Scarlato, Piergiorgio

Hasandağ volcano (Central Anatolia, Turkey) has recently underwent an increase in local seismicity and fumarolic activity since 2013. In the past, this volcano has produced multiple large explosive eruptions during the last million years. The Belbaşhanı Pumice is the product of a sub-Plinian to Plinian eruption dated at ~ 417 ± 20.5 ka (40 Ar/ 39 Ar). Here, we present a complete volcanological study including stratigraphy, glass chemistry, pumice morphology, geochronology, and eruption source parameters with the associated uncertainties, to characterize the Belbaşhanı Pumice eruption. The eruption involved a column of 18-29 km in height, with the main dispersal axis towards the northeast. A pumice layer up to ~ 17-m-thick accumulated in proximal deposits along the Belbaşhanı path, and up to 2-m-thick in medial-distal areas (~ 18 km northeast from the vent). The high and tubular vesicularity of the pumice clasts indicates that the Belbaşhanı eruption was predominantly magmatic. The bulk volume of the Belbaşhanı Pumice fallout deposit has been estimated as 0.5 and 8 km 3 (with ~ 2 km 3 being the mean value), which corresponds to Volcanic Explosivity Index (VEI) of at least 4 and up to 6. Both isopach and isopleth maps indicate that the volcanic vent may have been located at the intersection of the Tuz Gölü fault and Ulukışla caldera, within the Hasandağ volcanic complex. The glass composition of Belbaşhanı Pumice confirms that the eruption belongs to the Hasandağ magmatic system. The reconstruction of the Belbaşhanı Pumice eruption represents an essential baseline in providing volcanological constraints for further investigations of tephra fallout hazard assessment in Central Anatolia, especially considering that a new Plinian eruption cannot be ruled out at Hasandağ volcano in the future. The chemical and geochronological datasets presented here could aid in refining tephrochronological correlations, with the goal of synchronizing paleoenvironmental and paleoclimatic records alongside archaeological sites.

To explore the effect of conduit roughness on volcanic jet dynamics and on the related seismo-acoustic radiation we performed a series of shock-tube experiments using pipes with variable inner surface fractal dimension D. Variable starting pressure produced subsonic to supersonic jets visualized using high-speed shadowgraph and recorded with an array of accelerometers and microphones. At all starting pressures, increasing D increases the energy transfer from the gas to the conduit walls, decreasing the jet exit velocity (Mach number) and, for supersonic cases, the related shock-cell spacing, and increasing the seismic to acoustic radiation amplitude ratio. The roughness-induced changes in jet velocity and turbulence affect the dominant sources of the jet noise and modulates the spectral properties of the acoustic signals. From our study we show that conduit wall roughness is an important and yet largely neglected factor in the dynamics of explosive volcanic eruptions and their monitored geophysical signals.

