[S-VC28] International Volcanology

[SVC28-07] Establishing the timing of Late Quaternary explosive eruptions in East Asia: New insights from Lake Suigetsu (central Japan)

★Invited Papers

*Danielle McLean¹、Paul Albert²、Takeshi Nakagawa³、Richard Staff⁴、Takehiko Suzuki⁵、Sophie Vineberg¹、Gwydion Jones²、Christina Manning⁶、Keitaro Yamada³、Ikuko Kitaba³、SG06/SG14 Project Members、Victoria Smith¹ (1.School of Archaeology, University of Oxford, UK、2.Department of Geography, College of Science, Swansea University, UK、3.Research Centre for Palaeoclimatology, Ritsumeikan University, Japan、4.Scottish Universities Environmental Research Centre, University of Glasgow, UK、5.Department of Geography, Tokyo Metropolitan University, Japan,、6.Department of Geography, Royal Holloway University of London, UK)

キーワード：Tephrochronology, Lake Suigetsu, Cryptotephra, Eruption History, Large Magnitude Eruptions, Stratigraphy

Volcanoes distributed across the East Asian/Pacific region have been the source of some of the largest known eruption events blanketing Japan and the surrounding seas in ash. Accurately reconstructing the tempo and magnitude of prehistoric eruptions at these volcanoes is an essential component of risk and hazard assessments. However, the burial, destruction, and subsequent erosion of eruption deposits in nearsource areas contribute to an incomplete geological record, hampering our ability to accurately reconstruct eruption histories. Fortunately, volcanic ash (tephra) deposits are routinely identified in distal sedimentary archives in and around Japan which provide critical insights into the tempo, behaviour and ash dispersals of highly explosive volcanism in East Asia. The sediment cores from Lake Suigetsu (central Japan) are a remarkable repository of tephra layers and the unique high precision chronology (e.g. Bronk Ramsey et al., 2012) ensures that eruptions identified in the radiocarbon timeframe are robustly dated. In addition to preserving over thirty visible layers erupted from large magnitude Quaternary eruptions (Smith et al. 2013; Albert et al. 2019), four times more non-visible ash (cryptotephra) layers have now been identified within the sediment sequence using density separation methods (McLean et al. 2018; 2020). Major and trace element glass geochemistry obtained from all these layers allows the distal tephra to be correlated to their volcanic source. These data indicate that the layers were erupted from over twenty different sources that span the length of Japan, and from Ulleungdo (South Korea) and Changbaishan (North Korea/China).

The Suigetsu tephrostratigraphy has provided an unprecedented record into the timing and frequency of explosive eruption events that were dispersed to central Japan over the last 150 ka and also provide new layers for synchronising and dating disparate archives. Cryptotephra identifications show that many eruptions dispersed ash more widely than previously anticipated, and are also able to synchronise palaeoclimate records over hemispheric scales. For example, Lake Suigetsu provides the most southerly tephra occurrence of the B-Tm tephra (~1000 km from source), synchronising this mid-latitude record to the Greenland ice cores. We also find evidence of numerous large explosive eruptions that have yet to be identified in the geological record, which can now be precisely dated using the Suigetsu sedimentary age-model. This talk outlines how sedimentary records provide an important resource for volcanological research, with constraints on the frequency, reoccurrence intervals and dispersal of these eruption events. Moreover, this work serves as a critical reminder that even in volcanic regions that are intensely studied, numerous explosive events during the Quaternary remain poorly understood and are undocumented.

References:
Albert et al. (2019). Geochemical characterisation of the widespread Japanese tephrostratigraphic markers and correlations of the Lake Suigetsu sedimentary archive (SG06 core). Quaternary Geochronology. 52: 103 – 131.
Bronk Ramsey et al. (2012). A complete terrestrial radiocarbon record for 11.2 to 52.8 kyr BP. Science. 338, 370 to 374.
McLean et al. (2018). Integrating the Holocene tephrostratigraphy for East Asia using a high-resolution cryptotephra study from Lake Suigetsu (SG14 core), central Japan. Quaternary Science Reviews. 183: 36 to 58.
McLean et al. (2020). Constraints on the timing of explosive volcanism at Aso and Aira calderas (Japan) between 50 – 30 ka: New insights from the Lake Suigetsu sedimentary record (SG14 core). Geochemistry, Geophysics, Geosystems. 21: 8.
Smith et al. (2013). Identification and correlation of visible tephras in the Lake Suigetsu SG06 sedimentary archive, Japan: chronostratigraphic markers for synchronising of east Asian/west Pacific palaeoclimatic records across the last 150 ka. Quaternary Science Reviews, 67: 12 to 137.