Fig. 1. Map and simplified stratigraphic column depicting pre-AT and AT eruptions.

(A) Map showing the location of Aira Caldera in southern Kyushu Japan and the deposits from the caldera-forming “AT” eruption: Orange regions show the distribution of the Ito ignimbrite, and dashed isopach lines represent the thickness (in cm) of the Osumi fall deposit (23). The locations of other major middle-late Pleistocene calderas within the Kagoshima Graben are shown. Ka, Kakuto; Ko, Kobayashi; AtN, Ata North; AtS, Ata South. Sampling locations for the samples used in this study are shown as boxes colored according to the stratigraphic section. (B) Schematic stratigraphic section of Aira pyroclastic fall (Pfa) and flow (Pfl) units. Thickness of pre-AT units are scaled relative to DRE volume, which are 8x vertically exaggerated compared to Osumi Pfa. The thickness of Ito and Iwato ignimbrites are cut off at the top and bottom, respectively. For simplicity, we omit the Tsumaya and Tarumizu Pfl deposits, which erupted between Osumi and Ito, because they were not studied in detail in this study. Stratigraphic profiles of each unit are modified from Nagaoka et al. (24). Approximate ages are displayed to the left, where (i) this study (¹⁴C of underlying soil), (ii) Smith et al. (25) (¹⁴C of correlated lacustrine ash), and (iii) Nagaoka et al. (27) (approximate age from stratigraphy). Color scheme of units within the stratigraphic section will be used for all figures in this paper.