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Geophysical data provide the chance to investigate a volcano's dynamics; considerable information can especially be gleaned on the stress and strain patterns accompanying the internal processes and the effect of magma ascent on the main structures triggering earthquakes. Here, we analysed in detail the seismicity recorded over the last two decades on Etna volcano (southern Italy), focusing on earthquakes distribution and focal mechanism clustering; the ground deformation pattern affecting the volcanic edifice with the inflation and deflation phases was also examined. Analysed data were compared in order to shed light on possible relationships with the volcanic activity and to better understand the internal dynamics of the volcano over time. Significant steps during or shortly before major eruptions in the seismic strain release and ground deformation temporal series highlight a straightforward relationship between seismicity occurring at shallow level, inflation/deflation and volcanism. Furthermore, at depths greater than 5–7 km, down to about 20 km, the orientation of the P- and T-axes clearly indicate the existence of a pressure source in the central part of the volcano. All the results underline that the stress field related to the volcano plumbing system interferes with the regional field, partly overriding it. [ABSTRACT FROM AUTHOR]

Mount Somma–Vesuvius is a stratovolcano that represents a geological hazard to the population of the city of Naples and surrounding towns in southern Italy. Historically, volcanic eruptions at Mt. Somma–Vesuvius (SV) include high-magnitude Plinian eruptions, such as the infamous 79 CE eruption that occurred after 295 years of quiescence and killed thousands of people in Pompeii and surrounding towns and villages. The last eruption at SV was in 1944 and showed a Volcanic Explosivity Index (VEI) of 3 (0.01 km 3 of volcanic material erupted). Following the 1944 eruption, SV has been dormant for the past nearly 79 years, with only minor fumarolic and seismic activity. During its long history, centuries of dormancy at SV have ended with Plinian eruptions (VEI 6) that signal the beginning of a new cycle of eruptive activity. Thus, the current dormancy stage demands a need to better understand the mechanism involved in high-magnitude eruptions in order to better predict future eruption magnitude and style. Despite centuries of research on the SV volcanic system, many questions remain, including the evolution of magmatic volatiles from deep primitive magmas to shallower more evolved magmas. Developing a better understanding of the physical and chemical processes associated with volatile evolution at SV can provide insights into magma dynamics and the mechanisms that trigger highly explosive eruptions at SV. In this study, we present new data for the pre-eruptive volatile contents of magmas associated with four Plinian and two inter-Plinian eruptions at SV based on analyses of reheated melt inclusions (MIs) hosted in olivine. We correct the volatile contents of bubble-bearing MIs by taking into account the volatile contents of bubbles in the MIs. We recognize two groups of MIs: one group hosted in high-Fo olivine (Fo 85–90) and relatively rich in volatiles and the other group hosted in low-Fo olivine (Fo 70–69) and relatively depleted in volatiles. The correlation between volatile contents and compositions of host olivines suggests that magma fractionation took place under volatile-saturated conditions and that more differentiated magmas reside at shallower levels relative to less evolved/quasi-primitive magmas. Using the CO 2 contents of corrected MIs hosted in Fo 90 olivine from SV, we estimate that 347 to 686 t d -1 of magmatic CO 2 exsolved from SV magmas during the last 3 centuries (38–75 Mt in total) of volcanic activity. Although this study is limited to only few SV magmas, we suggest that further study applying similar methods could shed light on the apparent lack of correlation between the volatile contents of MIs and the style and age of eruptions. Further, such studies could provide additional constraints on the origin of CO 2 and the interaction between the carbonate platform and ascending magmas below SV. [ABSTRACT FROM AUTHOR]

The liquid line of descent from trachyte to pantellerite is controlled primarily by fractional crystallization of alkali feldspar, with whole-rock compositions following a fractionation path along the 'thermal valley' in the peralkaline haplogranite system Qz-Ab-Or-Ac-Ns and terminating at a minimum on the feldspar-quartz cotectic. Although whole-rock compositions for different pantelleritic suites follow nearly identical paths in a Qz-Ab-Or projection that terminate near the experimental minimum (Qz40.5Or34.5Ab25 at 100 MPa, projected from Ac-Ns), matrix glass from samples with near-minimum compositions record extreme differentiation and form a 'cotectic delta' beyond the terminus of the 'thermal valley'. Although each glass trend shows a continuing increase in Zr to >3000 μg/g, the most evolved compositions in each suite differ in peralkalinity (mol [Na + K] / Al) and in the proportions of FeOT, Qz, Ab, Or, and other components, which are related to subtle variations in the mafic phases controlled mainly by differences in oxygen fugacity (f O2) and pressure (P). To determine the controls over mafic mineral crystallization in pantelleritic magmas and the various paths these suites take beyond the apparent (whole-rock) minimum, amphibole-phyric suites from the ~159 ka Cala dell'Altura and Cala Gadir volcanic centres and the ~8–10 ka Cuddia Mida volcanic centre on Pantelleria have been analyzed and compared with each other and with the well-characterized and amphibole-free, compositionally zoned Green Tuff, the ~46 ka caldera-forming ignimbrite of the Cinque Denti caldera. Differences between the extended fractionation trends may be ultimately attributed to variations in oxygen fugacity, depth of emplacement, and water saturation. Shallower (lower pressure) magma reservoirs such as the one for the Green Tuff are water-saturated and undergo degassing, which leads to an increase in relative oxygen fugacity. Deeper (higher pressure) magma reservoirs remain water-undersaturated and retain water in the melt, which both maintains lower relative oxygen fugacities and enables the crystallization of amphibole. Amphibole formation appears to require melt water contents >4 wt%, low oxygen fugacity (<ΔNNO-1.5), and low temperatures (<700°C), although fluorine may stabilize it at higher temperatures in some rocks. [ABSTRACT FROM AUTHOR]

The most frequent volcanic eruptions are of low-intensity and small magnitude. They produce abundant ash-sized (< 2 mm) clasts, which are too small to establish quantitative links between magmatic processes and eruptive dynamics using classic approaches. This inhibits our ability to study the past behaviour of frequently erupting volcanoes, essential to predict their future activity and mitigate their impact. The Palizzi unit (10–13th century, Vulcano, Italy) includes a prototype sequence of ash deposits resulting from prolonged Vulcanian eruptions punctuated by those of two larger sub-Plinian events. We apply Hierarchical Clustering to chemical analyses of clinopyroxene collected along the stratigraphy to decipher magma dynamics during this eruptive period. We identify periods of magma input and we link deep magmatic processes to eruptive dynamics, also showing that our approach can be used to connect magma and eruptive dynamics in any volcanic sequence. This is essential to track the processes occurring during frequent eruptions and to identify the build-up to larger explosive events. [ABSTRACT FROM AUTHOR]

This study provides the first micro‐thermometric data of fluid inclusions (FIs) in mafic loose (disaggregated) xenocrysts and ultramafic xenoliths in explosive products of the melilitite‐carbonatite Mt. Vulture volcano (southern Italy). Pure CO2 late stage FIs hosted in rock‐forming minerals of wehrlite xenoliths and clinopyroxene xenocrysts were trapped at the local crust‐mantle boundary (32 km). In contrast, trapping pressures within the loose olivine xenocrysts are from 3.2 to 4.5 kbar (8–13 km). Considering the ongoing degassing of mantle‐derived CO2 rich gases, together with seismic evidences of the presence of low amount of melts at depth, and the tectonic control of the past volcanic activity, our study opens new perspective about the hazardous nature of the "quiescent" melilitite‐carbonatite volcanoes. Plain Language Summary: The study of fluid inclusions (FIs) (small amount of fluid trapped within minerals) provides important information on variable environments and magmatological processes in which the host minerals were formed. Investigation of the FIs with respect to their composition, trapping pressure and temperature, allow us to constrain magma ascent history. To understand the last explosive volcanic activity of Mt. Vulture volcano (southern Italy), we investigated FIs in mafic minerals and mantle fragments brought to the surface by a melilitite‐carbonatite magma. Our results show the presence of CO2‐rich FIs with trapping pressure corresponding to a depth of 32 km in mantle fragments, and a shallower depth (8–13 km) in mafic mineral. Estimates on magma ascent rate show rapid ascent dynamics to the surface. Our study emphasizes the importance of a multidisciplinary approach that combine geochemistry and petrology to investigate a volcanic system even if the volcano is considered "quiescent," as is the case of Mt. Vulture volcano, where mantle degassing is still ongoing. Key Points: Micro‐thermometric analyses show the occurrence of high‐density CO2‐rich fluid inclusions hosted by minerals within wehrlite xenolithsAscent rate between melilitite‐carbonatite (≈20 m/s) and kimberlite (≈45 m/s) magma is comparableMelilitite‐carbonatite volcanoes can be hazardous even after long time of quiescence (>105 years) [ABSTRACT FROM AUTHOR]

