A detailed record of large explosive eruptions from Japan between ∼120 and 50 ka preserved at Lake Suigetsu

Abstract

We present the findings of a detailed non-visible (cryptotephra) tephra investigation of the Lake Suigetsu (Japan) sedimentary sequence spanning ∼120 to 50 ka. Thirty-nine new cryptotephra and two visible tephra horizons are identified during this interval interspersed between visible tephra layers associated with large-magnitude eruptions and regional event markers (e.g., Aso-4, K-Tz, Ata). The newly identified volcanic deposits are geochemically analysed using major (EMP) and trace (LA-ICP-MS) element glass analyses, and the chemical fingerprints are used to trace these deposits to subduction related volcanoes located along the three main Japanese islands (Kyushu, Honshu and Hokkaido), as well as nearby intraplate volcanoes. Our findings provide geochemical, chronological and ash-fall constraints on the activity at multiple volcanic centres; in particular, the Kirishima volcanic complex in the southern volcanic region of Kyushu. Furthermore, the Lake Suigetsu cryptotephra record reveals distal ash-fall from two notable large magnitude (≥M6.0) eruptions, the Plinian Sambe Kisuki (SK) eruption and the caldera-forming Toya eruption, both of which are important widespread tephrostratigraphic markers suitable for linking regional terrestrial and marine sequences. Using the Lake Suigetsu age-depth model, they are dated to 100.4 ± 3.1 ka (±1σ) and 108.1 ± 3.9 ka (±1σ), respectively. Finally, our investigation reveals numerous eruption deposits which have not yet been identified in near-vent sequences, indicating eruption under-recording. This research re-affirms Lake Suigetsu as the single most comprehensive ash-fall record of East Asian explosive volcanism over the past 150 kyr, and contributes significantly to our understanding of the timing and ash dispersals of pre-historic eruptions.