Sri Budhi Utami

Juan Andùjar

Fidel Costa

Bruno Scaillet

Hanik Humaida

Simon Carn

Kayla Iacovino

Pre-eruptive excess volatiles and their relationship to effusive and explosive eruption styles in semi-plugged volcanoes

Keywords: experimental petrology, Kelud, Kelut, eruption style, volatiles, volcano monitoring, basaltic andesite, arc volcanoes

Understanding the role of various factors influencing eruption style is challenging, but it can aid in adapting different hazard mitigations and crisis responses for explosive or effusive events. Here, we focus on the role of magma storage conditions in controlling eruption styles at basaltic andesite volcanoes, and how they can be related to monitoring data. We study the cycle of explosive (1990, sub-Plinian) → effusive (2007, dome) → explosive (2014, sub-Plinian) eruptions from Kelud (Kelut) volcano, Indonesia. We conducted petrological analyses of the eruption products and phase equilibria experiments using pumice and explored a range of temperatures, pressures, oxygen fugacity, and volatile contents. We show that we can reproduce the main mineral assemblage (plagioclase ± pyroxenes ± magnetite ± amphibole ± olivine) and phenocryst content (30-50 wt%) of the magmas from the three eruptions at T = 975 ± 39 °C, p = 175 ± 25 MPa, fO 2 = nickel-nickel oxide buffer, and about 4-6 wt% water in the melt (ca. 3 to 5 wt% and ca. 4 to 7 wt% for the 1990 and 2014 eruptions, respectively). However, geothermobarometric results also indicate that some crystals of amphibole were sourced from higher pressures. We infer from a synthesis of our data and historical observations that the high phenocryst content of the 2007 dome (~70 wt%) likely resulted from slow magma ascent toward the surface alongside progressive degassing and re-equilibration at a lower volatile content (~1 wt% water in the melt). Mass balance calculations on the sulfur budget of the 1990, 2007, and 2014 magmas show that the explosive events contained an excess fluid phase at pre-eruptive conditions, and we propose that this led to their higher explosivity compared to the 2007 dome. The accumulation of excess fluids during decadal-long repose depends on how plugged the volcanic system is, or its ability to passively release magmatic fluids, prior to eruption. Such condition could be inferred from monitoring records, including changes in gravity of the plumbing system over time, and thus contribute to better anticipate eruptive style.

Introduction

Volcanoes can display a range of eruption styles, spanning from small phreatic events and dome growth to explosive events with tall eruptive columns. Moreover, changes can occur between consecutive eruptions from the same volcano, or within a single eruption. Some well-known examples of volcanoes that display large variations in eruptive styles between eruptions include Merapi (Indonesia; [START_REF] Surono | The 2010 explosive eruption of Java's Merapi volcano-A '100-year' event[END_REF], Soufrière Hills (Montserrat; Young et al., 1998), and Mt. St. Helens (United States;[START_REF] Pallister | Mount st. Helens a decade after the 1980 eruptions: Magmatic models, chemical cycles, and a revised hazards assessment[END_REF]. Examples of how a single volcanic eruption can also rapidly transform from effusive to explosive and vice versa were observed in the 1991 Pinatubo eruption [START_REF] Bernard | Petrology and geochemistry of the 1991 eruption products of Mount Pinatubo[END_REF][START_REF] Pallister | Magma mixing at mount Pinatubo: Petrographic and chemical evidence from the 1991 deposits[END_REF][START_REF] Scaillet | The 15 june 1991 eruption of mount Pinatubo. I. Phase equilibria and pre-eruption P-T-fO2-fH2O conditions of the dacite magma[END_REF], the 2009 eruption at Redoubt [START_REF] Bull | An overview of the 2009 eruption of Redoubt Volcano, Alaska[END_REF], the 2011 eruption at Puyehue-Cordón Caulle [START_REF] Jay | Locating magma reservoirs using InSAR and petrology before and during the 2011-2012 Cordón Caulle silicic eruption[END_REF][START_REF] Elissondo | Chronology and impact of the 2011 cordón Caulle eruption, Chile[END_REF]. The changes in eruptive style between eruptions are typically abrupt and difficult to anticipate, which makes the mitigation of associated hazards necessary but incredibly challenging.

Changes in eruptive styles can be due to a range of factors. For example, effusive to explosive eruption transition within an eruptive period can be driven by syn-eruptive processes related to water exsolution from the melt and microlite crystallization, which can induce rapid changes in physical properties of the magma that dramatically alter its potential for explosivity in the conduit [START_REF] Woods | Transitions between explosive and effusive eruptions of silicic magmas[END_REF][START_REF] Melnik | Modelling of conduit flow dynamics during explosive activity at Soufrière Hills Volcano, Montserrat[END_REF]1999). The magma's density, viscosity, and ascent rate change as the magma moves toward the surface and goes through the brittle-ductile transition [START_REF] Dingwell | Magma rheology[END_REF][START_REF] Cashman | How volcanoes work: A 25 year perspective[END_REF]. The evolution of these parameters is inter-related as a high volatile content in the melt that can produce a buoyant magma, which may accelerate during ascent as long as the volatile bubbles and magma do not decouple [START_REF] Corsaro | Buoyancy-controlled eruption of magmas at Mt Etna[END_REF].

The physical and chemical properties of the magmas before ascent can be primed at their pre-eruptive storage zones. This includes the storage pressure, temperature, crystallinity, melt composition, and dissolved volatile contents. The pre-eruptive volatile content of the melt is particularly important in determining how parameters change, namely, the magma viscosity, buoyancy, and ascent rate [START_REF] Giordano | Viscosity of magmatic liquids: A model[END_REF][START_REF] Gonnermann | Dynamics of magma ascent in the volcanic conduit[END_REF][START_REF] Cassidy | Controls on explosive-effusive volcanic eruption styles[END_REF]. In addition, the presence of an excess volatile phase at preeruptive conditions due to second boiling [START_REF] Sisson | Gas-driven filter pressing in magmas[END_REF] and volatile fluxing [START_REF] Caricchi | Modulation of magmatic processes by CO2 flushing[END_REF] has also been shown to be important in driving explosive eruptions [START_REF] Scaillet | The 15 june 1991 eruption of mount Pinatubo. I. Phase equilibria and pre-eruption P-T-fO2-fH2O conditions of the dacite magma[END_REF][START_REF] Shinohara | Excess degassing from volcanoes and its role on eruptive and intrusive activity[END_REF][START_REF] Longpré | Magmatic processes and associated timescales leading to the January 1835 eruption of Cosigüina Volcano, Nicaragua[END_REF][START_REF] Edmonds | Exsolved volatiles in magma reservoirs[END_REF], although it may have the opposite effect and lead to effusive eruptions [START_REF] Popa | Water exsolution in the magma chamber favors effusive eruptions: Application of Cl-F partitioning behavior at the Nisyros-Yali volcanic area[END_REF]2020). Yet it is still unclear whether the build-up of excess volatiles in the magma can influence the style of consecutive eruptions, and how these relate to unrest records.

In this study, we experimentally investigate the crystallization conditions and processes of the explosive-effusive-explosive eruptions of Kelud volcano (Indonesia), as exemplified by the 1990, 2007, and 2014 events. We also report new petrological observations and calculate mineral-melt geothermobarometers that we combine with experimental results to constrain the preeruptive storage conditions of the three eruptions. We found that the magmas that fed the 1990, 2007, and 2014 events were essentially stored at similar temperatures, pressures, and water content in the melt. Comparison of the S emissions to the atmosphere by satellite data with those degassed from the melt suggest that the explosivity of the 1990 and 2014 eruptions was driven by the presence of an exsolved excess volatile phase prior to eruption, which was lacking in the 2007 dome eruption. The existence of an exsolved phase at the source likely induced higher buoyancy and faster ascent rates compared to the slower ascent, enhanced degassing, and subsequent re-equilibration of the magma toward the surface that ultimately produced a dome in 2007.

2 Kelud volcano and an overview of the [START_REF]Kelut (Kelud). Report. Global Volcanism Program (GVP)[END_REF], 2007, and 2014 eruptions Kelud (Kelut) volcano is an active basaltic-andesite semiplugged composite strato-cone complex situated in East Java, Indonesia [START_REF] Wirakusumah | Some studies of volcanology, petrology and structure of Mt. Kelut, east Java, Indonesia[END_REF][START_REF] Whelley | The frequency of explosive volcanic eruptions in Southeast Asia[END_REF]. The volcano hosts a persistent circum-neutral crater lake during repose [START_REF] Bernard | Geochemical evolution of the young crater lake of Kelud volcano in Indonesia[END_REF], and explosive eruptions typically generate syn-eruptive and post-eruptive cold lahars [START_REF] Thouret | Origin, characteristics, and behaviour of lahars following the 1990 eruption of Kelud volcano, eastern Java (Indonesia)[END_REF]. Kelud typically generates short-lived explosive eruptions that escalate from the onset of unrest to eruption in mere hours [START_REF] Lesage | Seismic precursors of the february 10, 1990 eruption of Kelut volcano, Java[END_REF]Global Volcanism Program, 2013;Maeno et al., 2019a). Kelud has erupted at least 32 times in the last 100 years (Global Volcanism Program, 2013), but here we focus on the last three eruptions in 1990, 2007, and 2014. The 1990 explosive eruption began after ~3 months of unrest followed by quiescence for ~3 weeks (Bourdier et al., 1997a;[START_REF] Bourdier | Menaces volcaniques au Kelut (Java, indonésie) : Les enseignements de l'éruption de 1990[END_REF]. The final escalation toward eruption occurred in hours, giving communities only 1 hour to evacuate their homes (Global Volcanism Program, 1990a). The explosive eruption in 2014 largely followed a similar pattern in terms of duration of heightened unrest period of the 1990 eruption, although this was condensed into 1 month starting in January 2014. The final escalation toward eruption in 2014 was a steep increase in seismicity of only a few hours [START_REF] Hidayati | Differences in the seismicity preceding the 2007 and 2014 eruptions of Kelud volcano, Indonesia[END_REF]. These 1990 and 2014 events generated eruptive columns as high as 10-17 km (Bourdier et al., 1997a;[START_REF] Kristiansen | Stratospheric volcanic ash emissions from the 13 February 2014 Kelut eruption[END_REF][START_REF] Nakashima | Atmospheric resonant oscillations by the 2014 eruption of the Kelud volcano, Indonesia, observed with the ionospheric total electron contents and seismic signals[END_REF] with a VEI of 4 and dense rock equivalent (DRE) volumes of 6.3 × 10 7 m 3 (1990) and 2.1 × 10 8 m 3 (2014), respectively (Maeno et al., 2019a). Moreover, the eruptions were short-lived and volcanic activity and unrest returned to background levels within days to weeks of the main eruptive phase (Global Volcanism Program, 1990b;Global Volcanism Program, 2014;Global Volcanism Program 1990b).

The lava dome extrusion of November 2007 was preceded by some unrest that started as early as January 2007 [START_REF] Lubis | Uplift of Kelud volcano prior to the november 2007 eruption as observed by L-band insar[END_REF], with up to 11 cm of inflation around the summit region detected using ALOS-PALSAR interferometric synthetic aperture radar (InSAR). From July to August 2007, unrest involved intense degassing on the lake floor and an increase in seismicity [START_REF] Hidayati | Differences in the seismicity preceding the 2007 and 2014 eruptions of Kelud volcano, Indonesia[END_REF], and lake temperature rising up (from ~30 to ~75 °C), as well as heightened CO 2 emissions from the lake (Global Volcanism Program, 2007;[START_REF] Kunrat | Geochemical and thermodynamic modeling of volcanic fluids and their interpretation for volcano monitoring[END_REF][START_REF] Caudron | Carbon dioxide dynamics in Kelud volcanic lake[END_REF]. Continuous seismic unrest started around September 2007, involving multiple swarms and low frequency earthquakes [START_REF] Hidayati | Emergence of lava dome from the crater lake of Kelud volcano[END_REF]. The seismic unrest was further accompanied by inflation from 9th October until 3rd November, when the signal changed to deflation and gave way to slow dome extrusion [START_REF] Hidayati | Differences in the seismicity preceding the 2007 and 2014 eruptions of Kelud volcano, Indonesia[END_REF]. The 2007 dome was 200 m high and 400 m wide, with a volume of 3.5 × 10 7 m 3 , which is about half the volume of the 1990 eruption (Global Volcanism Program, 2008), but about one order of magnitude smaller than the 2014 event (Maeno et al., 2019a). Despite the diverse monitoring data available, it is still difficult to anticipate eruptions at Kelud, including whether the ensuing eruption will be effusive or explosive [START_REF] Nakamichi | Differences of precursory seismic energy release for the 2007 effusive dome-forming and 2014 Plinian eruptions at Kelud volcano, Indonesia[END_REF], and this is the main subject of our study.

Materials and methods

We conducted petrological analyses of two 2007 dome fragments, previously studied in [START_REF] Humaida | A geochemical study on Merapi and Kelud volcanic eruptions[END_REF], two pumices were sampled following the 2014 eruption (sampled by H. Humaida), and it included the data from the six main-stage pumices from the 1990 eruption studied in [START_REF] Utami | Fluid fluxing and accumulation drive decadal and short-lived explosive basaltic andesite eruptions preceded by limited volcanic unrest[END_REF]. We chose one basaltic andesite pumice from the 1990 eruption studied by [START_REF] Utami | Fluid fluxing and accumulation drive decadal and short-lived explosive basaltic andesite eruptions preceded by limited volcanic unrest[END_REF] (KELUD1990PL1, or 'PL1') as the starting material for our phase equilibria experiments. The pumice had the same mineral assemblage as other samples, except for the absence of olivine.

