Fig. 2

a Aerial photograph of Kusatsu–Shirane volcano (taken on 5 November 2015). PC = pyroclastic cone; MPCG = Motoshirane Pyroclastic Cone Group; SPCG = Shirane Pyroclastic Cone Group; YCL = Yugama Crater Lake. b Eruption cloud and ballistic block falls hitting the ski slope, (photograph taken by the Kusatsu Tourism Cooperation at 10:02 JST on 23 January 2018). c Weak volcanic cloud rising from the Kagamiike-kita PC at about 10:20 JST on 23 January 2018. d Aerial photograph of the new main crater (MC) at the Kagamiike-kita PC and the south crater (SC) at the Kagamiike PC formed during the 2018 eruption (photograph taken on 25 June 2018). The west crater (WC) is outside the photograph