Fig. 1

Map of Hakone volcano. a Distribution of stations in and around the caldera of the Hakone volcano. The study region is indicated by the red rectangle in the inset map. The bold line shows the caldera rim of the Hakone volcano. Gray lines indicate the detailed topography of the Hakone volcano. The red broken rectangle represents the location of the open crack as determined by Honda et al. (2017). b Magnified maps of the Owakudani geothermal region. The red circles depict the locations of the vents that formed during the phreatic eruption (Mannen et al. 2015). The numbers in the inset map indicate the index numbers of the vents defined in Mannen et al. (2015)