Description: In July and August 2019, two paroxysmal eruptions dramatically changed the morphology of the crater terrace that hosts the active vents of Stromboli volcano (Italy). Here, we document these morphological changes, by using 2259 UAS-derived photographs from eight surveys and Structure-from-Motion (SfM) photogrammetric techniques, resulting in 3D point clouds, orthomosaics, and digital surface models (DSMs) with resolution ranging from 8.1 to 12.4 cm/pixel. We focus on the morphological evolution of volcanic features and volume changes in the crater terrace and the upper part of the underlying slope (Sciara del Fuoco). We identify both crater terrace and lava field variations, with vents shifting up to 47 m and the accumulation of tephra deposits. The maximum elevation changes related to the two paroxysmal eruptions (in between May and September 2019) range from +41.4 to −26.4 m at the lava field and N crater area, respectively. Throughout September 2018–June 2020, the total volume change in the surveyed area was +447,335 m3. Despite Stromboli being one of the best-studied volcanoes worldwide, the UAS-based photogrammetry products of this study provide unprecedented high spatiotemporal resolution observations of its entire summit area, in a period when volcanic activity made the classic field inspections and helicopter overflights too risky. Routinely applied UAS operations represent an effective and evolving tool for volcanic hazard assessment and to support decision-makers involved in volcanic surveillance and civil protection operations.

Description: The partitioning of REE,Y and Sc (R3+) between olivine and melt has been investigated experimentally during basalt-carbonate interaction. Three synthetic basalts (meltMg#72, meltMg#75 and meltMg#78) were doped with 0, 10 and 20 wt% CaCO3 and then equilibrated for 72 h at 1 atm, 1,150, 1,200 and 1,250 °C, and the QFM oxygen buffer. The thermal decomposition of CaCO3 produced CaO contents in the melt up to ~22 wt%. Regular relationships are found between the ionic radius and the partition coefficient (DR3+), showing typical near-parabolic patterns. DR3+ is weakly dependent on temperature, but decreases with increasing CaCO3 in the starting material (e.g., DSc decreases from 0.20 to 0.13). From the point of view of the lattice strain theory, DR3+ is described in terms of the radius of the crystal site (r0), the Young Modulus (E) due to the elastic response of that site to lattice strain caused by cation insertion, and the strain-free partition coefficient (D03+). The value of r0 decreases as Ca cations are accommodated into the more distorted M2 site of olivine via progressive CaFe substitutions. This mechanism is accompanied by a higher proportion of Mg cations entering into the smaller M1 site, making the optimum ionic radius smaller and favoring the crystallization of more forsteritic olivines from decarbonated melts. The enrichment of Ca in the crystal lattice is also proportional to the number of Si and Ca cations available in the melt. This causes E to be anticorrelated either with Ca in olivine or the activity of CaO in the melt. R3+ cations behave as network modifiers and, during basalt-carbonate interaction, the increasing abundance of non-bridging oxygens enhances the solubility of REE, Y and Sc in the melt. As a consequence, D03+ is negatively correlated with the degree of melt depolymerization. Additionally, the strain of the crystal lattice dominates the DR3+ parabolic patterns and D03+ is strongly controlled by forsterite and aluminium concentrations in olivine. The accommodation of REE, Y and Sc in the crystal lattice requires maintenance of local charge-balance by the generation of vacancies, in accord with a paired substitution of R3+ and a vacancy for Mg in octahedral sites.

