A reconstruction of small-scale eruptions using pyroclastic deposits

概要

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Sedimentological and stratigraphical studies of the deposits accumulated by recent eruptions on Sakurajima volcano have clarified some features of the deposit of small-scale eruptions, and led to a method for reconstruction of those eruptive activity using the pyroclastic deposits. Depositional facies, bulk density and carbon content of the deposit are reflections of the accumulation rate of pyroclastic materials. The sequence of small-scale eruptive activity manifests by the different depositional facies in the proximal area. Laminated and/or massive volcanic sand layer usually indicates a period of highly active volcanism; brownish loamy volcanic sand layer a less active one and brownish loam and/or humic soil a dormant or inactive one. The duration of these periods of volcanic activity can be estimated from recent fallout ash data. This method is fed back to the deposits of Sakurajima volcano after the 1914 eruption and also applied to those of Suwanosejima volcano after the 1813-1814 eruption. It is ascertained that this method is useful in understanding of non-recorded small-scale eruptive activities. A pre-historical eruptive activity of Old-Takachiho volcano, one of the Kirishima volcanoes, is reconstructed by means of this method.
首都大学東京の論文