鬼界カルデラにおけるアカホヤ噴火以降の火山活動史

元データ 2002-03-31 東北大学

概要

Kikai Caldera, 17km wide and 20km long, is a Quaternary volcano located in the East China Sea 40km southwest of Cape Sata, southern Kyusyu. The caldera is nearly submerged in the sea. Two volcanoes, Iwo-dake (rhyolitic volcano) and Inamura-dake (basaltic volcano), on Satsuma-Iwojima Island at the marginal part of this caldera grew up after the large caldera-forming eruption of 6300 y.B.P. known as the Akahoya Eruption. The purpose of this study is to understand the geological feature of Iwo-dake and Inamura-dake, and to understand the relationship between volcanic activity and magma evolution based on geology and bulk rock chemistry. The volcanic activity after the Akahoya Eruption of 6300 y.B.P. was divided into three stages; the Former Iwo-dake stage, the Inamura-dake stage, and the Latter Iwo-dake stage. The Former Iwo-dake stage (Io-I, II) is the stage of main cone building with the flow out of rhyolitic lavas and continuous ejection of volcanic ash and lithic fragments. It was suggested that this stage owed to the same magma as that of the Akahoya Eruption. The Inamura-dake stage was characterized by the eruption of basaltic lava and scoria, and divided into three sub-stages (In-I, II, III). In-III sub-stage was characterized by pyroclastic surges due to phreato-magmatic eruption. During this stage, the chemical composition changed from basaltic to andesitic (Isomatsuzaki lava). In the Latter Iwo-dake stage (Io-III, IV, V, VI), explosive eruption occurred at the first, and followed by the effusion of rhyolitic lava flow from the summit crater. In the later of this stage, it became an intermittent activity with pumice and bomb fall out. It seems that the Latter Iwo-dake stage is different from the Former Iwo-dake stage in respect to the eruptive style and chemical composition of magma. The change from the Former Iwo-dake stage to the Latter stage suggests that the rhyolitic volcanic activity after the Akahoya Eruption changed dramatically into the new stage bordered by the Inamura-dake stage.論文Article

著者

宮本 毅 東北大
谷口 宏充 東北大
前野 深 東京大
前野 深 東北大学大学院理学研究科地学専攻
谷口 宏充 東北大学東北アジア研究センター
宮本 毅 東北大学東北アジア研究センター
宮本 毅 東北大東北アジア研

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