阿蘇火山における泥流堆積物の膠結物の生成

概要

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阿蘇山の箱石川流域において,2700年前に0jSの降下後に,2回以上の泥流が発生したと推察された.この泥流堆積物と発生前の渓床堆積物に,特異的に含鉄膠結物が見られ,｢鉄盤｣,｢パイプの形成とスライムの付着｣,｢高師小僧とノジュール｣の順になる生成系が認められた.泥流堆積物に含まれるスコリア粒が風化して鉄イオンが生成し,これに埋没した渓床堆積物と泥流堆積物の間での地下水の移動が関与して,含鉄膠結物が生成すると推察された.このような含鉄膠結物による土層の硬化は,斜面の安定性に影響があると考えられた.It is presumed that the mudflow occurred two times or more in Hakoishi River basin in Mt. Aso. These events happened after the scoria fall-out from Ojo-dake volcano, about 2.7 ka. B. P.. Iron concretions frequently developed in the mudflow deposits and the river bed sediment. In order of iron concretion formation, Takashikozo and nodule, slime grown in the pipe, iron pans were observed in that materials. The iron concretion was formed by the iron-ion produced from weathered scoria in the mudflow deposits, which was molded by the flow of ground water between the mudflow deposit and the river bed sediment. It is possible that this phenomenon influenced upon the slope stability.