Petrological studies of active volcanoes typically focus on eruptive phenomena occurring over long timescales of the order of days to years, aiming at identifying major changes in the physico-chemical state of magma during ascent towards the surface. Exceptionally, we present results from an integrated petrological and statistical approach based on the compilation of ∼5300 major and trace element data for glass and crystals, in combination with volcanological data on eruptive events occurred over timescales of minutes at Stromboli volcano (Sicily). On May 11, 2019, we had the rare opportunity to collect individual fresh fallout ash products from eighteen mostly consecutive explosions, erupted in a 2-h time span and, at the same time, to acquire continuous high frequency (50 Hz) infrared thermal data of the same explosions. Through video analysis, we observe that explosions were more frequent and ash-dominated at the southwestern crater area (SCA, 8–10 events/h) than at the northeastern crater area (NCA, 3–5 events/h), where coarser material was ejected. The statistical analysis of glass and plagioclase compositions reveals differences in the products erupted from the two crater areas. SCA explosions tapped less differentiated magmas (Mg#∼42–46, ∼257–365 LaN, ∼0.7–0.9 Eu/Eu*) in equilibrium with more anorthitic plagioclase cores (An∼72–88), whereas NCA area explosions are more differentiated (Mg#∼40–44, ∼286–387 LaN, ∼0.6–0.8 Eu/Eu*) and in equilibrium with less anorthitic plagioclase cores (An∼68–82). Thermometric calculations based on major and trace element clinopyroxene-plagioclase-melt equilibrium modeling highlight that the SCA explosions were statistically fed by hotter magmas in comparison to NCA explosions. Plagioclase-based diffusion modeling also indicates longer timescales for the dynamic ascent of NCA magmas, leading to preferential groundmass crystallization at the conduit walls and transition from sideromelane to tachylite groundmass textures. The final emerging picture is that in May 2019, concurrent normal eruptions from different crater areas at Stromboli were heralds of compositionally and thermally diverse magmas rising at different rates within the uppermost branched part of the conduit region. High frequency petrological investigations aided by statistical treatment of data have the potential to constrain dynamic conduit processes related to transient, explosive eruptions in persistently active volcanoes, thereby offering new insights on the interplay between magma dynamics, ascent timescales, and eruptive behavior.

The chemistry and mineralogy of slabs subducted into lower mantle control slab rheology and impact the deep volatile cycle. It is known that the metamorphism of little-altered oceanic crust results in eclogite rocks with subequal proportions of garnet and clinopyroxene. With increasing pressure, these minerals react to stabilize pyrope-rich tetragonal majoritic garnet. However, some eclogites contain higher proportions of omphacitic clinopyroxene, caused by Na- and Si-rich metasomatism on the ocean floor or during subduction. The mineralogy of such eclogites is expected to evolve differently. Here, we discuss the results of the crystallization products of omphacitic glass at ~ 18 and ~ 25 GPa and 1000 °C to simulate P-T regimes of cold subduction. The full characterization of the recovered samples indicates evidence of crystallization of Na-, Si-rich cubic instead of tetragonal majorite. This cubic majorite can incorporate large amounts of ferric iron, promoting redox reactions with surrounding volatile-bearing fluids and, ultimately, diamond formation. In addition, the occurrence of cubic majorite in the slab would affect the local density, favoring the continued buoyancy of the slab as previously proposed by seismic observations. Attention must be paid to omphacitic inclusions in sublithospheric diamonds as these might have experienced back-transformation from the HP isochemical cubic phase.

The explosive activity of the 2021 Tajogaite eruption eludes pigeonholing into well-defined eruption styles, with a variety of pyroclast ejection modes occurring both alternately and simultaneously at multiple vents. Visually, we defined four endmembers of explosive activity, referred to as fountaining, spattering, ash-poor jets and ash-rich jets. To capture the physical parameters of these activities, we deployed a camera array including one high-speed camera and three high-definition cameras in two field campaigns. Transitions between and fluctuations within activity occurred at the time scale of minutes to hours, likely driven by the same shallow conduit and vent processes controlling Strombolian activity at other volcanoes, but at higher gas and magma fluxes. From a physical standpoint, mean pyroclast rise velocity ranged 5–50 m/s, maximum ejection velocity 10–220 m/s, and sub-second mass flux of lapilli to bomb-sized pyroclasts at the vent 0.2–200 × 103 kg/s. The largest mass flux occurred during fountaining, which contributed by far more than other activities to cone building. All explosive activity exhibited well-defined pyroclast ejection pulses, and we found a positive correlation between the occurrence rate of ejection pulses and maximum pyroclast ejection velocity. Despite orders of magnitude variations, physical parameters shift gradually with no boundary from one activity endmember to another. As such, attributing this explosive activity specifically to any currently defined style variations is arbitrary and potentially misleading. The highly variable explosive activity of the Tajogaite eruption recalls previous definitions of violent Strombolian eruptions, an eruption style whose pyroclast ejection dynamics, however, were so far largely undefined.

