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The ash load of Strombolian volcanic plumes

Franck Donnadieu 1,2, Valentin Freret-Lorgeril1,2, Agathe Hantraye3, Julien Delanoë4, Corentin Soriaux1, Thierry Latchimy2, Frederic Peyrin2, Jean-Paul Vinson4, Christophe Caudoux4, Claude Hervier2

  • Affiliations: 1Université Clermont Auvergne, CNRS, IRD, OPGC, Laboratoire Magmas et Volcans, F-63000 Clermont-Ferrand, France; 2Université Clermont-Auvergne, CNRS, UAR 833, OPGC, F-63177 Aubière, France; 3Ecole et Observatoire des Sciences de la Terre -- EOST, University of Strasbourg, France; 4Laboratoire Atmosphères, Milieux, Observations Spatiales, UVSQ/CNRS/UPMC, Guyancourt, France 

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 97

  • Programme No: 3.12.23

  • Theme 3 > Session 12

Abstract

Eruptive source parameters of volcanic plumes control the ascent, dispersion and fallout of ash and their determination is key to assess related hazards. To estimate in particular the plume ash load, a field experiment was carried out at Stromboli volcano during normal strombolian activity. A new transportable mm-wave Doppler radar measured the reflectivity and Doppler velocity of ash emissions ~100 m above the vent at unprecedented space-time resolution (12.5 m; 1 s) while a disdrometer recorded particle sizes and fall velocities of proximal ash fallout (10 s). In situ reflectivities measured by the radar compared to the reflectivity-concentration correlation derived from the disdrometer provide estimates of the plume near-source particle concentrations. We find bulk and maximum concentrations commonly in excess of the aviation threshold for ash hazards by 2 to 3 orders of magnitude and up to 1 g.m-3. Ash-filled volumes initially total <50-80 m in thickness, growing up to 60-180 m in late stages, and show a Gaussian distribution of mass on average. Plume detection durations last in majority 25-50 s, up to 250 s, with the emission phase most frequently lasting less than 25 s. Space-time integration of inferred concentrations using measured ash detection duration, plume thickness, and ascent velocities further provides total ash masses released per emission of the order of a few tens of kg, with only a few percent exceeding 200 kg.