Università degli Studi di Firenze

An innovative method of estimating the relative risk of buildings exposed to seismic and tsunami hazards in volcanic islands is applied to Stromboli (Italy), a well-known stratovolcano affected by moderate earthquakes and mass-flow-induced tsunamis. The method uses a pre-existing quali-quantitative analysis to assess the relative risk indices of buildings, which provide comparative results useful for prioritisation purposes, in combination with a historical-geographical settlement analysis consistent with the ‘territorialist’ approach to the urban and regional planning and design. The quali-quantitative analysis is based on a new proposed survey-sheet model, useful to collect building information necessary for the relative risk estimation, whereas the historical-geographical investigation is based on the multi-temporal comparison of aerial and satellite images. The proposal to combine two consolidated methods represents an innovation in estimating relative risk. Considering that Stromboli Island had never been subjected to similar analyses, the results of the relative seismic risk assessment are novel and moreover identify buildings with a fairly-low and spatially-uniform relative risk. The results of the relative tsunami risk assessment are consistent with results of similar past studies, identifying buildings with a higher relative risk index on the northern coast of the island. The combined use of a building-by-building survey with a multi-temporal analysis of settlements allows obtaining a higher detail than previously available for the region. If adequately modified, the proposed combination of methods allows assessing relative risk also considering other geo-environmental hazards and their cascading effects, in a multi-hazard risk assessment perspective.

This study analyses the morphological changes induced by eruptive activity at Stromboli volcano (Italy) during and after events occurring during July–August 2019. This period was characterized by intense eruptive activity (two paroxysmal explosions, a two-month-long lava emission, and more intense and frequent “ordinary” explosive activity) that produced significant changes within the region known as Sciara del Fuoco, located on the most unstable, north-western flank of the volcano. Since September 2019, the eruptive activity waned but remained intense, and erosive phenomena continued to contribute to the re-shaping of the Sciara del Fuoco. The morphological changes described here were documented by integrating topographic (PLÉIADES satellite tri-stereo Digital Elevation Models) and multibeam bathymetric data, acquired before, during, and after the paroxysmal events. This allowed the study of the cumulative effect of the different processes and the characterization of the different phases of accumulation/emplacement, erosion, remobilization and re-sedimentation of the volcaniclastic materials. Data acquired at several periods between September 2018 and April 2020, allowed a comparison of the subaerial and submarine effects of the 2019 events. We find evidence of localized, significant erosion following the two pyroclastic density currents triggered by the paroxysmal explosion of the 3 July 2019. We interpret this erosion as being caused by submarine and subaerial landslides triggered by the propagation of pyroclastic density currents down the Sciara del Fuoco slope. Immediately after the explosion, a lava field accumulated on the sub-aerial slope, produced by effusive activity which lasted about two months. Subsequently, the newly emplaced lava, and in particular its breccia, was eroded, with the transfer of material onto the submarine slope. This work demonstrates how repeated topo-bathymetric surveys allowed identification of the slope processes that were triggered in response to the rapid geomorphological variations due to the eruptive activity. The surveys also allowed distinction of whether estimated volumetric losses were the result of single mass-flows or gradual erosive processes, with implications on the related geohazard. Furthermore, this work highlights how submarine slope failures can be triggered by the entry into the water of pyroclastic density currents, even of modest size. These results are important for the development and improvement of an early warning system for tsunami-induced by mass flows, both in Stromboli and for island-based and coastal volcanoes elsewhere, where landslides and pyroclastic density currents can trigger significant, potentially destructive, tsunami waves.

