Reevaluation of the 800-802 A.D. Eruption of Fuji Volcano, Japan, and Its Influence on the Ancient Traffic Network around the Volcano, Based on Eruptive Deposits and Historical Records

Reevaluation of places, type, magnitude, and influences of the 800-802 A.D. eruption (Enryaku eruption) of Fuji Volcano, Japan, was made through tephrochronology and analyses of historical records. The Nishi Kofuji fissure on the northeastern slope is newly recognized as a crater of the 802 A.D. flank eruption. The Nishi Kofuji fissure ejected fallout scoria toward ENE and lava flows, which can be correlated with Takamarubi and Hinokimarubi 11 Lavas on the northeastern foot. The Tenjinyama-lgatonoyama fissure on the northwestern slope probably erupted during the Enryaku eruption and ejected fallout scoria and lava fiows. A series of historical documents and paintings (Miyashita documents), which are unauthorized, personal records and are regarded to be unreliable by many historians, includes many detailed descriptions of paleogeogra-phy around Fuji Volcano and of the Enryaku eruption. Although some of the descriptions were exaggerated and conflict with geological observations, some of them are concordant with geologic data. The Enryaku eruption probably gave serious damages to ancient traffic routes particularly on the northwestern-northeastern foot of Fuji Volcano. The Gotenba area, which is located on the eastern foot, was also damaged by thin ash-fall and probably by lahars. This caused a temporal, southward relocation of the offical trafiic route, which had passed through the Gotenba area.