Correlation between the eruption of the yatsugatake younger tephra beds and volcanic products on the summit area of yatsugatake volcano, central japan

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The Yatsugatake Younger Tephra Beds (YYT) at the eastern foot of the Yatsugatake Volcanic Chain (YVC) are as follows: Yt-Kw, Yt-Pm1, Yt-Pm2, Yt-Pm3, and Yt-Pm4 tephra beds, in ascending order. All tephras are composed of pumiceous beds with fine gray ash layers, except for Yt-Pm4 which lacks fine ash. The source crater of Yt-Pm4 is located at the summit of Yokodake Volcano, based on its distribution pattern. Therefore, the Yokodake Volcano erupted at least five times in the last 29,000 years, and eruption rate is calculated to be 0.02 km^3 / ky. On the other hand, the eruption of Yt-Kw (171 ka) can be correlated with Ykl (159±7 ka, 185±7 ka), that of Yt-Pml (86-66 ka) with Tml (55±3 ka), and that of Yt-Pm2 and Yt-Pm3 (66 ka, 56 ka, respectively) with Tml (55±3 ka) or Tpl (42±20 ka), respectively, based on the age data and petrographical characteristics of lavas, welded tuff, and tephras. Consequently, Yt-Kw, Yt-Pml, Yt-Pm2, and Yt-Pm3 tephra beds were derived from Middle Yatsugatake that has two stratovolcanoes; Ioudake Volcano and Tengudake Volcano.