Infrasound is increasing applied as a tool to investigate magma dynamics at active volcanoes, especially at open-vent volcanoes, such as Mt. Etna (Italy), which are prodigious sources of infrasound. Harmonic infrasound signals have been used to constrain crater dimensions and track the movement of magma within the shallow plumbing system. This study interprets the remarkable systematic change in monotonic infrasound signals preceding a lava fountaining episode at Mt. Etna on 20 February 2021. We model the changing tones (0.7 to 3 Hz fundamental frequency) as a rise in the magma column from 172 ± 25 m below the crater rim to 78 ± 8 m over the course of 24 h. The infrasonic gliding disappears approximately 4 h before the onset of lava fountaining as the magma column approaches the flare of the crater and acoustic resonance is no longer supported. The featured 20 February event was just one of 52 lava fountain episodes that occurred at Mt. Etna over the course of 9 months in 2021 and was the only lava fountain episode where dramatic gliding was observed as a subsequent partial collapse of the crater prevented future resonance. The results presented here demonstrate that analysis of infrasonic gliding can be used to track the position of the magma free surface and hence may provide information on the processes taking place within the plumbing system before eruptive activity. [ABSTRACT FROM AUTHOR]

The Euganean Hills (NE Italy) magmatic district represents the final volcanic activity of the Veneto Volcanic Province. Alkaline to subalkaline magmatic suite dominated by intermediate to felsic volcanic rocks characterises the latest volcanic activity of the Euganean Hills. Magmatic (intrusive and volcanic) enclaves are common in Euganean Hills trachytes. We used the ability of clinopyroxene to record variations of P, T, and fO 2 to reconstruct the geological history of the volcanic enclaves and trachytic host. Despite similar major and trace elements composition, clinopyroxene from host is higher in Ca and Na (and Fe 3 + ) and lower in Mg than enclaves and is slightly enriched in trace elements but with the same pattern distribution. Minor differences in geochemistry and crystal structure of clinopyroxene from enclaves and trachytic host suggest similar parental magmas that differs by small degrees of fractional crystallisation. Clinopyroxene geobarometry performed combining X-ray diffraction with mineral geochemistry for volcanic enclaves–trachytic host combined with amphibole geobarometry for intrusive enclaves and crystal mushes points to a crystallisation pressure range between 4.8–2.0 kbars. Our data support the model of a complex system of magma chambers at intermediate to shallow crustal level where mafic magma accumulated, evolved by fractionation processes and mixed. [ABSTRACT FROM AUTHOR]

Rising magma, dike intrusions, and flank collapse are observed at many volcanoes worldwide, but how they interact is still poorly documented. Extensive synthetic aperture radar interferometry and continuous global positioning system observations captured a sharp dike intrusion at Mount Etna, Italy, during the 2018 paroxysm that triggered a vigorous seaward sliding of the eastern flank connected with brittle failure and deep magmatic resourcing. We propose a feedback process between flank acceleration and magma intrusion that derives from the interaction between the long- and short-term deformation of the volcano. The flank sliding acts as a valve that modulates the emplacement and eruption of magma within the shallow system. Rapid flank acceleration could potentially evolve into sudden collapses and seismic release at shallow depth. In turn, flank slip events could act as a sentinel for changes in magma depth and paroxysmal eruptions at Mount Etna. [ABSTRACT FROM AUTHOR]

Silicic volcanoes are increasingly understood to be underlain by crystal-rich and vertically extensive magma reservoirs within which disequilibrium is widespread. Observations from ignimbrite deposits demonstrate that silicic magma reservoirs are often compartmentalised and compositionally stratified. However, it is currently unclear whether the small (i.e., < 0.1 km3 dense rock equivalent) eruptions that dominate activity at many volcanoes, and peralkaline volcanoes in particular, are fed from similarly complex magma reservoirs as their larger counterparts. Here I report petrographic and geochemical observations from the products of a small peralkaline eruption on Pantelleria, Italy, with the aims of unravelling peralkaline magma assembly processes and evaluating the complexity of reservoirs feeding small silicic eruptions. Matrix glass and whole-rock compositions from the Khaggiar lava flow and Cuddia Randazzo pumice cone reveal that erupted magmas were assembled from at least three distinct magma types stored within a compartmentalised magma reservoir: trachytes, less-evolved pantellerites and evolved pantellerites. Chemical variability in the Khaggiar lava flow was created by at least three distinct processes: the accumulation of evolved macrocrysts into evolved pantellerites; the injection of trachytic magmas into less evolved pantellerites; and the accumulation of relatively primitive macrocrysts into trachytic magmas. Macrocryst textures indicate that both trachytic and pantelleritic domains of the magma reservoir experienced numerous recharge events prior to the one that ultimately triggered eruption. Overall, magmas forming the Khaggiar lava flow and Cuddia Randazzo pumice cone appear to have been assembled in analogous ways to those erupted in much larger events. My observations are in good agreement with those from other peralkaline volcanoes and confirm that magma mingling, crystal cannibalism and macrocryst entrainment are as ubiquitous in peralkaline systems as they are in their calc-alkaline counterparts. [ABSTRACT FROM AUTHOR]

Crustal-scale magmatic systems act as filters between the mantle and the atmosphere, and can generate large volcanic eruptions that pose significant hazards while altering Earth's climate. Quantifying the growth rates, magma fluxes, and duration of storage at different crustal levels is crucial for understanding such systems, but these parameters are poorly constrained due to the scarcity of exposed crustal sections. Here we present the first detailed reconstruction of magma emplacement and differentiation time scales of a complete crustal-scale igneous system exposed in the southern Alps (Ivrea-Sesia region, northern Italy) to quantify the magma fluxes and duration of transcrustal magmatism. Integrated zircon U-Pb petrochronology and numerical modeling provides unprecedented evidence that the volcanic and plutonic bodies are directly related to each other both chemically and temporally, suggesting that the entire magmatic system grew rapidly from its deepest roots to the erupted products. In the entire crustal section, zircons record 4 m.y. of magma accretion, but the bulk of the magma was emplaced within approximately 2 m.y. during an episode of enhanced magma flux from the mantle. Our results show the synchronous growth and differentiation of discrete magma bodies at various crustal levels beneath silicic caldera volcanoes and reconcile modeling and geochronological results on crustal-scale heat and mass transfer. [ABSTRACT FROM AUTHOR]