Selection of experimental conditions

We experimentally investigated a range of intensive variables that includes the estimates from mineral-melt geothermobarometers [START_REF] Utami | Fluid fluxing and accumulation drive decadal and short-lived explosive basaltic andesite eruptions preceded by limited volcanic unrest[END_REF]. We varied the temperature from 950 to 1,060 °C, pressure from 100 to 400 MPa, fO 2 at the Ni-NiO buffer (NNO) and up to two log units above (NNO +2), and varied a volatile composition in the capsule from pure water to pure CO 2 (see below for more details).

Preparation of experimental charges

A starting glass was prepared by finely crushing the pumice using a ceramic mortar and pestle and homogenized by fusing the powder at 1,400 °C and atmospheric pressure for around 6 h in a standard thermconcept furnace at 1750 °C. EPMA analyses of the fused glass confirmed that the glass was homogenous and of the same composition as the whole rock. This glass was crushed again to a fine dry powder with an agate mortar and pestle, which was used as a starting material for all phase equilibrium experiments. About 0.03 g of dry glass was loaded in Au capsules (of size 10-15 mm × 2.5 × 0.2 mm wall thickness) for the 950 and 1,000 °C experiments, whereas Au-Pd capsules were used for the 1,060 °C experiments.

We varied the fluid composition in the charges (referred to as

XH 2 O in = initial H 2 O/[H 2 O+ CO 2 ]
in moles) from 0 to 1 by adding various amounts of deionized water and CO 2 (in the form of silver oxalate) to the dry glass powder, according to the methodology of [START_REF] Scaillet | Experimental crystallization of leucogranite magmas[END_REF]. All the successful runs were fluid saturated. The capsules were arc-welded and weighed before being stored in a 60 °C oven to homogenize the fluid content for 6-12 h. After each experiment, the capsule was reweighed again to check for fluid loss during storage and subsequent experiments. To determine whether the charges were properly sealed, their weight had to be within 0.0005 g of the original value, which is the precision of the analytical balance. We observed that capsules from successfully quenched experiments were shrunk and flattened but had the same weight as before the experiment. Upon opening, the charges ejected gas with an audible pop. In contrast, failed charges appeared bloated and commonly showed a difference in mass (>0.0005 g) between before and after the experiments.

Experimental equipment

All experiments were conducted at the Institut de Sciences de la Terre Orléans, France using internally heated pressure vessels (IHPV), following the procedure outlined in [START_REF] Scaillet | The 15 june 1991 eruption of mount Pinatubo. I. Phase equilibria and pre-eruption P-T-fO2-fH2O conditions of the dacite magma[END_REF]. Argon was used as a pressurizing medium mixed with different H 2 concentrations at room temperature to establish different fO 2 conditions (ranging from NNO to NNO +2), and using a Shaw membrane to establish and maintain the fH 2 osmotic equilibrium [START_REF] Scaillet | Improvements of the Shaw membrane technique for measurement and control of fH2 at high temperatures and pressures[END_REF]. A factory calibrated pressure transducer was used to measure and monitor pressure (±2 MPa), whereas temperature was monitored with unsheathed type-S thermocouples, and the temperature of the IHPV "hotspot" was maintained at T < 10 °C and with an uncertainty of ±5 °C [START_REF] Scaillet | Improvements of the Shaw membrane technique for measurement and control of fH2 at high temperatures and pressures[END_REF]. Experiment temperatures were increased from room temperature directly up to run temperature in around an hour: each experimental run contained around 4-7 capsules, including one sensor for fO 2 (see below). Once the target conditions were achieved, experiments were run for 18-66 h. Experiments were terminated with a dropquench device, allowing the sample holder to fall in the cold part of the vessel at the bottom (<50 °C), ensuring isobaric quenching and cooling rates of 100 °C/s. A fast quench device was set up as part of the experiments [START_REF] Roux | A fast-quench device for internally heated pressure vessels[END_REF]. Previous studies [START_REF] Scaillet | The 15 june 1991 eruption of mount Pinatubo. I. Phase equilibria and pre-eruption P-T-fO2-fH2O conditions of the dacite magma[END_REF][START_REF] Prouteau | Experimental constraints on the origin of the 1991 Pinatubo dacite[END_REF][START_REF] Costa | Petrological and experimental constraints on the pre-eruption conditions of holocene dacite from volcan san pedro (36 S, Chilean andes) and the importance of sulphur in silicic subductionrelated magmas[END_REF][START_REF] Andújar | Storage conditions and eruptive dynamics of central versus flank eruptions in volcanic islands: The case of tenerife (canary islands, Spain)[END_REF] have shown that crystalmelt equilibrium is attained using the same set of protocols. General observations of equilibrium include homogeneous glass composition within the charge, lack of chemical zoning in experimental crystals, and systematic changes in petrologic variables (e.g., crystal content) with experimental variables (temperature and water content). Equilibrium, rather than quench-textures, are characteristic of the run products we report, and we believe they reflect attainment of chemical equilibrium at the desired run conditions.

Calculation of fO 2 and dissolved water content in experimental charges

The oxygen fugacity (fO 2 ) was calculated using a sensor capsule containing two water-saturated (10 mg added water), hand-pressed Ni-Pd-NiO powder pellets separated by inert ZrO powder [START_REF] Taylor | The calibration and application of accurate redox sensors[END_REF]. We forgot to add a sensor capsule for one experimental run (T = 1,060 °C, p = 200 MPa), and thus the final calculated fO 2 for the fluid saturated charge (XH 2 O in = 1.0) is the average fO 2 of the two closest isobaric runs (T = 1,060 °C, p = 100 and 400 MPa). For unsaturated charges, we calculated the fO 2 according to the following formula employed by [START_REF] Scaillet | The 15 june 1991 eruption of mount Pinatubo. I. Phase equilibria and pre-eruption P-T-fO2-fH2O conditions of the dacite magma[END_REF]:

f O charge 2 f O sensor 2 + 2log 10 XH 2 O charge final melt ,
where fO 2 (charge) is the calculated oxygen fugacity of the charge, fO 2 (sensor) is the sensor oxygen fugacity, and the XH 2 O charge final melt is the proportion of dissolved water content in the melt (see Table 5). We could not calculate fO 2 for dry charges (no water in the melt). Finally, the water content of the experimental glasses was obtained by determining the fluid composition with mass-balance calculations to determine the proportion of fluids put into the charge (XH 2 O in ) partitioned into the fluid (XH 2 O fluid ) and melt (XH 2 O melt ) phases during the experiments. The H 2 O solubility model from [START_REF] Shishkina | Solubility of H2O-and CO2-bearing fluids in tholeiitic basalts at pressures up to 500MPa[END_REF] and the pure CO 2 model from [START_REF] Dixon | Degassing of alkalic basalts[END_REF] were combined to calculate XH 2 O fluid and XH 2 O melt . From these proportions we calculated the dissolved water content in the melt.

We also compared our dissolved water contents with water contents calculated using the mixed H 2 O-CO 2 'MagmaSat' model of [START_REF] Ghiorso | An H2O-CO2 mixed fluid saturation model compatible with rhyolite-MELTS[END_REF] using VESIcal (v. 1.0.1;[START_REF] Iacovino | VESIcal Part I: An open-source thermodynamic model engine for mixed volatile (H2O-CO2) solubility in silicate melts[END_REF]. The differences between our initial calculation and MagmaSat model were ≤1 wt% (see Supplementary Material), which use as the nominal error in the water contents we reported. We used the 1σ of this difference as the error in the water content. To maintain consistency in other water contents reported, we calculated the saturation pressures with the same model. To do this, we also used VESIcal (v. 1.0.1;[START_REF] Iacovino | VESIcal Part I: An open-source thermodynamic model engine for mixed volatile (H2O-CO2) solubility in silicate melts[END_REF] to calculate the saturation pressure with the hybridized models of [START_REF] Shishkina | Solubility of H2O-and CO2-bearing fluids in tholeiitic basalts at pressures up to 500MPa[END_REF] pure H 2 O and Dixon (1997, "VolatileCalc") pure CO 2 model for all three eruptions. This hybridized model simulated the models we used to calculate the water content in the melt. We find that the differences are <300 bars or <30 MPa, which was within error of mineral-melt geobarometers.

Analytical techniques

Whole-rock analyses of samples, including the pumice starting material, were ground and fused into a lithium tetraborate disk before being analyzed for whole rock major element oxide compositions using X-ray fluorescence (XRF) at the Activation Laboratory in Ancaster, Canada, following the approach outlined in [START_REF] Norrish | An accurate X-ray spectrographic method for the analysis of a wide range of geological samples[END_REF]. Mineral proportions were obtained by counting the phenocryst content, using JMicrovision software on plain polarized images of the entire thin section (for the 1990 samples), and using a Pelcon mechanical point counting stage (for the 2007 and 2014 samples). For each sample, we counted between ca. 1,400-1,600 points to ensure statistically significant results with relative errors of <10%. Results from point counting (Table 2) and mineral compositions (Table 3) allowed us to determine the composition of the calculated matrix of the 1990, 2007, and 2014 samples (Table 1) by subtracting the mineral compositions weighted with their proportions from the whole rock compositions. Such calculations were necessary to remove the effect of the extensive microlite crystallization for the 2007 dome and to compare with experimental glass. We also used the calculated matrix for geothermobarometric calculations.

We made general observations of experimental charges and identified phases using the scanning electron microscope (SEM) at ISTO-Orléans, France and the Earth Observatory of Singapore. From these images, we determined the crystal content of the experimental charges by thresholding the greyscale of multiple back-scattered electron (BSE) images of a charge map using ImageJ, and we estimated the volumetric area of phases in all charges. With these results, we calculated the mass proportions of the main minerals using standard mineral densities.

Minerals and glass from natural samples and experimental charges were analyzed for their chemical compositions on the JEOL JXA-8530F electron microprobe (EPMA) at the Facility for the Analyses Characterization, Testing, and Simulation (FACTS), Nanyang Technological University, Singapore. Analyses of orthopyroxene, clinopyroxene, olivine, and Fe-Ti The mineral end-members were calculated using their molar compositions as in [START_REF] Utami | Fluid fluxing and accumulation drive decadal and short-lived explosive basaltic andesite eruptions preceded by limited volcanic unrest[END_REF], and with formulations according to [START_REF] Deer | An introduction to the rockforming minerals[END_REF]. Pyroxenes are characterized with the Mg # (Mg # = 100 × Mg/[Mg + Fe*] in mol, where Fe* is total iron as Fe 2+ ). We further characterize pyroxenes using their wollastonite (Wo = 100 × Ca/[Ca + Mg + Fe*]), ferrosilite (Fs = 100 × Fe/[Ca + Mg + Fe*]), and enstatite (En = 100 × Mg/[Ca + Mg + Fe*]) endmembers. Plagioclase end member compositions were classified using their molar compositions for anorthite (An = 100 × Ca/[Ca + Na + K]), albite (Ab = 100 × Na/[Ca + Na + K]), and orthoclase (Or = 100 × K/[Ca + Na + K]). Olivine is characterized using the forsterite content (Fo = 100 × Mg/ [Mg + Fe*]), whereas amphibole is classified according to the compositional end-members outlined in [START_REF] Leake | Nomenclature of amphiboles report of the subcommittee on amphiboles of the international mineralogical association commission on new minerals and mineral names[END_REF], as determined by [START_REF] Ridolfi | Stability and chemical equilibrium of amphibole in calc-alkaline magmas: An overview, new thermobarometric formulations and application to subduction-related volcanoes[END_REF]. Glass compositions were characterized using their normalized to 100% anhydrous major element oxides and total alkali-silica (TAS) composition. It was difficult to obtain good quantitative analyses of plagioclase crystals in experimental charges as they are typically small and may contain Fe-Ti oxide inclusions. To be able to report approximate An contents of plagioclase, we have filtered for analyses with FeO* < 1 wt% and TiO 2 < 0.1 wt%, and subtracted the composition of magnetite from the electron microprobe analyses to match these constraints. We report these recalculated compositions to fit the structural formulas labeled '-N.'

Remote sensing of SO 2 emissions

To evaluate sulfur dioxide (SO 2 ) emissions from Kelud during the 2007 effusive eruption, we used ultraviolet (UV) satellite data from the Ozone Monitoring Instrument (OMI) on NASA's Aura satellite. Aura/OMI was launched in 2004 and has a spatial resolution at nadir of 13×24 km and high sensitivity to atmospheric SO 2 , permitting detection of small plumes emitted by weak or passive volcanic degassing [START_REF] Carn | Multi-decadal satellite measurements of global volcanic degassing[END_REF]. OMI measurements since 2004 have provided a longterm record of passive and eruptive volcanic SO 2 emissions that continues to the present [START_REF] Carn | A decade of global volcanic SO2 emissions measured from space[END_REF][START_REF] Carn | Multi-decadal satellite measurements of global volcanic degassing[END_REF][START_REF] Carn | Multi-satellite volcanic sulfur dioxide L4 long-term global database V4[END_REF]. Column amounts of SO 2 are derived from the UV OMI measurements using a low-noise principal component analysis (PCA) retrieval algorithm [START_REF] Li | New-generation NASA Aura Ozone monitoring instrument (OMI) volcanic SO< sub>2</sub> dataset: Algorithm description, initial results, and continuation with the suomi-NPP Ozone mapping and profiler suite (OMPS)[END_REF]; the SO 2 column amounts measured in a volcanic plume are integrated to obtain SO 2 mass. The OMI SO 2 retrievals are altitudedependent, and here we assume a lower tropospheric (TRL) SO 2 plume altitude (~3 km above sea level) to approximate the expected volcanic plume altitudes at Kelud (summit elevation ~2 km). The results presented here are the first detailed analysis of OMI SO 2 measurements for the 2007 Kelud eruption.

