Thèses sur le sujet « Explosive activity »

Thesis (Ph. D.)--University of North Carolina at Chapel Hill, 2007.
Title from electronic title page (viewed Dec. 18, 2007). "... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Geological Sciences." Discipline: Geology; Department/School: Geological Sciences.

En plus de la destruction des sites à proximités des volcans, l'accumulation de cendres volcaniques dans les zones distales peut causer de graves dommages. De plus l'évaluation de ces dangers n'est pas pleinement prise en compte dans les plans de mitigation actuels. L'étude de la dispersion des retombées pyroclastiques produites par les éruptions explosives des volcans Italiens lors du Quaternaire est le sujet de cette thèse. L'étude tephrostratigraphique de trois carottes lacustres des lacs de Shkodra et Ohrid (Albanie) et d'une carotte marine du Nord de la mer Ionienne a été réalisée. Dix-sept niveaux de tephra ont été corrélés aux éruptions explosives de A. D. 472, Avellino (3. 9 cal. Ka BP) du Vésuve, Monte Pilato (A. D. 1200), Gabellotto-Fiumebianco (8. 6 cal ka BP) et Monte Guardia (22 ka BP) de l'île de Lipari, FL (3. 4 cal. Ka BP) de l'Etna, Astroni (4. 2 cal. Ka BP), Agnano Monte Spina (4. 5 cal. Ka BP), Agnano Pomici Principali (12. 3 cal. Ka BP), SMP1-Y3 (31 ka) et l'Ignimbrite Campanienne-Y5 (39 ka) des Champs Phlégréens, X6 (107 ka) de la région Campanienne, et de P11 (131 ka) de l'île de Pantelleria. Cinq autres niveaux de tephra possèdent la composition que les dépôts de l'éruption vésuvienne de Mercato. Cela suggère une activité explosive entre les éruptions pliniennes de Mercato (8. 9 cal ka BP) et Avellino (3. 9 cal ka BP). Toutes ces données ont été intégrées, avec les données préexistantes de la littérature, dans la banque de données d'un SIG. Cette banque de données couplée à un SIG permet de grandement améliorer les dispersions des cendres et représente un outil qui améliore la mitigation des risques volcaniques dans la région centrale de la Méditerranée
In addition to the destruction of the sites close to the volcanoes, the accumulation of volcanic ash in distal zones can cause serious damages but the evaluation of the related hazard is not fully addressed in present day mitigation plans. The dispersion study joined with the physical and geochemical characterization, of distal pyroclastics deposits produced by explosive eruption of Italian volcanoes during late Quaternary was the focus of this PhD project. The distal deposits were investigated through the tephrostratigraphic study of three lacustrine cores from Lake Shkodra and Lake Ohrid (Albania), and one marine core from the northern Ionian Sea. Seventeen tephra layers were correlated with explosive eruptions of A. D. 472, Avellino (3. 9 cal. Ka BP) from Somma-Vesuvius, Monte Pilato (A. D. 1200), Gabellotto-Fiumebianco (8. 6 cal ka BP) and Monte Guardia (22 ka BP) from Lipari Island, FL (3. 4 cal. Ka BP) from Mount Etna, Astroni (4. 2 cal. Ka BP), Agnano Monte Spina (4. 5 cal. Ka BP), Agnano Pomici Principali (12. 3 cal. Ka BP), SMP1-Y3 (31 ka) and Campanian Ignimbrite-Y5 (39 ka) from Phlegrean Fields, X6 (107 ka) from Campanian, P11 tephra layer (131 ka) from Pantelleria Island. Five other tephra layers have the Mercato deposit composition from Somma-Vesuvius. This suggests the occurrence of interplinian activity between the eruptions of Mercato (8. 9 cal ka BP) and Avellino (3. 9 cal ka BP). All the data were collated into a GIS and integrated with literature data. This data-base implemented in a GIS environment allows a significant improvement of the ash dispersal and represents an useful tool for the improvement of volcanic hazard mitigation in Central Mediterranean area

Volatile emissions from Cascades cinder cone eruptions have been well-documented; however the implications for understanding the effects that volcanic gases have on surrounding communities have not been addressed. This study examines the hazards from volatile degassing during explosive activity by (1) analyzing S, Cl, and F concentrations dissolved in olivine-hosted melt inclusions and matrix glass from cinder cones located in central Oregon and northern California, (2) estimating the mass of volcanic gas degassed during these eruptions, and (3) predicting gas concentrations downwind of the vent. Analyses reveal that the magmas degassed >88% S, <49% Cl, and <50% F during eruption, equating to a release of ≤4.5 Mt SO2, ≤0.2 Mt HCl, and ≤0.2 Mt HF. Predictions of gas concentrations downwind of the vent provides reassurance that the levels of volcanic gases were not high enough at the time of eruption to present acute or severe health hazards to nearby residents.