Description: Published

Description: 327-340

Description: 3V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcanici

Description: JCR Journal

Description: Rhyolite and felsite cuttings were collected at Krafla volcano during the perforation of the Iceland Deep Drilling Project Well 1 (IDDP-1). The perforation was stopped at a depth of 2100m due to intersection with a rhyolite magma that intruded the felsite host rock. Rhyolite cuttings are vitrophiric (glass ~95%, RHL) and exhibit a mineral assemblage made of plagioclase+augite+pigeonite+titanomagnetite. Felsite cuttings display evidences of partial melting, responding to variable degrees of quartz+plagioclase+alkali feldspar+augite+ titanomagnetite dissolution. The interstitial glass analyzed close to (i.e., FLS1) and far from (i.e., FLS2) the reaction surface of pyroxene from felsite cuttings shows continuous changes between the two end-members. FLS1 is compositionally similar to RHL, showing Na2O+K2O+REE depletions, counterbalanced by MgO+CaO enrichments. Conversely, FLS2 exhibits opposite chemical features. REE-exchange thermobarometric calculations reveal that plagioclase and augite cores from rhyolite and felsite formed under identical conditions, along a thermal path of 940–960 °C. However, in terms of major and trace element concentrations, plagioclase and augite crystal cores are not in equilibrium with the rhyolite magma, suggesting the incorporation of these minerals directly from the host felsite. To better understand the petrogenetic relationship between rhyolite and felsite, two sets of crystallization and partial melting experiments have been carried out at P=150 MPa and T=700–950 °C. Rhyolite crystallization experiments (RCE) reproduce the two-pyroxene assemblage of IDDP-1 rhyolite cuttings only at T≤800 °C, when the crystal content (≥19%) is higher than that observed in the natural rhyolite (~5%). Under such conditions, the RCE glass is much more differentiated (i.e., marked CaO depletion and Eu anomaly) than RHL. On the other hand, felsite partial melting (FPM) experiments show interstitial glass with a bimodal composition (i.e., FPM1 and FPM2) comparable to FLS1 (≈RHL) and to FLS2, only at T=950 °C. This effect has been quantified by fractional crystallization and batch melting modeling, denoting that FLS1 (≈RHL) and FLS2 reflect high (≥70%) and low (≤8%) degrees of felsite partialmelting, respectively. In contrast, modeling RHL by crystal fractionation requires the removal of an amount (~22%) of solid material that is inconsistent with the low crystal content of the natural IDDP-1 rhyolite. It is therefore concluded that natural rhyolite and felsite represent, respectively, the near-liquidus and sub-solidus states of a virtually identical silicic magma, either feeding aphyric to subaphiric rhyolitic eruptions, or solidifying at depth as phaneritic quartzofeldspathic rocks. Felsite lenses from the Krafla substrate may explore variable degrees of remelting and remobilization processes. The intrusion into felsite of a fresh silicic magma from depth may lead to low degrees of partial melting, whereas the persistent heat release from intense basaltic intrusive events at Krafla may be the source of high degrees of felsite partial melting and consequent rejuvenation of the previously solidified silicic magma.

Description: Published

Description: 603-618

Description: 2V. Struttura e sistema di alimentazione dei vulcani

Description: JCR Journal

Description: The April to May 2010 eruption of Eyjafjallajökull (Iceland) volcano was characterized by a large compositional variability of erupted products. To contribute to the understanding of the plumbing system dynamics of this volcano, we present new EMPA and LA-ICP-MS data on groundmass glasses of ash particles and minerals erupted between April 15 and 22. The occurrence of disequilibrium textures in minerals, such as resorption and inverse zoning, indicate that open system processes were involved in determining the observed compositional variability. The variation of major and trace element data of glasses corroborates this hypothesis indicating that mixing between magma batches with different compositions interacted throughout the whole duration of the eruption. In particular, the arrival of new basaltic magma into the plumbing system of the volcano destabilized and remobilized magma batches of trachyandesite and rhyolite compositions that, according to geophysical data, might have intruded as sills over the past 20 years beneath the Eyjafjallajökull edifice. Two mixing processes are envisaged to explain the time variation of the compositions recorded by the erupted tephra. The first occurred between basaltic and trachyandesitic end-members. The second occurred between trachyandesite and rhyolites. Least-squares modeling of major elements supports this hypothesis. Furthermore, investigation of compositional histograms of trace elements allows us to estimate the initial proportions of melts that interacted to generate the compositional variability triggered by mixing of trachyandesites and rhyolites.

