Julia Eychenne

Plusieurs volcans andésitiques dans le monde connaissent des périodes d’activité en système ouvert pendant plusieurs années, décennies voire siècles, qui sont caractérisées par des manifestations éruptives persistantes d’intensité fluctuante et ponctuées de phases explosives violentes et dangereuses, souvent accompagnées d’écoulements pyroclastiques. La compréhension de la dynamique et de l’origine de ces paroxysmes en système ouvert est un enjeu majeur de la recherche volcanologique dans le but d’améliorer la surveillance de ce type d’activité. Le Tungurahua en Equateur est un excellent exemple pour étudier un système andésitique ouvert : entré en activité en 1999, le volcan a connu une phase paroxysmale en août 2006, avec l’émission d’un panache éruptif de 15 km de hauteur et la mise en place d’écoulements pyroclastiques. Les objectifs de cette thèse sont, à partir de l’étude du dépôt de retombée, d’explorer la dynamique d’un volcan andésitique fonctionnant en système ouvert en étudiant le cas du paroxysme explosif du Tungurahua et de développer une méthode de suivi haute-résolution des budgets éruptifs massiques, transposable à différentes phases éruptives et différents volcans. A l’aide d’une déconvolution automatique des distributions granulométriques bimodales du dépôt, deux sous-populations ont été caractérisées et quantifiées. Ces dernières reflètent la syn-sédimentation de particules grossières depuis le panache éruptif, et de particules fines depuis des nuages co-écoulements pyroclastiques. Cette analyse granulométrique couplée à l’étude de l’amincissement du dépôt indiquent un volume total minimum de 42×106 m3 et un panache de 16-18 km au dessus du cratère. Cette éruption est classée comme une VEI 3 de type subplinien. Un nouveau protocole d’analyses de type et densité de clastes révèle une distribution sigmoïdale des densités des particules vésiculées avec la granulométrie. Cette loi empirique permet de déterminer la charge massique de chaque classe de constituants latéralement dans le dépôt à partir des données de comptage de grains. L’intégration des lois de décroissance massique exponentielle et puissance de chaque classe de constituant dans le dépôt permet d’estimer leur masse totale. Ces budgets massiques indiquent une magnitude~3,5 et une intensité ~9,2. La faible masse de ponces acides (<0.4 wt.%) exclus une origine par mélange de magma. Une proportion de ~98 wt.% et la faible densité de produits juvéniles révèle le caractère magmatique de l’éruption et l’absence d’interactions phréato-magmatiques. Les xénoclastes témoignent d’une fragmentation et d’une érosion des 2 km supérieurs du conduit. Des analyses morphologiques de particules menées avec un outil automatique et innovant (Morphologi G3 de Malvern) montrent le caractère hautement vésiculé des particules juvéniles et la faible viscosité de la lave. L’explosivité élevée d’août 2006 apparaît comme une manifestation extrême d’un système ouvert alimenté par des injections irrégulières de magma andésitique profond. L’activité du Tungurahua depuis 1999 définit un système caractérisé par un conduit très ouvert, une lave peu visqueuse et un dégazage par le biais d’explosions stromboliennes de faibles à hautes intensités. La méthode de détermination des budgets éruptifs est un atout majeur pour le suivi et la surveillance des phases éruptives en système ouvert.

Fine volcanic ash can have an adverse health impact. It is readily produced during explosive eruptions but also can be generated in large quantities by secondary processes. We evaluated the production and resuspension of sub-10 μm volcanic particulate matter (PM ₁₀ ) by road traffic as these processes may generate an increased respiratory exposure hazard. We conducted experiments on the slopes of Etna volcano, where we drove with a small SUV-type car over an area of road artificially covered with tephra and investigated the resulting grain size distribution (GSD) and concentration of PM ₁₀ in the air as a function of (1) the number of car passages, (2) the starting thickness of the tephra deposit, and (3) vehicle speed. Our data show that increasing the number of car passages, deposit thickness, and vehicle speed rapidly induces a decrease in the GSD of tephra deposits and results in increased airborne PM ₁₀ . We show that vehicles will cause comminution (i.e., reduction to a smaller average particle size) and resuspension of basaltic ash, so local communities can expect that, after an eruption, concentrations of PM ₁₀ may increase with time and affect exposures close to roads.

Volcanic eruptions release gases and particulates that may adversely affect human health. The Tajogaite eruption on La Palma provided a unique opportunity to evaluate inorganic pollutant exposure in a directly affected population. As part of the ISVOLCAN study, blood samples from 393 adults residing in the island’s western region were analyzed for 43 inorganic elements using Inductively Coupled Plasma Mass Spectrometry (ICP-MS), including 20 toxic elements identified by the Agency for Toxic Substances and Disease Registry (ATSDR). The median age of participants was 51 years, and 56.7% were female. Higher levels of Hg and Mn were associated with long-term occupational exposure, while smoking was linked to elevated Cd, Pb, and Sr levels. Participants living within 6.5 km of the volcano had significantly higher concentrations of Al and Ti. Ash cleanup activities were associated with increased levels of Ni and Cu, and those spending over five hours outdoors daily showed elevated Se and Pb. This is the first biomonitoring study to assess blood concentrations of inorganic pollutants in a population exposed to volcanic emissions. The findings highlight key exposure factors and underscore the need for continued research to assess long-term health effects and inform public health measures.

