Reconstruction and dynamics of the ~ 5,200 cal BP Penoleken pumice andesitic–dacitic Plinian eruption of the Batur volcanic field, Bali, Indonesia

Abstract The ~ 5,200 cal BP Penoleken pumice (PP) fall deposit from the Batur volcanic field (BVF), Bali, Indonesia, has been proposed by previous studies as a product of a Plinian eruption. However, this claim is yet to be justified by standard stratigraphic techniques and quantitative models (e.g., isopach and isopleth maps, flux rate, and volume and plume height estimations). In this study, we identified three pumiceous layers: PP-base, PP-lower, and PP-upper. PP-base originates from a series of phreatomagmatic events, as indicated by the intense stratification between lapilli and ash, and the ubiquitous presence of accretionary lapilli. Meanwhile, both PP-lower and PP-upper correspond to dry magmatic Plinian events, with an estimated plume height and mass discharge rate of 32 km and 1 × 10 8 kg/s and 35 km and 2 × 10 8 kg/s, respectively. The total bulk volume of the PP deposit is estimated at 3.1–5.2 km 3 (PP-lower: 1.0–2.1 km 3 ; PP-upper: 2.1–3.1 km 3 ), hence scaling it as a volcano explosivity index (VEI) 5 eruption. Both PP-lower and PP-upper include similar juvenile clasts (white pumice, grey pumice, scoria, and banded pumice) and lithic clasts, although each clast’s content varies across layers. All juvenile clasts are aphyric, with a SiO 2 groundmass glass composition varying from 65.8–66.8 wt.% (white pumice) through 67.2–69.6 wt.% (grey pumice) to 61.2–62.3 wt.% (scoria). The PP-lower is dominated by white pumice, whereas the PP-upper is dominated by grey pumice and scoria. This contrasting clast composition, and thus different chemical composition between layers, suggests progressive magma withdrawal from upper (trachydacitic) to lower (trachyandesitic) levels of a zoned magma reservoir. Further, in contrast with the white pumice, the grey pumice and scoria clasts have the highest groundmass vesicle and microlite number densities, suggesting that the eruption experienced its highest decompression rate during the PP-upper phase. The present-day BVF's magmatic system fuels dominating basaltic effusive activity. However, future BVF's explosive volcanism of comparable VEI 5 Plinian scale could produce major regional disruption. Graphical Abstract