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Volcanic eruptions are driven by magma rising through Earth’s crust. The style of an eruption depends on intrinsic and extrinsic parameters and is commonly a dynamic process. Thorough investigation of the related products is fundamental to understanding eruptive phenomena.In this context, quantitatively constraining the dispersal area, grain size distribution and pyroclast textures is essential. Volume determination of pyroclasts is fundamental to constrain density and porosity. However, volume determination of irregularly shaped pyroclast cannot be done with geometrical laws but hat to be assessed with different methodologies. In this study, we have collected a set of clasts from Santorini, Greece, to test three methodologies: a manual methodology to measure three orthogonal axes with a calliper; an optical methodology to measure longest and shortest axis through multiple photographs; and the Archimedean methodology.All three methodologies found similar volume results with little impact on the subsequent assessment of porosity and density. The discrepancy between Archimedean and manual/optical methodologies is observed to be smaller than the revealed natural variability. For this reason, we advertise the manual methodology to be used for future field campaigns as a simple and fast yet reliable approach to gain insights into the textural state of magma at eruption., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Direct observation of eruptive activity and related measurements are limited to above the vent and correlations to the source conditions remain challenging. While interpretation of data to infer source conditions relies critically on high-quality data, measurements are commonly conducted at distances safe from the inherent dangers linked to volcanic explosions adding a degree of uncertainty due to enhanced signal path effects. Here, we present custom-built sensors designed to acquire data at high proximity (within 10s of meters) to volcanic vents where direct access would otherwise represent an intolerable risk. These sensors can be deployed by uncrewed aerial vehicles at the desired location. They are equipped with an environmental sensor capable of measuring temperature, relative humidity and barometric pressure, a microphone (6Hz-20kHz) to reconstruct the acoustic pressure and an electrical resonant circuit to detect electrical signals in the 500kHz frequency band. The data is recorded to a ring-buffer capable of storing ~38s of data that can be downloaded after individual explosions. Communication and data transfer is achieved through a LoRa (long range) radio link between the sensor platform and the base station. We tested the feasibility of near-vent deployment at Stromboli, volcano, Italy during two field campaigns in September 2018 and May 2019. During the second campaign we deployed 13 sensors at distances between 15 and 354m and recorded 47 events. This dataset confirmed the influence of near vent topography on the propagation of acoustic signals and electrical activity in low magnitude explosive activity., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

It is well known that explosive volcanic eruptions pose serious hazards to local communities and may have worldwide impacts. However, the products of explosive eruptions on volcanic ocean islands are almost inevitably incompletely preserved as a significant portion of the erupted material is deposited into the ocean, thereby impeding our ability to accurately reconstruct past events, determine eruptive source parameters and ultimately assess the associated hazards. Sete Cidades is the westernmost central volcano of São Miguel Island, Azores. Although currently dormant, it has been the most active volcano on the island in the last 5 ky, with at least 17 trachytic explosive eruptions, some of which sub-Plinian, that took place inside the summit caldera. The last paroxysmal explosive eruption took place at ∼16 ka, enlarging the caldera to its present dimensions, and is recorded by the Santa Bárbara Formation. We here present evidence of a mid-distal deposit (>25 km from the vent) that can be correlated with the proximal (on Sete Cidades volcanic edifice) pumice fall deposit of the Santa Bárbara Formation based on deposit characteristics, textural features and geochemistry. This is the first evidence of a decimeter-thick deposit of Sete Cidades volcano in the central part of São Miguel Island, which allows to constrain eruptive source parameters and wind conditions. Given the predominant winds blowing from westerly directions, Sete Cidades is considered the most hazardous volcano for the entire island of São Miguel with its current population of >137,000 inhabitants. Most critically, the main harbor, only airport and hospital are located in the capital city of Ponta Delgada, ∼12 km SE from Sete Cidades caldera. In case of a future explosive eruption, under westerly blowing wind conditions, the impact on São Miguel could be catastrophic, with long-term economic consequences., Frontiers in Earth Science, 7, ISSN:2296-6463

