Large vesicles record pathways of degassing at basaltic volcanoes
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Volcanic degassing is directly linked to magma dynamics and controls the style of eruptive activity. To better understand how gas is transported within basaltic magma we perform a 3D investigation of vesicles preserved in scoria from the 2005 activity at Stromboli volcano (Italy). We find that clasts are characterized by the ubiquitous occurrence of one to a few large vesicles, exhibiting mostly irregular, tortuous, channel-like textures, orders of magnitude greater in volume than all the other vesicles in the sample. We compare observations on natural samples with results from numerical simulations and experimental investigations of vesicle size distributions and demonstrate that this type of vesicle invariably forms in magmas with vesicularities > 0.30 (and possibly > 0.10). We suggest that large vesicles represent pathways used by gas to flow non-explosively to the surface and that they indicate the development of an efficient system that sustains persistent degassing in basaltic systems.
KeywordsBasaltic magmas Degassing 3D vesicle textures
We thank the SYRMEP beamline of Elettra Sincrotrone Trieste, Stefano Favretto and Livia Colò for their help in the acquisition of tomographic images of natural samples and Mark Rivers of GeoSoilEnviroCARS, Advanced Photon Source, for his help with microtomography of the experimental samples. We also thank Daniele Andronico, Mauro Rosi and Mario Zaia for sample collection. Thoughtful reviews by N. Métrich and an anonymous reviewer greatly improved the manuscript. This work was supported by Istituto Nazionale di Geofisica e Vulcanologia and Dipartimento per la Protezione Civile, and NSERC Discovery grant to D.R.B.
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