[S-VC32] Dynamics of volcanic eruptions and their physical and chemical processes

[SVC32-04] Numerical Simulations of the Ballistics Ejected during the 2018 Eruption of Kusatsu-Shirane Volcano

*Yasuhiro Ishimine¹, Akihito Sakai², Takashi Yokota² (1.Mount Fuji Research Institute, Yamanashi Prefectural Government, 2.Aichi Institute of Technology)

Keywords:Kusatsu-Shirane Volcano, Ballistics, Numerical Simulations

We will present preliminary results of numerical calculations that simulate the 2018 eruption of Kusatsu-Shirane volcano in order to discuss the fundamental processes of ballistics. We developed an original numerical model based on the assumption that the ballistics are ejected from a volcanic vent at a high speed and affected by gravitational acceleration and drag force due to air resistance. The numerical model adopts fourth order Runge-Kutta method to solve ordinary differential equations and codes in C language. We describe the drag force with the three different approximate expressions proposed by Clift et al. (1978), Nauman (1993), and Bird (2002). After some verification calculations with simple conditions, we carried out more realistic simulations on 187 ballistic samples that are obtained by the field research soon after the eruption. The simulation indicates that the ejection speed is approximately 88 m/s or larger for the ballistic that has been sampled at 740 m, the largest distance from the volcanic vent. The simulation indicates that 174 samples among 187, i.e., 93 percent ballistics, are ejected with elevation angles larger than 70 degrees from the volcanic vent if we assume that all ballistics are ejected at the same speed.