We note that Kelud was not identified as a major source of persistent volcanic SO 2 emissions in the 2005-2015 period covered by the global inventory of [START_REF] Carn | A decade of global volcanic SO2 emissions measured from space[END_REF], indicating that passive SO 2 emissions from the volcano are generally absent or below OMI detection limits (~20-80 tons/ day). However, Semeru, Bromo, Raung and Kawah Ijen volcanoes, located to the east of Kelud, are all persistently active [START_REF] Carn | A decade of global volcanic SO2 emissions measured from space[END_REF], and their SO 2 plumes are often advected west over the Kelud region, which can impact the detection of Kelud's SO 2 emissions in an easterly wind regime. Frequent cloud cover and convection over the higher elevations of East Java can also hamper the detection of volcanic SO 2 emissions by OMI.

Results

Petrological observations and geothermobarometry of the 1990-2007-2014 magmas

We document petrological observations and calculate geothermobarometric estimates from the deposits of the 1990, 2007, and 2014 eruptions. Whole rock major elements vary over a small range across eruptions, and samples are classified as basaltic andesite (Table 1). The calculated matrix compositions, the measured interstitial glasses, and clinopyroxene-hosted melt inclusions are of a similar dacitic composition (see [START_REF] Utami | Fluid fluxing and accumulation drive decadal and short-lived explosive basaltic andesite eruptions preceded by limited volcanic unrest[END_REF]. The three eruptions have deposits with different phenocryst (>100 µm) content: 31-47 wt% in the 1990 pumices; 70-72 wt% for the 2007 dome; and 29-35 wt% in 2014 pumices (Table 2). The mineral assemblage for all three eruptions includes phenocrysts of plagioclase (Plag), clinopyroxene (Cpx), orthopyroxene (Opx), and magnetite (Mag).

Accessory minerals include apatite (Apa), which is found in all three eruptions. Quartz (Qz)-rich enclaves occur in the 1990 late-stage pumice; cristobalite (Crs) is found as vesicle infill in the 2007 dome samples (see Supplementary Figure S3). Ilmenite (Ilm) is present as rims around Mag in the 1990 late-stage pumice and as exsolution lamellae in Mag in the 2007 deposits (see Supplementary Material). The 1990 and 2014 pumices also host partially reacted amphibole (Amph), and we have also identified pseudomorphs of Amph megacrysts and symplectites after Ol breakdown in the 2007 dome, meaning that both Amph and Ol may have also been stable in the 2007 magma (see Supplementary Figure S3). We also found partially reacted olivine (Ol) microphenocrysts (<100 µm) in the 2014 pumice. The compositions of the main minerals of the three eruptions are also broadly similar, with the histograms of compositional mineral indicators (e.g., Mg Number) typically overlap for the three eruptions (Figures 1A-C; Table 3) and are also similar to those of previous studies from the same eruptions (e.g., [START_REF] Jeffery | The pre-eruptive magma plumbing system of the 2007-2008 dome-forming eruption of Kelut volcano, East Java, Indonesia[END_REF][START_REF] Cassidy | Explosive eruptions with little warning: Experimental petrology and volcano monitoring observations from the 2014 eruption of Kelud, Indonesia[END_REF][START_REF] Putirka | Amphibole thermometers and barometers for igneous systems and some implications for eruption mechanisms of felsic magmas at arc volcanoes[END_REF].

We made geothermobarometric estimates under the 1990-2014 magma storage conditions from mineral and whole rock/calculated matrix compositions (Table 4). For this we use core-whole rock and rim-calculated matrix pairs (see also [START_REF] Utami | Fluid fluxing and accumulation drive decadal and short-lived explosive basaltic andesite eruptions preceded by limited volcanic unrest[END_REF] for the 1990 eruption). The pyroxene-liquid or two pyroxene equilibria formulations of [START_REF] Putirka | Thermometers and barometers for volcanic systems[END_REF] give temperatures that range from about 1,030 °C for the crystal cores, to about 975 °C (down to 950 °C) for the crystal rims. Moreover, the mineral and glass compositions of the three eruptions give pre-eruptive temperatures that are within about ±30 °C (Table 4). These temperature estimates also overlap with those obtained from amphibole-melt equilibria at about 960 °C for the 1990 and 2014 eruptions. Pressure estimates we obtained come from the amphibole-melt geobarometer formulation of [START_REF] Putirka | Amphibole thermometers and barometers for igneous systems and some implications for eruption mechanisms of felsic magmas at arc volcanoes[END_REF], where pressures range from 450 MPa up to 700 MPa for the 1990 and 2014 eruptions, respectively.

The dissolved water content in the 1990 and 2014 magmas are calculated using the plagioclase-melt hygrometer of [START_REF] Waters | An updated calibration of the plagioclase-liquid hygrometer-thermometer applicable to basalts through rhyolites[END_REF], with temperatures calculated using Opx-melt geothermometers of mineral core/whole rock and rim/calculated matrix pairs. For the 2007 dome, we use the core/whole rock pair for the Opx-melt temperatures and adjacent Opx-Cpx pairs for the two-pyroxene temperatures. Water contents range from 3.1 to 4.7 wt% (Table 4), which are consistent with previous estimates in [START_REF] Utami | Fluid fluxing and accumulation drive decadal and short-lived explosive basaltic andesite eruptions preceded by limited volcanic unrest[END_REF]. These water contents in the melt correspond to H 2 O-CO 2 saturation pressures of ~170-220 MPa using the combined model of [START_REF] Shishkina | Solubility of H2O-and CO2-bearing fluids in tholeiitic basalts at pressures up to 500MPa[END_REF] and [START_REF] Dixon | Degassing of alkalic basalts[END_REF]. These pressures are also similar to the range of pressures obtained in [START_REF] Utami | Fluid fluxing and accumulation drive decadal and short-lived explosive basaltic andesite eruptions preceded by limited volcanic unrest[END_REF]. The water content in the melt estimated for the 2007 samples using plagioclase rim and core, and the calculated matrix glass is about 3 wt% water, which is slightly lower than those of the 1990 and 2014 eruptions.

General observations from the experimental results

Successful experimental charges range from complete glass to almost fully crystallized. Glass-rich charges are devoid of vesicles (Figure 2). Most charges (Figures 2B-H) have a porphyritic texture, with subhedral to euhedral crystals set in interstitial glass with vesicles. Crystals may vary in size from phenocrysts (>100 µm) to microlites (<10 µm). Typically, Opx and Ol are subhedral to euhedral, commonly with Mag and Plag inclusions (>100 µm) (Figure 2C). Some charges have clusters of Fe-Ti oxides microlites, as well as Fe-Ti oxides distributed throughout the charge (Figure 2D). Despite the large range in crystal sizes, minerals, and glass appear to be unzoned, according to BSE images, which is likely indicative of compositional equilibrium. Due to the small size of many crystals, it was very challenging to obtain a good quantitative chemical analysis, and thus we relied on mineral identification using EDS spectra obtained in SEM or electron probe. We obtained glass compositions from glass-rich experimental charges or for those where glass "pools" larger than about 10 μm, and we found that they are homogeneous in composition (Figures 2A-D). For charges with low water b Phase proportions were calculated using grayscale thresholding of BSE, charge maps using ImageJ software and then converted to phase proportions. c See Table 2 for meaning of abbreviations, with the addition of Gl that we refer to glasses only. For charges where only CO 2 was added, we could not calculate the log (fO 2 ). d log (fO 2 ) determined using water saturated Ni-Pd alloy capsules, calculated using the formulation by [START_REF] Pownceby | Thermodynamic data from redox reactions at high temperatures. IV. Calibration of the Re-ReO2 oxygen buffer from EMF and NiO+Ni-Pd redox sensor measurements[END_REF]. For undersaturated charges, we calculated the fO 2 using the formula outlined in Section 3.4. e ΔNNO, log (fO 2 ) -log (fO 2 ) at Ni-NiO, buffer. f XH 2 Oin = H 2 O/(H 2 O + CO 2 ) loaded in capsules in moles.

Frontiers in Earth Science frontiersin.org contents, phases are often very small to analyze. For charges that failed, that is, where the fluid escaped the capsule during the experiment, we consistently observe a very high crystal content and a quench texture, with abundant microlites of Opx and Plag, and rare Ilm and glass; these were not used further.

Phase relation, crystallinities, and mineral assemblages

The complete experimental phase assemblage of all charges includes Opx, Plag, Cpx, Mag, Ilm, Amph, Ol, and glass (Figures 2A-H). We did not identify experimental apatite, but it may be present. The crystal content from experimental charges varies from virtually none to about 88 wt% (Table 5). The crystal content generally increases as both temperature and water content decreases and as fO 2 increases. We produced liquidus or near-liquidus experiments with <1 wt% of crystals, at 1,060 °C (Figure 2B), and in charges at water saturated conditions (about 5-9 wt% H 2 O in the melt), 200-400 MPa, and fO 2 of NNO (Figures 4A-C). These conditions match the model liquidus temperature calculated from rhyolite-MELTS in [START_REF] Utami | Fluid fluxing and accumulation drive decadal and short-lived explosive basaltic andesite eruptions preceded by limited volcanic unrest[END_REF]. At 100 and 200 MPa and 1,000 °C, the crystal content varies between about 68 and 44 wt% for 2-4 wt% water in the melt. Increasing the temperature to 1,060 °C decreases the crystal content to 52 to 31 wt% at 3-4 wt% water in the melt, but it increases up to 74 wt% for <2 wt% in the melt. Similar changes in the crystal content with temperature and water content in the melt for different experimental pressures (see Supplementary Material). Increasing fO 2 from NNO to NNO +2 results in an increase in the proportion of magnetite toward slightly higher crystal contents.

The relationship between crystallinity, temperature, and water content in the melt can be used to obtain first-order constraints on the 'pre-eruptive conditions' (Figure 3). By 'pre-eruptive conditions' we mean those that best reproduce the natural phenocryst content, the mineral assemblage, and when possible, the phase compositions. They apply to the conditions before the magma started to move toward the surface and erupted. We have neither directly investigated the syn-eruptive processes, such microlite density or size, nor the vesicle characteristics, as was conducted in decompression experiments [START_REF] Martel | Eruption dynamics inferred from microlite crystallization experiments: Application to plinian and dome-forming eruptions of Mt. Pelee (Martinique, lesser antilles)[END_REF]. Such definition of pre-eruptive storage conditions is relatively straightforward to apply to the explosive eruptions of 1990 and 2014, which quickly moved toward the surface. However, it is more ambiguous for the 2007 dome, which ascended more slowly and re-equilibrated to lower volatile contents, and contains a higher amount of phenocrysts. We attempt to clarify these differences in the following paragraphs.

Using a temperature of magma storage of 975 ± 39 °C for the three eruptions, as suggested by geothermobarometric data of all eruptions (Table 4), we find that the melt of the 1990 and 2014 magmas could contain about 4-6 wt% water at 150-200 MPa (Figures 3,4). At 100 MPa and 400 MPa, this range corresponds to 3-4 wt% and 5-7 wt% water in the melt, respectively (Supplementary Figures S7,S8). The considerably higher phenocryst content of the 2007 dome would imply significantly lower water content in the melt (~1 wt%). However, as we have discussed in the geothermobarometry results section earlier, we believe this does not reflect the 2021) and this study (Table 2). Average temperature estimates from each eruption are calculated from mineral-melt geothermobarometry listed in Table 4.

storage conditions before the magma started to move toward the surface. In addition to the same temperature, the plagioclasematrix equilibria suggest similar water contents in the melt for all eruptions. Thus, we propose that the trend reflects reequilibration and maturation during slow ascent; in essence, we consider this an initial ascent phase of that eruption, which allowed for degassing and consequent crystallization.

We find that experimental Opx and Plag are present at all conditions below the liquidus, and the Cpx stability field is somewhat smaller (Figures 4A-C, Supplementary Figure S4). Although we suspect amphibole was stable in our charges by comparison with the results of other phase equilibrium studies with similar bulk compositions [START_REF] Pichavant | Physical conditions, structure, and dynamics of a zoned magma chamber: Mount Pelée (Martinique, Lesser Antilles Arc)[END_REF][START_REF] Prouteau | Experimental constraints on the origin of the 1991 Pinatubo dacite[END_REF][START_REF] Erdmann | Constraints from phase equilibrium experiments on pre-eruptive storage conditions in mixed magma systems: A case study on crystal-rich basaltic andesites from mount Merapi, Indonesia[END_REF], we were not able to confidently identify it with EDS spectra or quantitative electron microprobe analysis owing to the high crystallinity of the charges and its small crystal size. To circumvent this problem, we applied principal component analysis to electron microprobe analyses of mineral compositions using the R package 'FactoMineR' [START_REF] Lê | FactoMineR: An R package for multivariate analysis[END_REF], and we successfully identified experimental amphibole at 950-1,000 °C and 200-400 MPa, with 4.5-6 wt% water in the melt (Figures 4A,B), which overlaps with our pressure estimates from natural amphiboles from the 1990 and 2014 eruptions. We identified experimental Ol with 3-4 wt% water in the melt at NNO and <150 MPa (Figure 4B). At NNO +2, Ol stability extends to higher pressures and water content (at 200 MPa, 1,000 °C, and about 4-6 wt% water in the melt; Figure 4C). The stability of Fe-Ti oxides is also controlled by the dissolved water content and fO 2 . Ilmenite is stable at lower dissolved water contents than Mag, whereas with increasing fO 2 makes magnetite more stable at low water contents.

Mineral and glass compositions

We strived to quantitatively analyze as many phases in as many charges as possible. However, we were only able to obtain a limited number of quantitative compositions, given the small sizes of many phases as described in the methods. This makes it difficult to directly make a close match between the natural phase compositions to the experimental ones, although we found some overlapping compositions at similar P-T-water under the melt conditions that was suggested by the crystallinity and phase assemblage relations (Figures 3,4) Data tables for experimental mineral compositions are found in the Supplementary Tables S3-S7.