Exposure to ambient particulate matter (PM) with an aerodynamic diameter of 10) is a well‐established health hazard. There is increasing evidence that geogenic (Earth‐derived) particles can induce adverse biological effects upon inhalation, though there is high variability in particle bioreactivity that is associated with particle source and physicochemical properties. In this study, we investigated physicochemical properties and biological reactivity of volcanic ash from the April 2021 eruption of La Soufrière volcano, St. Vincent, and two desert dust samples: a standardized test dust from Arizona and an aeolian Gobi Desert dust sampled in China. We determined particle size, morphology, mineralogy, surface texture and chemistry in sub‐10 μm material to investigate associations between particle physicochemical properties and observed bioreactivity. We assessed cellular responses (cytotoxic and pro‐inflammatory effects) to acute particle exposures (24 hr) in monocultures at the air‐liquid interface using two types of cells of the human airways: BEAS‐2B bronchial epithelial cells and A549 alveolar type II epithelial cells. In acellular assays, we also assessed particle oxidative potential and the presence of microorganisms. The results showed that volcanic ash and desert dust exhibit intrinsically different particle morphology, surface textures and chemistry, and variable mineralogical content. We found that Gobi Desert dust is more bioreactive than freshly erupted volcanic ash and Arizona test dust, which is possibly linked to the presence of microorganisms (bacteria) and/or nanoscale elongated silicate minerals (potentially clay such as illite or vermiculite) on particle surfaces.

Tungurahua volcano (Ecuador) intermittently emitted ash between 1999 and 2016, enduringly affecting the surrounding rural area and its population, but its health impact remains poorly documented. We aim to assess the respiratory health hazard posed by the 16–17 August 2006 most intense eruptive phase of Tungurahua. We mapped the spatial distribution of the health‐relevant ash size fractions produced by the eruption in the area impacted by ash fallout. We quantified the mineralogy, composition, surface texture, and morphology of a respirable ash sample isolated by aerodynamic separation. We then assessed the cytotoxicity and pro‐inflammatory potential of this respirable ash toward lung tissues in‐vitro using A549 alveolar epithelial cells, by electron microscopy and biochemical assays. The eruption produced a high amount of inhalable and respirable ash (12.0–0.04 kg/m² of sub‐10 μm and 5.3–0.02 kg/m² of sub‐4 μm ash deposited). Their abundance and proportion vary greatly across the deposit within the first 20 km from the volcano. The respirable ash is characteristic of an andesitic magma and no crystalline silica is detected. Morphological features and surface textures are complex and highly variable, with few fibers observed. In‐vitro experiments show that respirable volcanic ash is internalized by A549 cells and processed in the endosomal pathway, causing little cell damage, but resulting in changes in cell morphology and membrane texture. The ash triggers a weak pro‐inflammatory response. These data provide the first understanding of the respirable ash hazard near Tungurahua and the extent to which it varies spatially in a fallout deposit.

Volcanic tephra fall deposits, which form during explosive eruptions, are commonly characterized in terms of their thickness and grainsize. While significant efforts have been undertaken to relate spatial trends in thickness to plume dispersion processes, comparably few studies have focused on understanding variations in grainsize. Yet, grainsize is a key parameter providing insight into eruption dynamics, from magma fragmentation to plume transport processes, and modulates the impacts of tephra. Here, we present a set of grainsize data extracted from the published record for 56 deposits that represent a range of eruption intensities and magnitudes. We systematically analyze the deposits in terms of modality (bimodal or unimodal grainsize distributions) and provide the median particle diameter with distance from source for component distribution modes. We found that bimodal fall deposits are formed by eruptions with large amounts of fine particles (<100 µm) and that all tephra-fall deposits show characteristic patterns of grainsize decay with distance from source that can be related to eruption plume height and thus intensity. The grainsize decay trends are also related to ash dispersion and deposition processes such as individual particle settling versus collective settling mechanisms. The maximum distance from source reached by particles of different sizes is controlled by a combination of source and transport processes. This data set provides insight into the preservation potential of deposits of different grainsizes at varying distances from their sources. Finally, we emphasize the importance of using grainsize trends in combination with thickness trends to interpret tephra-fall deposit records.

Background: Tungurahua volcano (Ecuador) intermittently emitted ash between 1999 and 2016, enduringly affecting the surrounding rural area and its population, but its health impact remains poorly documented. Objectives: We aim at assessing the respiratory health hazard posed by the 16-17 August 2006 most intense eruptive phase of Tungurahua. Methods: Based on detailed field surveys and grain size analyses, we mapped the spatial distribution of the health-relevant ash size fractions produced by the eruption in the area impacted by ash fallout. We used Scanning Electron Microscopy and Raman Spectroscopy to quantify the mineralogy, composition, surface texture and morphology of a respirable ash sample isolated by aerodynamic separation. The cytotoxicity and pro-inflammatory potential of this respirable ash towards lung tissues was assessed in-vitro using A549 alveolar epithelial cells, by Electron Microscopy and biochemical assays (LDH assay, RT-qPCR, multiplex immunoassays). Results: The eruption produced a high amount of inhalable and respirable ash (12.0-0.04 kg/m ² of sub-10 µm and 5.3-0.02 kg/m ² of sub-4 µm ash deposited). Their abundance and proportion vary greatly across the deposit within the first 20 km from the volcano. The respirable ash is characteristic of an andesitic magma and no crystalline silica is detected. Morphological features and surface textures are complex and highly variable, with few fibres observed. In-vitro experiments show that respirable volcanic ash are internalized by A549 cells and processed in the endosomal pathway, causing little cell damage, but some changes in cell morphology and membrane texture. The ash trigger a weak pro-inflammatory response. Discussion: These data provide the first understanding of the respirable ash hazard near Tungurahua, and the extent to which it varies spatially in a fallout deposit. Given the long exposure duration of the surrounding population, the chronic effects of this inhalable, weakly bio-reactive ash on health could be further investigated.