek Elsworth, Dannie Hidayat, Eylon Shalev, Peter Malin, Christina WidiwijayantiAbstract:[1] The collapse of the Soufriere Hills Volcano lava dome on Montserrat in July 2003 is the largest such event worldwide in the historical record. Here we report on borehole dilatometer data recording a remarkable and unprecedented rapid (∼600s) pressurisation of a magma chamber, triggered by this surface collapse. The chamber expansion is indicated by an expansive offset at the near dilatometer sites coupled with contraction at the far site. By analyzing the strain data and using added constraints from Experimental Petrology and long-term edifice deformation from GPS geodesy, we prefer a source centered at approximately 6 km depth below the crater for an oblate spheroid with overpressure increase of order 1 MPa and average radius ∼1 km. Pressurisation is attributed to growth of 1–3% of gas bubbles in supersaturated magma, triggered by the dynamics of surface unloading. Recent simulations demonstrate that pressure recovery from bubble growth can exceed initial pressure drop by nearly an order of magnitude.