Glass

Experimental glass compositions vary with water content, temperature, and pressure (Figures 5A-L), with compositions evolving from basaltic andesite to dacite as temperature decrease from 1,060 to 950 °C (Supplementary Table S3). The most evolved glass composition that we are able to analyze is dacitic with 68 wt % SiO 2 at 200 MPa, 1,060 °C, NNO, 1 wt% water in the melt, and with 50-54 wt% crystals in the charge (Figure 5A). The glass we analyzed from the rest of the charges ranges from basaltic andesite to andesite. For the same temperature, pressure, and fO 2 , the major element oxides such as SiO 2 and K 2 O increase as the water content in the melt decreases, indicating the melt is becoming more evolved (Figures 5A-C,J-L). Conversely, oxides such as Al 2 O 3 and CaO decrease with decreasing water content. Changing the fO 2 from NNO to NNO +2 does not significantly affect the SiO 2 content of the melt for the same pressure, temperature, and dissolved water content. The FeO* (3-9 wt %), MgO (1.5-7 wt%), and TiO 2 (0.7-1.7 wt%) of experimental glasses (see Supplementary Figure S4) are controlled by

FIGURE 5

Major element oxide compositions of experimental glasses (in wt%) vs. dissolved water content in the melt according to three different temperatures SiO 2 (A) 950 °C, (B) 1,000 °C, (C) 1,060 °C; Al 2 O 3 (D) 950 °C; (E) 1,000 °C, (F) 1,060 °C; CaO (G) 950 °C; (H) 1,000 °C; (I) 1,060 °C; K 2 O (J) 950 °C, (K) 1,000 °C, (L) 1,060 °C. Yellow horizontal band denotes the range of whole rock compositions. The thick gray band is the composition of calculated matrix for the explosive eruptions (1990,2014); the thin gray band is the calculated matrix of the 2007 dome (Table 1). The calculated matrix compositions for the 1990, 2007, and 2014 eruptions were estimated by mass balance calculations [START_REF] Albarede | Introduction to geochemical modeling[END_REF] (see Methodology section). Vertical dashed lines are water content in the melt inferred from crystallinity and phase assemblage (Figures 3,4 crystallization of ferromagnesian minerals such as pyroxenes and magnetite. The limited number of natural and experimental glasses that we are able to analyze means we do not have a direct match to the natural compositions. Yet the calculated matrix and the experimental glasses overlap at around 950-1,000 °C, 150-200 MPa, 4-4.5 wt% water in the melt, and fO 2 of NNO to NNO +2. The general lack of agreement between the calculated matrix and experimental glasses in some major element oxides (e.g., FeO and K 2 O) could be due to the effect of syn-eruptive crystallization of Plag and oxide microlites in natural rocks. We also observe microlites in one 1990 pumice and the 2007 dome, which may explain why the natural rocks have a higher SiO 2 content than the experimental glasses.

Plagioclase

It is difficult to obtain "pure" analyses of experimental plagioclase due to its elongated shape (e.g., very thin in one direction) and the presence of mineral inclusions such as oxides and/or pyroxenes, so we report the recalculated analyses after subtraction of the effect of mineral inclusions (see Methodology section). We first filtered the experimental Plag analyses for their FeO* and TiO 2 contents to remove Mag inclusions. Yet the MgO content remains higher than expected for a plagioclase (~1 wt%). We thus suspect that there may be some analyses that are mixtures of Plag and Opx, which we have not attempted to correct further. However, this should not affect the relative Ca-Na-K concentrations and thus determination of the stoichiometric Plag end-members. Experimental plagioclase ranges in composition from about An 59 to An 65 (Supplementary Table S4; Figure 6A), and varies according to the water content in the melt and to a lesser extent, by temperature. For the same T, P, and fO 2 , we find that the water content negatively correlates with An content. We have neither been able to analyze experimental Plag for near liquidus charges nor from those with very high crystal content. Some of the experimental Plag compositions overlap with natural Plag microlites and rims from the 1990-2014 eruptions as described in [START_REF] Utami | Fluid fluxing and accumulation drive decadal and short-lived explosive basaltic andesite eruptions preceded by limited volcanic unrest[END_REF] and in this study with An 65 (Figure 6A; Supplementary Table S1). Phenocryst rims and microlites (An content from 65 to 68) overlap with experimental Plag that crystallized at 200 MPa, 1,000 °C, and 4 wt% water in the melt and at NNO.

No experimental Plag composition that we analyzed have An content >65. However, we find that Plag cores and some oscillatory growth zones from all three eruptions with An content of >71 in this study by [START_REF] Utami | Fluid fluxing and accumulation drive decadal and short-lived explosive basaltic andesite eruptions preceded by limited volcanic unrest[END_REF] and [START_REF] Cassidy | Volatile dilution during magma injections and implications for volcano explosivity[END_REF] (see Figure 1 and Supplementary Figure S3). To check whether it is possible to produce Plag with An content of >71 as observed in the 2014 cores (Table 2), we modeled the evolution of the Plag chemistry with rhyolite-MELTS v.1.2.0 using the mixed H 2 O-CO 2 model by [START_REF] Ghiorso | An H2O-CO2 mixed fluid saturation model compatible with rhyolite-MELTS[END_REF]. We used the isobaric crystallization model and the composition of the starting material, with the addition of 4 wt% water and 336 ppm CO 2 in the melt from [START_REF] Cassidy | Volatile dilution during magma injections and implications for volcano explosivity[END_REF], and fO 2 buffered at NNO. We found that Plag with An content of 70-86 can be produced through isobaric crystallization from 933 to 1,063 °C, which is somewhat lower than the highest plagioclase An core compositions at 88-90 (Table 3).

Orthopyroxene

Experimental Opx composition mainly varies with temperature and water content in the melt (Mg Number: 57-71; Figure 6B, Supplementary Table S5). The Wo component of some of the experimental Opx is high (Wo 6-10 ), and is thus classified as pigeonite according to [START_REF] Deer | An introduction to the rockforming minerals[END_REF]. For the same pressure and fO 2 (e.g., 400 MPa, NNO), a temperature increase from 950 to 1,000 °C results in a corresponding increase in the Mg Number of about 56-61; a decrease in the water content in the melt also results in an increase in the Mg Number. A strong influence of water content in the Opx-melt Mg Number partitioning was reported in previous experimental studies [START_REF] Waters | An experimental study of Fe2+-MgKD between orthopyroxene and rhyolite: A strong dependence on H2O in the melt[END_REF]. The 1990-2014 Opx cores and glomerocrysts range from Mg Number 66 to 76 (average of 66). This Mg Number range overlaps with experimental orthopyroxene compositions at 1,000 °C, 200 MPa, and 4-4.5 wt% water in the melt and NNO to NNO +2 for all eruptions. We have not identified pigeonite in the natural samples.

Clinopyroxene

Experimental Cpx is present in most charges (Mg Number: 61-76, Wo 34-41 En 39-46 Fs 15-26 ) (Figure 6C, Supplementary Table S5). The Mg Number of experimental Cpx increases from 61 to 76, with increasing temperature and decreasing water content in the melt. There appears to be some effect of pressure, temperature, and water content on the Cpx composition. At 950 °C, the experimental Cpx at 200 MPa have higher Mg Number (69-76) than at 400 MPa (61-64); one exception is one Cpx with Mg Number of 72 at 1,000 °C, 400 MPa, NNO, and 6 wt% water. The Mg Number increases as water content decreases for isobaric charges at 950 °C and 400 MPa. As we could not obtain good quantitative analysis of Cpx for all charges, we have no clear indication of the effect of fO 2 on clinopyroxene composition. The 1990, 2007, and 2014 clinopyroxene cores and glomerocrysts compositions (Mg Number 70-76, average ~74) somewhat overlaps with experimental clinopyroxene at 1,000 °C, 200 MPa,~4 wt% in the melt, and NNO +2.

Olivine

Experimental Ol (Fo content: 59-76) is present in charges at 950-1,000 °C, p = 100-150 MPa at NNO, and 1,000 °C, 200 MPa, at NNO +2 (Figure 6D, Supplementary Table S6). The Fo content increases strongly with temperature for a water content of 3-5 wt %. There is no discernible systematic change in Fo with increasing fO 2 from NNO to NNO +2. We can only compare the experimental Ol compositions to Ol from the 2014 eruption because the Ol from the 1990 and 2007 eruptions have completely reacted to symplectites. The Ol population from the 2014 eruption ranges in the Fo content from 67 to 73. The 2014 eruption Ol overlaps with experimental Ol at 200 MPa, 1,000 °C, NNO +2, and 4.5 wt% water.

Amphibole

It was particularly difficult to confidently identify Amph in our experimental charges, and we were only able to obtain good quantitative analysis of one experimental Amph (magnesio-hornblende; Mg Number = 69; Supplementary Table S6) in the charge at 950 °C, 400 MPa, and 6 wt% dissolved water in the melt (Figures 2G,H). We also identified additional Amph crystals in other charges using principal component analyses of mineral compositions obtained with EPMA analysis (Supplementary Figure S2). Geothermobarometry results from the natural Amph of the 1990 and 2014 eruptions agree with the experimental Amph stability field we have found (Figure 4). We reconstructed the composition melt from natural Amph from 1990 to 2014 using the Al/Si values, and the methodology of [START_REF] Li | Apatite crystals reveal melt volatile budgets and magma storage depths at Merapi volcano, Indonesia[END_REF] to 3 and Supplementary Table S2 compare the equilibrium SiO 2 content of the parental melt of Amph with that of our glasses. We found that the Amph from 1990 is in equilibrium with 53-60 wt% SiO 2 in the melt, which is close to the SiO 2 content of the starting material glass. The Amph from 2014 is in equilibrium with more silica-rich melt of 68-70 wt% SiO 2 , which overlaps with the interstitial glasses. This shows that a range of amphibole composition are stable in the Kelud system. However, it is unclear if the difference between the 1990 and 2014 Amph represents a real difference under magmatic crystallization conditions or is an artifact of the sampling and the limited number of Amph compositions we have. We note that there are many examples of fully reacted Amph crystals in erupted products from the three eruptions. For the 2007 dome, this could be to the progressively shallowing of the magma (see the following discussion section); for the 1990 and 2014 eruptions it suggests that the magmas were stored at conditions straddling the boundary of the Amph stability field.

Fe-Ti oxides

Magnetite and less common ilmenite were produced in the experimental charges depending on the water content in the melt. Experimental magnetite (X usp = 0.24-0.60) is present in almost all water-saturated charges (Supplementary Table S7). Ilmenite occurs in water poor charges. Although we have identified ilmenite in charges with EDS analyses, we were not able to quantitatively determine their compositions.

SO 2 emissions of 2007 dome extrusion

Kelud emitted around 150 kT and 200-300 kT SO 2 for the 1990 and 2014 eruptions, respectively [START_REF] Carn | Multi-satellite volcanic sulfur dioxide L4 long-term global database V4[END_REF]. In 1990, ~150 kT SO 2 was measured on 11 February, around 1 day after the onset of the main Kelud eruption on 10 February. The measured SO 2 emission is therefore a minimum amount. Similarly, most of the SO 2 emissions from the 2014 eruption (~200 kT) was injected during the main phase of the eruption and detected by satellites 12 h after the eruption, meaning the actual emissions could be higher (up to ~300 kT). Thus, we used the total SO 2 emissions for the 1990 eruption (~150 kT) and a range of emissions for the 2014 eruption (~200-300 kT) to calculate the excess SO 2 from each eruption (Table 6).

We analyzed Aura/OMI SO 2 measurements from July 2007 through May 2008, covering the few months prior to the 2007 dome extrusion at Kelud and the approximate duration of lava dome growth. Volcanic SO 2 emissions clearly attributable to Kelud were only apparent on a few days during this period, although, as noted earlier, SO 2 emissions from other active volcanoes in East Java are frequently advected over the Kelud region and may have obscured any weaker emissions from Kelud. However, significant SO 2 emissions from Kelud would still have been detectable.

No significant SO 2 emissions from Kelud were detected in July-October 2007, when Crater Lake temperatures and CO 2 fluxes were elevated (Global Volcanism Program, 2007;[START_REF] Kunrat | Geochemical and thermodynamic modeling of volcanic fluids and their interpretation for volcano monitoring[END_REF][START_REF] Caudron | Carbon dioxide dynamics in Kelud volcanic lake[END_REF]. It is likely that any SO 2 emissions in this period would have been scrubbed by Kelud's hydrothermal system or Crater Lake. A drifting SO 2 cloud (containing ~100 tons SO 2 ) was first observed west of Kelud on 2 November 2007, a few days before the new lava dome was first directly observed in the crater (Global Volcanism Program, 2008). This SO 2 cannot be unequivocally attributed to Kelud but could represent emissions associated with the initial dome eruption. A clear SO 2 plume (~200 tons SO 2 ) was observed south-west of Kelud on November 5, the day after fresh lava dome extrusion was confirmed (Global Volcanism Program, 2008). Further SO 2 emissions from Kelud were detected on November 7 (~140 tons SO 2 ) and November 25 (~200 tons SO 2 ). These SO 2 observations were made when a favorable wind direction and/or reduced activity at other East Javan volcanoes allowed us to attribute the detected SO 2 emissions to Kelud with some confidence. After 25 November 2007, no further significant SO 2 emissions from Kelud were detected by OMI during the November 2007-May 2008 dome extrusion phase.

Total observed volcanic SO 2 emissions from Kelud during the 2007 dome extrusion thus amount to ~600-700 tons. However, due to frequent cloud cover and generally weak emissions this likely represents a minimum amount. The coincidence of elevated SO 2 emissions and the beginning of subaerial lava dome effusion in early November 2007 is consistent with other observations of effusive eruptions, which typically show a 'waxing-waning' trend in SO 2 emissions, with peak gas fluxes close to the eruption onset. Using the emissions for the 2007 dome and SO 2 concentrations from Plag-hosted melt inclusions [START_REF] Jeffery | The pre-eruptive magma plumbing system of the 2007-2008 dome-forming eruption of Kelut volcano, East Java, Indonesia[END_REF], we calculated the excess SO 2 for the 2007 dome eruption (Table 6).

