岩石残留磁気を用いたヴェスヴィオ火山472年火砕流の堆積温度の検討

概要

論文の詳細を見る
The 472AD eruption of Mt.Vesuvius in Italy started from the explosive eruption which formed air-fall scoria, and was followed by pyroclastic-flows. The pyroclastic-flows changed from scoria flows in the early stage to pyroclastic surge, and lithic-rich pyroclastic flows at the last stage. The emplacement temperature of the flow deposits were estimated applying the progressive thermal demagnetization experiments for essential fragments and lithic fragments. The experiments show that the most of specimens exhibit stable magnetizations composed commonly of one or two components. Temperatures recorded in essential fragments of pyroclastic flows could be separated into several groups; more than 590℃, around 300℃ and normal ambient temperature. Some lithic fragments show 200℃ indicating heating after entrapment within a flow. The estimated emlacement temperature of lithic-rich pyroclastic flow varies in different flow unit. It was presumed that the relatively cool lithic-rich pyroclastic flows were formed by the collapse of the eruption columns of explosive phreatomagmatic eruptions which eroded the volcanic conduit entraining a large amount of lithic fragments. Water-magma interaction during the eruption may have caused cooling of some essential fragments.
2008-01-18