Collezione Completa 2022

This study investigates the potential use of micro-Raman spectroscopy for the quantification of water in ultrapotassic silicate glasses. A calibration was developed using experimental phono-tephritic glasses with water content ranging from ~ 1 to ~ 3 wt%. The calibration curve showed a typical direct proportionality between water content and the ratio of high- (3100–3750 cm−1) and low-wavenumber (100–1500 cm−1) spectral regions, with a linear fit coefficient m = 1.74. The comparison with the m coefficients available in literature for other silicate compositions showed a deviation of our composition as a function of some major oxides such as FeO, TiO2 and K2O, highlighting the possible influence of the polymerization degree (NBO/T: non-bridging oxygens per tetrahedron) on m coefficient. In this respect, we observed a linear relationship between m coefficient and NBO/T and a positive correlation between the area underneath the silicate region (100–1500 cm−1) and NBO/T for the phono-tephrite of this study and for other compositions spanning from basalts to phonolite and rhyolites available in literature. For ultrapotassic natural and experimental glasses characterized by the presence of CO2, documented by the carbonate peak at 1062–1092 cm−1, it has been possible to extrapolate the CO2 content by using the model of Morizet et al. (2013) obtaining values of ~ 1.1 ± 0.3 and ~ 1.7 ± 0.2 wt%, respectively. The obtained m coefficient was applied to estimate water content of natural phono-tephritic glasses belonging to the Colli Albani Volcanic District. Moreover, we estimated water content also for some natural K-foiditic glasses from the same volcanic district. Since the m coefficient results to be strongly dependent on the chemical composition of the sample of interest, the coefficient estimated for the phono-tephrites of this study could result in significant overestimation or underestimation of the water content of the Colli Albani Volcanic District K-foiditic natural samples. Thus, we extrapolated the m coefficient for the K-foiditic samples by means of an equation obtained in this study as function of the polymerization degree (NBO/T).

Il manoscritto presenta un software basato su OpenFOAM per modellare diversi tipi di dinamiche magmatiche pre- e syn-eruttive, come ad esempio mingling, mixing e risalita di slug. Il software è distribuito liberamente, ed il manoscritto una serie di casi test per la validazione dei solutori e di tutorial per facilitarne l'uso anche ai meno esperti.

We report on the characterization of a thick sequence of pyroclastic deposits exposed on the summit area and flanks of Mount Melbourne volcano, in northern Victoria Land, Antarctica related to eruptions during the Late Glacial period. We provide a complete characterization of tephra deposits including mineralogy, single shard major- and trace-element glass compositions, and an 40Ar-39Ar age of feldspar crystals extracted from the deposit. The pyroclastic deposits are trachybasaltic to trachytic in composition and are interpreted to have resulted from four Strombolian/Vulcanian to sub-Plinian/Plinian eruptions. The younger and more intense sub-Plinian/Plinian eruption (our eruption 2) yielded an 40Ar-39Ar age of 13.5±4.3 ka (±2σ). The study ofMountMelbourne
proximal deposits provides significant new data for the reconstruction of the volcano eruptive history and a better assessment of the volcanic risk connected to a possible future eruption. We also explore geochemical correlations between MountMelbourne proximal deposits and distal tephra layers recognized in ice cores and blue ice fields of East Antarctica. A good geochemical match exists between the composition
of products from the trachytic sub-Plinian/Plinian eruption 2 and some tephra layers from Talos Dome and shards in Siple Dome which is also compatible in age (c. 9.3 ka) with our 40Ar-39Ar age determination. Our new insights into the volcanic history of Mount Melbourne and the new high-quality electron microprobe and trace element composition data on its proximal productswill help improve future correlations and synchronization of tephra archives in the region.

