[M-IS23] Fusion of volcanology and meteorology

[MIS23-02] Spatial and grain size distributions of the May 14, 2018 Shinmoedake eruption deposit, Kirishima Volcano (Japan), inferred from field and meteorological data

*Yasuo Miyabuchi¹, Eiichi Sato² (1.Center for Water Cycle, Marine Environment and Disaster Management, Kumamoto University, 2.Meteorological Research Institute)

Keywords:tephra dispersal, grain size distribution, erupted mass, meteorological condition, Kirishima Volcano

Following the 2011 magmatic activity, intermittent eruptions were recognized in 2018 at Shinmoedake Volcano, part of Kirishima Volcanic Complex in southern Kyushu, southwestern Japan. The May 14, 2018 eruption, which was one of the major events in 2018, began with a vulcanian eruption at 14:44, and the eruption plume rose 4500 m above the crater rim. Thereafter, the eruption shifted to ash eruption, and the plume heights gradually decreased, ceasing at 16:10. The tephra-fall deposits distributed more than 27 km southeast of the source crater, and the mass of the tephra-fall deposit was calculated at about 2.1 × 10⁴ tons based on the isomass map. The difference in occurrence of deposits between east and west of the main dispersal axis was recognized. Deposits observed east of the main dispersal axis were composed mainly of coarse to medium sand sized particles and wholly well sorted, lacking fine fraction (fine sand to silt size). In contrast, deposits west of the axis were finer grained and poorer sorted than those east of the axis. Photographs of eruption plume, meteorological data, distribution and grain-size characteristic of deposits lead to the following conclusion. During the May 14, 2018 eruption, the wind directions above the Shinmoedake crater differed between altitudes according to meteorological data. Higher eruption plume contained coarser tephra associated with the 14:44 vulcanian eruption was dispersed easterly than the main axis by westerly wind. On the contrary, lower ash eruption plume rich in fine materials was scattered westerly than the main axis affected by northerly wind.