The 2010 explosive eruption (VEI 4) of Merapi volcano, Indonesia, was the volcano’s largest since 1872. In contrast, volcanism over the last century has been characterised by dome-building and gravitational dome collapse, such as in 2006 (VEI 1). The driving forces behind effusive and explosive activity, as well as factors that affect transitions in eruptive style are investigated through petrological and textural analysis, using the well-documented 2006 and 2010 eruptions as case-studies. Pre- and syn-eruptive crystallisation and degassing processes are examined via whole rock geochemical analysis, mineral compositions and thermobarometry, quantitative textural analysis of feldspar microlites and analysis of volatiles and light lithophile elements in melt inclusions. These data were gathered from a detailed set of stratigraphically controlled samples, correlated to eruptive chronology and style, which were collected during several field campaigns. Both the 2006 and 2010 eruptions produced basaltic andesite, similar in terms of major and trace element compositions. A major zone of crystallisation is proposed at between ~ 14 and 29 km depth, although crystallisation occurs throughout the crust. Magmatic temperatures are estimated to be ~920–1020 °C. Maximum H2O contents reach 3.94 wt.% in 2010 melt inclusions and up to 3.73 wt.% in those from 2006. CO2 concentrations are < 200 ppm, although they may reach up to 695 ppm in some melt inclusions from the 2010 eruption. An exsolved brine phase was present during both eruptions which “buffered” melt Cl concentrations and enriched Li at shallow depths within the conduit or edifice. Eruptive style and transitions at Merapi are linked to magma ascent rate, crystallisation and open- and closed-degassing processes, which can be influenced by magma influx. The findings of this work are crucial for understanding the full range of eruptive behaviour that Merapi is capable of producing.

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.

The genotoxicity of energetic compounds (i.e., explosives) that are known to be present in contaminated soils at military training sites has not been extensively investigated. Thus, the Salmonella mutagenicity and Muta(TM)Mouse assays were employed as in vitro assays to examine the mutagenic activity of twelve explosive compounds, as well as three soil samples from Canadian Forces Base Petawawa. Salmonella analyses employed strains TA98 (frameshift mutations) and TA100 (base-pair substitution mutations), as well as the metabolically-enhanced YG1041 (TA98 background) and YG1042 (TA100 background), with and without exogenous metabolic activation (S9). For Salmonella analyses, the results indicate that ten of the explosive compounds were mutagenic, and consistently elicited direct-acting, base-pair substitution activity. All three soil samples were also observed to be mutagenic, eliciting direct-acting, frameshift activity. Mutagenic potencies were significantly higher on the metabolically-enhanced strains for all compounds and soil samples. For Muta(TM)Mouse analyses on FE1 cells, the results indicate that the majority of explosive compounds did not exhibit mutagenic activity. All three soil samples elicited significant positive responses (PET 1 and PET 3 without S9, and PET 2 with S9), and although there is some evidence of a concentration-related trend, the responses were weak. Correspondence of the mutagenic activity observed with the two assay systems, for both the explosive compounds and soil samples, was negligible. The differential response is likely due to differences in metabolic capacity between the two assay systems. Furthermore, it is likely that there are unidentified compounds present in these soil samples that are, at least in part, responsible for the observed mutagenic activity. Additional testing of other explosive compounds, as well as soil samples from other military training sites, using a variety of in vitro and in vivo assays, is warranted in order to reliably estimate mutagenic hazard and subsequently assess risk to human health.

Les études psychophysiologiques de la concentration sportive ont souvent porté sur des disciplines où la contrainte énergétique est faible. L'analyse de l'activité neurovégétative constitue un molèle inférentiel des opérations mentales contrôlées par le système nerveux central. En utilisant des microcapteurs non-invasifs, on dispose d'une méthode ambulatoire permettant d'étudier, en situation réelle, les processus mentaux de préparation à l'action. Les résultats montrent une élévation sélective de l'activation et de l'attention lors de la concentration, en fonction des exigences et des contraintes des activités sportives étudiées. L'élévation de l'attention servirait à construire l'image mentale du geste, partiellement ou totalement. De ce fait, elle pourrait être induite plus facilement par l'observation du mouvement à réaliser. Les différentes modalités d'observation d'un mouvement simple (virtuelle ou réelle)̀ entraînent une activité neurovégétative semblable