New textural and petrological data are presented on products from five paroxysms at Stromboli (Aeolian Islands, Italy) including the two from 2019 and three historical (1930, undated, sixteenth century) eruptions. The data are used to con- strain timescales associated with the initiation of paroxysms and to examine current models for their triggering. Samples were collected from the deposits and a subset selected for mineral separation and petrological and textural characterization. Minerals and glass were imaged by scanning electron microscopy (SEM), and chemical composition and zonation were analysed by electron microprobe. Trace elements in olivine were also determined. Vesicle number densities, vesicularities and vesicle diameters were measured by X-ray microCT techniques. The data were systematically compared with results of experiments simulating, on the one hand, ascent, vesiculation, degassing and crystallization of LP (low-porphyricity) magma and, on the other hand, interaction between LP and HP (high-porphyricity) magma. Paroxysm samples are mixed and include portions representative of both LP and HP magma. They host in variable proportions minerals and glass textur- ally and compositionally typical of these two magma types. Small but systematic variations in matrix glass compositions are found between each of the five eruptions considered. All samples host a population of vesicles ranging from 1000 μm in diameter and whose size distributions follow mixed exponential to power law distributions. Vesicularities are high (75% on average) and vesicle number densities range from 10 2 -10 3 to 10 3 -10 4 mm -3 . Using experimental calibrations, the vesicle textural data suggest average LP magma ascent rates of 1–2 m/s (i.e. ~1.5 hours from depths between 7 and 1.5 km). The correlation between ascent rate and textures demonstrates systematic variations between eruptions, the most ener- getic (i.e. that of 1930) being associated with the highest ascent rate (~2 m/s). Widths of plagioclase reaction zones indicate that LP and HP magmas interacted for a maximum a few hours before eruption. Olivine reaction also implies durations of a few hours for LP-HP interaction and is followed by crystallization for 20 hours in the HP magma. Our results stress the fast ascent of LP magma from their storage region and their short residence times at shallow levels before being erupted. They clarify the respective roles of the deep and shallow feeding systems. An integrated phenomenological model for paroxysm initiation at Stromboli is outlined.

Lithium and boron are trace components of magmas, released during exsolution of a gas phase during volcanic activity. In this study, we determine the diffusivity and isotopic fractionation of Li and B in hydrous silicate melts. Two glasses were synthesized with the same rhyolitic composition (4.2 wt% water), having different Li and B contents; these were studied in diffusion-couple experiments that were performed using an internally heated pressure vessel, operated at 300 MPa in the temperature range 700–1250 °C for durations from 0 s to 24 h. From this we determined activation energies for Li and B diffusion of 57 ± 4 kJ/mol and 152 ± 15 kJ/mol with pre-exponential factors of 1.53 × 10–7 m2/s and 3.80 × 10–8 m2/s, respectively. Lithium isotopic fractionation during diffusion gave β values between 0.15 and 0.20, whereas B showed no clear isotopic fractionation. Our Li diffusivities and isotopic fractionation results differ somewhat from earlier published values, but overall confirm that Li diffusivity increases with water content. Our results on B diffusion show that similarly to Li, B mobility increases in the presence of water. By applying the Eyring relation, we confirm that B diffusivity is limited by viscous flow in silicate melts. Our results on Li and B diffusion present a new tool for understanding degassing-related processes, offering a potential geospeedometer to measure volcanic ascent rates.

L’obiettivo del lavoro è di quantificare la relazione tra l’energia delle eruzioni dell’Etna e il tasso di decompressione dovuto alla risalita finale del magma. Tre eruzioni recenti con esplosività variabile sono state scelte per questo scopo. L’approccio utilizzato è basato sulla diffusione di alcuni elementi volatili all’interno di “melt-embayment”. Nel lavoro è dimostrato come esplosività e tasso di decompressione siano correlati positivamente. Lo studio mette in evidenza la capacità dell’Etna di trasferire i magmi attraverso il sistema di alimentazione superficiale con cinetiche estremamente variabili, determinando una variabilità dell’esplosività finale delle eruzioni pur considerando magmi con simili condizioni fisiche e chimiche.