Numerical simulations of volcanic processes play a fundamental role in understanding the dynamics of magma storage, ascent, and eruption. The recent extraordinary progress in computer performance and improvements in numerical modeling techniques allow simulating multiphase systems in mechanical and thermodynamical disequilibrium. Nonetheless, the growing complexity of these simulations requires the development of flexible computational tools that can easily switch between sub-models and solution techniques. In this work we present MagmaFOAM, a library based on the open-source computational fluid dynamics software OpenFOAM that incorporates models for solving the dynamics of multiphase, multicomponent magmatic systems. Retaining the modular structure of OpenFOAM, MagmaFOAM allows runtime selection of the solution technique depending on the physics of the specific process and sets a solid framework for in-house and community model development, testing, and comparison. MagmaFOAM models thermomechanical nonequilibrium phase coupling and phase change, and it implements state-of-the-art multiple volatile saturation models and constitutive equations with composition-dependent and space–time local computation of thermodynamic and transport properties. Code testing is performed using different multiphase modeling approaches for processes relevant to magmatic systems: Rayleigh–Taylor instability for buoyancy-driven magmatic processes, multiphase shock tube simulations propaedeutical to conduit dynamics studies, and bubble growth and breakage in basaltic melts. Benchmark simulations illustrate the capabilities and potential of MagmaFOAM to account for the variety of nonlinear physical and thermodynamical processes characterizing the dynamics of volcanic systems.

n 2011-2012 Santorini was characterized by seismic-geodetic-geochemical unrest, which was unprecedented since the most-recent eruption occurred in 1950 and led to fear an eruption was imminent. This unrest offered a chance for investigating the processes leading to volcanic reactivation and the compositional characteristics of involved magma. We have thus analyzed the He-Ne-Ar-isotope composition of fluid inclusions in olivines and clinopyroxenes from cumulate mafic enclaves hosted in cogenetic dacitic lavas of the 1570–1573 and 1925–1928 eruptions of Nea Kameni. These unique data on Aegean volcanism were compared with those of gases collected in quiescent periods and during the unrest. The 3He/4He-ratios (3.1–4.0Ra) are significantly lower than the typical arc-volcano values (R/Ra~7–8), suggesting the occurrence of magma contamination in Santorini plumbing system, which would further modify the 3He/4He-ratio of parental magmas generated in the local metasomatized mantle. The 3He/4He-values of enclaves (3.1–3.6Ra) are comparable to those measured in gases during quiescent periods, confirming that enclaves reflect the He-isotope signature of magma residing at shallow depths and feeding passive degassing. A significant increase in soil CO2 flux from Nea Kameni and anomalous compositional variations in the fumaroles were identified during the unrest, accordingly with previous studies. Simultaneously, 3He/4He-ratios up to 4.0Ra were also measured, demonstrating that the unrest was due to the intrusion into the shallow plumbing system of a more-primitive 3He-rich magma, which is even volatile richer and less contaminated than mafic magma erupted as enclaves. This new intrusion did not however trigger an eruption.

We report a high-resolution paleomagnetic investigation constrained by new qualitative and semi-quantitative analyses of planktic and benthic foraminifera, nannofossil assemblages, integrated with oxygen and carbon isotope measurements, for the middle Eocene Scaglia limestones of the Contessa Highway section, central Italy. Calcareous plankton assemblages enable recognition of several biostratigraphic events from planktic foraminiferal Zone P11 to the lower part of Zone P15 and from calcareous nannofossil Zone NP15 to the upper part of Zone NP17, which results in refinement of the magnetobiostratigraphy of the Contessa Highway section. Correlation of the paleomagnetic polarity pattern with the geomagnetic polarity timescale provides a direct age interpretation for strata around the middle Eocene Scaglia limestones of the Contessa Highway section, from Chrons C21n (47 Ma) through to Subchron C18n.1n (38.5 Ma). Bulk carbon isotope values indicate a distinct carbon isotopic shift at 40 Ma that is interpreted to represent the first evidence in the northern hemisphere of the middle Eocene climatic optimum (MECO) that has recently been observed as a stable isotope anomaly in multiple records from the Indian-Atlantic sector of the Southern Ocean. This demonstrates a global response of the carbon cycle to the proposed transient increased pCO2 levels during the late middle Eocene and a consequent global CO2-driven climate change.