The active volcano of Ischia, an island off-shore the city of Naples, Southern Italy, has a discontinuous volcanic activity characterized by caldera-forming paroxysmal eruptions, lava flows, and lava domes, and thus offers the opportunity to study the complexity of magma storage, differentiation, and extraction mechanisms in a long-lived magma reservoir. The overall geochemical composition of erupted magmas varies from shoshonite to latite and trachyte/trachyphonolite. Their Sr and Nd, isotope composition variation is typical of subduction-related magmas, akin to other potassic magmas of the Neapolitan District, and there is a complete overlap of radiogenic isotope composition among shoshonite, latite, and trachyte/trachyphonolite. The lack of systematic radiogenic isotope covariation during differentiation suggests that the radiogenic isotope variability could be a signature of each magma pulse that subsequently evolved in a closed-system environment. Erupted magmas record a recurrent evolutionary process consisting of two-step fractional crystallization along similar liquid lines of descent for each magma pulse, suggesting near steady-state magma chamber conditions with balanced alternating periods of replenishment, differentiation, and eruption. The dominant role of fractionating feldspars determines a significant depletion of Sr (<10 ppm) coupled with high Rb/Sr (>200) in the residual trachyte magma. Several more-evolved trachytes have anomalous radiogenic 87Sr/86Sri (>0.707) coupled with high 87Rb/86Sr (>50), all other geochemical and isotopic characteristics being similar to normal 87Sr/86Sri trachytes at the same degree of evolution. This radiogenic Sr isotope signature is not consistent with assimilation of crustal material and demands for a time-related in-growth of 87Sr during storage within the magma chamber. Rb-Sr isochrons on separated mineral-groundmass pairs provide robust constraints on a prolonged pre-eruptive history ranging from a few tens to hundreds of thousands of years at relatively low temperature (~750 °C). Remarkably, also normal trachytes with high 87Rb/86Sr (>200) yield a magma residence time from some 4 to 27 kyr, implying that the long-lived history of Ischia magmas is not limited to the anomalous 87Sr/86Sri trachytes. This long-lived history could be a characteristic feature of the magma chamber reservoir of this active volcano, which other volcanic products (i.e., shoshonite and latite) cannot disclose due to their lower Rb/Sr (i.e., low 87Sr in-growth rate) and higher magma storage temperature (>900 °C) (i.e., rapid Sr isotope homogenization via diffusion). The magma chamber dynamics of the active volcano of Ischia, probed on the basis of geochemical and radiogenic isotope tools, is consistent with recent models of complex magma chamber reservoirs made up of multiple discrete melt pockets, isolated by largely crystalline mush portions, maintained in a steady-state thermal flux regime with no mass exchange, and with reactivation shortly before eruption. [ABSTRACT FROM AUTHOR]

Magma ascent velocities, v (dH/dt; where H is depth and t is time), can be determined from decompression rates (dP/dt), and rates of cooling (dT/dt): , where ρ is magma density, P is pressure, T is temperature and g is the acceleration due to gravity. This equation for v provides a key to investigating the relationships between the initial ascent velocity of magmas and the depths of magma dehydration. Ascent velocities can be calculated using pressure and temperature (P–T) estimates from mineral–liquid thermobarometry and cooling rates inferred from crystal size distribution (CSD) theory. For recent Mt. Etna lava flows, both dP/dT and dT/dt have been characterized for the portion of the feeding system between the Moho (∼27 km) and 6 km based, respectively, on clinopyroxene thermobarometry and clinopyroxene CSDs. Deep-level (>6 km) magma ascent velocities range from practically zero (where clinopyroxene P–T estimates form a cluster, and so dP/dT ≈ 0), to about 10 m h–1 for flows that yield very steep P–T trajectories. Many lava flows at Mt. Etna yield P–T paths that follow a hydrous (∼3% water) clinopyroxene saturation surface, which closely approximates the water content inferred from melt inclusions. Independent assessments of deep-level water contents have been obtained by means of a new geohygrometer and yield ascent rates of ∼1 m h–1, in agreement with the slowest rates derived for magma effusion or vapor-driven ascent (∼0·001 to >0·2 m s–1, or 3·6–720 m h–1). Changes in P–T slope, as determined by pyroxene thermobarometry, indicate an upward acceleration of magma, which may be due to the onset of deep-level magma dehydration linked to the non-ideal behavior of water and CO2 mixtures that induce a deep-level maximum of water loss at P ≈ 0·4 MPa and T ≈ 1200°C for a CO2 content >1000 ppm. [ABSTRACT FROM PUBLISHER]

As the water concentration in magma decreases during magma ascent, olivine-hosted melt inclusions will reequilibrate with the host magma through hydrogen diffusion in olivine. Previous models showed that for a single spherical melt inclusion in the center of a spherical olivine, the rate of diffusive reequilibration depends on the partition coefficient and diffusivity of hydrogen in olivine, the radius of the melt inclusion, and the radius of the olivine. This process occurs within a few hours and must be considered when interpreting water concentration in olivine-hosted melt inclusions. A correlation is expected between water concentration and melt inclusion radius, because small melt inclusions are more rapidly reequilibrated than large ones when the other conditions are the same. This study investigates the effect of diffusive water loss in natural samples by exploring such a correlation between water concentration and melt inclusion radius, and shows that the correlation can be used to infer the initial water concentration and magma ascent rate. Raman and Fourier transform infrared spectroscopy measurements show that 31 melt inclusions (3.6-63.9 μm in radius) in six olivines from la Sommata, Vulcano Island, Aeolian Islands, have 0.93-5.28 wt% water, and the host glass has 0.17 wt% water. The water concentration in the melt inclusions shows larger variation than the data in previous studies (1.8-4.52 wt%). It correlates positively with the melt inclusion radius, but does not correlate with the major element concentrations in the melt inclusions, which is consistent with the hypothesis that the water concentration has been affected by diffusive water loss. In a simplified hypothetical scenario of magma ascent, the initial water concentration and magma ascent rate are inferred by numerical modeling of the diffusive water loss process. The melt inclusions in each olivine are assumed to have the same initial water concentration and magma ascent rate. The melt inclusions are assumed to be quenched after eruption (i.e., the diffusive water loss after eruption is not considered). The model results show that the melt inclusions initially had 3.9-5.9 wt% water and ascended at 0.002-0.021 MPa/s before eruption. The overall range of ascent rate is close to the lower limit of previous estimates on the ascent rate of basalts. [ABSTRACT FROM AUTHOR]

Abstract: To understand the relationship between volcano deformations, magma overpressure and flank instability, the results of analog experiments of slope instability and ground deformations, recorded by the GBInSAR system on the western flank of the Stromboli volcano during the period 2009–2011 have been analyzed. Analog experiments that consider both the external (accumulation on the slope) and the endogenous (intrusion-related bulging) trigger phenomena. The effect of accumulation on the sub-aqueous slope on the initiation of sub-marine mass movements has been analyzed. By combining the monitoring data with analog modeling, the observed deformations from the combined action of overpressure in the volcanic system and gravity have been related. The results suggest that the superficial movements observed by the GBInSAR system represent the response of the Stromboli volcano to overpressure changes in the conduit. The movements observed on the Sciara del Fuoco were slope instability phenomena where the gravitational component produced a constant creep, while changes in the magma overpressure explain why certain periods are characterized by accelerations, which induce instability on the external flanks of the crater area and in the Sciara del Fuoco and eventually promote failure of the volcanic slopes. [Copyright &y& Elsevier]

For the first time a physical model, constrained by monitoring data, is used to derive a quantitative estimate of the evolution in time of magmatic gases that enter a hydrothermal system of an active volcano. The site is Campi Flegrei (west of Naples, in Italy), a caldera that had a large ground inflation in 1982-1984 followed by 20 yr of subsidence. More recently the behavior of the system has changed: the magmatic component of fumaroles has increased, swarms of earthquakes are more frequent, and the ground has started a general uplifting trend, indicating that the hydrothermal system undergoes repeated injections of magmatic fluid. Physical simulations of the process show that total injected fluid masses are the same order of magnitude as those emitted during small to medium size volcanic eruptions, and their cumulative curve highlights a current period of increasing activity. Gas emission studies coupled with physical modeling can be extremely effective in predicting magmatic evolution and eruptive activity at volcanoes. [ABSTRACT FROM AUTHOR]