Discussion

Geothermobarometry and experimental constraints on magma storage conditions of sub-Plinian eruptions and dome extrusions

Combining the geothermobarometric and experimental results, we found that the initial pre-eruptive magma crystallization conditions that match the phenocryst content (Figure 3), natural mineral assemblage (Figure 4), and some of the mineral compositions for the three eruptions (Figure 5) are at 975 ± 39 °C, 175 ± 25 MPa, with about 4-6 wt% water in the melt and a fO 2 of NNO. These conditions correspond to about 7 km of storage below the crater if we use a crustal density of 2,640 kg m -3 . However, geothermobarometry indicates that amphibole which could also be derived from deeper parts are that the 1990 and 2014 amphibole record deep pressures of 450-700 MPa (Table 4), and many crystals are reacted [START_REF] Utami | Fluid fluxing and accumulation drive decadal and short-lived explosive basaltic andesite eruptions preceded by limited volcanic unrest[END_REF]this study). Moreover, the reaction textures in olivine suggest that the magma storage could have straddled the stability fields of amphibole and olivine.

A key difference between the 1990 and 2014 eruptions and that of the 2007 dome is the much higher phenocryst content of the latter (Table 2). This could be due to crystal accumulation in the dome, but the whole-rock major and trace element compositions of the three eruptions are similar, including incompatible trace elements such as Zr (this study; [START_REF] Jeffery | The pre-eruptive magma plumbing system of the 2007-2008 dome-forming eruption of Kelut volcano, East Java, Indonesia[END_REF], meaning that the observed difference in the crystal content is due to in situ crystallization. According to experimental results, the lava dome's higher phenocryst content (Table 2; Figure 3) can be reproduced with ~1 wt% water in the melt for a temperature of about 975 °C. Thus, we propose that although the storage conditions for the 2007 magma were similar to that of the 1990 and 2014 magmas before it started moving to the surface, the lower apparent water content is likely the result of slow transport toward the surface that in turn led to water loss and cooling. The slower ascent observed in 2007 resulted in the re-equilibration of phenocryst proportions and compositions to shallower depths. [START_REF] Cassidy | Explosive eruptions with little warning: Experimental petrology and volcano monitoring observations from the 2014 eruption of Kelud, Indonesia[END_REF] performed partial melting experiments using samples from the 2014 eruption. They explored a smaller range of P-T and water conditions than we report, and they used a crushed rock as starting material and thus 'partial equilibrium' experiments (for discussion about full vs. partial equilibrium experiments, see [START_REF] Pichavant | Equilibration scales in silicic to intermediate magmas implications for experimental studies[END_REF]. Given the different experimental approaches, it is not straightforward to directly compare our results to those of [START_REF] Cassidy | Explosive eruptions with little warning: Experimental petrology and volcano monitoring observations from the 2014 eruption of Kelud, Indonesia[END_REF]. Some notable differences are that our experiments crystallized amphibole and olivine (and we also find them in the natural rock), which are absent in [START_REF] Cassidy | Explosive eruptions with little warning: Experimental petrology and volcano monitoring observations from the 2014 eruption of Kelud, Indonesia[END_REF], but this is likely because we investigated a wider range of experimental parameters. Our inferred crystallization temperatures are similar to those of [START_REF] Cassidy | Explosive eruptions with little warning: Experimental petrology and volcano monitoring observations from the 2014 eruption of Kelud, Indonesia[END_REF] for all the eruptions, but we find higher pressures and water contents in the melt.

The importance of excess volatiles in modulating eruption style

The explosive → effusive → explosive eruption sequence shown by the 1990-2007-2014 events is one of the most interesting aspects of Kelud volcano. The contrasting eruptive style is particularly intriguing because we have shown that the "initial" (i.e., before ascent) conditions of temperature, pressure, and water content in the melt are broadly the same for the three events. Other factors that could be responsible for the differences in eruptive style are the conduit dynamics, where parameters such as the magma flow rate and overpressure work together to determine whether the magma will erupt explosively or effusively [START_REF] Woods | Transitions between explosive and effusive eruptions of silicic magmas[END_REF][START_REF] Mastin | Insights into volcanic conduit flow from an open-source numerical model[END_REF][START_REF] Campagnola | Confort 15 model of conduit dynamics: Applications to pantelleria green tuff and etna 122 BC eruptions[END_REF]. Syn-eruptive processes at the conduit level certainly played a key role in the eruption style at Kelud, but several observations point toward the importance of other parameters, especially the possible presence of a pre-eruptive volatile phase. (2022).

Frontiers in Earth Science frontiersin.org 20

Our mass balance calculations and those of [START_REF] Utami | Fluid fluxing and accumulation drive decadal and short-lived explosive basaltic andesite eruptions preceded by limited volcanic unrest[END_REF] for the SO 2 budget of the 1990 and 2014 eruptions indicate the presence of an exsolved volatile phase at pre-eruptive conditions, with up to 130 kT SO 2 for the 1990 eruption and 276 kT SO 2 for the 2014 eruption (Table 6). In contrast, the calculated amount of the exsolved volatile fluid phase for the 2007 dome eruption is virtually negligible. Pre-eruptive excess fluid can be developed via progressive magma crystallization and volatile buildup to supersaturation [START_REF] Tait | Pressure, gas content and eruption periodicity of a shallow, crystallising magma chamber[END_REF][START_REF] Tramontano | Internal triggering of volcanic eruptions: Tracking overpressure regimes for giant magma bodies[END_REF][START_REF] Arzilli | The unexpected explosive sub-Plinian eruption of Calbuco volcano (22-23 April 2015; southern Chile): Triggering mechanism implications[END_REF][START_REF] Cassidy | Explosive eruptions with little warning: Experimental petrology and volcano monitoring observations from the 2014 eruption of Kelud, Indonesia[END_REF], and/or with fluid fluxing from a deep-seated basaltic magma reservoir [START_REF] Giuffrida | Effects of CO2flushing on crystal textures and compositions: Experimental evidence from recent K-trachybasalts erupted at Mt. Etna[END_REF][START_REF] Caricchi | Modulation of magmatic processes by CO2 flushing[END_REF], or limestone assimilation [START_REF] Deegan | Boron isotope fractionation in magma via crustal carbonate dissolution[END_REF][START_REF] Deegan | Magma-carbonate interaction processes and associated CO2 release at Merapi volcano, Indonesia: Insights from experimental petrology[END_REF][START_REF] Jeffery | The pre-eruptive magma plumbing system of the 2007-2008 dome-forming eruption of Kelut volcano, East Java, Indonesia[END_REF]. Although we can only calculate the amount of SO 2 , the fluid phase would have also included other volatiles including water and CO 2 . The presence of an exsolved fluid phase under preeruptive conditions means the magma buoyancy is greatly increased, as fluids can expand from the moment the magma starts its ascent, lithostatic pressure decreases [START_REF] Gonnermann | Dynamics of magma ascent in the volcanic conduit[END_REF].

A critical aspect to the role of exsolved volatiles in the explosivity of the eruption is whether they separate from the melt during transport, and thus increase the magma permeability. [START_REF] Popa | Water exsolution in the magma chamber favors effusive eruptions: Application of Cl-F partitioning behavior at the Nisyros-Yali volcanic area[END_REF] proposed a model where effusive eruptions can be driven by magmas with an exsolved volatile phase under pre-eruptive conditions and a higher water content in the melt (and somewhat hotter due to mafic intrusion) than explosive events. The lower viscosity of the melt combined with the higher bubble content at the starting conditions would facilitate fluid escape through the magma column due to higher permeability, thus decreasing the explosivity. Although this may be responsible for the contrasting eruptive styles at the Nisyros-Yali volcanic system [START_REF] Popa | Water exsolution in the magma chamber favors effusive eruptions: Application of Cl-F partitioning behavior at the Nisyros-Yali volcanic area[END_REF]2020), at Kelud we did not find the magma that produced the dome in 2007 had a lower viscosity than the explosive events [START_REF] Utami | Petrological and monitoring insights into the mechanisms driving eruptions of Kelud volcano, Indonesia[END_REF]. There was also no initial explosive event recorded before the dome extrusion itself (Global Volcanism Program, 2008). Rather, we propose that the exsolved volatile phase that was likely related to the 2007 magma was passively released during the repose between 1990 and 2007, which was punctuated by at least two significant unrest events involving gas release (see below).

The accumulation of an excess fluid also requires the plumbing system to be a plugged or semi-plugged system during repose [START_REF] Whelley | The frequency of explosive volcanic eruptions in Southeast Asia[END_REF], or with the mass flux of exsolved fluids production being larger than that, which is degassed, and further implying limited passive degassing between eruptions. Prior to the 1990 eruption, volatiles accumulating at depth were likely blocked by a plug of crystalline magma from the previous event in 1966 and ~4 million m 3 of lake water [START_REF] Lesage | Seismic precursors of the february 10, 1990 eruption of Kelut volcano, Java[END_REF][START_REF] Vandemeulebrouck | Hydroacoustic noise precursors of the 1990 eruption of Kelut Volcano, Indonesia[END_REF], whereas before the 2014 eruption, the volcano was plugged by the 2007 dome (Global Volcanism Program, 2014). In contrast, between the 1990 eruption and up until 2007 dome, the system appears to have been much more open for gas escape, including two unrest crisis (Figure 7 and next section). This included fumarolic activity and two heating crises observed in 1996 and 2001, when the lake water increased in temperature from 35 to 40-~50 °C [START_REF] Bernard | Geochemical evolution of the young crater lake of Kelud volcano in Indonesia[END_REF]. Hence, the observed post-and inter-eruptive crises between 1990 and 2007 suggest the magma system was partially open, allowing the shallow magma body to further degas volatiles out of the system and thus was not able to accumulate excess fluids.

Our proposed interpretation, that the 1990 and 2014 eruptions resulted from the accumulation of pre-eruptive gas, is similar to that of [START_REF] Cassidy | Explosive eruptions with little warning: Experimental petrology and volcano monitoring observations from the 2014 eruption of Kelud, Indonesia[END_REF] and [START_REF] Cassidy | Volatile dilution during magma injections and implications for volcano explosivity[END_REF]. However, we do not find evidence for the replenishment of hotter and wetter magma involved in the 2007 dome extrusion. Instead, we propose the 2007 dome was the result of leftover magma from the 1990 eruption that underwent slow ascent and degassing until it extruded as a lava dome. This is possible even if the 2007 magma was likely stored under the same conditions as the 1990 and 2014 magmas before it started slow ascent toward the surface.

Relating magma storage conditions and transport to the surface with unrest signal

Volcanic unrest at Kelud before and during these three eruptions was monitored using a range of observations and data, including seismicity, deformation, and the chemistry and temperature of the lake. Unrest signals preceding all three events started around 2-3 months before eruption, and included seismic swarms with unrest signals spanning volcano-tectonic, shallow volcanic (VB-type), low frequency, and tremor seismicity [START_REF] Lesage | Seismic precursors of the february 10, 1990 eruption of Kelut volcano, Java[END_REF][START_REF] Hidayati | Differences in the seismicity preceding the 2007 and 2014 eruptions of Kelud volcano, Indonesia[END_REF]2009). Seismicity rapidly increased (e.g., < 24 h) before the 1990 and 2014 eruptions, and earthquake hypocenters are mostly at shallow depths beneath the crater (<7 km) [START_REF] Lesage | Seismic precursors of the february 10, 1990 eruption of Kelut volcano, Java[END_REF][START_REF] Hidayati | Differences in the seismicity preceding the 2007 and 2014 eruptions of Kelud volcano, Indonesia[END_REF]. Sharp increases in lake temperature and input of magmatic volatiles such as Cl-and CO 2 into the lake have also been proposed for the unrest prior to the 1990 and 2007 eruptions [START_REF] Vandemeulebrouck | Hydroacoustic noise precursors of the 1990 eruption of Kelut Volcano, Indonesia[END_REF][START_REF] Bernard | Geochemical evolution of the young crater lake of Kelud volcano in Indonesia[END_REF][START_REF] Kunrat | Geochemical and thermodynamic modeling of volcanic fluids and their interpretation for volcano monitoring[END_REF][START_REF] Caudron | Carbon dioxide dynamics in Kelud volcanic lake[END_REF].

Tiltmeters and interferometric synthetic aperture radar (InSAR) detected changes in local and regional deformation from inflation to rapid deflation, preceding 2014 eruption and 2007 dome extrusion, respectively [START_REF] Lubis | Uplift of Kelud volcano prior to the november 2007 eruption as observed by L-band insar[END_REF][START_REF] Cassidy | Explosive eruptions with little warning: Experimental petrology and volcano monitoring observations from the 2014 eruption of Kelud, Indonesia[END_REF][START_REF] Hidayati | Differences in the seismicity preceding the 2007 and 2014 eruptions of Kelud volcano, Indonesia[END_REF]. [START_REF] Lubis | Uplift of Kelud volcano prior to the november 2007 eruption as observed by L-band insar[END_REF] analyzed InSAR images of the 2007 dome extrusion and detected inflation 1-2 months before the dome extrusion, where they further interpreted the inflation as due to an increase in volume of magma in a shallow reservoir and magma migration to the surface. Tiltmeters from two stations installed at Kelud recorded inflation in the radial and tangential directions in January 2014; rapid inflation was also recorded after a M4.5 volcano-tectonic earthquake was recorded in Blitar/Kediri [START_REF] Hidayati | Differences in the seismicity preceding the 2007 and 2014 eruptions of Kelud volcano, Indonesia[END_REF]. These observations both record inflation at least 1 month before the 2007 and 2014 eruptions.

