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

一层灰色的火山粘土被发现就在朝开东侧的托瓦达火山灰（公元915年）下面。这与公元871年日本三代实宿火山喷发的记录相吻合。据《日本山代实宿》描述，两条大蛇被认为是火山喷发期间沿火山侧翼下降的两条活跃熔岩流。明显的地质特征，如地面裂缝或由碎片雪崩和火山泥流形成的沉积物，镶嵌在赤城南麓90世纪的地平线上。它们与公元818年瑞州国岛所描述的地震有关，然而，致病断层尚未被发现。估计复发周期为万年一次。公元1707年会惠喷发是富士火山历史上唯一一次在东海-关东南部地区有大量目击记录的喷发。这些记录被仔细阅读，以澄清在16天的喷发期间发生了什么。重新发现，伊藤岛野神的日记中详细地描述了火山喷发，并绘制了地图。济州岛（汉拿山）于2002年和1907年两次喷发。关于这些喷发的基本文献是《高丽史》，它在15世纪中期编辑时添加了信息。本文以这些史料为背景，研究了东亚的自然哲学和思想，并指出了它们与火山喷发时高丽政府的历史评价的关系。从15世纪下半叶到20世纪上半叶关于这些火山喷发的报告中可以看出，在济州岛内确定火山喷发具体地点的依据很薄弱。

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.