Orientador: Miguel de Arruda
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Educação Fisica
Made available in DSpace on 2018-08-11T21:36:55Z (GMT). No. of bitstreams: 1 Hespanhol_JeffersonEduardo_D.pdf: 2704427 bytes, checksum: c7eaede2484eeffb41fa05a527236222 (MD5) Previous issue date: 2008
Resumo: O propósito desse estudo consistiu em investigações nas mudanças no desempenho da força explosiva (FE), força explosiva elástica (FEE), força explosiva elástica reflexa (FEER) em voleibolistas durante um ciclo anual. A amostra examinada foi composta por 43 voleibolistas do sexo masculino. Os desempenhos das variáveis dependentes foram mensurados através dos testes de salto verticais com meio agachamento partindo de uma posição estática (SJ), teste de salto vertical com contra-movimento, sem a contribuição dos membros superiores (CMJ), e o teste de saltos verticais contínuos com duração de 5 segundos sem a contribuição dos joelhos e membros superiores (CJ5s). As coletas foram realizadas antes e depois dos períodos de preparação e competição, sendo as medidas feitas em tapete de contato Jump Test. Superiores desempenhos dos pos-púberes comparado aos púberes foram observados. O estágio de maturidade, massa corporal e área muscular da coxa contribuíram significantemente, mas com contribuições diferentes para variação do desempenho da produção de força, explicando cerca de 5 a 14% da variância (p<0,05). Em púberes foram observadas significantes mudanças no ciclo anual nas variáveis do desempenho da FE e FEE apresentando aumentos, no entanto não foram encontradas mudanças significantes na FEER, mesmo que os resultados revelando aumentos de desempenho. Os pos-púberes demonstraram aumentos significantes para os desempenhos da FE, FEE e FEER. Deste modo conclui-se que as mudanças foram lineares para os púberes e não lineares para os pós-púberes.
Abstract: The objective of this study it consisted of verify in the changes in the performance of the explosive strength (ES), elastic explosive strength (EES), and reflex explosive strength elastic (REES) in volleyballs players during a years cycle. The sample was composed for 45 volleyball players of the man sex. The participants were submitted the anthropometrical measures (stature, body weight, percentage of fat, fat mass, lean body mass, and thigh muscle area), and vertical jump tests (squat jump, countermovement jump,, and continuous jumps 5s) at three moments: in the beginning and the end of the pre-season; in the beginning and the end of the season, being the measures made in carpet of contact Jump Test. Higher performances of the after-pubescent than pubescent were observed. Maturity, corporal mass and muscular area of the thigh had contributed significantly, but with different contributions for variation of the performance of the strength production, explaining about 5-14% of the variance (p< 0,05). In pubescent significant changes in the annual cycle in the variable of the performance of ES and EES had been observed presenting increases, however, the changes had not been significant in the REES, even if showed increases the performance. The after pubescent showed significant increases in performances the ES, EES, and. In this way one concludes that the changes had been linear for pubescent and the not linear ones for the after-pubescent.
Doutorado
Ciencia do Desporto
Doutor em Educação Física

