西南北海道における新第三紀火山岩相の特徴と噴火活動略史  [in Japanese] Lithofacies of Neogene volcanic rocks and the eruptive history in Southwest Hokkaido  [in Japanese]

Most of the Neogene volcanic rocks in Southwest Hokkaido are products by submarine effusions and explosions. By detail observation for their occurrences and lithofacies, they are classified into hyaloclastites associated with subaqueous lavas and feeder dykes, subaqueous pyroclastic rocks and epiclastic volcanic rocks. The regional and horizontal changes in the types of these volcanic rocks are summarized as follows. The Fukuyama Stage was characterized by subaerial eruptiont; producing welded tuffs and massive lavas. The Kunnui Stage was represented by submarine eruptions, the southern part of the Oshima Peninsula was mostly occupied by subaqueous pyroclastic flows. The middle part of the peninsula was occupied by basaltic to andesitic hyaloclastites, associated with scoriaceous agglomerates by Strombolian eruptions. The northern part was primarily characterized by subaqueous pumice flow deposits accompanied with rhyolitic and basaltic lavas. Later, the part was occupied by andesitic hyaloclastites. The Yakumo-Kuromatsunai Stage was primarily represented by deposition of pyroxene andesitic hyaloclastites, however, ended with emplacement of homblende andesitic and dacitic hyaloclastites. The Setana Stage and Quaternary are defined by transition from submarine to subaerial eruptions, the latter of which have formed andesitic massive lavas.