Two major explosive eruptions occurred in Narugo volcano around 40 and 80 ka. Eeruption features of the explosive magmatism must be elucidated by revealing these major pyroclastic flow events in detail. I subdivided Nizaka Tuff into 5 flow units.Early ejection lacks clinopyroxene phenocryst,and rich in SiO2.Later eruptives contain clinopyroxene phenocryst,and come silica-poor and TiO2, Al2O3, FeO*, MnO, CaO-rich compositions. Yanagisawa tuff has newly been divided into 4 units.Pyroclastic surge deposit was also recognized in Unit3.Unit1 shows SiO2 rich, mafic mineral poor characteristics.Unit2 and 3 show the largest variation among the 4 units.Unit4 is somewhat similar to the Unit1,although K2O contents are distinctive. Because of Yanagisawa tuff involves pyroclastic surge deposit along with hornblende phenocryst in the Unit3,H2O contents of the Yanagisawa tuff had possibly been higher than that of the Nizaka tuff.