An important observation is that during the inter-eruptive period between 1990 and 2007, the system seems to have been able to degas more freely. This is reflected in the volcanic crises that occurred in 1996 and 2001, when lake temperature increased by +4 and +13 °C, respectively (Global Volcanism Program, 1990a;Global Volcanism Program, 2007) (Figure 7). Other unrest signals included white plumes (1996), lake pH decrease, and lake level increase (2001). These releases of heat/mass may represent purging of outgassed magmatic fluids. The 2007 magma would then have lost some of its volatile content, aiding final extrusion in an effusive manner. Given the high crystal content (70 vol%) and complex zoning observed in the crystal cargo, including oscillatory zoning of plagioclase, the lava dome was likely a residual magma batch from the 1990 eruption or earlier. Indeed, we find that the synextrusive 2007 dome SO 2 emissions amounted to 0.6-0.7 kT, which is about 1,000 times lower than the 1990 and 2014 eruptions (150 and 200-300 kT, respectively) (Table 6). The low water content is also established in the experiments, Bourdier et al. (1997aBourdier et al. ( ) for 1990;;Global Volcanism Program (2008) for 2007 lava dome; and [START_REF] Kristiansen | Stratospheric volcanic ash emissions from the 13 February 2014 Kelut eruption[END_REF] for 2014. Timeline for volcanic unrest is provided for the 1990 eruption (Global Volcanism Program, 1990a;Global Volcanism Program, 1990b;[START_REF] Lesage | Seismic precursors of the february 10, 1990 eruption of Kelut volcano, Java[END_REF][START_REF] Vandemeulebrouck | Hydroacoustic noise precursors of the 1990 eruption of Kelut Volcano, Indonesia[END_REF]), 2007dome extrusion (Global Volcanism Program, 2008;[START_REF] Caudron | Carbon dioxide dynamics in Kelud volcanic lake[END_REF][START_REF] Lubis | Uplift of Kelud volcano prior to the november 2007 eruption as observed by L-band insar[END_REF][START_REF] Hidayati | Differences in the seismicity preceding the 2007 and 2014 eruptions of Kelud volcano, Indonesia[END_REF]), and 2014eruption (Global Volcanism Program, 2014;[START_REF] Hidayati | Differences in the seismicity preceding the 2007 and 2014 eruptions of Kelud volcano, Indonesia[END_REF], as well as the inter-eruptive unrest in 1996and 2001(Global Volcanism Program, 1990a;Global Volcanism Program, 2007).

which showed the 2007 magma had at most ~1 wt% water in the melt. Due to frequent cloud cover and the relatively short atmospheric lifetime of SO 2 in the tropics, the OMI satellite measurements of syn-extrusive 2007 dome SO 2 emissions are likely underestimates of actual emissions. However, even in the unlikely event that Kelud had degassed SO 2 continuously throughout the period of most active lava dome growth (November 2007-January 2008;Global Volcanism Program, 2013) at similar levels to those observed by OMI in November 2007, total SO 2 emissions would only have amounted to ~9 kT; that is, still two orders of magnitude lower than the 1990 and 2014 eruptions. We are therefore confident that the syn-extrusive 2007 lava dome emissions were significantly poorer in SO 2 than the 1990 and 2014 eruptions.

If our hypothesis is correct, identifying and tracking whether a volcanic system is opened or closed to volcanic gases escaping could be useful to anticipate its likely eruptive style. A key component could therefore be to monitor for several unrest signals linked to volcanic gas escape from the magma, and changes to conduit permeability. This includes increased fumarolic activity, decreases in the pH of the lake water, visible upwelling and bubbling, increasing lake temperature, hydroacoustic signals, and clusters of VB-type seismicity [START_REF] Lesage | Seismic precursors of the february 10, 1990 eruption of Kelut volcano, Java[END_REF][START_REF] Vandemeulebrouck | Hydroacoustic noise precursors of the 1990 eruption of Kelut Volcano, Indonesia[END_REF][START_REF] Bernard | Geochemical evolution of the young crater lake of Kelud volcano in Indonesia[END_REF][START_REF] Hidayati | Emergence of lava dome from the crater lake of Kelud volcano, East Java[END_REF]. These unrest signals could suggest the impending eruption would be effusive. On the contrary, monitoring signals that could be related to fluid accumulation and magma degassing, or magma transfer within the plumbing system, could be useful in anticipating explosive eruptions. For example, identification of deep-long period seismicity using broadband seismometers, which could come from degassing of volatile-rich magma at depth [START_REF] Melnik | Modelling of conduit flow dynamics during explosive activity at Soufrière Hills Volcano, Montserrat[END_REF] or deformation signals before and after the eruption [START_REF] Spang | Quantification of volcano deformation caused by volatile accumulation and release[END_REF]. Finally, microgravity surveys or continuous gravity monitoring could be beneficial because we expect that significant fluid accumulation would lead to subtle changes in density of the plumbing system over time, which was demonstrated at Masaya volcano (Nicaragua) [START_REF] Williams-Jones | Gravity changes and passive SO2 degassing at the Masaya caldera complex, Nicaragua[END_REF].

Conclusion

We present petrological and experimental constraints under the pre-eruptive storage conditions of the basaltic andesite magma feeding the 1990, 2007, and 2014 eruptions of Kelud volcano, which alternated between explosive → effusive → explosive eruption styles. The three eruptions share similar whole rock compositions and mineralogy, implying that their magma storage conditions were also similar. We found that the natural phenocryst content and mineral assemblage can be experimentally reproduced at 975 ± 39 °C, 175 ± 25 MPa (~7 km below the crater level), NNO, and with ca. 4-6 wt% water in the melt. We also infer that the 1990 and 2014 magmas co-existed with an exsolved volatile phase under pre-eruptive conditions and propose that this played a main role to their explosive style. Our mass balance of SO 2 suggests the magma that led to the 2007 lava dome had no or negligible excess fluids. This is likely the result of several inter-eruptive crises after the 1990 eruption that likely allowed gases to be released. Thus, tracking the degree to which volcanoes may be opened or closed to gases escaping in inter-eruptive periods may help to anticipate eruption styles.

FIGURE 1

 1 FIGURE 1 Histograms of representative mineral compositions from the 1990-2014 eruptions (A) pyroxenes, (B) olivine, and (C) plagioclase. Plagioclase composition from the 2014 eruption comes from a combination of this study and Cassidy et al. (2016) and those of the 1990 from Utami et al. (2021).

FIGURE 2

 2 FIGURE 2 Annotated BSE images of selected representative experimental charges in order of increasing crystallinity. (A) 1,060 °C-200 MPa-NNO. (B) 1,000 °C-100 MPa-ΔNNO + 2. (C) 950 °C-150 MPa-NNO. (D) 1,000 °C-200 MPa-NNO. (E) 950 °C-200 MPa-ΔNNO + 2. (F) 950 °C-400 MPa-NNO. (G) 950 °C-400 MPa-NNO. (H) Inset of charge in (G) Labeled with abbreviated mineral names (Gl = glass, Plag = plagioclase, Cpx = clinopyroxene, Opx = orthopyroxene, Mag = magnetite, and Amph = amphibole).

FIGURE 3

 3 FIGURE 3 Dissolved water content in the melt vs. crystal content of experimental charges for (A) 200-400 MPa, NNO; (B) 100-200 MPa, NNO. Dashed lines denote extrapolated crystal contents of experimental charges. Gray, red, and blue semitransparent boxes represent the field bounded by the phenocryst content of natural samples, water content in the melt for the given temperature with SEE errors from Opx-melt geothermometer (975 ± 39 °C) for the 1990 pumices (explosive), 2007 dome fragments (effusive), and 2014 pumices (explosive). Dashed arrows indicate possible changes of water in the melt during ascent for the 2007 magma. The phenocryst contents of the erupted rocks are from Utami et al. (2021) and this study (Table2). Average temperature estimates from each eruption are calculated from mineral-melt geothermobarometry listed in Table4.

FIGURE 4

 4 FIGURE 4 Phase relations for (A) 200-400 MPa, NNO; (B) 100-200 MPa, NNO. Gray, red and blue semi-transparent boxes represent the same parameters as Figure 3. Dashed lines denote inferred phase stability fields at the given temperature and water content. Dashed arrows indicate potential degassing pathways for the 2007 dome. Mineral name abbreviations are the same as in Figure 1, with the addition of Liq for liquid and Ilm for ilmenite. Pressure-specific stability is specified next to the boundary line. Red line with 'liq' represents the liquidus boundary at the given pressure and temperature.

  FIGURE 5Major element oxide compositions of experimental glasses (in wt%) vs. dissolved water content in the melt according to three different temperatures SiO 2 (A) 950 °C, (B) 1,000 °C, (C) 1,060 °C; Al 2 O 3 (D) 950 °C; (E) 1,000 °C, (F) 1,060 °C; CaO (G) 950 °C; (H) 1,000 °C; (I) 1,060 °C; K 2 O (J) 950 °C, (K) 1,000 °C, (L) 1,060 °C. Yellow horizontal band denotes the range of whole rock compositions. The thick gray band is the composition of calculated matrix for the explosive eruptions(1990, 2014); the thin gray band is the calculated matrix of the 2007 dome (Table1). The calculated matrix compositions for the 1990, 2007, and 2014 eruptions were estimated by mass balance calculations[START_REF] Albarede | Introduction to geochemical modeling[END_REF] (see Methodology section). Vertical dashed lines are water content in the melt inferred from crystallinity and phase assemblage (Figures3, 4). Filled symbols represent experiments at NNO; open lined symbols represent experiments at NNO +2.

FIGURE 6

 6 FIGURE 6 Experimental mineral compositions compared to natural minerals from the 1990, 2007, and 2014 eruptions (A) An content in Plag, (B) Mg Number in Opx, (C) Mg Number in Cpx, and (D) Fo content in Ol. Gray horizontal bands are of the mineral compositions from the three eruptions taken from the core compositions of the minerals (Data fromTable 3 and Supplementary Table S2 of this study). Only the rim compositions of the Plag are to compare with experiments. Filled symbols represent the experiments at NNO; open-lined symbols represent experiments at NNO +2.

  FIGURE 6 Experimental mineral compositions compared to natural minerals from the 1990, 2007, and 2014 eruptions (A) An content in Plag, (B) Mg Number in Opx, (C) Mg Number in Cpx, and (D) Fo content in Ol. Gray horizontal bands are of the mineral compositions from the three eruptions taken from the core compositions of the minerals (Data fromTable 3 and Supplementary Table S2 of this study). Only the rim compositions of the Plag are to compare with experiments. Filled symbols represent the experiments at NNO; open-lined symbols represent experiments at NNO +2.

FIGURE 7

 7 FIGURE 7Conceptual model of the proposed magmatic conditions and processes occurring for the 1990-2014 eruptions. Black rectangles in the magma reservoirs represent the crystal cargo or crystallization in the conduit. White flattened circles represent accumulation of the pre-eruptive exsolved fluid phase. Solid white arrows represent fluid fluxing through the system either from a deep-seated degassing basaltic magma, or from limestone assimilation for explosive eruptions. Dashed white arrows represent fluid release through a semi-permeable conduit leading up to dome extrusion. Symbols and codes are listed in the legend. Storage pressures are converted to depth below the crater using the density calculated in[START_REF] Smyth | The deep crust beneath island arcs: Inherited zircons reveal a gondwana continental fragment beneath East Java, Indonesia[END_REF]. The volcaniclastic and carbonate layers are taken from[START_REF] Jeffery | The pre-eruptive magma plumbing system of the 2007-2008 dome-forming eruption of Kelut volcano, East Java, Indonesia[END_REF], and references therein. Volcano Explosivity Indices (VEI) reported come from Global Volcanism Program (2013). Plume height are reported inBourdier et al. (1997aBourdier et al. ( ) for 1990;; Global Volcanism Program (2008) for 2007 lava dome; and[START_REF] Kristiansen | Stratospheric volcanic ash emissions from the 13 February 2014 Kelut eruption[END_REF] for 2014. Timeline for volcanic unrest is provided for the 1990 eruption(Global Volcanism Program, 1990a; Global Volcanism Program, 1990b;[START_REF] Lesage | Seismic precursors of the february 10, 1990 eruption of Kelut volcano, Java[END_REF][START_REF] Vandemeulebrouck | Hydroacoustic noise precursors of the 1990 eruption of Kelut Volcano, Indonesia[END_REF], 2007 dome extrusion(Global Volcanism Program, 2008;[START_REF] Caudron | Carbon dioxide dynamics in Kelud volcanic lake[END_REF][START_REF] Lubis | Uplift of Kelud volcano prior to the november 2007 eruption as observed by L-band insar[END_REF][START_REF] Hidayati | Differences in the seismicity preceding the 2007 and 2014 eruptions of Kelud volcano, Indonesia[END_REF]), and 2014 eruption (Global Volcanism Program, 2014;[START_REF] Hidayati | Differences in the seismicity preceding the 2007 and 2014 eruptions of Kelud volcano, Indonesia[END_REF], as well as the inter-eruptive unrest in1996 and 2001 (Global Volcanism Program, 1990a; Global Volcanism Program, 2007).

TABLE 1

 1 Representative whole rock and glass compositions for the starting glass, whole rock, clinopyroxene-hosted melt inclusions, and interstitial glassfrom the 1990, 2007, and 2014.