La capacité d'un athlète à accélérer un objet ou son propre corps constitue un déterminant essentiel de la performance sportive dans de nombreuses disciplines. Cette qualité d'explosivité est liée aux limites mécaniques du système neuromusculaire et notamment à la puissance maximale que l'athlète est capable de produire. L'évaluation précise de ce paramètre peut se révéler particulièrement intéressante pour les sportifs experts de disciplines nécessitants des qualités de puissance et d'explosivité. En effet, elle permet de mieux définir leur profil athlétique et d'individualiser la calibration des contenus d'entraînement musculaire. Ce travail se proposait d'explorer les liens possibles entre des indicateurs innovants de la fonction neuromusculaire et la performance explosive appréhendée au plus près des conditions de compétition. Dans le cadre d'une première partie expérimentale, nos travaux ont d'abord consisté à évaluer la validité et la reproductibilité de méthodes de terrain communément utilisées pour déterminer les qualités de puissance dans un mouvement explosif : le squat jump. L'effet de la charge sur les coordinations musculaires impliquées lors de la réalisation de ce mouvement balistique ont ensuite été analysées afin d'étudier les facteurs nerveux de la production d'un mouvement explosif. Les méthodes validées dans la première étude nous ont ensuite permis de montrer que les relations force-vitesse étaient dépendantes de l'activité sportive. Ces profils n'étaient par ailleurs pas systématiquement optimisés chez des sportifs très entraînés. La deuxième partie expérimentale a consisté à appliquer ces méthodes d'évaluation innovantes à l'étude de l'escrime. Dans un premier temps, les patterns mécaniques et neuromusculaires ont été décrits lors d'un assaut spécifique (i. E. Marché-fente), mettant en évidence l'importance de la capacité à produire des niveaux de force élevés, notamment avec la jambe arrière, dans des mouvements exécutés à vitesse élevée. Les relations entre les profils force-puissance-vitesse optimaux, et les déterminants de la performance en escrime ont ensuite été identifiés, afin de vérifier la pertinence d'évaluer ces paramètres innovants dans cette discipline explosive. Enfin, les derniers travaux n'ont pas montré d'effet d'un entraînement musculaire balistique, calibré à partir des profils force- et puissance-vitesse des escrimeurs. Les résultats de cette étude préliminaire ouvrent toutefois des perspectives de recherche intéressantes, qui permettraient de mieux comprendre l'impact des adaptations neuromusculaires sur la performance explosive
The capacity of an athlete to quickly accelerate an object or her/his own body is a determinant of performance in many sports. This explosive quality is related to the mechanical limits of the neuromuscular system and especially to the maximal power output capacity of the athlete. Accurate quantification of this parameter can be particularly interesting in elite athletes practicing activities requiring power and explosive abilities. Indeed, it allows for a better assessment of athletic profile and individualization of muscle training contents. This work intended to explore the possible links between innovative indicators of the neuromuscular function and explosive performance determined in conditions closest to the competition. In a first experimental section, our work primary consisted in evaluating the validity and reproducibility of field methods commonly used to assess the power output capacity in an explosive movement : the squat jump. The load effect on muscular coordination involved in the execution of this ballistic movement was then investigated in order to explore the neural factors of an explosive movement. Then, the methods validated in the first study allowed us to show that the force-velocity relationships were dependant of the practiced sport and that these profiles were not always optimized in highly trained athletes. The second experimental section consisted in the application of these innovative assessment methods to analyze the fencing activity. First, the mechanical and neuromuscular patterns of a specific fencing assault (i. E. Marché-fente) were described. These patterns highlighted the importance of the ability to produce high levels of force, especially with the rear leg, in the execution of high velocity movement. The correlation between the optimal force-power-velocity profiles and the performance determinants of fencing were then identified, to ensure the relevance of evaluating these innovating parameters in this explosive sport. Finally, the last investigation did not show any effect of ballistic training calibrated to the fencers force- and power-velocity profiles. Nevertheless, the results of this pilot study raise interesting research perspectives, which would lead to a better understanding of the neuromuscular adaptations on explosive performance

Current models for predicting the environmental fate of munitions constituents (MC) in soils are based mostly on chemical distribution parameters and neglect the larger considerations of other soil parameters. We are working towards a new approach based on the whole soil activity for predicting the long-term residence time and fate of MC in soils with connection to agronomic soil fertility concepts. These relationships are demonstrated by correlating experiments involving full physical and chemical characterization of eight taxonomically distinct soils, with batch reactor studies determining MC degradation potential. Soils were incubated in a slurry for 10 days in a closed reactor system with temperature, pH, and Eh readings recorded every 24 h. Air and slurry samples were taken eight times within the 168 h incubation period. Carbon dioxide, TNT, and nutrient solution concentrations were assessed to obtain a full picture of soil chemistry changes associated with microbial activity in response to additions of TNT. Multivariate analysis was used to determine the main factors impacting degradation rate. Principle Components Analysis (PCA) statistically classified the soils based on the variance of their soil property data. Partial Least Squares Analysis (PLS) showed that TNT degradation was possibly correlated with soil fertility characteristics. Although this is an exploratory study, results show promise in moving towards a more effective way of predicting TNT environmental fate in soils.

Cette étude traite de la dynamique des éruptions volcaniques explosives, depuis les mécanismes de sub-surface jusqu'aux processus d'émission et de dispersion des pyroclastes. A cet effet un radar Doppler sol est utilisé (VOLDORAD), lequel renseigne sur la charge / vitesse des ejectas. Les données sont intégrées avec d'autres techniques géophysiques, et des modèles numériques sont développés afin de simuler les émissions pyroclastiques, générer des signaux radar synthétiques, pour finalement améliorer notre compréhension des processus qui leurs sont sous-jacents. L'Arenal (Costa Rica) est utilisé comme volcan cible, où de fréquentes éruptions de faible magnitude émettent des panaches de cendres et des projections balistiques jusqu'à quelques centaines de mètres au-dessus de l'évent. Dans un premier temps, nous combinons des données sismiques et radar afin d'explorer la relation entre les processus de conduit et les émissions pyroclastiques. Leurs interactions complexes sont interprétées via un modèle conceptuel, lequel décrit les fractures parsemant le bouchon de lave comme responsables du dégazage du système, et en retour des signaux sismiques et radar collectés (ces derniers dépendants de la charge en cendres des émissions de gaz). Par ailleurs, nous investiguons la dynamique des émissions pyroclastiques à travers l'étude de radargrammes Doppler. La distribution spatio-temporelle de la vitesse des ejectas indique l'existence de deux phénomènes aux dynamiques distinctes. Des modélisations numériques permettant la reconstruction de signaux synthétiques indiquent qu'il s'agit de l'émission simultanée de blocs balistiques et de panaches de cendres. Une procédure d'inversion de type Monte Carlo couplée d'un algorithme d'optimisation permet de retrouver les radargrammes synthétiques qui reproduisent au mieux ceux observés. Les résultats apportent des contraintes sur divers paramètres éruptifs, tels que les tailles, trajectoires, vitesses des ejectas et des gaz, ainsi que la vitesse / direction de dispersion des panaches de cendres par le vent. Enfin, nous discutons du potentiel des radars Doppler appliqués à la surveillance opérationnelle des émissions volcaniques. En particulier, la possibilité de quantifier les masses éjectées dans l'atmosphère ou retombant sur les flancs du volcan, fournit des paramètres éruptifs à la source pouvant alimenter les modèles de dispersion de panaches de cendres.

