[S-VC43] Volcanic and igneous activities, and these long-term forecasting

[SVC43-16] Did Bandai Volcano, NE Japan, erupt in 806AD (Daido Gan-nen)?

*Takahiro Yamamoto¹ (1.Geological Survey of Japan, AIST)

Keywords:Bandai Volcano, 806 AD, collapse, phreatic eruption

Although there is the record of 806 AD in historic activity of Bandai Volcano before the 1888 eruption, its event has been uncertain. This simply interpreted a disaster written in history books about the origin of Dainichi Temple as eruption. I have found other documents describing dammed-up and bursting of the Sukawa river due to landslide debris from Bandai and collapse of Iwahashi Shrine on the southern slope in 806 AD. In addition, radiocarbon ages indicating the beginning of Heian era were previously reported from the burying tree along the Sukawa river, and it will be certain that a large-scale sediment disaster got up at the eastern foot of the volcano. Probably this disaster was causes by small sector collapse of the NNE slope on Kushigamine, and triggered by the earthquake that broke Iwahashi Shrine. On the other hand, there are phreatic fallout units beneath the 1888 products around Numanotaira and Nakanoyu, and the top of them was considered to be a product of the eruption for 806 AD. However, new radiocarbon age from this unit was determined as 2540±20 yBP, that is consistent with previous ages from the Biwasawa Debris Avalanche in the eastern foot. Therefore, the collapse of 806 AD was not more likely to be accompanied by remarkable eruption. In addition, new radiocarbon age of 11210±40 yBP is obtained from the lower unit from the Happodai craters, and it is considered to have been formed Bokodai Lava which flowed out of these crater to the north by this eruption.