The Azores hotspot marks the triple junction between the North American, Eurasian, and African plates, and is responsible for the ~20 Ma Azores plateau, and ongoing, off-axis volcanism today. The dynamics of the interaction between the Azores hotspot and the slow-spreading North Atlantic ridge has led to short wavelength V-shaped bathymetric and geochemical anomalies along the mid-ocean ridge, suggesting variations in the flow of mantle plume material towards the southwest. The depth extent of the Azores plume is unclear, or indeed whether it constitutes a traditional plume at all. Surface-wave models have suggested that the “plume” is confined to the upper 250–300 km of the mantle, suggesting either a shallow origin to the Azores hotspot, or that the plume is waning. In contrast, recent finite-frequency body-wave tomography has suggested that the Azores conduit may extend to the core-mantle boundary, and that the Azores, Canary, and Cape Verde hotspots may have a common origin under West Africa. Here we assess geophysical constraints on crustal and mantle structure beneath the Azores hotspot. Geochemical constraints and body-wave tomography results argue for a deep origin of the Azores hotspot. Radial anisotropy suggests significant vertical flow in the vicinity of the hotspot, and this is consistent with the geoid and gravity field. Calculations of plume conduit dynamics in simulations of the global mantle flow field suggest that the present conduit tilts towards West Africa, as observed in the body-wave tomography, and support a common origin for the Azores, Canary, and Cape Verde plumes.

Volcanic ash is a heterogeneous mineral dust that is typically composed of a mixture of amorphous (glass) and crystalline (mineral) fragments. It commonly contains an abundance of the crystalline silica (SiO2) polymorph cristobalite. Inhalation of crystalline silica can induce inflammation by stimulating the NLRP3 inflammasome, a cytosolic receptor complex that plays a critical role in driving inflammatory immune responses. Ingested material results in the assembly of NLRP3, ASC, and caspase-1 with subsequent secretion of the interleukin-1 family cytokine IL-1β. Previous toxicology work suggests that cristobalite-bearing volcanic ash is minimally reactive, calling into question the reactivity of volcanically derived crystalline silica, in general. In this study, we target the NLRP3 inflammasome as a crystalline silica responsive element to clarify volcanic cristobalite reactivity. We expose immortalized bone marrow-derived macrophages of genetically engineered mice and primary human peripheral blood mononuclear cells (PBMCs) to ash from the Soufrière Hills volcano as well as representative, pure-phase samples of its primary componentry (volcanic glass, feldspar, cristobalite) and measure NLRP3 inflammasome activation. We demonstrate that respirable Soufrière Hills volcanic ash induces the activation of caspase-1 with subsequent release of mature IL-1β in a NLRP3 inflammasome-dependent manner. Macrophages deficient in NLRP3 inflammasome components are incapable of secreting IL-1β in response to volcanic ash ingestion. Cellular uptake induces lysosomal destabilization involving cysteine proteases. Furthermore, the response involves activation of mitochondrial stress pathways leading to the generation of reactive oxygen species. Considering ash componentry, cristobalite is the most reactive pure-phase with other components inducing only low-level IL-1β secretion. Inflammasome activation mediated by inhaled ash and its potential relevance in chronic pulmonary disease was further evidenced in PBMC using the NLRP3 small-molecule inhibitor CP-456,773 (CRID3, MCC950). Our data indicate the functional activation of the NLRP3 inflammasome by volcanic ash in murine and human macrophages in vitro. Cristobalite is identified as the apparent driver, thereby contesting previous assertions that chemical and structural imperfections may be sufficient to abrogate the reactivity of volcanically derived cristobalite. This is a novel mechanism for the stimulation of a pro-inflammatory response by volcanic particulate and provides new insight regarding chronic exposure to environmentally occurring particles.

Pyroclast ejection during explosive volcanic eruptions occurs under highly dynamic conditions involving great variations in flux, particle sizes, and velocities. This variability must be a direct consequence of complex interactions between physical and chemical parameters inside the volcanic plumbing system. The boundary conditions of such phenomena cannot be fully characterized via field observation and indirect measurements alone. In order to understand better eruptive processes, we conducted scaled and controlled laboratory experiments. By performing shock‐tube experiments at known conditions, we defined the influence of physical boundary conditions on the dynamics of pyroclast ejection. If applied to nature, we are focusing in the near‐vent processes where, independently of fragmentation mechanism, impulsively released gas‐pyroclast mixtures can be observed. These conditions can be met during, e.g., Strombolian or Vulcanian eruptions, parts of Plinian eruptions, or phreatomagmatic explosions. The following parameters were varied: (1) tube length, (2) vent geometry, (3) particle load, (4) temperature, and (5) particle size distribution. Gas and particles in the experiments are not coupled (St >> 1). The initial overpressure, with respect to atmosphere, was always at 15 MPa. We found a positive correlation of pyroclast ejection velocity with (1) particle load, (2) diverging vent walls, and (3) temperature as well as a negative correlation with (1) tube length and (2) particle size. Additionally, we found that particle load strongly affects the temporal evolution of particle ejection velocity. These findings stress the importance of scaled and repeatable laboratory experiments for a better understanding of volcanic phenomena and therefore volcanic hazard assessment.