The 3.7 ka year-old Averno 2 eruption is one of the rare eruptions to have occurred in the northwest sector of the Phlegraean Fields caldera (PFc) over the past 5 ka. We focus here on the fallout deposits of the pyroclastic succession emplaced during this eruption. We present major and trace element data on the bulk pumices, along with major and volatile element data on clinopyroxene-hosted melt inclusions, in order to assess the conditions of storage, ascent, and eruption of the feeding trachytic magma. Crystal fractionation accounts for the evolution from trachyte to alkali-trachyte magmas; these were intimately mingled (at the micrometer scale) during the climactic phase of the eruption. The Averno 2 alkali trachyte represents one of the most evolved magmas erupted within the Phlegraean Fields area and belongs to the series of differentiated trachytic magmas erupted at different locations 5 ka ago. Melt inclusions record significant variations in HO (from 0.4 to 5 wt%), S (from 0.01 to 0.06 wt%), Cl (from 0.75 up to 1 wt%), and F (from 0.20 to >0.50 wt%) during both magma crystallization and degassing. Unlike the eruptions occurring in the central part of the PFc, deep-derived input(s) of gas and/or magma are not required to explain the composition of melt inclusions and the mineralogy of Averno 2 pumices. Compositional data on bulk pumices, glassy matrices, and melt inclusions suggest that the Averno 2 eruption mainly resulted from successive extrusions of independent magma batches probably emplaced at depths of 2-4 km along regional fractures bordering the Neapolitan Yellow Tuff caldera. [ABSTRACT FROM AUTHOR]

Decompression experiments have been conducted to simulate syn-eruptive crystallization in volcanic conduits, to infer magma ascent rates and conditions during dome-forming and Plinian eruptions of silicic arc volcanoes. The experiments were carried out on starting material with the composition of Mt. Pelée rhyolitic interstitial melt (76 wt % SiO2) and consisted of three consecutive steps: hydration, decompression, and annealing. Hydration (saturated and undersaturated) was performed at 850°C and 200 MPa and was followed by isothermal decompression, either linearly or stepwise, to a final pressure, Pf, of 30 or 5–10 MPa. Decompression rates range from 0·003 to 25 MPa min−1 (decompression durations of 15 min to 40 days). Two samples were cooled by 25°C and 50°C during a 3 day step at Pf. Subsequent to decompression, the samples were held for up to 15 days at Pf. The experiments generated three types of crystals as products of pre-, syn-, and post-decompression crystallization. The experiments basically differ from previous studies in that they are specifically designed to discriminate crystal nucleation from growth and to evaluate the influence of pre-decompression crystals on the decompression-induced crystallization. The effects of pre-decompression crystals, decompression rate, undercooling (Pf), and terminal cooling have been determined on plagioclase nucleation, growth, morphology, and composition. The main results suggest a positive correlation between decompression rate and the number density of plagioclase crystals nucleated at Pf and highlight the effect of pre-decompression crystals in further decompression-induced crystallization. The relations between the decompression conditions and the plagioclase characteristics have been used to infer Mt. Pelée eruption dynamics, suggesting that (1) Plinian magmas ascend from the reservoir within less than 1 h (1–10 m s−1), (2) dome and block-and-ash flow magmas ascend within more than 2–5 days, giving time for syn-decompression crystallization around pre-existent microlites, (3) dome magmas provide evidence for long stagnation and cooling at low pressure, and (4) surge magmas ascend without significant crystallization (within less than ∼4 days) and massively nucleate plagioclase at very low pressure. The extent and violence of dome destruction may depend on the size or age of the dome, with large or old domes favouring mildly explosive block-and-ash flows, whereas small or young protodomes may generate highly explosive surges. [ABSTRACT FROM PUBLISHER]

In situ Sr-isotope data by microdrilling, coupled with major and trace element analyses, have been performed on plagioclase and clinopyroxene from seven samples collected during the 2002-2003 eruptive crisis at Stromboli volcano (Aeolian Islands, Italy). On 28 December 2002, the persistent moderate explosive activity was broken by an effusive event lasting about 7 months. A more violent explosion (paroxysm) occurred on 5 April 2003. Two magma types were erupted, namely a volatile-poor and highly porphyritic magma (HP-magma) poured out as scoria or lava and a volatile-rich, phenocryst-poor magma (LP-magma) found as pumice. LP-magma differs from the HP-magma also for its slightly less-evolved chemistry, the groundmass composition and the lower Sr-isotope ratios. Micro-Sr-isotope data show the presence of zoned minerals in strong isotope disequilibrium, as previously found in products erupted in 1984, 1985 and 1996 AD, with Sr/Sr values generally decreasing from cores to rims of minerals. Only some outer rims testify for equilibrium with the host groundmass. The internal mineral zones with high Sr-isotope ratios (0.70665-0.70618) are interpreted as 'antecrysts', crystallised during the previous activity and recycled in the present-day system since the opening shoshonitic activity of the Recent Period, which occurred at about 2.5 ka ago. This result has implications for the dynamics of the present-day plumbing system of Stromboli at intermediate pressure (about 2-3 km depth) and allows us to propose a model whereby an HP-magma reservoir is directly interconnected at the bottom with a cumulate crystal much reservoir. Efficient mixing between residing HP- and input LP-magmas can occur in this reservoir, due to more similar rheological characteristics of the two magmas than in the conduit, where crystallisation is enhanced by degassing. Antecrysts (and possibly melts) re-enter in the HP-magma reservoir both from the bottom, recycled by ascending LP-magmas crossing the crystal mush, and from the top, recycled by descending degassed and dense HP-magma, residual of the periodic Strombolian explosions at the surface. The isotope variation measured in the groundmasses allows calculating the proportion of the LP-magma entering the shallow HP-magma reservoir at ~20%. From this proportion, we estimate that the total volume of LP-magma input during 2002-2003 closely matches the magma volume erupted in the effusive event, suggesting a steady-state system at broadly constant volume. The comparison with estimates of the LP-magma volume ejected by the paroxysm indicates that the LP-magma amount directly reaching the surface during the 5 April paroxysm is minimal with respect to that entering the system. [ABSTRACT FROM AUTHOR]

Magma degassing processes are commonly elucidated by studies of melt inclusions in erupted phenocrysts and measurements of gas discharge at volcanic vents, allied to experimentally constrained models of volatile solubility. Here we develop an alternative experimental approach aimed at directly simulating decompression-driven, closed-system degassing of basaltic magma in equilibrium with an H–C–O–S–Cl fluid under oxidized conditions (fO2 of 1·0–2·4 log units above the Ni–NiO buffer). Synthetic experimental starting materials were based on basaltic magmas erupted at the persistently degassing volcanoes of Stromboli (Italy) and Masaya (Nicaragua) with an initial volatile inventory matched to the most undegassed melt inclusions from each volcano. Experiments were run at 25–400 MPa under super-liquidus conditions (1150°C). Run product glasses and starting materials were analysed by electron microprobe, secondary ion mass spectrometry, Fourier transform infrared spectroscopy, Karl-Fischer titration, Fe2+/Fe3+ colorimetry and CS analyser. The composition of the exsolved vapour in each run was determined by mass balance. Our results show that H2O/CO2 ratios increase systematically with decreasing pressure, whereas CO2/S ratios attain a maximum at pressures of 100–300 MPa. S is preferentially released over Cl at low pressures, leading to a sharp increase in vapour S/Cl ratios and a sharp drop in the S/Cl ratios of glasses. This accords with published measurements of volatile concentrations in melt inclusion and groundmass glasses at Stromboli (and Etna). Experiments with different S abundances show that the H2O and CO2 contents of the melt at fluid saturation are not affected. The CO2 solubility in experiments using both sets of starting materials is well matched to calculated solubilities using published models. Models consistently overestimate H2O solubilities for the Stromboli-like composition, leading to calculated vapour compositions that are more CO2-rich and calculated degassing trajectories that are more strongly curved than observed in experiments. The difference is less acute for the Masaya-like composition, emphasizing the important compositional dependence of solubility and melt–vapour partitioning. Our novel experimental method can be readily extended to other bulk compositions. [ABSTRACT FROM AUTHOR]