	Frontiers in Earth Science	Whole rock a	Whole rock	Whole rock	Starting dry glass	Calculated matrix b	Measured interstitial	Calculated matrix b	Measured interstitial	Calculated matrix b	Cpx glass inclusion a	Cpx glass inclusion
							glass a		glass
	Eruption	1990	2007	2014	1990	1990	1990	2007	2014	2014	1990	2014
	year
	N	1	1	1	1 0	1	2 3	1	5	1	2 3	5
	Normalized
	wt%
	SiO 2	54.3	54.9	55.3	55.0 (0.4)	63.0	68.5 (1.4)	72.9	67.1 (0.38)	60.56	69.4 (1.5)	68.5 (0.8)
	TiO 2	0.70	0.64	0.65	0.64 (0.11)	0.34	0.53 (0.07)	0.20	0.61 (0.07)	0.32	0.49 (0.06)	0.64 (0.07)
	Al 2 O 3	19.00	18.62	18.55	18.97 (0.13)	17.42	15.33 (0.41)	11.91	15.45 (0.22)	18.79	16.09 (0.42)	15.60 (0.25)
	FeO*	9.28	9.15	8.95	8.92 (0.56)	5.18	4.12 (0.30)	2.75	4.57 (0.16)	4.85	2.77 (0.77)	4.05 (0.18)
	MnO	0.20	0.20	0.20	0.19 (0.03)	0.17	0.15 (0.03)	0.11	0.17 (0.05)	0.15	0.12 (0.03)	0.16 (0.06)
	MgO	3.67	3.71	3.60	3.81 (0.06)	2.28	1.13 (0.14)	0.69	1.37 (0.06)	2.09	0.49 (0.18)	0.99 (0.07)
	CaO	9.08	9.04	8.97	8.74 (0.04)	6.77	3.87 (0.38)	5.11	4.45 (0.11)	8.65	2.94 (0.26)	3.55 (0.29)
	Na 2 O	2.91	2.90	2.98	2.93 (0.07)	3.13	4.48 (0.20)	3.78	4.35 (0.18)	3.33	4.77 (0.41)	4.37 (0.12)
	K 2 O	0.69	0.68	0.69	0.68 (0.03)	1.35	1.59 (0.12)	2.11	1.57 (0.10)	1.05	1.78 (0.17)	1.63 (0.07)
	P 2 O 5	0.16	0.13	0.14	0.13 (0.02)	0.33	0.21 (0.03)	0.43	0.25 (0.03)	0.20	0.25 (0.06)	0.24 (0.03)
	Total c	99.7	101.1	101.0	100.4 (1.0)	100.0	98.9 (1.1)	100.0	99.0 (0.4)	100.0	94.9 (1.3)	93.6 (0.7)
	Na 2 O+	3.60	3.58	3.67	3.62 (0.08)	4.48	6.07 (0.26)	5.88	5.91 (0.21)	4.38	6.08 (0.50)	5.73 (0.27)
	K 2 O
	SO 2 (ppm)	n.a.	n.a.	n.a.	n.a.	n.a.	46-110	n.a.	b.d.	n.a.	316-904	278-565
	Cl (wt%)	n.a.	n.a.	n.a.	0.03 (0.01)	n.a.	0.12 (0.02)	n.a.	0.13 (0.01)	n.a.	0.19 (0.01)	0.16 (0.02)
	a Average values of compositions from Utami et al. (2021).
	b Calculated matrix is determined from whole rock composition minus mineral chemistry (in major element oxide) weighted by mass proportion (see Methodology section). c Individual major element oxide compositions are normalized in wt%, but the
	original total is presented.
	Note. n. a. = not analyzed. b.d.l. = below detection limit.
	frontiersin.org

TABLE 2

 2 Mineral assemblage and phenocryst content ofsamples from 1990, 2007, and 2014 eruptions.

	Sample label	90-23 a	PL1 a	2007A	2007B	14-PUMI-1	14-PUMI-2
	Eruption	1990	1990	2007	2007	2014	2014
	Phase b	wt%	wt%	wt%	wt%	wt%	wt%
	Glm c	52.8	69.1	27.8	30.2	70.5	65.1
	Plag	37.6	14.1	48.2	47.7	21.2	19.9
	Cpx	3.3	6.6	4.6	3.9	1.2	2.1
	Opx	3.9	5.4	10.6	12.0	3.0	7.5
	Mag	2.4	4.8	8.5	6.2	3.6	4.7
	Amph		<0.1	0.3		0.5
	Ol		<0.1				0.7
	Apa d	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1
	Total	100.0	100.0	100.0	100.0	100.0	100.0
	Phenocryst content e	47.3	30.9	71.9	69.8	29.0	34.2

a Samples PL1 and 90-23 here are the same as '1990-PL1' and '90-23′ that were reported in

[START_REF] Utami | Fluid fluxing and accumulation drive decadal and short-lived explosive basaltic andesite eruptions preceded by limited volcanic unrest[END_REF]

. b Opx = orthopyroxene; Cpx = clinopyroxene; Plag = plagioclase; Mag = magnetite; Ol = olivine; Amph = amphibole; Apa = apatite. c Glm means the sample's matrix. d Apatite was identified as an accessory mineral. e Phenocryst size is defined as grains larger than 100 μm.

TABLE 3

 3 Summary of representative mineral compositions from the 1990-2014 eruptions. Pyroxene end-members: wollastonite, Wo = 100 x Ca/[Mg + Fe* + Ca]; enstatite, En = 100 x Mg/[Mg + Fe* + Ca]; ferrosilite, Fs = 100 x Fe*/[Mg + Fe* + Ca]; Mg # = 100 x Mg/[Mg + Fe*]. Amphibole end-members according to[START_REF] Leake | Nomenclature of amphiboles report of the subcommittee on amphiboles of the international mineralogical association commission on new minerals and mineral names[END_REF], as calculated in[START_REF] Ridolfi | Stability and chemical equilibrium of amphibole in calc-alkaline magmas: An overview, new thermobarometric formulations and application to subduction-related volcanoes[END_REF]. Mg-Hst = magnesio-hastingsite; Ts-Prg = Tschermakite-Pargasite.Notes. n. a. = not analyzed, and b.d. = below detection limit. FeO* or Fe* = total Fe as Fe 2+ . Glom = glomerocryst. See Table2for meaning of mineral abbreviations.TABLE 4 New storage condition estimates from mineral-melt geothermobarometers, hygrometers, and H 2 O-CO 2 saturation models for the 1990, 2007, and 2014 mineral populations. for 2007 dome, Opx-, and Cpx-liquid geothermometer calculations used whole rock/core mineral compositions. Plag-melt hygrometer calculations used whole rock/Opx-melt temperatures for cores, and calculated interstitial glasses/two-pyroxene temperatures for rims. QUILF, two-pyroxene geothermometer[START_REF] Andersen | QUILF: A pascal program to assess equilibria among Fe-Mg-Mn-Ti oxides, pyroxenes, olivine, and quartz[END_REF]; SEE = ± 37 °C, assuming a constant pressure of 100 MPa[START_REF] Utami | Fluid fluxing and accumulation drive decadal and short-lived explosive basaltic andesite eruptions preceded by limited volcanic unrest[END_REF]. d Saturation P is calculated using VESIcal[START_REF] Iacovino | VESIcal Part I: An open-source thermodynamic model engine for mixed volatile (H2O-CO2) solubility in silicate melts[END_REF] with hybrid of pure H 2 O model[START_REF] Shishkina | Solubility of H2O-and CO2-bearing fluids in tholeiitic basalts at pressures up to 500MPa[END_REF]) + pure CO2 model[START_REF] Dixon | Degassing of alkalic basalts[END_REF] + water content from Plag-melt hygrometer[START_REF] Waters | An updated calibration of the plagioclase-liquid hygrometer-thermometer applicable to basalts through rhyolites[END_REF]. CO 2 content taken from[START_REF] Cassidy | Volatile dilution during magma injections and implications for volcano explosivity[END_REF] (Max: 336 ppm). e Dissolved water contents were calculated using the Plag-melt hygrometer by[START_REF] Waters | An updated calibration of the plagioclase-liquid hygrometer-thermometer applicable to basalts through rhyolites[END_REF] (SEE ±0.35 wt%) with plag compositions from[START_REF] Utami | Fluid fluxing and accumulation drive decadal and short-lived explosive basaltic andesite eruptions preceded by limited volcanic unrest[END_REF] and this study.Temperatures are from Opx-melt and two-pyroxene geothermometers from[START_REF] Putirka | Thermometers and barometers for volcanic systems[END_REF].

	Mineral	Plag	Plag	Plag	Plag	Mineral	Amph c		Amph
	Eruption year	1990	2007	2014	1990	2007	2014		2014
	Rock type/stage	Main-stage	Dome	Pumice	Main-stage	Dome	Pumice
		pumice			pumice
	Texture	Cores,	Cores,	Cores,	Cores,	Glomerocryst Cores,
		glomerocryst	glomerocryst	glomerocryst	glomerocryst		glomerocryst
	N	8	1 6	2 6	2 0	7	2 7		2 7
	wt%
	SiO 2	51.6 (0.7)	51.8 (0.4)	51.2 (0.6)	52.7 (0.2)	52.9 (0.1)	52.7 (0.5)	SiO 2	36.9 (0.4)
	TiO 2	0.48 (0.30)	0.33 (0.04)	0.36 (0.07)	0.28 (0.12)	0.16 (0.01)	0.19 (0.04)	TiO 2	0.02
									(0.02)
	Al 2 O 3	1.78 (0.62)	1.71 (0.18)	2.00 (0.44)	1.24 (0.34)	0.91 (0.17)	1.09 (0.36)	Al 2 O 3	b.d.
	FeO*	9.24 (0.58)	9.54 (0.16)	9.48 (0.26)	18.53 (1.18)	19.2 (0.2)	18.44 (1.38)	FeO*	25.9 (1.6)
	MnO	0.50 (0.09)	0.52 (0.03)	0.49 (0.05)	0.87 (0.18)	0.90 (0.04)	0.84 (0.11)	MnO	0.65
									(0.09)
	MgO	14.47 (0.09)	14.30 (0.23)	14.40 (0.22)	23.5 (0.5)	22.84 (0.07)	23.71 (0.90)	MgO	35.1 (1.4)
	CaO	21.1 (0.4)	20.8 (0.3)	20.8 (0.3)	1.71 (0.43)	1.44 (0.08)	1.59 (0.22)	CaO	0.18
									(0.05)
	Na 2 O	0.27 (0.02)	0.29 (0.02)	0.28 (0.02)	0.02 (0.01)	0.02 (0.01)	0.01 (0.01)	P 2 O 5	0.04
									(0.04)
	Total	99.4 (0.2)	99.3 (0.4)	99.0 (0.3)	98.9 (0.3)	98.4 (0.1)	98.6 (0.4)	Total	98.8 (0.4)
	Pyroxene end-
	members a
	Wo	43.6 (0.8)	43.2 (0.6)	43.1 (0.6)	3.50 (0.87)	2.99 (0.16)	3.24 (0.44)	Fo	70.7 (2.1)
								content b
	En	41.6 (0.3)	41.3 (0.5)	41.6 (0.5)	66.9 (1.2)	65.9 (0.3)	67.4 (2.0)
	Fs	14.88 (0.91)	15.46 (0.31)	15.34 (0.42)	29.6 (2.0)	31.1 (0.2)	29.4 (2.4)
	Mg Number	73.7 (1.3)	72.8 (0.5)	73.0 (0.6)	69.3 (1.8)	67.9 (0.2)	69.6 (2.4)
	Mineral	Plag	Plag	Plag	Plag	Mineral	Amph c	Amph c	Amph
	Eruption year	1990	2007	2014	2014	Eruption year	1990	1990	2014
	rock type/stage	Main-stage pumice	Dome	Pumice	Pumice	Rock type/stage
	Texture	Microlite/rim	Rim	Core	Rim	Texture
	n of new spots	11	12	4	2	N	13	4	4
	SiO 2	50.9 (1.3)	50.6 (1.3)	45.3 (1.4)	51.0 (0.1)	SiO 2	41.3 (0.2)	42.5 (0.5)	43.7 (3.1)
	Al 2 O 3	30.2 (0.6)	30.4 (0.9)	33.6 (0.3)	29.3 (0.1)	TiO 2	1.47 (0.10)	1.54 (0.14)	1.60 (0.60)
	FeO*	0.45 (0.16)	0.62 (0.06)	0.53 (0.05)	0.67 (0.01)	Al 2 O 3	15.14 (0.32)	13.92 (1.01)	11.37 (3.99)
	MgO	0.07 (0.02)	0.06 (0.02)	0.01 (0.01)	0.08 (0.01)	FeO*	11.25 (0.28)	11.29 (0.19)	11.33 (2.05)
	CaO	13.58 (0.45)	13.48 (0.88)	17.93 (0.90)	13.42 (0.05)	MnO	0.15 (0.01)	0.17 (0.02)	0.19 (0.13)
	Na 2 O	4.06 (0.23)	3.62 (0.50)	1.31 (0.18)	3.86 (0.08)	MgO	13.84 (0.25)	14.21 (0.11)	15.15 (1.0)
	K 2 O	0.09 (0.02)	0.09 (0.03)	n.a.	n.a.	CaO	12.06 (0.16)	11.71 (0.07)	11.14 (1.63)
	Total	99.4 (1.0)	98.9 (0.6)	98.7 (0.8)	98.35 (0.01)	Na 2 O	2.25 (0.08)	2.23 (0.02)	1.77 (0.67)
						K 2 O	0.31 (0.02)	0.29 (0.02)	n.a.
	Plag				Cl	0.01 (0.01)	0.01 (0.01)	n.a.
	end-member d
	An	64.4 (1.8)	67.0 (4.5)	89.2 (0.9)	65.8 (0.5)	F	0.08 (0.07)	0.15 (0.12)	n.a.
	Ab	35.1 (1.7)	32.5 (4.4)	10.8 (0.9)	34.2 (0.5)	Total	97.9 (0.5)	98.0 (0.2)	96.2 (0.8)
	Or	0.4 (0.2)	0.50 (0.15)	n.a.	n.a.
						Amph	Mg-Hst	Ts-Prg	Ts-Prg
						end-member e
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a b Olivine Fo content, Fo = 100 x Mg/[Mg + Fe*]. c Amphibole composition from Utami et al. (2021). d Plagioclase end-members: anorthite, An = 100 x Ca/[Ca + Na + K]; albite, Ab = 100 x Na/[Ca + Na + K]; orthoclase, Or = 100 x K/[Na + Ca + K]. e a b c f Amph-melt geothermobarometer (Eq. 7a SEE = ± 30 °C) from Putirka (2016) with Al/Si equilibrium test described in Li et al. (2021) (K d (Al/Si)= 0.96 ± 0.4).

