飯繩火山について : その南西部からみた(火山シリーズ3)

概要

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The Iizuna volcano situates near Nagano city in central Japan on the terrain of Tertiary, which seems to compose a gentle synclinal structure. A ruinned volcano, consisting of pyroxene andesites and hornblende andesites, also exists at the skirt of the Iizuna volcano. From the survey of the southwestern part of the volcano, the history of the Iizuna volcano may be summarized as the follows. The activities of the somma were divided into two phases ; the earlier one was an outflow of lavas of rather acidic glassy pyroxene andesites, being followed by repeated eruptions of tuff breccia, and the later one, after a eruption of tuff breccia, flew out rather basic olivine-pyroxene andesites. An ultravolcanic explosion shattered at least the northwestern side of the somma and formed an vshaped caldera. The activities of central cones in the caldera, began with the construction of a small stratovolcano consisting of tuff breccia, glassy pyroxene andesite and olivine-pyroxene andesite. A parasitic dome of pyroxene andesite seems to have been erupted at the same time in the northwestern side of the somma. The final activities were the construction of many domes of hornblende andesite in the caldera.
地学団体研究会の論文
1960-05-03