14 research outputs found

    Temporal magmatic evolution of the Fani Maoré submarine eruption 50 km east of Mayotte revealed by in situ sampling and petrological monitoring

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    The “Fani MaorĂ©â€ eruption off the coasts of Mayotte has been intensively monitored by applying methods similar to those used for subaerial eruptions. Repeated high-resolution bathymetric surveys and dredging, coupled with petrological analyses of time-constrained samples, allowed tracking the evolution of magma over the whole submarine eruptive sequence. Indeed, after one year of direct ascent (Phase 1), basanitic magma switched to a different pathway that sampled a tephriphonolitic subcrustal reservoir (Phase 2). Later, the magma pathway shifted again in the crust resulting in a new eruption site located 6 km northwest of the main edifice (Phase 3). The petrological signature of lava flows reveals both an evolution by fractional crystallization and syn-eruptive mixing with a tephri-phonolitic magma. We demonstrate that high-flux eruption of large volumes of basanitic magma from a deep-seated reservoir can interact with shallower reservoirs and remobilize eruptible magma. This has significant hazards implications with respect to the capacity of such large eruptions to reactivate shallow-seated inactive reservoirs froma transcrustal magmatic system that could be located potentially at a distance from the high-flux eruptive site.L’éruption au large de Mayotte a Ă©tĂ© intensĂ©ment surveillĂ©e en appliquant des mĂ©thodes similaires aux Ă©ruptions sub-aĂ©riennes. Une Ă©tude pĂ©trologique et gĂ©ochimique des Ă©chantillons draguĂ©s couplĂ©e Ă  de nombreux relevĂ©s bathymĂ©triques, nous a permis de suivre l’évolution du magma au cours de l’éruption. Le trajet du magma change aprĂšs un an de remontĂ©e directe (Phase 1), un rĂ©servoir magmatique sous-crustal et plus diffĂ©renciĂ© est alors Ă©chantillonnĂ© (Phase 2). Un mois plus tard, le trajet change Ă  nouveau et engendre une migration du site Ă©ruptif Ă  6 km au nord-ouest de l’édifice principal (Phase 3). La signature pĂ©trologique des coulĂ©es de lave rĂ©vĂšle Ă  la fois une Ă©volution par cristallisation fractionnĂ©e et un mĂ©lange syn-eruptif avec un magma tĂ©phri-phonolitique. Nous dĂ©montrons qu’une Ă©ruption Ă  haut dĂ©bit impliquant de grands volumes de magma basanitique et provenant d’un rĂ©servoir profond peut interagir avec des rĂ©servoirs plus superficiels et remobiliser le magma Ă©ruptible. Ceci a des implications significatives en termes de risques quant Ă  la capacitĂ© de ces grandes Ă©ruptions Ă  rĂ©activer des rĂ©servoirs inactifs peu profonds provenant d’un systĂšme magmatique transcrustal et potentiellement situĂ© Ă  distance du site Ă©ruptif

    First cases of Omicron in France are exhibiting mild symptoms, November 2021–January 2022

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    International audienceObjectivesWe aimed to investigate the first Omicron cases detected in France in order to assess case characteristics and provide supporting information on the possible impact of this variant on the healthcare system.MethodsA standardized questionnaire was used to collect information from confirmed and probable Omicron cases.ResultsMedian age of 468 investigated cases was 35 years, 376 were symptomatic (89%); 64% were vaccinated with two doses and 7% had received three doses. Loss of smell and taste were reported by 8.3% and 9% of cases, respectively. Seven cases were hospitalized, three of those were unvaccinated (including two with reported precondition). No admissions to intensive care and no deaths were reported.ConclusionsOur results confirm a mild clinical presentation among the first Omicron cases detected in France and highlight the importance for the national COVID-19 surveillance system to quickly detect and adapt to the emergence of a new variant
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