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Size limits on particle rounding and their use in comparison between pyroclastic flow and fallout units

Natalia Lipiejko1 , Thomas J. Jones1 , Josef Dufek2 & Ulrich Kueppers3

  • Affiliations: 1 Lancaster Environment Centre, Lancaster University, Lancaster, United Kingdom; 2 Department of Earth Sciences, University of Oregon, Eugene, United States; 3 Earth and Environmental Sciences, Ludwig-Maximilians-Universität München, Munich, Germany;

  • Presentation type: Poster

  • Presentation time: Friday 16:30 - 18:00, Room Poster Hall

  • Poster Board Number: 198

  • Programme No: 3.9.25

  • Theme 3 > Session 9

Abstract

Pyroclastic deposits provide a crucial record of explosive eruptive processes, which contribute to the construction of a volcanic record for a particular volcano or region. Common classification of pyroclastic deposits include the fundamental distinction between fallout units deposited as an air fall from an eruption column or plume and flow unit deposits from density currents and granular flows, the most common of which being pyroclastic density currents (PDCs). Rounded pyroclast shapes are commonly used as a primary feature to distinguish flow from fallout units. Furthermore, specific properties (e.g., the size and shape) of pyroclasts within fallout and flow units and details about the transition between units are useful for both modelling tephra dispersion and modelling PDC run out, and thus are important for hazard management. Here, we investigate pyroclastic deposits from Oregon, USA - the Bend Pumice and the Tumalo Tuff, a pumice-fallout and a pyroclastic flow unit, respectively. We analyse the deposits in terms of the particle size distribution and the shape of particles within each size fraction. These data are used to determine the shape parameters and grain sizes, that can be used to differentiate between the fallout and flow units. In doing this, we investigate several shape parameters to analyse the lower size limits on particle rounding and discuss the responsible energetics. Together these data inform on both deposit classification and secondary fragmentation processes within granular flows.