Description: Published

Description: 1173-1186

Description: 5V. Dinamica dei processi eruttivi e post-eruttivi

Description: JCR Journal

Description: Understanding the viscosity of mantle-derived magmas is needed to model their migration mechanisms and ascent rate from the source rock to the surface. High pressure–temperature experimental data are now available on the viscosity of synthetic melts, pure carbonatitic to carbonate–silicate compositions, anhydrous basalts, dacites and rhyolites. However, the viscosity of volatile-bearing melilititic melts, among the most plausible carriers of deep carbon, has not been investigated. In this study, we experimentally determined the viscosity of synthetic liquids with ~31 and ~39 wt% SiO2, 1.60 and 1.42 wt% CO2 and 5.7 and 1 wt% H2O, respectively, at pressures from 1 to 4.7 GPa and temperatures between 1265 and 1755 C, using the falling-sphere technique combined with in situ X-ray radiography. Our results show viscosities between 0.1044 and 2.1221 Pa s, with a clear dependence on temperature and SiO2 content. The atomic structure of both melt compositions was also determined at high pressure and temperature, using in situ multi-angle energy-dispersive X-ray di raction supported by ex situ microFTIR and microRaman spectroscopic measurements. Our results yield evidence that the T–T and T–O (T = Si,Al) interatomic distances of ultrabasic melts are higher than those for basaltic melts known from similar recent studies. Based on our experimental data, melilititic melts are expected to migrate at a rate ~from 2 to 57 km yr􀀀1 in the present-day or the Archaean mantle, respectively.

Description: Published

Description: 267

Description: 3V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcanici

Description: JCR Journal

Description: Radon monitoring represents an important investigation tool for environmental changes assessment and geochemical hazard surveillance. Despite anomalous radon emissions are commonly observed prior to earthquakes or volcanic eruptions, radon monitoring alone is not yet successful in correctly predicting these catastrophic events because contrasting radon signals are unexpectedly measured by lithologically distinct areas. This contribution aims to summarize and integrate natural and laboratory studies pertaining to the transport behavior of radon in different rock types experiencing variable stress and thermal regimes at subvolcanic conditions. The final purpose is to ignite novel and pioneer experimental researches exploring the causes and consequences of radon anomalous emissions, in order to elucidate in full the relationship between the physicochemical changes in substrate rocks and the radon signal.

Description: Published

Description: 309-328

Description: 4V. Processi pre-eruttivi

Description: The April to May 2010 eruption of Eyjafjallajökull (Iceland) volcano was characterized by a large compositional variability of erupted products. To contribute to the understanding of the plumbing system dynamics of this volcano, we present new EMPA and LA-ICP-MS data on groundmass glasses of ash particles and minerals erupted between April 15 and 22. The occurrence of disequilibrium textures in minerals, such as resorption and inverse zoning, indicate that open system processes were involved in determining the observed compositional variability. The variation of major and trace element data of glasses corroborates this hypothesis indicating that mixing between magma batches with different compositions interacted throughout the whole duration of the eruption. In particular, the arrival of new basaltic magma into the plumbing system of the volcano destabilized and remobilized magma batches of trachyandesite and rhyolite compositions that, according to geophysical data, might have intruded as sills over the past 20 years beneath the Eyjafjallajökull edifice. Two mixing processes are envisaged to explain the time variation of the compositions recorded by the erupted tephra. The first occurred between basaltic and trachyandesitic end-members. The second occurred between trachyandesite and rhyolites. Least-squares modeling of major elements supports this hypothesis. Furthermore, investi- gation of compositional histograms of trace elements allows us to estimate the initial proportions of melts that interacted to generate the compositional variability triggered by mixing of trachyandesites and rhyolites.