Clinopyroxene phenocrysts from the mafic calc-alkaline lavas of Salina (Aeolian arc, southern Tyrrhenian Sea, Italy) have been analysed to determine the hydrogen content and iron oxidation state of this early crystallized phase. The volcanic activity of Salina, starting at 168 ka and developed in several centres up to 24 ka, was dominated by calc-alkaline and high-K calc-alkaline basalts and andesites, with minor dacites and rhyolites. The presence of OH vibrational bands was detected in the IR spectra of clinopyroxenes phenocrysts from Corvo, Rivi-Capo (168-87 ka), Fossa delle Felci (108-59 ka) and Monte dei Porri (57 ka) eruptions. Corvo-Rivi-Capo basalts have clinopyroxenes with the lowest water contents 75-97 ppm HO by weight, whereas an increase in the hydrogen contents of clinopyroxenes from Fossa delle Felci centre, with 171-286 ppm HO by weight, and Monte dei Porri with 343-390 ppm HO by weight, was observed. Mössbauer spectroscopy showed only a limited variation on the Fe/Fe ratio of the studied samples, and a very similar atomic Fe content (0.042-0.047 a.p.f.u.) suggesting that only minor variation on fO occurred during the crystallization of these clinopyroxenes. The water content of parental melts, calculated by applying an Al-dependent partition coefficient to the measured hydrogen contents of clinopyroxenes, is 0.4-0.8 wt% of water in melt for the Rivi-Capo-Corvo basalts, 0.5-3.7 wt% water in melt for Fossa delle Felci lavas and 1.6-2.6 wt% of water in melt for Monte dei Porri lavas. An increase in the maximum hydrogen contents of clinopyroxenes can be recognized during the evolution of the Salina volcano, with the highest hydrogen content measured in clinopyroxenes from Monte dei Porri where the eruptions were characterized by a high degree of explosivity, suggesting a key role of volatiles. [ABSTRACT FROM AUTHOR]

The article discusses the evidence for the carbon dioxide (CO2)-driven origin of the explosion of Stromboli volcano in Italy. It states that the explosions are systematically preceded by a brief phase of increasing CO2/ S02 weight ration. It cites that non-linear magma flow could account to the observed C02 degassing patterns. It also mentions that C02-rich gas triggers demonstrates possibility to forecast explosions.

Pyrometamorphic ejecta erupted during recent paroxysmal explosions and hydrothermally altered volcanic and subvolcanic rocks from Stromboli volcano (Aeolian Islands, Italy) were studied by combined polarizing microscopy, electron microprobe, scanning electron microscope, X-ray diffraction, transmission electron microscope and whole-rock inductively coupled plasma optical emission spectrometry–mass spectrometry analysis. The pyrometamorphic ejecta are compositionally heterogeneous at the macro- and micro-scale, and are classified as buchites; that is, glass coupled with a high-temperature, low-pressure modal mineralogy. Three distinct facies (i.e. cordierite–plagioclase, mullite–plagioclase palisade and tridymite–clinopyroxene) are recognized among the buchites, whose bulk-rock chemistry is compatible with aluminous- to silica-rich protoliths. Abundant mineral growth (e.g. plagioclase palisades and clinopyroxene coronae) occurs at the contact between the ejecta and the crystal-rich host shoshonitic basalt, which typically coats the pyrometamorphic blocks. Mineral constraints, pseudoporphyritic microstructures, plagioclase relict phenocrysts and major and trace element compositions strongly support the origin of the buchite ejecta as hydrothermally altered rocks from the Vancori edifice (a period of activity spanning >10 kyr), which underwent high-temperature, low-pressure contact metamorphism. In the uppermost magmatic system of an active island arc volcano, such as Stromboli, volcanic and subvolcanic rocks usually undergo alteration processes induced by acid–sulphate hydrothermal systems. The circulation of acidic fluids results in leaching of the Stromboli rocks (in the upper part of the volcano edifice) and, depending on the pH, temperature and exposure time to the hydrothermal fluids, production of different alteration facies. The hydrothermally altered Stromboli rocks show facies consistent with argillic to silicic alteration, containing abundant hydrous sulphate and hydroxy-sulphate minerals such as the alunite group minerals, hexahydrite, millosevichite, pickeringite and kieserite. The hydrothermally altered wall-rocks, heated by contact with the basaltic magma of the feeder dyke system of Stromboli, can easily undergo pyrometamorphic processes, inducing partial melting and subsolidus crystallization of the volcanic protoliths. This results in the development of buchite rocks at the magma–hydrothermal system interface. [ABSTRACT FROM AUTHOR]

The processes leading to successful versus failed coalescence of similar magma batches upon their emplacement are investigated at Elba Island (Tuscany), where several magma bodies were generated at a single magmatic center over a time span of 1 Ma during the Late Miocene. Three nested Christmas-tree laccoliths made up of separated, shallow level felsic sheets were emplaced at 2-3 km depth with associated roof uplift. Then, at a deeper level, a granite pluton was constructed over a short time span by three magma pulses stacked downward as subhorizontal intrusive sheets, with space for magma generated mostly by roof uplift and tectonic-gravitational displacement of the overburden. Length-to-thickness relationships for individual laccolith layers, as well as for pluton sheets, show a power-law correlation interpreted as the frozen evidence for the occurrence of a vertical inflation stage during intrusion growth. We infer that laccolith sheets failed to coalesce and form a larger pluton because their magma driving pressure exceeded the lithostatic load in a crustal section rich in subhorizontal magma traps (a thrust stack of bedded rocks). However, the driving pressure of the first magma batch of the Monte Capanne pluton was presumably enhanced by an increased magma supply rate, so that the driving pressure exceeded the load at the level of a deeper magma trap represented by a major thrust fault. The following magma batches arrived in rapid succession and were not able to penetrate the still mushy tabular mass. Thus the laccolith sheets and the sheeted pluton represent different outcomes of similar processes occurring under slightly different conditions. [ABSTRACT FROM AUTHOR]

At Mount Etna, Italy, vigorous gas-rich eruptions in A.D. 2001, 2002, and 2003 were followed by gas-poor eruptions in 2004, 2006, and 2007. Analyses of volatile (CO2, H2O, S, Cl, F), semivolatile (Cu), and involatile (Nb, La) elements trapped in olivine-hosted melt inclusions from these latest eruptions reveal the effects of the sustained interaction between a percolating gas phase and the stored magma. Melt inclusion compositions indicate that magmas erupted from 2004 to 2007 were residual from the 2001-2003 eruptions, and show significant evolution in the volatile content of the melt. These melt inclusion observations, and variations in the C/S of volcanic gases, can be accounted for if melts reequilibrated with CO2-rich gases during storage and prior to entrapment as melt inclusions. Sustained gas percolation caused loss of water and enhancement of CO2 in the evolving melt and may strongly influence the behavior of Cu, which potentially partitions into the gas phase. Vapor-melt interactions during magma storage are important controls on magma evolution at persistently degassing volcanoes. [ABSTRACT FROM AUTHOR]

Mount Vesuvius, Italy, quiescent since A.D. 1944, is a dangerous volcano currently characterized by elevated CO2 emissions of debated origin. We show that such emissions are most likely the surface manifestation of the deep intrusion of alkalic-basaltic magma into the sedimentary carbonate basement, accompanied by sidewall assimilation and CO2 volatilization. During the last eruptive period (1631-1944), the carbonate-sourced CO2 made up 4.7-5.3 wt% of the vented magma. On a yearly basis, the resulting CO2 production rate is comparable to CO2 emissions currently measured in the volcanic area. The chemical and isotopic composition of the fumaroles supports the predominance of this crust-derived CO2 in volatile emissions at Mount Vesuvius. [ABSTRACT FROM AUTHOR]

In September 2002, a series of tectonic earthquakes occurred north of Sicily, Italy, followed by three events of volcanic unrest within 150 km. On 28 October 2002, Mount Etna erupted; on 3 November 2002, submarine degassing occurred near Panarea Island; and on 28 December 2002, Stromboli Island erupted. All of these events were considered unusual: the Mount Etna northeast-rift eruption was the largest in 55 yr; the Panarea degassing was one of the strongest ever detected there; and the Stromboli eruption, which produced a landslide and tsunami, was the largest effusive eruption in 17 yr. Here we investigate the synchronous occurrence of these clustered events, and develop a possible explanatory model. We compute short-term earthquake-induced dynamic strain changes and compare them to long-term tectonic effects. Results suggest that the earthquake-induced strain changes exceeded annual tectonic strains by at least an order of magnitude. This agitation occurred in seconds, and may have induced fluid and gas pressure migration within the already active hydrothermal and magmatic systems. [ABSTRACT FROM AUTHOR]

