Characterization of pyroclastic fall deposits from virtual volcanoes using a new tephra simulation code (TWiCE)

Toshitaka Sakai ¹, Yuta Mitsui¹, Kazutaka Mannen²

• Affiliations: ¹Faculty of Science, Shizuoka University, Japan; ²Hot Springs Research Institute of Kanagawa Prefecture, Japan

• Presentation type: Poster

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

• Poster Board Number: 84

• Programme No: 3.12.10

• Theme 3 > Session 12

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Abstract

We employed a new tephra simulation code based on an advection-diffusion model named TWiCE to simulate pyroclastic eruptions under simplified topographic and wind conditions, aiming to quantitatively understand the mode of tephra dispersal. Specifically, we focused on the simulation results plotted against the classical D--F diagram by Walker (1973) to evaluate both the validity of the simulation and the D--F diagram itself. In Walker's scheme, the maximum mass loading at the source vent is defined as Smax. The parameters D and F are defined as the area enclosed by an isopach of 0.1Smax (in km²) and the percentage of the <1 mm fraction along the dispersal axis of 0.01Smax, respectively. Our numerical experiments demonstrated that, within realistic ranges of eruption intensity and initial grain size distribution, the simulation successfully reproduced D and F values consistent with the empirical relationships depicted in Walker's diagram. However, the results revealed that determining Smax, which is challenging to observe in actual eruptions, significantly influences the outcomes. Additionally, we identified a notable dependency on a parameter called "plume thickness", which governs particle segregation as a function of plume length.