Fig. 1

a Locations of the mountains and their mountain strata (red triangle, granite; white triangle, limestone; grey triangle, pyrostatic rocks; brown triangle, sandstone/conglomerate/rhyolite tuff breccia; blue triangle, serpentinite). b Picture of the collapse of Mayu-yama with flames (in a collection of ERI, University of Tokyo). c Picture of the landslide at Mt. Iwakura sketched by S. Aoki (in a collection of Sanada Treasure Museum). d Sketch of geological structure of Mt. Ibuki by Koto (1910), with Japanese terms translated into English. e Configuration and f equipment view of Charpy impact tester and g test rocks fixed to both holders at the bottom and the pendulum (upper)