The eruptive products of the last 1000 years at La Fossa volcano on the island of Vulcano (Italy) are characterized by abrupt changes of chemical composition that span from latite to rhyolite. The wide variety of textural features of these products has given rise to several petrological models dealing with the mingling/mixing processes involving mafic-intermediate and rhyolitic magmas. In this paper, we use published whole-rock data for the erupted products of La Fossa and combine them in geochemical and thermodynamic modelling in order to provide new constrains for the interpretations of the dynamics of the active magmatic system. The obtained results allow us to picture a polybaric plumbing system characterized by multiple magma reservoirs and related crystal mushes, formed from time to time during the differentiation of shoshonitic magmas, to produce latites, trachytes and rhyolites. The residing crystal mushes are periodically perturbated by new, fresh magma injections that, on one hand, induce the partial melting of the mush and, on the other hand, favor the extraction of highly differentiated interstitial melts. The subsequent mixing and mingling of mush-derived melts ultimately determine the formation of magmas erupted at La Fossa, whose textural and chemical features are otherwise not explained by simple assimilation and fractional crystallization models. In such a system, the compositional variability of the erupted products reflects the complexity of the physical and chemical interactions among recharging magmas and the crystal mushes. [ABSTRACT FROM AUTHOR]

The results of an experimental study of limestone assimilation by hydrated basaltic magmas in the range 1,050–1,150°C, 0.1–500 MPa are reported. Alkali basalts doped with up to 19 wt% of Ca, Mg-carbonates were equilibrated in internally heated pressure vessels and the resulting phase relationships are described. The major effects of carbonate incorporation are: (1) generation of CO2-rich fluid phases; (2) change in liquidus phase equilibria; the crystallization of Ca-rich clinopyroxene is favored and the other phases (e.g. olivine, plagioclase), present in the absence of carbonate assimilation, are consumed. As a consequence of the massive clinopyroxene crystallization, the residual melt is strongly silica-depleted and becomes nepheline-normative. Compositional and mineralogical evolutions observed in Mt. Vesuvius eruptive products match those documented in our experiments with added carbonates, suggesting the possibility that carbonate assimilation increased during the last 25 ka of activity. In Central-Southern Italy, carbonate assimilation at shallow levels probably superimposes on deeper source heterogeneities. [ABSTRACT FROM AUTHOR]

It is generally accepted, but not experimentally proven, that a quantitative prediction of volcanic eruptions is possible from the evaluation of volcanic gas data. By discussing the results of two years of real-time observation of H2O, CO2, and SO2 in volcanic gases from Mount Etna volcano, we unambiguously demonstrate that increasing CO2/SO2 ratios can allow detection of the pre-eruptive degassing of rising magmas. Quantitative modeling by the use of a saturation model allows us to relate the pre-eruptive increases of the CO2/SO2 ratio to the refilling of Etna's shallow conduits with CO2-rich deep-reservoir magmas, leading to pressurization and triggering of eruption. The advent of real-time observations of H2O, CO2, and SO2, combined with well-constrained models of degassing, represents a step forward in eruption forecasting. [ABSTRACT FROM AUTHOR]

Campi Flegrei (Phlegrean Fields) is an active volcanic center near Naples, Italy. Numerous eruptions have occurred here during the Quaternary, and repeated episodes of slow vertical ground movement (bradyseism) have been documented since Roman times. Here, we present a quantitative model that relates deformation episodes to magma degassing and fracturing at the brittle-ductile transition in a magmatic-hydrothermal environment. The model is consistent with field and laboratory observations and predicts that uplift between 1982 and 1984 was associated with crystallization of ∼0.83 km³ of H2O-saturated magma at 6 km depth. During crystallization, ∼6.2 × 1010 kg of H2O and 7.5 × 108 kg of CO2 exsolved from the magma and generated ∼7 × 1015 J of mechanical (PΔV) energy to drive the observed uplift. For comparison, ∼1017 J of thermal energy was released during the 18 May 1980 lateral blast at Mount St. Helens. [ABSTRACT FROM AUTHOR]

The morphology of tourmaline nodules occurring in the Capo Bianco aplite (Elba Island, Italy) is studied. Outcrop features indicate that tourmaline nodules are the product of magmatic crystallization, as they are aligned along flow fields developed within the magmatic hosting mass. Mesoscopic observations indicate that nodule morphologies are very variable, from rounded to dendritic. Morphometric analyses show that tourmaline nodules are fractals and that fractal dimension quantifies their degree of irregularity. Numerical simulations of nodule growth are performed by using a Diffusion-Limited Aggregation process. The presence in natural samples of nodules with different morphologies is explained by considering a chaotic magmatic system characterized by a complex interplay between growth rate in different dynamical regions, latent heat of crystallization, and local convection dynamics. It is suggested that higher growth rates correspond to growth of tourmaline nodules in dynamical regions where the transfer of nutrients is very efficient. In such conditions, the latent heat released by the growing nodule is high, inducing strong local convection dynamics, destabilizing the nodule interface, and promoting the formation of dendritic morphologies. On the contrary, the growth of nodules in dynamical regions characterized by weak transfer of nutrients is inhibited leading to weak local convection dynamics and, consequently, to the formation of rounded morphologies. [ABSTRACT FROM AUTHOR]

The volcanic hazard potential of Mount Etna volcano is currently nourished by long- lasting, powerful eruptions of basaltic magmas coupled with increased seismicity and ground deformation, and the world's largest discharge of volcanic gases. The current evolutionary cycle of Mount Etna activity is consistent with subduction-related chemical modifications of the mantle source. Arrival of a new mantle-derived magma batch beneath the volcano has been hypothesized, but is still elusive among the erupted products. Here we demonstrate petrological and geochemical affinities between the magmas supplying modern eruptions and high-Mg, fall-stratified (FS) basalts ejected violently ~4 k.y. ago. The ES primitive magmas (~13 wt% MgO) are characteristically volatile enriched (at least 3.8 wt% H2O and 3300 ppm CO2), and bear a trace element signature of a garnet-bearing, metasomatized source (high Gd/Yb, K/La, U/Nb, Pb/Ce, Ca/Al). They started crystallizing olivine (Fo91), clinopyroxene (Mg# 92.5), and Cr spinel deep in the plumbing system (>5 kbar), contributing to the cumulate piles at depth and to differentiated alkaline basalt and trachybasalt magmas in the shallow conduit. Continuous influx of mantle-derived, volatile-rich magmas, such as those that supplied the ES fallout, provides a good explanation for major compositional and eruptive features of Mount Etna. [ABSTRACT FROM AUTHOR]

A supereruption that occurred in the Campi Flegrei area, Italy, ca. 39 ka had regional- and global-scale environmental impacts and deposited the Campanian Ignimbrite (CI). We attempt to shed light on critical aspects of the eruption (depth of magma chamber, intensive pre-eruptive magma conditions) and the large-volume magma plumbing system on the basis of information derived from analyzing melt inclusion (MI) data. To achieve these aims, we provide new measurements of homogenization temperatures and values of dissolved H2O within phenocryst-hosted MIs from pumices erupted during different phases of the CI eruption. The MI data indicate that a relatively homogeneous overheated trachytic magma resided within a relatively deep magma chamber. Dissolved water contents in MIs indicate that prior to the eruption the magma chamber underwent radical changes related to differential upward movement of magma. Decompression of the rising trachytic magma caused a decrease in water solubility and crystallization, and trachytic bodies were emplaced at very shallow depths. The proposed eruptive model links portions of the main magma chamber and apophyses with specific eruptive units. [ABSTRACT FROM AUTHOR]

Evaluating volcanic hazards requires knowledge of the processes that trigger eruptions and the nature and timing of geophysical signals related to these processes. One approach to addressing this need is to link geophysically observable signals (e.g., those related to seismic, aerornagnetic, inflationary, or degassing processes) to pre-eruptive magmatic events deduced (in hindsight) from studies of erupted magmas. Here we present data on sanidine crystals from the A.D. 79 eruption of Vesuvius that show abrupt changes in Ba concentration caused by magma chamber recharge events prior to eruption. These changes have been degraded by diffusion during the time interval between recharge and eruption, and we have determined the length of this time interval by modeling the measured Ba concentration gradients. The results identify three distinct recharge events in the century before the eruption, the most recent occurring ~20 yr beforehand. [ABSTRACT FROM AUTHOR]

