Studies on history of volcanic eruption in Japan by correlation between old documents and eruptive deposits.

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A layer of gray volcanic clay was found immediately below the Towada-a ash (AD 915) on the eastern flank of Chokai. It is correlated with the AD 871 eruption recorded in Nippon Sandai Jitsuroku. Two big snakes described in Nippon Sandai Jitsuroku were believed to be two active lava flows descending the flanks during the eruption.Conspicuous geologic features such as ground cracks or deposits from debris avalanches and lahars are embedded in the 9^<th> century horizon on the southern foot of Akagi. They are correlated with the AD 818 earthquake described in Ruiju Kokushi, however, the causative fault is yet to be discovered. The recurrence interval is estimated once in tens of thousand years.Hoei AD 1707 is the only eruption among historical eruptions of Fuji in which abundant eyewitness records exist in the Tokai - Southern Kanto area. Those records were critically read to clarify what happened during the eruption over 16 days. It is rediscovered that the eruption is described in detail by Ito-Shima-no-kami's Diary including pictorial maps.Two eruptions took place on the Korean island of Jeju (Mt. Halla) in 1002 and 1007. Fundamental document of these eruptions is History of Koryo, which has had information added when it was edited in the mid-fifteenth century. As background to these historical materials, the natural philosophy and ideology of East Asia are researched, and their relation with historical evaluations of the government of Koryo at the time of eruption is pointed out. From an examination of reports on these eruptions made from the latter half of the fifteenth to the first part of the twentieth centuries, it is noted that the basis for specifying the particular location of eruption within Jeju is weak.