Syn-emplacement processes revealed by textural analyses of PDC deposits from 2006 eruption of Tungurahua volcano (Ecuador): impact on flow mobility

Abstract:

Pyroclastic density currents (PDC) are remarkably mobile flows that threaten many people worldwide: a better understanding of their behavior is crucial for hazard assessment purposes. Since close observations of coarse parts of PDCs remain impossible, the deposits offer valuable information to infer syn-emplacement processes. The aim of this study is to precisely quantify componentry and grain size parameters of PDC deposits, which is still a major issue due to wide deposits heterogeneities. We use here a method based on image analysis to extract 2D information from high resolution images of sections in PDC deposits from the 2006 eruption of Tungurahua volcano (Ecuador) coupled with stereological and density conversions to obtain masses. This method allows us to document a large size range (from-1phi up to-7phi) and reveals complex polymodal distribution. Based on color, shape and surface texture we identified 7 componentry classes in the deposits and recalculated bulk componentry assemblages in terms of volume

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