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Mass and Energy Exchange in Pyroclastic Density Currents: Development and Application of Physics-based Parameterizations

Josef Dufek1 , Eric Breard2

  • Affiliations: 1Center for Volcanology, Department of Earth Sciences, University of Oregon 2School of Geosciences, University of Edinburgh

  • Presentation type: Poster

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

  • Poster Board Number: 194

  • Programme No: 3.9.23

  • Theme 3 > Session 9

Abstract

Pyroclastic density currents encompass many fluid dynamic extremes from concentrated currents to dilute, turbulent flows. These currents are manifestly dynamic; spatial and temporal variability are an inevitable consequence gravity and momentum exchange. These exchange processes are crucial in determining runout, inundation area, deposit formation and ultimately the hazards of these currents. This presentation focuses on these momentum, mass and energy exchange rates using high resolution multiphase numerical simulations (MFIX) and comparison to large-scale experiments and observed PDC and deposits. We first validate the multiphase modeling through comparison to the PELE experiments and provide thermal energy, entrainment and mixing relationships. These parameterizations are compared to a compendium of experimental data for gravity currents. These parameterizations are appropriate for augmenting multilayer depth-averaged approaches and provide physics-based guidance for the demarcation between layers and the appropriate exchange terms. The mixing relationships presented are also useful for comparison to a range of thermal proxies. We next scale the multiphase simulation up to natural scale flows, specifically looking at the role of channelization and change in slope. Avulsion conditions are compared to flows from Tungurahua and Merapi. Finally, we consider the case of pyroclastic density currents encountering a water interface and compare the mixing zone dynamics of different scales of flows from small scale flows from Montserrat to larger scale dynamics relevant for Hunga Tonga. Particularly for the Hunga case we examine potential plunge conditions and the initial propagation of submarine currents in channels to examine propagation velocities and concentration gradients.