十和田火山二の倉スコリア群の層序区分の再検討 : 二の倉スコリア期の噴火活動の推移

抄録

The activity of Towada Volcano started about 200,000 years ago and more than 20 eruptive episodes are geologically recognized. Ninokura scoria group is collective name of the series of pyroclastic fall deposits which erupted just after the latest caldera-forming Hachinohe pyroclastic flow (13,000 y. b. p.). On the basis of field investigation, systematic sampling and analysis of Ninokura pyroclastic fall deposits, we divided Ninokura scoria group into 11 tephra layers in descending order ; NK-a～NK-k. Each eruption mass of the layer is about 1.2〜35.9×10¹⁰ kg. Total mass of Ninokura scoria is about 1.74×10¹² kg. Ninokura scoria group eruption starts without long dormant time after Hachinohe pyroclastic flow eruption. The mean interval of Ninokura scoria group eruptions is about a few hundred years.