La thèse rapporte un ensemble de données sur les relations entre une activation de la protéine kinase C et deux activités fonctionnelles du polynucléaire neutrophile humain (PN) : le déplacement et l'explosion oxydative.

L’estirament és una tècnica que manté o millora l’amplitud de moviment d’una articulació o d’un conjunt d’articulacions, per una acció d’allargament i tracció de les estructures que sol·licita. Suposa una tècnica per cuidar, prevenir i mantenir o desenvolupar les capacitats de cada individu. No tots els estiraments es realitzen de la mateixa manera ni tenen el mateix objectiu, en funció de la seva aplicació s’obté un efecte o un altre. Tot estirament realitzat durant l’escalfament influeix en nombroses variables, com la força explosiva i l’estat d’ànim, que contribueixen a afrontar d’una manera més o menys òptima un entrenament o una competició. Aquesta tesi doctoral es basa en l’estudi sobre l’estirament i el seu objectiu ha estat avaluar i comparar l’eficàcia aguda o immediata de diferents tipus d’estirament en l’escalfament esportiu de l’esportista sa i veure com influeixen sobre aspectes fisiològics, psicològics i de percepció, és a dir: l’opinió del participant a l’estudi. L’estudi s’ha dividit en dues fases que comparteixen el mateix protocol, amb diferents intervencions, així en la primera fase s’ha analitzat la repercussió de diferents tipus d’estirament estàtic durant l’escalfament esportiu. S’han comparat els estiraments estàtics actius, els passius i les tècniques neuromusculars (contracció, relaxació, estirament) i el no estirament. En la segona fase s’ha analitzat la repercussió de diferents tipus d’estirament actiu durant l’escalfament esportiu. Els estiraments comparats són: l’estirament estàtic actiu en tensió activa, l’estirament dinàmic i el no estirament. La força explosiva de l’extremitat inferior es pot objectivar mitjançant el test de salts proposat per Bosco. L’estat d’ànim, mitjançant la prova de perfils d’estat d’ànim POMS (Profile of Mood States) i les preferències del participant amb un qüestionari d’opinió. La mostra total emprada en les dues fases de l’estudi ha estat de 97 participants.

VOLDORAD, un radar Doppler UHF moyenne puissance, est un système portable basé au sol, développé par l'Observatoire de Physique du Globe de Clermont-Ferrand (France), spécifiquement pour l'étude de l'activité volcanique explosive. La capacité de ces méthodes de télédétection à sonder l'intérieur des jets et des panaches volcaniques dangereux constitue un vrai pas en avant concernant l'analyse des paramètres physiques qui contrôlent la dynamique des éruptions volcaniques. L'objectif principal de cette thèse est d'apporter des contraintes plus précises, notamment à partir du développement de procédures méthodologiques, sur l'interprétation des données radar Doppler, dans le but final d'améliorer notre compréhension de la dynamique explosive. Ce travail a été réalisé à partir de mesures radar Doppler acquises pendant l'éruption du cratère Sud-Est de l'Etna en Juillet 2001, et s'intéresse plus particulièrement à l'activité Strombolienne. Cependant, les méthodes de traitement, les modèles directs et les procédures d'inversion développés dans cette étude ont été réalisés dans une optique plus générale, et applicable sur différents types de dynamismes. L'étude détaillée de l'activité Strombolienne par la méthode radar Doppler a permis d'obtenir une large gamme de paramètres sources, notamment : les vitesses et masses de gaz et de particules, ainsi que les caractéristiques géométriques des jets. L'estimation quantitative précise de ces paramètres et de leur évolution au cours du temps est cruciale pour (1) la surveillance et la détection précoce de l'activité volcanique, ainsi que (2) pour l'apport de contraintes sur les hypothèses formulées dans les modèles de dynamique éruptive et dans les modèles de prédiction de dispersion des cendres, indispensables à la minimisation des risques.

