[M-IS23] Fusion of volcanology and meteorology

[MIS23-P04] Tephra segregation profiles from Vulcanian eruptions on Sakurajima volcano, Japan, based on the tephra deposit load observations

*Kosei Takishita^1,2, Masato Iguchi², Alexandros P. Poulidis³ (1.Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University, 2.Sakurajima Volcano Research Center, Disaster Prevention Research Institute, Kyoto University, 3.Institute of Environmental Physics, University of Bremen)

Keywords:Vulcanian eruption, Disdrometer, tephra, tephra segregation profile

The profile of tephra concentration along a volcanic plume, i.e. the Tephra Segregation Profile (TSP), is one of the important source parameters in the estimation of the tephra deposit load. Assuming that the mass eruption rate; MER, is the constant during an eruption, the buoyant plume theory (e.g. Morton et al., 1956), can be applied in the volcanic column formation and generally produces profiles in which most of the tephra segregate at the top of the plume. However, case studies based on observations have revealed that large amount of particles can also segregate at the lower part (e.g. Mannen, 2014; Cao et al., 2021). To investigate this discrepancy, here we consider the dependency of plume height to the temporal variations in the MER. To this end, we use an advection-diffusion model (Tephra4D; Takishita et al., 2021) with MER estimates obtained from the measurement of ground deformation and seismogram (Iguchi, 2016) and maximum plume height observations to calculate the spatial distribution of the tephra deposit load of 39 Vulcanian eruptions and long-lasting particle emissions with lower plume height from Sakurajima Volcano, Japan.
The evaluation of the consistency between calculations and observations obtained by a disdrometer network (Takishita et al., 2022) revealed that, for both kinds of activity, maxima in tephra segregation can occur at heights below the reported plume height. TSPs of Vulcanian eruptions at Sakurajima volcano were seen to be consistent with the profiles in which most of the tephra segregate at the top of the plume, but only if we allow for the temporal variation of MER in order to properly represent the total series of eruptive events that make up the sequence. This highlights the fact that even though Vulcanian eruptions are generally characterized as instantaneous particle emissions, not only the primary plume developed due to the initial explosion, but also the subsequent continuous plume that can accompany the eruption plays an important role in particle emissions.