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Burgisser, Alen
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- PublicationOpen AccessMeMoVolc consensual document: a review of cross-disciplinary approaches to characterizing small explosive magmatic eruptions(2015)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;; ; ; ; ; ;; ; ; ; ; ;; ; ; ; ; ; ; ; ; ; ; ;; ; ; ; ; ; ; ; ;; A workshop entitled “Tracking and understanding volcanic emissions through cross37 disciplinary integration: A textural working group.” was held at the Université Blaise Pascal (Clermont-Ferrand, France) on the 6-7th November 2012. This workshop was supported by the European Science Foundation (ESF). The main objective of the workshop was to establish an initial advisory group to begin to define measurements, methods, formats and standards to be applied in the integration of geophysical, physical and textural data collected during volcanic eruptions so as to homogenize procedures to be applied and integrated during both past and ongoing events. The working group comprised a total of 35 scientists from six countries (France, Italy, Great Britain, Germany, Switzerland and Iceland). The group comprised eleven advisors from the textural analysis field, eleven from deposit studies, seven geochemists and six geophysicists. The four main aims were to discuss and define: 1) Standards, precision and measurement protocols for textural analysis; 2) Identify textural, field deposit, chemistry and geophysical parameters that can best be measured and combined; 3) Agree on the best delivery formats so that data can be sheared between, and easily used by, each group; 4) Review multi-disciplinary sampling and measurement routines currently used, and measurement standards applied, by each community. The group agreed that community-wide cross-disciplinary integration, centered on defining those measurements and formats that can be best combined, is an attainable but key global focus. Consequently, we prepared a final document to be used as the foundation for a larger, international textural working group to serve as the basis of fully realizing such a pandisciplinary goal in volcanology. Thus, we here report our initial conclusions and recommendations.605 267 - PublicationRestrictedGeneration of CO2-rich melts during basalt magma ascent and degassing(2013-07)
; ; ; ; ; ; ; ;Pichavant, M.; CNRS-Orleans ;Di Carlo, I.; CNRS-Orleans ;Rotolo, S. G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Scaillet, B.; CNRS-Orleans ;Burgisser, A.; CNRS-Orleans ;Le GAll, N.; CNRS-Orleans ;MArtel, C.; CNRS-Orleans; ; ; ; ; ; To testmechanisms of basalticmagma degassing, continuous decompressions of volatile-bearing (2.7–3.8 wt% H2O, 600–1,300 ppm CO2) Stromboli melts were performed from 250–200 to 50–25 MPa at 1,180–1,140 C.Ascent rates were varied from 0.25 to *1.5 m/s. Glasses after decompression show a wide range of textures, from totally bubblefree to bubble-rich, the latter with bubble number densities from 104 to 106 cm-3, similar to Stromboli pumices. Vesicularities range from 0 to *20 vol%. Final melt H2O concentrations are homogeneous and always close to solubilities. In contrast, the rate of vesiculation controls the finalmelt CO2 concentration. High vesicularity charges have glass CO2 concentrations that follow theoretical equilibrium degassing paths, whereas glasses from low vesicularity charges show marked deviations from equilibrium, with CO2 concentrations up to one order of magnitude higher than solubilities. FTIR profiles and maps reveal glass CO2 concentration gradients near the gas–melt interface. Our results stress the importance of bubble nucleation and growth, and of volatile diffusivities, for basaltic melt degassing. Two characteristic distances, the gas interface distance (distance either between bubbles or to gas–melt interfaces) and the volatile diffusion distance, control the degassing process. Melts containing numerous and large bubbles have gas interface distances shorter than volatile diffusion distances, and degassing proceeds by equilibrium partitioning of CO2 and H2O between melt and gas bubbles. For melts where either bubble nucleation is inhibited or bubble growth is limited, gas interface distances are longer than volatile diffusion distances. Degassing proceeds by diffusive volatile transfer at the gas– melt interface and is kinetically limited by the diffusivities of volatiles in the melt. Our experiments show that CO2-oversaturated melts can be generated as a result of magma decompression. They provide a new explanation for the occurrence of CO2-rich natural basaltic glasses and open new perspectives for understanding explosive basaltic volcanism222 42