Options
Favretto, S.
Loading...
2 results
Now showing 1 - 2 of 2
- PublicationRestrictedVesiculation in magmas from Stromboli and implications for normal Strombolian activity and paroxysmal explosions in basaltic systems(2009-01-30)
; ; ; ; ; ;Polacci, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia ;Baker, D. R.; Earth and Planetary Sciences, McGill University, Montreal, Quebec, Canada ;Mancini, L.; SYRMEP Group, Basovizza, Italy ;Favretto, S.; Dipartimento Materiali e Risorse Naturali, Università di Trieste,Trieste, Italy ;Hill, R.; Department of Chemical Engineering, McGill University, Montreal, Quebec, Canada; ;; ; We performed a series of X-ray tomographic experiments and lattice Boltzmann permeability simulations on pyroclastic products from explosive activity at Stromboli between December 2004 and May 2006. We reconstructed the 3-D textures of vesicles to investigate the relationship between the nature of vesiculation in the erupted products and the dynamics of gas transport in the shallow conduit in order to derive implications for the eruptive behavior of basaltic volcanoes. Scoriae from normal Strombolian explosions display remarkably consistent vesicle volume distributions fit by power laws with an exponent of 1 (±0.2). We ascribe the origin of such distributions to the combined effect of coalescence and continuous nucleation events in the steady state, shallow magma system that supplies normal Strombolian activity. Volume distributions and textures of vesicles in pumice clasts from the 5 April 2003 and 15 March 2007 paroxysmal activity are markedly different from those in the scoriae. Besides a power law function with a higher exponent, portions of these distributions can be also fit by an exponential function, suggesting the attempt of the system to reach near-equilibrium conditions. The investigated pumice clasts also lack the large, connecting vesicles responsible for the development of degassing pathways in the Stromboli magma that erupts the scoriae. This testifies to a decreased degassing efficiency of the magma associated with paroxysmal explosions and potential overpressure buildup at depth. By comparison with degassing experiments on basaltic melts, we derive a time constraint on the order of minutes to hours for the incubation of paroxysms at Stromboli.114 15 - PublicationRestrictedThe role of syn-eruptive vesiculation on explosive basaltic activity at Mt. Etna, Italy(2009-01-20)
; ; ; ; ; ; ;Polacci, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia ;Burton, M. R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia ;La Spina, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;Murè, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;Favretto, S.; Dipartimento Materiali e Risorse Naturali, Trieste, Italy ;Zanini, F.; SYRMEP Group, Sincrotrone Trieste S.C.p.A., Basovizza, Italy; ; ; ; ; We investigated the dynamics of explosive activity at Mt. Etna between 31 August and 15 December 2006 by combining vesicle studies in the erupted products with measurements of the gas composition at the active, summit crater. The analysed scoria clasts present large, connected vesicles with complex shapes and smaller, isolated, spherical vesicles, the content of which increases in scoriae from the most explosive events. Gas geochemistry reports CO2/SO2 and SO2/HCl ratios supporting a deep-derived gas phase for fire-fountain activity. By integrating results from scoria vesiculation and gas analysis we find that the highest energy episodes of Mt. Etna activity in 2006 were driven by a previously accumulated CO2-rich gas phase but we highlight the lesser role of syn-eruptive vesicle nucleation driven by water exsolution during ascent. We conclude that syn-eruptive vesiculation is a common process in Etnean magmas that may promote a deeper conduit magma fragmentation and increase ash formation.454 26