I vulcani in stato di attività persistente a condotto aperto spesso ospitano un’attività definita stromboliana. Questo stile di attività è caratterizzato da rilasci frequenti (intervalli da secondi a minuti) e impulsivi (della durata di alcuni secondi) di piroclasti e gas, dovuti alla risalita e allo scoppio di grosse bolle di gas (dette slug) vicino alla superficie della colonna di magma. Nel tempo, tali vulcani possono mostrare continui cambiamenti nell’evoluzione e nella migrazione delle proprie bocche attive, dalle quali si può osservare anche un comportamento altamente variabile dell’attività. Le origini di tale variabilità devono essere studiate a scale spaziali e temporali variabili. In una scala di anni/centinaia di metri, l’osservazione diretta della migrazione delle bocche nello spazio e nel tempo nei vulcani contraddistinti da più bocche è ancora limitata, e resta da capire la relazione tra questa attività variabile e il sistema di condotti superficiale. Su una scala di secondi/metri, molti autori si sono focalizzati sulla dinamica del rilascio di gas e sulle modalità di formazione dei piroclasti, finora trascurando ampiamente la dinamica di risalita dei piroclasti dalla profondità di rilascio, dove gli slug scoppiano, sino alla loro espulsione dalla bocca. Lo scopo del mio studio è la definizione delle relazioni tra i parametri fisici all’interno del condotto vulcanico e la loro influenza sulla modalità di espulsione dei piroclasti nelle eruzioni stromboliane, tenendo conto delle due scale sopramenzionate. Per raggiungere tale scopo ho adottato due metodologie separate ma complementari. La prima richiede la caratterizzazione delle eruzioni stromboliane in natura, indagando i cambiamenti temporali nella posizione delle bocche sulla terrazza craterica di Stromboli e i parametri di esplosione (durata e geometria del getto) usando i video delle telecamere di sorveglianza a infrarossi raccolti tra il 2005 e il 2009. I risultati di questa prima metodologia forniscono un database dettagliato dell’attività stromboliana normale a diverse scale temporali, oltre a consentire di delineare una gerarchia di profondità a cui il sistema di condotti superficiale controlla l’attività esplosiva entro le tre principali aree (cioè la nord-est, la centrale e la sud-ovest) che raggruppano più bocche vicine a Stromboli. Alla profondità più bassa, dove gli slug scoppiano, la forma della bocca e le dimensioni degli slug controllano i parametri di esplosione locali, mentre la ramificazione più in superficie dei condotti determina l’evoluzione delle bocche che esplodono simultaneamente o alternativamente. Al di sotto della profondità di scoppio degli slug, il sistema di condotti che alimenta ciascuna area di bocche controlla quale specifica bocca ospiterà le esplosioni e anche alcune caratteristiche generali di esplosione all’interno di queste aree. A questa profondità si suppone ci sia un collegamento tra l’area centrale e quella sudovest, come supportato da diverse osservazioni. Al livello più profondo, il sistema di condotti è comune a tutte le aree e imposta il tasso eruttivo globale del vulcano, bilanciandolo tra l’area nord-est e quella congiunta sud-ovest e centrale. Questo tipo di analisi può essere eseguito anche in altri sistemi persistenti contraddistinti da più bocche in tutto il mondo, fornendo deduzioni di base sulla geometria e la dinamica del loro sistema di condotti e sulla valutazione della pericolosità connessa. La seconda metodologia è dedicata alle simulazioni di getti gas-particelle per mezzo di esperimenti analogici in scala utilizzando uno shock-tube trasparente. Questo approccio è incentrato sull’effetto delle condizioni iniziali (cioè, pressione e volume del gas, posizione del campione, dimensione e quantità di particelle, geometria della bocca) sia sull’accelerazione delle particelle all’interno del condotto che sull’espulsione risultante dalla bocca. I risultati mostrano che la velocità massima delle particelle ha una correlazione positiva con l’energia iniziale e una correlazione negativa sia con la profondità del campione rispetto alla bocca che con la dimensione delle particelle. Inoltre, gli esperimenti mostrano tendenze di accelerazione e decelerazione delle particelle all’interno dello shock-tube che dipendono in modo variabile da alcune condizioni iniziali (cioè energia iniziale, profondità del campione e dimensione delle particelle) e influiscono sulla velocità massima delle particelle registrata all’uscita. Rispetto ai processi che si verificano durante le eruzioni esplosive a piccola scala, questi risultati aprono la strada a nuove potenziali deduzioni riguanti i processi che controllano la dinamica dei piroclasti. Le tendenze di accelerazione e decelerazione all’interno dei condotti influenzano i modelli correnti che correlano la velocità di espulsione dei piroclasti con la loro profondità di origine nel condotto vulcanico. Dimostro che le assunzioni del modello non sono più valide nei casi di bassa energia iniziale e un campione più profondo. Pertanto, è necessaria una revisione del modello che tenga conto anche di queste tendenze prima di applicarlo alle eruzioni reali. Questi risultati aprono la strada a numerosi scenari futuri. Ad esempio, ulteriori esperimenti possono chiarire meglio gli effetti dell’accoppiamento gas- particella, analizzare il ruolo di altri parametri sull’espulsione dei piroclasti (ad esempio il diametro del condotto) o studiare altri aspetti (ad esempio, i pennacchi vulcanici utilizzando particelle molto fini, o collisioni particella-particella e particelle-parete nel condotto).