Mafic alkaline magmas, such as those feeding the persistent eruptive activity of Stromboli and Mt. Etna volcanoes in Italy, are dominated by the crystallization of plagioclase via cooling and degassing phenomena related to the dynamics of shallow crustal reservoirs and eruptive conduits. Because plagioclase textures and compositions are extremely sensitive to the changes of intensive variables in subvolcanic plumbing systems, the phenomenological variability of erupted crystals preserves detailed evidence of complex growth histories. From this point of view, we reappraise the textural maturation and compositional complexity of plagioclase by allying thermodynamic and kinetic principles to natural and experimental observations, with the purpose of drawing up guidelines for reconstructing magma dynamics in mafic alkaline volcanic settings. A multifaceted statistical method is adopted to parameterize the decay of crystal growth rate with increasing crystallization time, as relaxation kinetics prevails over melt supersaturation effects. This model parameterization is combined with the textural analysis of natural plagioclase crystals to quantify the residence time of phenocrysts in equilibrium with magmas at Stromboli and Mt. Etna and/or the timescale of rapid microlite growth during disequilibrium ascent of magmas within the conduit. The role played by temperature and melt-water content on plagioclase components and major cation substitution mechanisms is also evaluated under both isobaric-isothermal and decompression conditions. The emerging paradigm is that the influence of dissolved water on anorthite-albite exchange between plagioclase and melt is overwhelmingly mitigated by changes in temperature at conditions of P = 30–300 MPa, T = 1050–1150 °C, fO2 = NNO + 1.9-NNO + 2.3, and melt-H2O = 0.6–4.4 wt%. As a corollary, anorthite and albite melt activities are almost fully encapsulated in the variation of anhydrous melt components as the crystallization of plagioclase proceeds during magma cooling. Following this line of reasoning, we propose an integrated modeling approach to decipher complex zoning patterns in natural plagioclase phenocrysts from mafic alkaline eruptions. Key findings from our re-assessment of equilibrium, thermometric, and hygrometric models indicate that temperature and dissolved water can be iteratively estimated for different plagioclase textural patterns if crystals are sufficiently strongly zoned and probability-based criteria are applied to determine the maximum probability distribution from kernel density analysis.

In this study we parameterize the textural attributes of plagioclase phenocrysts and microlites from nineteen pyroclasts ejected during mild to violent explosions at Stromboli over a timespan of ∼18 years, from 2003 to 2021. By allying kinetic and crystal size distribution principles, we document that the morphological stability of large-sized, euhedral phenocrysts is superimposed on an internal textural heterogeneity due to growth-dissolution phenomena associated with the input rate of hot, H2O-rich recharge magmas rising from depth. As a result, the volumetric plagioclase proportion, dominant size, and number of phenocrysts per unit volume decrease from mild to violent explosions responding to a more efficient magma mixing process via sustained injections of mafic magmas into the shallow reservoir. On the other hand, the crystallization of anhedral plagioclase microlites is controlled by fast growth kinetics taking place in the uppermost part of the conduit during magma acceleration towards the surface. Under such highly dynamic crystallization conditions, the microlite number density closely depends on the increase of melt liquidus temperature via magma decompression and H2O exsolution. This mutualism allows to model the degassing rate and ascent velocity of magma under open-conduit flow regimes for the different eruptive styles, thereby supporting the idea that violent explosions at Stromboli are driven by sustained influxes of recharge magmas favoring strong acceleration (∼12–27 m/s), decompression (∼0.25–0.49 MPa/s), and H2O exsolution (∼0.005–0.01 wt%/s) before magma discharge at the vent.

