Sketch of the outcrop at Sekinehama, Mutsu City, Aomori Prefecture, Japan, photographs showing the occurrence and shape of drift pumice clasts, and major element composition of volcanic glass shards

Appendix S1 Sketch of the outcrop

Appendix S2 Closeup photograph of drift pumice of the U-2 and To-Cu tephras, and ash-fall deposit of the To-Cu tephra

Appendix S3 Major element composition of volcanic glass shards

ave.: mean (wt%). std.: standard deviation. *: total iron oxide as FeO. **: raw data before recalculations to 100 % on a water-free basis. Determined by JSM-6930 and EDAX GENESIS APEX2 Energy Dispersive X-Ray Spectrometer using 0.6 nA current at 15 kV, beam diameter is 10 μm, and live time is 200 seconds.

Appendix S4 Photographs of SKN-2, SKN-3, To-Cu, and U-2  (a) pumice clasts of U-2 sampled on Ulleungdo (Machida Hiroshi collection in Sagamihara City Museum, No. MW0048), (b) pumice clasts of SKN-2, (c) pumice clasts of To-Cu sampled near Towada volcano (collected at Tashirotai, Aomori Pref., 10 km southeast from the source), (d) pumice clasts of SKN-3. The size of the squares of (b) and (d) are 1 cm.