New Sr–Nd–Pb isotopic ratios and trace element data for volcanic mafic rocks outcropping along a E–W transect in southern Italy, from Mt. Vulture to Neapolitan volcanoes, are reported. The variation of LILE/HFSE, HFSE/HFSE and radiogenic isotopes along this transect indicates that all of these volcanoes contain both intra-plate and subduction-related signatures, with the former decreasing from Mt. Vulture to Campanian volcanoes. New data are also reported for the Paleocene alkaline rocks from Pietre Nere (Apulia foreland), which show isotopic ratios mostly overlapping the values for Mediterranean intra-plate volcanoes as well as the Eocene–Oligocene alkaline mafic lavas from the northern Adria plate. Pietre Nere provides evidence for an OIB mantle composition of FOZO-type, free of subduction influences, that is present beneath the Adria plate (Africa) before its collision with Europe. After this collision, and formation of the southern Apennines, westward inflow of mantle from the Adria plate to the Campanian area occurred, as a consequence of slab break off. Interaction of subduction components with inflowing Adria mantle generated hybrid sources beneath the Vulture–Campania area, which can explain the compositional features of both Mt. Vulture and the Campanian mafic rocks. Therefore, mafic magmas from these volcanoes represent variable degrees of mixing between different mantle components. [ABSTRACT FROM AUTHOR]

Strombolian and fire fountain activities represent a common expression of explosive basaltic eruptions. However, the transition between these two eruptive styles and their source mechanisms are still debated. We use textural and compositional studies to characterize pyroclastic material from both the Strombolian and Hawaiian-style fire fountain phases of the January-June 2000 Etna activity. We find that basaltic scoria presents distinctive textural and compositional features that reflect different modes of magma vesiculation and crystallization in the two eruptive regimes. Overall, magma that forms Strombolian scoria is far more crystallized, less vesicular, and more evolved, indicating strong volatile depletion and longer residence time before being erupted. Fire fountain scoria indicates a fast-rising magma with evidence of moderate syneruptive volatile ex-solution. The new textural and compositional data set is integrated with previous volcanological and geophysical investigations to provide further insights into the dynamics of fire fountains, and to frame the transition from Strombolian explosions to fire fountain activity into a model that may apply to future eruptions at Mount Etna as well as other active basaltic volcanoes. [ABSTRACT FROM AUTHOR]

An integrated petrological, geophysical, and fluid-inclusion model is presented for the internal structure of the active Vulcano Island, Southern Tyrrhenian Sea. The present structure of the magma storage system in the crust consists of two major deep accumulation zones located at 17-21 km and 8-13 km depth, plus a minor one at 1-5 km depth, beneath Fossa Cone. The deepest magma accumulation zone contains mafic melts and is located at the transition between the upper mantle and a granulitic lower crust. This reservoir has been active since the onset of the exposed volcanism, and has undergone continuous fractional crystallization, crustal assimilation, and mixing with primary melts from the mantle. Slightly differentiated magmas from the deep reservoir feed a shallower accumulation zone in the middle and upper crust, or erupt directly to the surface through lateral vents. Deep melts probably enter the shallowest reservoir shortly before magma outbreak at the surface, and may represent the trigger of eruptions. According to our model, magmatic eruptions at Vulcano are related to deep magma dynamics, whereas most of the changes in the geochemical and geophysical parameters observed at the active cone in the last century could be due to shallow depth modification of rock permeability, possibly as a result of cone gravitative instability and/or tectonic events. Implications for strategies of volcano monitoring and for forecasting eruptions are briefly discussed. [ABSTRACT FROM AUTHOR]

Over the last several hundred years, Stromboli has been characterized by steady-state Strombolian activity. The volcanic products are dominated by degassed and highly porphyritic (HP-magma) black scoria bombs, lapilli and lava flows of basaltic shoshonitic composition. Periodically (about one to three events per year), more energetic explosive eruptions also eject light coloured volatile-rich pumices with low phenocryst content (LP-magma) that have more mafic compositions than the HP-magma. An in situ major and trace element and Sr isotope microanalysis study is presented on four samples chosen to characterize the different modes of activity at Stromboli: a lava flow (1985–1986 effusive event), a scoria bomb from the ‘normal’ present-day activity of Stromboli (April 1984), and a scoria and coeval pumice sample from a recent more explosive eruption (September 1996). Plagioclase (An62–90) and clinopyroxene (Mg-number between 0·69 and 0·91) phenocrysts in all samples record marked major element variations. Large and comparable Sr isotope variations have been detected in plagioclase and clinopyroxene. HP-magma crystals have resorbed cores, with either high 87Sr/86Sr (0·70635–0·70630) or low 87Sr/86Sr (0·70614–0·70608); the latter values are similar to the values of the outer cores. Mineral rims and glassy groundmasses generally have intermediate 87Sr/86Sr (0·70628–0·70613). Similarly, mineral growth zones with three groups of 87Sr/86Sr values characterize minerals from the LP-pumice, with the lowest values present in mineral rims and groundmass glass. These results define a mixing process between HP- and LP-magmas, plus crystallization of clinopyroxene, plagioclase and olivine, occurring in a shallow magma reservoir that feeds the present-day magmatic activity of Stromboli. An important observation is the presence of a third component (high 87Sr/86Sr in mineral cores) considered to represent a pre-ad 1900 cumulus crystal mush reservoir situated just below the shallow magma chamber. These cumulus phases are incorporated by the LP-magma arriving from depth and transported into the shallow reservoir. A rapid decrease of 87Sr/86Sr in the replenishing LP-magma immediately prior to eruption of the ad 1985 lava flow is associated with an increased volume of LP-magma in the shallow magma chamber. The HP-magma in the shallow reservoir is not fully degassed when it interacts with the LP-magma, making efficient mixing possible that ultimately produces a well overturned homogeneous magma. Further degassing and crystallization occur at shallower levels as the HP-magma moves through a conduit to the surface. [ABSTRACT FROM AUTHOR]

Strombolian eruptions are caused by the bursting of large gas bubbles through essentially stagnant melt that resides in the uppermost part of the conduit. We investigate the physical properties of this shallow melt via a detailed analysis of vesicularity textures in lapilli ejected during a period of moderate-intensity activity at Stromboli volcano (Italy) in 2002. The lapilli show clear evidence that the erupted material is the product of a late- stage dynamic mingling of melts that are distinct in terms of density and rheology. Vesicle- volume distributions for two end-member melts indicate contrasting degrees of outgassing that can be linked to different residence times in the shallow conduit. We propose a model in which actively vesiculating melt rises with the gas phase and mingles with more mature stagnant melt en route to the magma's free surface. We suggest that the complex rheology of this mingled melt feeds back to strongly influence eruption dynamics. [ABSTRACT FROM AUTHOR]

The persistent explosive activity of Stromboli volcano (Italy) ceased in December 2002 and correlated with the onset of a seven-month-long effusive eruption on the volcano flank from new vents that opened just below the summit craters. We intensively monitored this effusive event, collecting and interpreting, in real time, an extensive multiparametric geophysical data set. The resulting data synergy allowed detailed insights into the conduit dynamics that drove the eruption and the transition back to the typical Strombolian activity. We present a direct link between gas flux, magma volume flux, and seismicity, supporting a gas driven model whereby the balance between gas flux and gas overpressure determines whether the system will support effusive or explosive activity. This insight enabled us to monitor the migration of the magma column up the conduit and to explain the onset of explosive activity. [ABSTRACT FROM AUTHOR]

