A pilot study for the mitigation of volcanic hazard caused by collapse of volcano : Maebashi mudflow deposit in time and space estimated from 14C ages of wood blocks and Sr isotope ratios of volcanic blocks

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  • 火山体崩壊に起因する火山災害軽減のためのパイロット研究 : 木片の14C年代測定と火山岩塊のSr同位体比からみた前橋泥流の時空分布

Abstract

Age of the Maebashi mudflow deposit, currently estimated to be 24,000 BP, was re-evaluated by AMS-14C dating of a wood specimen from an outcrop on the Tone River bank. The specimen yielded 22,570±60 BP (±1σ). The calibrated age was 27,180−26,589 cal BP (±2σ) and 3000 years older than the previous estimate. Origin and distribution of the Maebashi mudflow deposit were identified by 87Sr/86Sr ratios of volcanic blocks within the mudflow deposits, in comparison with 87Sr/86Sr data for surrounding volcanoes. The mudflow was generated by the collapse of Asama volcano, flowed down along the Agatsuma and Tone rivers, and deposited in the wide area around Maebashi and Takasaki. Distribution of the Stone Age remains appears to reflect the extent of the Maebashi mudflow deposit.

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