Fig. 6

a Deposit of the PDC in Zone d ~ 2 km from the crater (Loc. 1). Photograph was taken in November 2016, ~ 1.5 years after the eruption. The deposit is subdivided into L and U parts. L1, L2, and U indicate the level of sampling for grain-size analysis. b Deposit of the PDC in Zone e, ~ 1 km from the crater (Loc. 2). Photograph taken in March 2017. The deposit is divided into the normal-grading volcanic sand layer in the lower portion (L) covered by the fine grained volcanic ash (U). c Block-and-ash flow deposit at Loc. 4, ~ 1 km from the crater. Photograph taken in March 2017. The deposit exhibits yellowish color in March 2017, 1.5 years after the eruption due to the surface weathering of the materials. d Cross section of the block-and-ash flow deposit of the PDC in Zone c (Loc. 4). Photograph taken in March 2017. The deposit overlies the 2014 tephra which contains plenty of plant fragments. e Ash-fall deposit in Zone f (Loc. 3). The level for sampling for grain-size analysis is indicated by bar with “F”