Crystal-chemical variations of pyroxene (px) and plagioclase (plg) have been analysed by X-ray electron-microprobe (EPMA) mapping to quantify their actual chemical dispersions. These phases were experimentally crystallised from a basaltic liquid (B100, MORB from Iceland) at cooling rates of 1, 7, 60 and 180 °C/h from 1300 °C down to 800 °C. Experiments were run at ambient conditions applying defined temperature paths mirroring characteristic cooling rates from innermost to outermost portions of metre- to centimetre-thick lavas, dikes and bombs emplaced under submarine to subaerial conditions. As the cooling rate increases from 1 to 180 °C/h, the run-products become progressively enriched in pyroxene and depleted in plagioclase, while spinel is invariably low (few area%) and glass is significant only at 180 °C/h. An increase of cooling rate generally leads to enrichment of Al2O3 and depletion of MgO in px, while the opposite behaviour is observed for plg; these trends are mirrored by calculated cations (apfu: atom per formula unit) and components. Average variations as a function of cooling rate are similar to those already observed through classical analysis performed by single point EPMA. However, the actual chemical distributions of CaO versus MgO, Al2O3 and FeOtot oxides unveil the presence of a wider range in pyroxene chemistry. In particular, one px (px-1, CaO-rich, diopsidic type) is present at all the applied cooling rates; a very low CaO-px (px-2, pigeonite or orthopyroxene type) is detected at 1 °C/h; and, finally, once more population of px (px-3, CaO-poor diopsidic type) appears at 60 and 180 °C/h. By contrast, plg analyses yield invariably identical compositions. Textural variations as a function of cooling rate and geothermometric estimations indicate that px-1 crystallised at high-T (or low ΔT), while plg mainly grew in the residual melt produced by the saturation of px. If only textures were evaluated, this order of segregation would like remain unrecognised since px at low cooling rates is smaller than plg. The abundance of phases, their crystal-chemical features, and their order of segregation can be regarded through a theoretical framework of a time-temperature-transformation (TTT) diagram. The most significant chemical variations are displayed by MgO and Al2O3 for both px and plg, which faithfully capture the evolution of cooling conditions. The chemical compositions of px-1 is close to the thermodynamic equilibrium only at 1 °C/h. As the cooling rates increase, the px chemistry indicates disequilibrium conditions. Finally, this study shows that as ΔT/Δt increases, the most abundant px (px-1) and plg are forced towards compositions that become progressively closer to those of the parental liquid.

Open-conduit basaltic volcanoes can be characterised by sudden large explosive events (paroxysms) that interrupt normal effusive and mild explosive activity. In June-August 2019, one major explosion and two paroxysms occurred at Stromboli volcano (Italy) within only 64 days. Here, via a multifaceted approach using clinopyroxene, we show arrival of mafic recharges up to a few days before the onset of these events and their effects on the eruption pattern at Stromboli, as a prime example of a persistently active, open-conduit basaltic volcano. Our data indicate a rejuvenated Stromboli plumbing system where the extant crystal mush is efficiently permeated by recharge magmas with minimum remobilisation promoting a direct linkage between the deeper and the shallow reservoirs that sustains the currently observed larger variability of eruptive behaviour. Our approach provides vital insights into magma dynamics and their effects on monitoring signals demonstrating the power of petrological studies in interpreting patterns of surficial activity.

Identifying accurate topographic variations associated with volcanic eruptions plays a key role in obtaining information on eruptive parameters, volcano structure, input data for volcano processes modelling, and civil protection and recovery actions. The 2021 eruption of Cumbre Vieja volcano is the largest eruptive event in the recorded history for La Palma Island. Over the course of almost 3 months, the volcano produced profound morphological changes in the landscape affecting both the natural and the anthropic environment over an area of tens of km2. We present the results of a UAS (Unoccupied Aircraft System) survey consisting of >12,000 photographs coupled with Structure-from-Motion photogrammetry that allowed us to produce a very-high-resolution (0.2 m/pixel) Digital Surface Model (DSM). We characterised the surface topography of the newly formed volcanic landforms and produced an elevation difference map by differencing our survey and a pre-event surface, identifying morphological changes in detail. The present DSM, the first one with such a high resolution to our knowledge, represents a relevant contribution to both the scientific community and the local authorities.