We have developed a Bayesian method for the inversion of static ground deformations at volcanic areas. The method allows inference of the conditional probability density on the location and mechanism of point sources representing volcanic phenomena (isotropic strain nuclei, tensile faults) embedded in homogeneous, elastic media. The method has been tested with simulated and real data from volcanic areas. We have then analysed vertical displacements recorded at Mt Etna (southern Italy) from 1994 to 1998, by high precision levelling. Measurements in this period had been carried out yearly, so resulting displacements have been analysed both in consecutive periods and in the cumulative one. Measurement periods 1994–1995 and 1997–1998 show significant uplift, of several centimetres. The maximum cumulative displacement amounts to 6.5 cm., with a trend similar to each of the two periods 1994–1995 and 1997–1998. The shape of displacement is well approximated by a circular symmetry, thus allowing one to hypothesize an isotropic overpressure model as the source, simulating magma intrusion at shallow depth. The application of the inverse method gives the most probable location at about 4.5 km of depth (b.s.l.) at about 1.5 km north of the central craters. The 95 per cent of probability density is concentrated within a radius of about 0.5 km on the horizontal, 1 km on depth. The obtained results give important insight on the interpretation of recent eruptive episodes. [ABSTRACT FROM AUTHOR]

Crystal-rich materials (scoriae and lava flows) emitted during the 1985-2000 activity of Stromboli were taken into consideration for systematic study of bulk rock/matrix glass chemistry and in particular for the study of chemical and textural zoning of plagioclase, the most abundant mineral phase. Over the considered time period, bulk rock composition remained fairly constant in both major (SiO2 49.2-50.9 wt% and K2O 1.962.18 wt%) and trace elements. The quite constant chemistry of matrix glasses also indicates that the degree of crystallization of magma was maintained at around 50 vol%. Plagioclase ranges in composition between An62 and An88 and is characterized by alternating, < 10100 µm thick, bytownitic and labradoritic concentric layers, although the dominant and representative plagioclase of scoriae is An68. The labradoritic layers (An62-70) show small-scale (1-5 µm), oscillatory zoning, are free of inclusions, and appear to record episodes of slow crystal growth in equilibrium with a degassed liquid having the composition of the matrix glass. In contrast the bytownitic layers (An70-An88) are patchy zoned, show sieve structure with abundant micrometric glass inclusions and voids, and are attributed to rapid crystal growth. A key to understanding the origin of bytownitic layers can be retrieved from the texture and composition of the coronas of plagioclase xenocrysts, inherited from crystal-rich magma, in nearly aphyric pumice which are erupted during more energetic events and represent a deep, volatile-rich, HK-basaltic magma. They show a continuum from fine-sieve to evident skeletal texture from the inner to the outer part of the corona associated with normal compositional zoning from An90 to An75. In the light of these observations, we propose that input of H2O-rich melt blobs, and their mixing with the residing magma, causes partial dissolution of the labradoritic layers followed by the growth of bytownitic composition whose sieve texture attests of rapid crystallization occurring under undercooling conditions mainly induced by degassing. As a whole, the zoning of plagioclase in the scoriae records successive and discrete intrusions of volatile-rich magma blobs, its degassing and mixing with the resident degassed magma at shallow level. [ABSTRACT FROM AUTHOR]

We analyse a microgravity data set acquired along the Etna network and spanning a 5 year long period (1994-1999). The main feature observed is a complete gravity increase (19941996)—decrease (1997-1999) cycle mainly affecting the southeastern sector of the volcano and reaching a maximum amplitude of approximately 100 µGal peak-to-peak. The gravity changes are principally due not to elevation changes but rather to the direct gravitational effect of magma accumulation and drainage below the volcanic pile. In particular, a complete mass increase-decrease cycle took place within a 2-4 km bsl deep reservoir that is elongated, oriented NNW-SSE, and lies in the southeastern sector of the volcano. The observed cycle accounts for a volume of magma ranging between 3 and 10 × 10[sup 8] m³, which is believed to have passed through the inferred reservoir between 1994 and 1999. Since most of this magma has not been erupted nor accumulated at shallower levels (at the summit Etna stations a compatible gravity increase has not been observed), it could have been recycled by the Etna plumbing system, sinking down to a level deeper than that of the inferred source. [ABSTRACT FROM AUTHOR]

Investigates the transition of Mount Etna lavas from a mantle-plume to an island-arc magmatic source in Italy. Characterization of the trace-element composition of a series of lava emissions; Reflection of the compositional change in primary magmas; Implication on the calc-alkalinity of volcanism of the mount.

Stromboli, in the Aeolian Archipelago, is famous for its persistent volcanic activity. The ‘normal’ activity, consisting of rhythmic explosions ejecting crystal-rich scoriae, is periodically interspersed with more energetic explosions during which, in addition to crystal-rich scoriae, crystal-poor pumices are also emitted. The scoriae contain ∼50 vol. % crystals (Plag ∼65; Cpx ∼25; Ol ∼10) whereas the pumices display <10 vol. % crystals (Plag ∼42–50; Cpx ∼47–30; Ol ∼11–20). The bulk rocks, mainly ranging between K-rich basalts and shoshonitic basalts, surprisingly exhibit only slight variations in major and trace element contents, and rare earth element patterns. Systematic studies of melt inclusions (MI) and their host minerals were performed on three scoria–pumice pairs erupted together during the violent explosions. The MI cover a compositional range (CaO/Al2O3 = 0·99–0·29) far wider than that of the whole rocks (CaO/Al2O3 = 0·69–0·52) and attest to the presence of rather primitive melts not yet identified as erupted magmas. On the basis of MI analyses, the crystal-poor magmas contain between 2·3 and 2·8 wt % H2O, 894–1689 ppm CO2, 2250–1660 ppm S and 2030–1660 ppm Cl, with the S/Cl ratio close to unity. In contrast, the crystal-rich magma is extensively degassed. We propose that this degassed magma, which sustains the ‘normal’ activity, results from the crystallization of volatile-rich magmas within the cone itself, driven by decompression and H2O exsolution at low pressure. The crystallization is accompanied by S and Cl fractionation into the gas phase, consistent with partition coefficients DS and DCl between fluid and melt of 40 and 10, respectively. The most violent explosions appear to result from the uprising and emission of volatile-rich magma blobs. [ABSTRACT FROM PUBLISHER]

Presents information on a study which investigated the influence of magma dynamics on the structure of natural volcanic glasses from the Cretaio Tephra of Ischia, Italy using spectroscopic instruments. Background on the Cretaio Tephra of Ischia; Sampling and analytical procedures; Chemical composition of the volcanic glasses.

Presents information on a study which defined the pre-eruption conditions of the AD 79 Vesuvius magma chamber in Italy. Texture and morphology of melt inclusions; Composition of the melt inclusions; Discussion on the phases involved in the pre-eruptive state.

Emplacement of mantle-derived magma (magmatic accretion) is often presumed or inferred to be an important cause of regional granulite facies metamorphism and crustal anatexis. The juxtaposition of mafic cumulates and regionally distributed granulite facies rocks has led some to consider the Ivrea zone (northern Italy, Southern Alps) as an important exposure that demonstrates this causal relationship. However, regional PTt paths indicated by metamorphic reaction textures and PT conditions inferred from geothermobarometry indicate that the emplacement of mafic plutonic rocks (Mafic Complex) at the Ivrea zone occurred during decompression from ambient pressures at the regional thermal maximum. Field and petrographic observations, supported by PT estimates, indicate that regional retrograde decompression and emplacement of the upper parts of the Mafic Complex probably accompanied extension during the Late Carboniferous–Early Permian. A spatially restricted decompression-melting event accompanied final emplacement, depleting supracrustal rocks enclosed by an ∼2–3 km aureole overlying the upper Mafic Complex by 20–30% granite component. The upper Mafic Complex provided the thermal energy to reset mineral assemblages and locally overprint the regional prograde metamorphic zonation. The limited extent of the contact aureole suggests that magmatic accretion may not inexorably cause regional metamorphism and crustal anatexis. [ABSTRACT FROM PUBLISHER]

Presents the subsurface mass distributions at Mount Etna in Italy during the 1995-1996 explosive activity detected by microgravity studies. Role of seasonal changes in water level within the volcano in inducing gravity changes; Occurrence of significant magma movement within and below Etna's edifice between 1994 and 1996; Redistribution of the magma within the volcanic edifice.