Constraints on the timing of East Asian explosive volcanism: insights from cryptotephra deposits preserved in marine and lacustrine archives

Volcanic hazard assessments are in part constrained by understanding the past behaviour of a volcano (e.g., eruptive frequency and magnitude), this is largely reconstructed using tephra deposits preserved proximal to source. However, these near-vent eruption records are often fragmentary and incomplete owing to burial and erosion processes, thus hampering the accuracy of hazard assessments. Here, we capitalise on the potential of long, undisturbed records of ash fall events preserved in East Asian marine and lacustrine sedimentary archives, typically positioned >100 km from volcanic sources, to plug the gaps in near-source eruption records. The extraction and identification of microscopic ash layers (cryptotephra) from sedimentary archives is adopted to provide important constraints on the timing of mid-intensity explosive eruptions, which are frequently under-reported at source.

Following detailed cryptotephra investigations, we present a new eruption record captured by high-resolution sediment cores collected from the Sea of Japan spanning approximately the last 200,000 years. Detailed geochemical fingerprinting is used to assign tephra and cryptotephra deposits to volcanic source, and where possible to known eruption units, some of which are the target of zircon double-dating (ZDD). Furthermore, the chemical signatures are used to link the Sea of Japan tephra layers to those preserved in the precisely dated sediments of Lake Suigetsu (Honshu Island), providing important chronological constraints on our newly developed eruption record. Our investigations provide evidence of near-vent under-reporting of explosive eruptions and new insights into the repose periods between pre-historic eruptions at specific volcanoes.