Notes. See Table

2

for meaning of mineral abbreviations. Parameters in italics are average calculated values from

[START_REF] Utami | Fluid fluxing and accumulation drive decadal and short-lived explosive basaltic andesite eruptions preceded by limited volcanic unrest[END_REF]

and this study. The Standard Error of Estimate for mineral-melt geothermobarometers and hygrometers is abbreviated to SEE, numbers in brackets refer to the standard deviation away from the calculated mean, or 1σ.

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TABLE 5

 5 Summary of experimental conditions, calculated melt volatile contents, and run products and their phase proportions.

					Calculated melt volatile	Phase proportions b,c (wt%)
					content a
	Charge ID log (fO 2 ) d	ΔNNO e XH 2 O in f	(wt%) XH 2 O melt H 2 O melt	melt CO 2-	Opx Cpx Plag Mag Ilm Ol Amph Gl
		(bar)					(wt.
							ppm)
	T = 1,000 °C, p = 100 MPa, t = 66 h
	SUPL1-1	-9.5	0.8	1.00	1.0	3.5	0	6.0	2.8	30	1.1	3.4	56
	SUPL1-2	-9.8	0.6	0.80	0.7	3.0	162	12.4	8.1	30	2.1		48
	SUPL1-3	-10.0	0.3	0.66	0.6	2.5	267	13.2	8.7	34	2.7		42
	SUPL1-4	-10.1	0.2	0.56	0.5	2.3	312	14.9	8.3	43	2.3		32
	T = 1,000 °C, p = 150 MPa, t = 19 h
	SUPL1-5	-8.5	1.8	1.00	1.0	4.4	0	18.0	25	2.0			55
	SUPL1-6	-8.7	1.6	0.82	0.8	3.8	250	3.7	2.3	23	0.5	4.3	66
	SUPL1-7	-9.0	1.4	0.67	0.6	3.2	414	13.1	7.6	30	1.8		48
	SUPL1-8	-9.0	1.3	0.63	0.6	3.1	444	13.4	12.1	35	1.8		38
	SUPL1-9	-9.5	0.9	0.41	0.3	2.3	633	13.4	5.3	56	3.7		22
	SUPL1-10	n.a.		0.00	0.0	0.0	888	24		58	0.7		17.9
	T = 1,000 °C, p = 200 MPa, t = 22 h
	SUPL1-11	-9.4	0.9	0.84	0.7	3.0	421	7.6	4.1	26	0.9		62
	SUPL1-12	-9.6	0.8	0.75	0.6	3.9	573	5.1	6.8	29	1.0		58
	SUPL1-13	-9.9	0.4	0.55	0.4	3.1	835	11.2	8.2	36	1.2		44
	SUPL1-14	-10.7	-0.4	0.30	0.2	1.8	1,090	14.6	15.3	36	0.6		34
	SUPL1-15	n.a.	n.a.	0.00	0.0	0.0	1,263	25		53	0.6		21
	T = 1,000 °C, p = 400 MPa, t = 23 h
	SUPL1-16	-9.5	0.8	0.85	0.7	6.5	1,681	13.9	1.8	5.6	0.3	<0.01	78
	SUPL1-17	-10.4	0.0	0.54	0.3	3.8	2,977	16.5	12.0	22	0.3		50
	SUPL1-18	-11.4	-1.0	0.27	0.1	1.9	3,438	16.0	12.0	28	0.8		43
	SUPL1-19	n.a.	n.a.	0.00	0.0	0.0	3,638	25		38	0.4		37
	T = 950 °C, p = 150 MPa, t = 66 h
	SUPL1-20	-10.0	1.1	1.00	1.0	4.3	0	7.1	1.2	19.3	3.5	5.1	64
	SUPL1-21	-10.2	0.9	0.84	0.8	3.7	245	14.4	3.6	29	4.3		48
	SUPL1-22	-10.3	0.8	0.75	0.7	3.5	327	16.8	7.6	28	0.6		47
	SUPL1-23	-10.8	0.3	0.49	0.4	2.5	582	14.0	10.8	34	0.8		41
	SUPL1-24	-11.0	0.1	0.39	0.3	2.2	647	13.5	11.0	42	0.6		32
	SUPL1-25	n.a.	n.a.	0.00	0.0	0.0	890	36		52	0.5		12.0
	T = 950 °C, p = 200 MPa, t = 49 h
	SUPL1-26	-10.7	0.4	1.00	1.0	5.1	0	19.9	13.2	29	3.0		35
	SUPL1-27	-10.9	0.2	0.86	0.8	4.6	291	19.0	7.6	38	4.3	<0.01	31
	SUPL1-28	-11.1	0.0	0.68	0.6	3.8	588	17.7	21	32	0.9		29
	SUPL1-29	-11.4	-0.3	0.54	0.4	3.2	797	12.8	15.4	44	1.6		26
	T = 950 °C, p = 400 MPa, t = 67 h
	SUPL1-30	-9.8	1.3	1.00	1.0	8.1	0	17.9	8.4	10.7	3.2		60
	SUPL1-31	-10.3	0.8	0.78	0.6	5.8	2066	14.3	3.7	16.0	3.0	<0.01	63
	SUPL1-32	-10.6	0.6	0.71	0.4	4.9	2,526	11.2	3.9	29	3.2		52
	SUPL1-33	-11.0	0.1	0.50	0.3	4.3	3,029	11.0	2.9	35	3.2		48
	SUPL1-34	-11.5	-0.4	0.35	0.1	2.6	3,322	12.9	10.2	31	2.7		44
	SUPL1-35	n.a.	n.a.	0.00	0.0	0.0	3,685	30		39	0.4		30
											(Continued on following page)
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TABLE 5 (

 5 Continued) Summary of experimental conditions, calculated melt volatile contents, and run products and their phase proportions. Water and CO 2 content in the melt were calculated from mass balance and the combined solubility models of[START_REF] Shishkina | Solubility of H2O-and CO2-bearing fluids in tholeiitic basalts at pressures up to 500MPa[END_REF] for pure H 2O and Dixon (1997) for pure CO 2 .

					Calculated melt volatile	Phase proportions b,c (wt%)
					content a
	Charge ID log (fO 2 ) d	ΔNNO e XH 2 O in f	(wt%) XH 2 O melt H 2 O melt	melt CO 2-	Opx Cpx Plag Mag Ilm Ol Amph Gl
		(bar)					(wt.
							ppm)
	T = 1,060 °C, p = 100 MPa, t = 18 h
	SUPL1-36	-8.1	1.4	1.00	1.0	3.6	0			29	1.9		69
	SUPL1-37	-8.4	1.1	0.78	0.7	3.0	168			57	2.4	<0.1	41
	SUPL1-38	-8.5	1.0	0.73	0.6	2.8	220			46	3.6	0.9	49
	SUPL1-39	-8.6	0.9	0.67	0.6	2.6	251	4.9	3.1	44	0.4		48
	SUPL1-40	-9.2	0.2	0.37	0.3	1.7	424	9.5	7.7	44	3.7		35
	SUPL1-41	n.a.	n.a.	0.00	0.0	0.0	563	23	0.8	38	12.6		26
	T = 1,060 °C, p = 200 MPa, t = 94 h
	SUPL1-42	-8.4	1.1	1.00	1.0	5.3	0			0.8			99
	SUPL1-43	-8.9	0.5	0.72	0.5	3.6	696	16.6	2.1	16.9	2.1		62
	SUPL1-44	-9.3	0.1	0.53	0.3	2.8	914	12.9	7.9	28	0.9		50
	SUPL1-45	-10.3	-0.8	0.27	0.1	1.4	1,153	20	1.3	38	2.0		39
	SUPL1-46	n.a.	n.a.	0.00	0.0	0.0	1,260	21		43	0.9		35
	T = 1,060 °C, p = 400 MPa, t = 49 h
	SUPL1-47	-8.6	0.9	1.00	1.0	8.6	0						100
	SUPL1-48	-10.1	-0.7	0.59	0.2	3.0	3,206	2.7	1.8	13.8	0.2		81
	SUPL1-49	-11.6	-2.1	0.22	0.0	1.1	3,543	9.1	6.4	22	1.7		61
	T = 1,000 °C, p = 100 MPa, t = 77 h
	SUPL1-50	-8.4	1.9	1.00	1.0	3.5	0	5.8	5.6	26	3.2	0.9	59
	SUPL1-51	-8.6	1.7	0.83	0.8	3.0	143	11.0	2.5	29	2.8		55
	SUPL1-52	-8.7	1.6	0.77	0.7	2.9	178	11.8	4.3	31	2.8		51
	SUPL1-53	-9.0	1.3	0.57	0.5	2.3	311	13.7	4.1	38	3.1		41
	SUPL1-54	-9.4	0.9	0.42	0.3	1.8	399	16.0	11.1	33	0.4		39
	SUPL1-55	n.a.	n.a.	0.00	0.0	0.0	564	24		45	2.4		29
	T = 1,000 °C, p = 200 MPa, t = 19 h
	SUPL1-56	-8.5	1.8	1.00	1.0	5.2	0	14.3	3.1	15.7	0.6		66
	SUPL1-57	-8.7	1.6	0.85	0.8	4.5	355	2.0	1.5	20	1.0	4.0	71
	SUPL1-58	-8.9	1.4	0.73	0.6	3.9	575	6.4	4.7	21	3.3	5.9	58
	SUPL1-59	-9.1	1.2	0.59	0.5	3.5	726	13.2	6.3	28	1.6		51
	SUPL1-60	-10.0	0.3	0.29	0.2	1.9	1,086	15.5	13.0	28	3.0		41
	SUPL1-61	n.a.	n.a.	0.00	0.0	0.0	1,263	23		39	9.4		29
	T = 950 °C, p = 200 MPa, t = 71 h
	SUPL1-62	-9.3	1.8	1.00	1.0	5.1	0	15.3	18.0	19.9	1.0		46
	SUPL1-63	-9.5	1.7	0.86	0.8	4.5	303	16.7	5.2	31	3.7		43
	SUPL1-64	-10.0	1.1	0.54	0.4	3.1	804	15.0	11.1	34	3.1		36
	SUPL1-65	-10.9	0.2	0.28	0.2	1.7	1,104	25	22.2	21	0.5		30
	SUPL1-66	n.a.	n.a.	0.00	0.0	0.0	1,266	43		41	0.6		15.4

a

TABLE 6

 6 Mass balance calculation of SO 2 exsolved from the melt and measured by satellite. Concentrations of SO 2 in melt inclusion and interstitial glass from the 2007 dome were taken from[START_REF] Jeffery | The pre-eruptive magma plumbing system of the 2007-2008 dome-forming eruption of Kelut volcano, East Java, Indonesia[END_REF], recalculated from S to SO 2 , in ppm. c SO 2 concentrations of interstitial glasses from the 2014 eruption pumices are below the detection limit. Instead, the interstitial glass concentrations of ashes from the 2014 eruption were used. d Data to calculate glass proportions are taken from Table2. For the 2007 dome, the glass proportion is calculated glass before microlite crystallization. e Total SO 2 emissions for 1990 is from[START_REF] Carn | Multi-satellite volcanic sulfur dioxide L4 long-term global database V4[END_REF]. The 2007 dome emissions are from 5 to 7 November 2007 (this study). Emissions for 2014 eruption is from[START_REF] Zhu | Persisting volcanic ash particles impact stratospheric SO 2 lifetime and aerosol optical properties[END_REF] and Carn

	Year of eruption	1990	2007	2014
	Eruption style	Explosive	Lava dome	Explosive
	VEI	4	2	4
	Erupted volume (DRE) a	0.13	0.035	0.14-0.28	km 3
	Rock density	2,352-2,402	2,500	2,404	kg/m 3
	Mass of magma	306-312	88	337-673	Mt
	Conc. of SO 2 in melt inclusion	471-800	256-368 b	296-596	ppm
	Conc. of SO 2 in interstitial glass	47-230	300-352 b	62-236 c	ppm
	Glass proportion d	0.5-0.7	0.3	0.7
	SO 2 degassed from the melt	20-164	0-1.7	24-260	kt
	Atmospheric SO 2 e	150	0.6-0.7	200-300	kt
	Excess SO 2	0 to 130	0 to 0.7	0 to 276	kt

a Erupted volume for all eruptions are taken from

Maeno et al. (2019a)

,

Maeno et al. (2019b). b

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Acknowledgments

We would like to thank R. Champallier and I. di Carlo from ISTO-Orléans for assistance with experiments and sensor analyses.

Data availability statement

The original contributions presented in the study are included in the article/Supplementary Material, and stored in the data repository of Nanyang Technological University, Singapore (DR-NTU).

Author contributions

SU: conceptualization, project administration, funding acquisition, formal analyses, investigation, data curation, visualization, and writing (original draft; review and editing). JA: methodology, investigation, formal analyses, resources, writing-review and editing, supervision, and final approval of manuscript. FC: conceptualization, investigation, resources, methodology, writing-review and editing, supervision, project administration, funding acquisition, and final approval of manuscript. BS: methodology, writing-review and editing, supervision, funding acquisition, and final approval of manuscript. HH: supervision, writing-review and editing, and final approval of manuscript. SC: analyses, writing-review and editing, and final approval of manuscript. Y-J Hsu and J. Oalmann from the Earth Observatory of Singapore are thanked for assistance with analyses on the analytical procedures and discussions around experimental petrology. We thank S. Jenkins, C. Widiwijayanti, P. Lesage, and P. Allard for discussions on Kelud volcano. We also thank K. Iacovino for assistance with understanding VESIcal v.1.0.1. We would like to acknowledge the Facility for Analysis, Characterization, Testing and Simulation, Nanyang Technological University, Singapore, for the use of their electron microscopy/X-ray facilities.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher's note

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Supplementary material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/feart. 2022.882097/full#supplementary-material