Ojika-Jima monogenetic volcano group (OMVG), northwestern Kyushu islands, contains over 41 monogenetic volcanoes of Quaternary age. These volcanoes could be divided into three types in terms of evolution: 1) Single volcanoes subdivided into scoria cone and hybrid cone (maar or tuff-ring+scoria cone+lava flow), 2) Multiple cone which consists of several contemporary cones on branched off vent system, 3) Composite cone, complex of several cinder cones of the different age. These traces of eruption record a four-stage eruptive cycle that was largely or wholly repeated at many cinder cones in OMVG. Stage I were the first phenomenon at many cones whose initial erupted products were exposed as deposits of base surge and pyroclastic fall. Stage I only occurred during the opening stages of eruption at any vent. Stage II began with a lava fountain which produced densely welded layers due to sufficiently high magma ascent rate after bubble growth was sufficiently high. After magma incubation period, the eruption style changed to Strombolian explosions (stage III). Fall back of tephra into the crater and inner-wall collapse, partially blocking the vent, caused vent-cleaning eruption. Finally lava flow emitted from cinder cone (stage IV).

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The Ito pyroclastic flow was erupted from the Aira Caldera 25,000 years ago and emplaced in a wide area of the Southern Kyushu district. This one of the large-scale pyroclastic flow deposits in the late Quaternary Japanese Islands, is mostly massive with no distinct internal flow boundaries. A component analysis of the coarse ash fraction (2-0.25 mm in diameter), however, shows that lithic fragments and crystals decrease and glass fragments increase outward from the caldera center to distal areas and downward from the upper part to lower part of the single flow unit. Density differences of particles may cause the lateral variation but cannot account for the vertical variation. Provided a single steady eruption, the lateral and vertical variations probably reflects the temporal changes the proportion of the ejected components and particle-by-particle emplacement from the sustained turbulent pyroclastic flow.

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Kurikoma volcano is located at the volcanic front of northeastern Japan arc. The volcano can be divided into 6 volcanic edifices on the bases of the inferred eruption centers, relative preservation of primary micro-topographic features on the eruptive materials, and stratigraphic relations. Lava flow has been dominant through the development history of each edifice, while pyroclastic deposits are conspicuous near the craters of several ones. Newly analyzed 7 K-Ar ages for the representative samples range from ca. 0.53 to around 0.11 Ma, practically reconcilable with the stratigraphy. Based on these data, an internally consistent scenario on the development history is summarized as follows: 1) Magmatic eruption started at about 0.5 Ma to make up the southern volcanic row. South and east to northeast flank of the Higashi-Kurikoma volcanic edifice was probably formed nearly the same time. Following these eruptions from the southern vents, central vents effused lava flows, resulting to build the Higashi-Kurikoma edifice and Kokuzou lavas (part of Kurikoma edifice) around 0.4 Ma. 2) After terminating eruption from the southern and east-north eastern vents, the Higashi-Kurikoma vent had been active until 0.1 Ma, and Kurikoma vent lasted several tens of thousands years ago. 3) Magusadake cone was built through repeated lava effusions from several vents in the western part of the volcano from 0.45 Ma to 0.1 Ma. 4) Viscous magma erupted to form Tsurugidake lava dome as the last event of magmatic eruption so far in the Sukawa horse-shoe shaped crater which was formed in northern portion of the Kurikoma (Okomayama) volcanic edifice.

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