北関東,高原火山の約6500cal yr BP の噴火

概要

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Fujisan lava dome (Fj-D) is situated at the center of Yumoto-Shiobara flssures on the northern foot of Takahara volcano, central Japan. Based on the volcanic landform and stratigraphy of this area, the sequence of the eruption forming this lava dome is estimated to be started from phreatic eruption and ceased with effusion of lava. The tephra from vents along the fissures, named Takahara-Uenohara tephra (Tk-Ue), consists of accessory ash and lithic fragments, The bulk volume of the tephra is about 9.9×10^7 m^3. Four radiocarbon (^<14>C) dates of humic soil just below the tephra converge at 5700 yr BP. The average of these dates, 5700±100 yr BP, can be dendrochronologically calibrated to a calendar year ranging from 6636 to 6404 cal yr BP (probability: 100%). Fj-D is a dacitic lava dome surrounded by talus slopes. On the other hand, Fujisan cryptodome (Fj-C) is a flat hill on the western side of Fj-D. Total amount of extruded magma by this eruption is estimated to be ca. 0.2 km^3.
特定非営利活動法人日本火山学会の論文
1997-12-26