Estimation of the origin and the age of tephra found in tsunami deposits at the mouth of Ota River

Takuto Muraki; Kohei Fujiwara; Syogo Yamada; Syunta Miyahira

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Poster

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[O-02] Poster presentations by senior high school students

Sun. May 22, 2016 1:45 PM - 3:15 PM Poster Hall (International Exhibition Hall HALL6)

Convener:*Tatsuhiko Hara(International Institute of Seismology and Earthquake Engineering, Building Research Institute), Miwa Kuri(International Research Institute of Disaster Science, Tohoku University), Keiko Konya(Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology), Hajime Naruse(Department of Geology and Mineralogy, Graduate School of Science, Kyoto University), Kou Yamada(Waseda University)

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1:45 PM - 3:15 PM

[O02-P49] Estimation of the origin and the age of tephra found in tsunami deposits at the mouth of Ota River

*Takuto Muraki¹, Kohei Fujiwara¹, Syogo Yamada¹, Syunta Miyahira¹ (1.Iwata Minami High School)

Keywords:tsunami deposits, widely distributed tephra, Kozu island Mt.Tenjo

When we did simple boring research with hand auger at Shoshuji Temple in Fukuroi city, which is located 3.5 kilometers upstream from the mouth of Ota River, we discovered the deposits which were porous and yellowish white like tephra, with tsunami deposits. If this deposits were really tephra, we could specify the origin and the age of the eruption, moreover, estimate the age of the tsunami. Therefore we decided to research it deposits.
We compared the form of volcanic glasses included in the tephra from Shoshuji Temple, with widely distributed tephra. We also estimated the age of the deposition by ¹⁴ C included in the dead plants.
As a result, we revealed that the tephra found at Shoshuji Temple is the deposits from the eruption of Mt.Tenjo in Kozu Island in 838. It was scattered by floods and tsunami, and then they reaccumulated.