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VolcaPot – Sylvain Charbonnier (Mercredi 4 Juillet 15h)

4 juillet 2018 à 15 h 00 min - 16 h 00 min

Assessing hazards from small-volume Pyroclastic Density Currents (PDCs): a multi-disciplinary approach with emphasis on their potential for avulsion

Dr Sylvain Charbonnier, School of Geosciences, University of South Florida, USA

Small-volume (< 0.5 km3) pyroclastic density currents (PDCs) occur relatively frequently and pose severe threats to surrounding populations and infrastructures at active volcanoes. They are responsible for the two deadliest eruptions of the 21st century (Merapi 2010, Fuego 2018). Regardless of the generation mechanism, these small-volume PDCs are characterized by a short duration and complex multiphase flow dynamics due to time and space variability in their physical properties. In addition, the complex topography of active volcanoes largely controls the dynamics of small-volume PDCs, and rugged terrains can greatly affect the mobility and final impacts of these events. Compilation of pre-, syn- and post-eruptive data obtained from three selected, well-constrained, major PDC events (Merapi 2006 and 2010, Colima 2015) allows us to better understand the influence of varying topographic parameters on the internal flow dynamics. Results include (1) careful mapping of the stratigraphy, distribution, thicknesses and surface morphologies of the different deposit units, (2) identification of longitudinal and lateral lithofacies variations based on changes in grain-size distribution, coarse-tail grading and matrix componentry inside each stratigraphic unit, and (3) a geomorphic characterization of the variations of local topography and channel geometries along the flow paths. Combining the data sets from the three targeted eruptions led to the identification of quantifiable relationships between deposit footprint and surficial/sedimentological features, retaining capacity of the receiving landscape and scale-dependent tendencies for PDCs to overspill confined channels and avulse. These findings aim to: (1) define new semi-empirical relationships between the processes that control the emplacement and deposition of such PDCs and their potential for overspill/avulsion related to channel geomorphic parameters; (2) invert some key flow parameters at critical locations that will constitute part of the source database needed for enhancing and calibrating standard PDC hazard models.

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Détails

Date :
4 juillet 2018
Heure :
15 h 00 min - 16 h 00 min

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