Description: Published

Description: 51

Description: 5V. Dinamica dei processi eruttivi e post-eruttivi

Description: JCR Journal

Description: A peculiar characteristic of the paroxysmal sequence that occurred on March 16, 2013 at the New South East Crater of Mt. Etna volcano (eastern Sicily, Italy) was the eruption of siliceous crustal xenoliths representative of the sedimentary basement beneath the volcanic edifice. These xenoliths are quartzites that occur as subspherical bombs enclosed in a thin trachybasaltic lava envelope. At the quartzite-magma interface a reaction corona develops due to the interaction between the Etnean trachybasaltic magma and the partially melted quartzite. Three distinct domains are observed: (i) the trachybasaltic lava itself (Zone 1), including Al-rich clinopyroxene phenocrysts dispersed in a matrix glass, (ii) the hybrid melt (Zone 2), developing at the quartzite-magma interface and feeding the growth of newly-formed Al-poor clinopyroxenes, and (iii) the partially melted quartzite (Zone 3), producing abundant siliceous melt. These features makes it possible to quantify the effect of magma contamination by siliceous crust in terms of clinopyroxene-melt element partitioning. Major and trace element partition coefficients have been calculated using the compositions of clinopyroxene rims and glasses next to the crystal surface. Zone 1 and Zone 2 partition coefficients correspond to, respectively, the chemical analyses of Al-rich phenocrysts andmatrix glasses, and the chemical analyses of newly-formed Al-poor crystals and hybrid glasses. For clinopyroxenes fromboth the hybrid layer and the lava flow expected relationships are observed between the partition coefficient, the valence of the element, and the ionic radius. However,with respect to Zone 1 partition coefficients, values of Zone 2 partition coefficients show a net decrease for transition metals (TE), highfield strength elements (HFSE) and rare earth elements including yttrium(REE+Y), and an increase for large ion lithophile elements (LILE). This variation is associated with coupled substitutions on theM1, M2and T sites of the type M1(Al, Fe3+)+TAl=M2(Mg, Fe2+)+TSi. The different incorporation of trace elements into clinopyroxenes of hybrid origin is controlled by cation substitution reactions reflecting local charge-balance requirements. According to the lattice strain theory, simultaneous cation exchanges across the M1,M2, and T sites have profound effects on REE+Y and HFSE partitioning. Conversely, both temperature and melt composition have only a minor effect when the thermal path of magma is restricted to ~70 °C and the value of non-bridging oxygens per tetrahedral cations (NBO/T) shifts moderately from 0.31 to 0.43. As a consequence, Zone 2 partition coefficients for REE+Y and HFSE diverge significantly fromthose derived for Zone 1, accounting for limited cation incorporation into the newly-formed clinopyroxenes at the quartzite-magma interface.

Description: Published

Description: 447-461

Description: 3V. Proprietà dei magmi e dei prodotti vulcanici

Description: JCR Journal

Description: Imaging, in general, and high speed imaging in particular are important emerging tools for the study of explosive volcanic eruptions. However, traditional 2-D video observations cannot measure volcanic ejecta motion toward and away from the camera, strongly hindering our capability to fully determine crucial hazard-related parameters such as explosion directionality and pyroclasts’ absolute velocity. In this paper, we use up to three synchronized high-speed cameras to reconstruct pyroclasts trajectories in three dimensions. Classical stereographic techniques are adapted to overcome the difficult observation conditions of active volca- nic vents, including the large number of overlapping pyroclasts whichmay change shape in flight, variable light- ing and clouding conditions, and lack of direct access to the target. In particular, we use a laser rangefinder to measure the geometry of the filming setup andmanually track pyroclasts on the videos. This method reduces uncertainties to 108 in azimuth and dip angle of the pyroclasts, and down to 20% in the absolute velocity esti- mation.We demonstrate the potential of this approach by three examples: the development of an explosion at Stromboli, a bubble burst at Halema’uma’u lava lake, and an in-flight collision between two bombs at Stromboli

Description: Published

Description: 4268–4275

Description: 5V. Dinamica dei processi eruttivi e post-eruttivi

Description: 6V. Pericolosità vulcanica e contributi alla stima del rischio

Description: JCR Journal

Description: High-speed imaging of Strombolian explosions brings into view the motion of pyroclasts upon leaving the volcanic vent. The erupted gas-pyroclast mixtures form jets with well-defined leading vortex rings that rise at almost constant velocity proportional to the time-averaged velocity of pyroclasts. The ejection velocity of pyroclasts decreases over time and defines a conical profile centered on the jet central streamline. Pyroclast deceleration patterns are related to their velocity and compatible with drag force but are also strongly controlled by jet dynamics. These patterns include constant, decreasing, or abruptly increasing decelerations up to 10(4)ms(-2). Nonuniform deceleration focuses at the jet sides and, mostly, in a narrow zone across the vortex ring. This deceleration zone is trailed by a reduced drag zone, where deceleration is drastically reduced. In these highly transient eruptions, both zones move upward and attenuate over time. Our results provide the first quantitative mapping of reduced drag zones.

Description: Published

Description: 6253-6260

Description: 5V. Processi eruttivi e post-eruttivi

Description: JCR Journal