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Abstract:
Explosive volcanic eruptions are one of the major natural hazards in East Asia. The study of eruptive history and volcanic ash dispersal are the key to understand eruption frequency and to identify the level of risk from different volcanoes. Here we use cryptotephra extraction techniques to examine a marine core from the southwestern Sea of Japan. The results reveal that six tephra layers are preserved in the Holocene core section, four of which are cryptotephra layers. Glass compositions of tephra shards indicate that these ashes are the B-Tm from Changbaishan volcano (China/N Korea), the K-Ah from Kikai caldera (Japan) and four tephras (U-1 to U-4) from the Ulleungdo volcano (S Korea). Except for the U-1 tephra whose age is previously unknown, terrestrially-based ages of the other tephras are used to constrain the marine reservoir effect and the age-depth model of the record. Through 14C dating of marine sediment and reservoir correction, we report for the first time, a precise eruptive age for the Ulleungdo U-1 eruption (3354-3080 cal yr BP, 95.4%). The Holocene eruptive history of the volcano is now fully revealed, with four eruptions occurred at ca. 10.2, 8.4, 5.6 and 3.2 cal ka BP. Using the identified ash layers, we can now synchronize the marine record with sedimentary archives from in and around the Sea of Japan, to as far as the Arctic and the tropical regions. Our cryptotephra study shows the potential of this approach for future studies in the region.
