Fig. 1

Map of Kusatsu-Shirane Volcano and the occurrence of eruption products produced by the 2018 eruption. a Locations of the craters formed by the 2018 eruption, the ski resort, and survey points in c, d. The blue dashed line indicates the limit of volcanic blocks (modified from Fig. 2 of Yoshimoto and The joint research team for ballistic ejecta from the Kusatsu-Shirane 2018 eruption 2020). TNN and WJM indicate the locations of the radiosonde observation points. b Aerial photograph of the crater produced by the 2018 eruption, viewed from the south. Dashed lines indicate the rim of pre-exiting craters. c Occurrence of the fall deposit at location c (4.6 km ENE from the MC). The number in the figure indicates the MPUA (mass per unit area), as shown in d. d Occurrence of the fall deposit at location d (0.2 km NE from the MC). e Occurrence of the fall deposit on the rim of the MC. Arrowheads indicate pre-eruption surfaces. MC main crater, WC west crater, SC south crater, Fd Futagoyama Lava Dome (Uto et al. 1983), APC ainomine pyroclastic cone, SPCG Shirane Pyroclastic Cone Group