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.

附录 S1：出露岩层的素描
附录 S2：U-2 和 To-Cu 熔岩碎屑的特写照片，以及 To-Cu 火山灰沉积物
附录 S3：火山玻璃碎片的常量元素组成
平均（wt%）：平均值。标准差：标准偏差。*: 总氧化铁以 FeO 计。**：未重新计算至 100% 水分基准前的原始数据。由 JSM-6930 和 EDAX GENESIS APEX2 能量色散X射线光谱仪测定，电流为 0.6 nA，电压为 15 kV，束径为 10 μm，记录时间为 200 秒。
附录 S4：SKN-2、SKN-3、To-Cu 和 U-2 的照片
(a) 在乌岭岛采集的 U-2 熔岩碎屑（Sagamihara 市博物馆 Machida Hiroshi 收藏，编号 MW0048），(b) SKN-2 的熔岩碎屑，(c) 在田代火山附近采集的 To-Cu 熔岩碎屑（青森县田代町采集，距源区东南方向 10 公里），(d) SKN-3 的熔岩碎屑。图 (b) 和 (d) 中方格的大小为 1 厘米。