Persistent, open-vent volcanoes frequently host Strombolian explosions. This style of activity is characterized by frequent (intervals of seconds to minutes) and impulsive (seconds- long) releases of pyroclasts and gases, due to the rise and burst of large gas bubbles (i.e., slugs) near the surface of the magma column. Over time, such volcanoes can show continuous changes in the evolution and migration of their active vents, from which also a highly variable behavior of the activity can be observed. The sources of such variability need being investigated at variable spatial and temporal scales. On a scale of years/hundred of meters, direct observation of space-time vent migration at multi-vent volcanoes is still limited, and the relationship between this variable activity and the shallow conduit system remains to be understood. On a scale of seconds/meters, many authors are focused on the dynamics of gas release and modes of pyroclasts formation, so far largely neglecting the ascent dynamics of pyroclasts from their release depth, where slugs burst, to their ejection from the vent. The aim of my study is the definition of the relationships between the physical parameters inside the volcanic conduit and their influence on the modes of pyroclast ejection in Strombolian explosions, accounting for the two scales abovementioned. To achieve this aim, I considered two separate yet complementary methodologies. The first one requires the characterization of Strombolian eruptions in nature investigating temporal changes in vent position at the crater terrace of Stromboli and explosion parameters (jet duration and geometry) using infrared surveillance camera videos collected between 2005 and 2009. Results by this first methodology provide a detailed database of normal Strombolian activity at different time-scales, as well as allowing one to outline a hierarchy of depths at which the shallow conduit system controls the explosive activity within the three main vent areas (i.e., south-west, central, and north-east) at Stromboli. At the shallowest depth, where slugs burst, vent shape and slug size control local explosion parameters, while shallower conduit branching determines the evolution of simultaneous or alternating twin vents. Below the depth of the slug burst, the conduit system feeding each vent area controls which specific vent will host the explosions and also some more general explosion features within a vent area. A link between the central and south-west vent areas is supposed at this depth, as supported by several observations. At the deepest level, the conduit system is common to all vent areas and sets the overall explosion rate of the volcano, balancing it between the north-east and the joint south-west and central vent areas. This kind of analysis may be performed also in other persistent multi-vent systems worldwide, providing basic inferences on geometry and dynamics of their conduit systems and on the hazard assessment. The second methodology is addressed on gas-particle jet simulations by means of scaled analogue experiments using a transparent shock-tube. This approach focuses on the effect of the initial source conditions (i.e., gas pressure and volume, sample position, size and amount of particles, vent geometry) both on the acceleration of the particles within the conduit and on the resulting ejection from the vent. Results show that maximum particle velocity has a strong positive correlation with initial energy and a weaker, negative correlation with both sample depth from the vent and particle size. Moreover, the experiments show trends of particle acceleration-deceleration in the shock-tube that variably depend on some initial conditions (i.e., initial energy, sample depth, and particle size) and influence particle maximum velocity recorded at the exit. When compared to processes occurring during low-scale explosive eruptions, these results open the way for potential, new inferences on the processes controlling the dynamics of pyroclasts. The acceleration-deceleration trends inside the conduits impact current models relating pyroclast ejection velocity with their source depth in the volcanic conduit. I show that, for a lower initial energy and a deeper sample, the model assumptions do not hold true anymore. Therefore, a model revision taking into account these trends is necessary before applying it to real eruptions. These results open the way to numerous future scenarios. Further experiments may, for instance, clarify, the effects of particle-gas coupling, analyze the role of other source parameters on pyroclast ejection (e.g., conduit diameter) and study other aspects (e.g., the volcanic plumes using very fine particles, or particle-particle and particle-wall collisions in the conduit).