The research program of cruise M128 Azores Plateau mainly aimed at improving our understanding of the igneous and tectonic processes that occur during the initial emplacement of large igneous plateaus and the subsequent interaction between intraplate volcanism and ultraslow rifting. The sampling program targeted the oldest and youngest igneous volcanic edifices in the Azores to better constrain the age of the submarine Plateau and the processes that led to changes in the magmatic activity. We obtained a total of more than 330 rock samples and more than 435 biological specimens during 70 TV grab stations (63 containing samples) and 19 successful ROV dives. The combination of bathymetric maps (1980 km hydroacoustic profile length) and petrological samples allows us to better constrain the evolution of rift systems in this tectonically and magmatically active region. A major sampling focus were the volcanic rift systems west of the islands along the Terceira Rift axis and west of São Jorge and Faial. In addition, six stratigraphic dive profiles will yield important constraints on the early magmatic evolution of the Azores Plateau. The samples and geochemical, petrological, volcanological and biological data will provide a unique and detailed picture of how and when the Azores submarine Plateau formed and the extent to which the local tectonic processes influenced the formation and ascent of melts. The macrofauna samples will yield detailed information on the function of the Azores Plateau as a bathymetric swell in the Central Atlantic Ocean.

[1] Explosive volcanic eruptions are defined as the violent ejection of gas and hot fragments from a vent in the Earth's crust. Knowledge of ejection velocity is crucial for understanding and modeling relevant physical processes of an eruption, and yet direct measurements are still a difficult task with largely variable results. Here we apply pioneering high-speed imaging to measure the ejection velocity of pyroclasts from Strombolian explosive eruptions with an unparalleled temporal resolution. Measured supersonic velocities, up to 405 m/s, are twice higher than previously reported for such eruptions. Individual Strombolian explosions include multiple, sub-second-lasting ejection pulses characterized by an exponential decay of velocity. When fitted with an empirical model from shock-tube experiments literature, this decay allows constraining the length of the pressurized gas pockets responsible for the ejection pulses. These results directly impact eruption modeling and related hazard assessment, as well as the interpretation of geophysical signals from monitoring networks.

The eruption that started off the south coast of El Hierro, Canary Islands, in October 2011 has emitted intriguing eruption products found floating in the sea. These specimens appeared as floating volcanic "bombs" that have in the meantime been termed "restingolites" (after the close-by village of La Restinga) and exhibit cores of white and porous pumice-like material. Currently the nature and origin of these "floating stones" is vigorously debated among researchers, with important implications for the interpretation of the hazard potential of the ongoing eruption. The "restingolites" have been proposed to be either (i) juvenile high-silica magma (e.g. rhyolite), (ii) remelted magmatic material (trachyte), (iii) altered volcanic rock, or (iv) reheated hyaloclastites or zeolite from the submarine slopes of El Hierro. Here, we provide evidence that supports yet a different conclusion. We have collected and analysed the structure and composition of samples and compared the results to previous work on similar rocks found in the archipelago. Based on their high silica content, the lack of igneous trace element signatures, and the presence of remnant quartz crystals, jasper fragments and carbonate relicts, we conclude that "restingolites" are in fact xenoliths from pre-island sedimentary rocks that were picked up and heated by the ascending magma causing them to partially melt and vesiculate. They hence represent messengers from depth that help us to understand the interaction between ascending magma and crustal lithologies in the Canary Islands as well as in similar Atlantic islands that rest on sediment/covered ocean crust (e.g. Cape Verdes, Azores). The occurrence of these "restingolites" does therefore not indicate the presence of an explosive high-silica magma that is involved in the ongoing eruption.