Fig. 3

Formation process of ash layer from a dilute PDC. Magnifications of the same photographs in Fig. 2. a A PDC lobe extending to the north and covering the peak that is seen on the right-hand side of the photographs in Fig. 2. The width of the photograph is ~50 m. The whitish ash layer was formed from the PDC ash cloud between 11:54:30 and 11:54:48, and the co-PDC liftoff cloud is sustained behind the peak (11:55:52). b Another PDC lobe emerged from a depression between the two peaks. The photograph width is ~30 m. White arrows in b indicate a preexisting boulder (~1 m in diameter) covered by a thin ash layer. The ash layer was deposited from the PDC body between 11:55:52 and 11:56:14