Open-vent volcanic activity is typically sustained by ascent and degassing of shallow magma, in which the rate of magma supply to the upper feeding system largely exceeds the rate of magma eruption. Such unbalance between supplied (input) and erupted (output) magma rates is thought to result from steady, degassing-driven, convective magma overturning in a shallow conduit/feeding dyke. Here, we characterize shallow magma circulation at Stromboli volcano by combining independent observations of heat (Volcanic Radiative Power; via satellite images) and gas (SO2, via UV camera) output in a temporal interval (from August 1, 2018 to April 30, 2020) encompassing the summer 2019 effusive eruption and two paroxysmal explosions (on July 3 and August 28, 2019). We show that, during the phase of ordinary strombolian explosive activity that preceded the 2019 effusive eruption, the average magma input rate (0.1-0.2 m3/s) exceeds the magma eruption rate (0.001-0.01 m3/s) by ∼2 orders of magnitude. Conversely, magma input and output rates converge to an average of ∼0.4 m3/s during the summer 2019 summit effusion, implying an overall suppression of magma recycling back into the feeding system, and hence of excess degassing. We find that, during the effusive eruption, the peak in SO2 emissions lags behind the thermal emission peak by ∼27 days, suggesting that magma output, feeding the lava flow field, initially dominates over magma input in the conduit. We propose that this conduit mass unloading, produced by this initial phase of the effusive eruption, leads to an overall decompression (of up to 30 Pa/s) of the shallow plumbing system, ultimately causing ascent of less-dense, volatile-rich magma batch(es) from depth, enhanced explosive activity, and elevated SO2 fluxes culminating into a paroxysmal explosion on August 28. Our results demonstrate that combined analysis of thermal and SO2 flux time-series paves the way to improved understanding of shallow magmatic system dynamics at open-vent volcanoes, and of the transition from explosive to effusive activity regimes.

The impact of hazardous pyroclastic density currents (PDCs) increases with runout distance, which is strongly influenced by the mass flux. This article shows that the mass flux of a PDC may derive not only from vent discharge during the eruption, but also from partly hot, temporary stores (accumulations) of aerated pyroclastic material perched high on the volcano. The unforeseen PDC at Fuego volcano (Guatemala) on 3 June 2018 happened c.1.5 hr after the eruption climax. It overran the village of San Miguel Los Lotes causing an estimated 400+ fatalities. Analysis of the facies architecture of the deposit combined with video footage shows that a pulsatory block-and-ash flow flowed down the Las Lajas valley and rapidly waxed, the runout briefly increasing to 12.2 km as it filled and then spilled out of river channels, entered a second valley where it devastated the village and became increasingly erosive, prior to waning. Paleomagnetic analysis shows that the PDC contained only 6% very hot (>590°C) clasts, 39% moderately hot (∼200°C–500°C) clasts, and 51% cool (<200°C) clasts. This reveals that the block-and-ash flow mostly derived from collapse of loose and partly hot pyroclastic deposits, stored high on the volcano, gradually accumulated during the last 2–3 years. Progressive collapse of unstable deposits supplied the block-and-ash flow, causing a bulk-up process, waxing flow, channel overspill and unexpected runout. The study demonstrates that deposit-derived pyroclastic currents from perched temporary tephra stores pose a particular hazard that is easy to overlook and requires a new, different approach to hazard assessment and monitoring.

Prevedere un'eruzione è una delle sfide più importanti della vulcanologia. Fino ad oggi, prevedere un'eruzione mesi o settimane prima che essa avvenga è molto difficile. Qui mostriamo come nelle caldere basaltiche con camera magmatica superficiale i tassi di apporto di magma, ottenuti invertendo i dati di deformazione, sono un potente indicatore della probabilità che si possa avere o meno la propagazione di magma al di fuori della camera magmatica, condizione ultima per un'eruzione, entro un anno dall'inizio della deformazione. Modelli viscoelastici supportano questi risultati mostrando come i tassi controllino le sovrappressioni critiche per rompere la camera magmatica.

L’individuazione di anomalie in grado di segnalare il potenziale risveglio di un vulcano, di grande interesse per la sorveglianza vulcanica, beneficia da diversi anni dell’utilizzo di tecniche di Machine Learning (ML). In questo lavoro viene affrontato il problema di trovare soglie utili per l’allertamento considerando un’applicazione di ML al vulcano Etna mediante lo studio del tremore vulcanico.