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Modelling the transport and dispersion of a co-PDC ash cloud: an evaluation of source geometry and mass eruption rate

Marie Hagenbourger 1, Thomas Jones1, Frances Beckett2, Samantha Engwell3

  • Affiliations: 1Lancaster Environment Centre, Lancaster University, Lancaster, United Kingdom; 2Met Office, Exeter, United Kingdom; 3British Geological Survey, The Lyell Centre, Edinburgh, United Kingdom

  • Presentation type: Talk

  • Presentation time: Thursday 08:30 - 08:45, Room R280

  • Programme No: 6.4.1

  • Theme 6 > Session 4

Abstract

Pyroclastic density currents (PDCs) are gravity currents that frequently form during explosive volcanic eruptions. These ground-hugging density currents consist of high-temperature mixtures of pyroclasts (e.g., ash), lithics, and gas. These flows have the potential to generate co-PDC plumes, which detach from the underlying PDC as they buoyantly rise into the atmosphere. Co-PDC plumes, comprised of fine-grained ash particles and hot gas, can reach heights of tens of kilometres, potentially dispersing large volumes of ash over continental scale areas, impacting the environment, and posing a risk to aviation. Owing to their formation mechanism co-PDCs have unique characteristics, such as a restricted, fine (e.g., < 90 μm) particle size distribution and a high-aspect ratio, irregular shaped source geometry. Despite the frequency of their occurrence, the atmospheric dispersion model, NAME, used by the London Volcanic Ash Advisory Centre, has never been applied to co-PDC plumes. This study performed a sensitivity analysis to determine which co-PDC source parameters are important for modelling these plumes. Variations in the source geometry, i.e. total area and aspect ratio, show only a minor impact on the modelled plume location and concentration. Whereas plume heights, and hence associated mass eruption rates, show a significant impact on the area, location, and concentration of the modelled plume.