The March-April 2007 Piton de la Fournaise (PdF) eruption was the most significant eruption on La Réunion island in historical times. The eruption was characterised by different styles of volcanic activity on different parts of the volcano. In particular, during the April eruptive phase, fluctuating high fountains occurred at a vent on the southeastern flank of the volcano at about 590 m a.s.l. (Piton Tremblet), and rootless littoral hydro-volcanic explosive activity occurred at the coast, whereas the volcano summit experienced caldera collapse. On the 5th - 6th April, the major caldera collapse occurred affecting the plateau and wall of the Dolomieu crater. Subsequent to caldera collapse events on the 6th and 12th April, an increase in the flank fountain activity was recorded. High discharge, 300-350 m fountain height, and textural change in the products were produced at Piton Tremblet. Lavas fed by the Piton Tremblet activity reached the coast and interacted with seawater generating hydro-volcanic explosive activity, which rapidly built a littoral cone. A link among these eruptive events and their chronology was suggested syn-eruptively due to change in the eruptive intensity and discharge, which showed significant increase, and textural change in the magma, passing from basalt to olivine-basalt to oceanite. This study provides the reconstruction of the complete chronology of the April 2007 eruptive phase, describes the eruptive dynamics involved in the different eruptive events and their peculiar characters, determines the link among different eruptive events, and investigates the PdF plumbing system. Available syn-eruptive records were analysed to reconstruct the chronology of the eruption. Available multidisciplinary monitoring data on the 2007 eruption were used. Deposits of the eruptive activity and their stratigraphy were analysed. Products from the lava fountain and the littoral cone were analysed in the lab for clast density, and grain size. Products from the entire range of eruptive activity were morphologically analysed for componentry. Microtextural observations were produced on the caldera collapse and flank fountain products. Quantitative microtextural analysis using image analysis method and stereological and volumetric data conversion of vesicularity was performed on 16 pyroclasts (16-32 mm diameter) from Piton Tremblet fountaining activity, selected among the modal densities within the diverse morphology range. Comparisons with other similar eruptive activity and/or eruptions occurred worldwide were investigated. The increase in discharge at 6th April and the reactivation on the 12th April of the fountaining at Piton Tremblet flank vent were linked with summit caldera collapse events. The collapses perturbed the pressure conditions within the volcano’s plumbing system. At the summit, the caldera collapse activity showed the involvement of magma and hydrothermal system which produced phreatic and phreatomagmatic explosions and lavas, although gravity driven collapses and numerous landslides played the major role in the collapse dynamics. The magma source of the summit activity can be related to a pre-2007 intrusion emplaced at shallow depth below the eastern summit area and is not related with the Piton Tremblet magma source. Piton Tremblet fountaining dynamics were characterised by magma and volatiles coupling during ascent subsequent to volatile exsolution and bubble nucleation stage as inferred by quantitative vesicle data interpretation. Variations in degassing and eruptive activity were generated by deep magmatic inputs, caldera collapse events, and increasing crystal content in the magma. The rootless hydro-volcanic explosive activity occurred on the 6th April when channel-fed ‘a‘ā lavas produced by Piton Tremblet interacted with seawater, and produced a nested littoral cone structure in four stages. The fragmentation was generated by steam explosions which produced three different particle components (vesicular, transitional and dense clasts) and three different particle transport types (tephra jet, fall and surge). Comparisons between the April 2007 PdF eruptive phase and similar events at other basaltic volcanoes worldwide showed that: 1) Piton Tremblet fountain activity is comparable with basaltic fountains at Kilauea (Hawaii), despite its lower maximum fountain height; however, the crystal content had an important role in modifying magma rheology and enhancing viscosity, and trapping bubbles leading to largely coupled ascent during fountaining activity; 2) the caldera collapse compared with other recent caldera collapses that occurred at different basaltic volcanoes (Fernandina, Miyakejima) is very similar in terms of caldera formation processes, eruptive features, and products, despite its smaller size; 3) the rootless hydro-volcanic activity was more powerful than the recent littoral activity occurred in Hawaii and comparable with the Hawaiian historical littoral cones. The evolution of the April 2007 eruption and the temporal links among the different volcanic stages demonstrate the connection of the magma plumbing system (which includes three main magma storage zones) at different levels and that perturbations of pressure within the system can drive dramatic increases of eruptive activity. The 2007 PdF eruption also showcased the range of possible volcanic hazards which could occur during a large eruption at a basaltic volcano, and showed how these hazards directly impacted the population of La Réunion island.