Koya pyroclastic-flow deposit from the 7.3ka event of Kikai caldera is a low-aspect ratio ignimbrite (LARI). The pyroclastic flow was considered to traveled across the sea and reachs up to the adjacent islands and the mainland of south Kyushu which is about 40-80km away from the caldera. Representing the proximal facies of Koya pyroclasticflow deposit, Takeshima pyroclastic-flow deposit comprises three or more flow units with a maximum thickness of 30m. However, in contradiction with the distal deposits collectively called Koya pyroclasitc-flow deposit that consist of one exculusively very thin flow unit. Koya and Takeshima pyroclastic-flow deposits are underlain by pumice-fall deposits and overlain by ash-fall deposits (Akahoya ash). These pyroclastic units represent 7.3ka Akahoya eruption from the Kikai caldera and commonly contains highly silicic glass shards and pumice of c. 75wt% SiO₂. Koya pyroclastic-flow and Akahoya ash-fall deposits characteristically contain a lesser amount of glass shards and pumice fragments of lower silica content (c. 65wt%). Contribution of the less silicic component to the deposits increases upwards from the basal to middle level of the deposit. This vertical variation likely indicates the progressive aggradation of pyroclasts. Less silicic glass fragments are almost absent from the upper part at one proximal place and exceptionally poor at some, distal and proximal places, perhaps reflecting heterogeneous contribution of the less silicic component to the source magma and/or locally different erosional and depositional conditions within the flow.

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Eruptions of the Fuji volcano during the Younger-Fuji periods generated basaltic scoria and ash pyroclastic flow deposits. Pyroclastic flows are destructive volcanic hazard because they are high-velocity gravity driven flows and contain extremely high-temperature pyroclastic materials. On the northeast flank of the Fuji volcano, pyroclastic flows were triggered by the collapse of scoria cones and lava, which erupted in the last 1,500 years. Takizawa B1 pyroclastic flow deposit is distributed as far as 5-7km from the vent. How these pyroclastic flows resulted from basaltic eruptions and how they reached such distances from the vent are poorly understood. In our field investigations, Takizawa B1 pyroclastic flow and cone deposits were identified. In the middle-lower altitude areas, the lower part of the Takizawa B1 pyroclastic flow deposit consists of a scoria- and lithic lapilli-reduced ash units interbedded with a thin ash-rich units. The upper part consists of ash-rich flow units. Scoriaceous materials vary vertically in the Takizawa B1 pyroclastic flow deposit at the middle altitude areas. In the high-altitude area, we found four scoria cone deposits - the Yoshidaguchi cones, which contained scoriaceous materials. This vertical variation in scoriaceous materials within the Takizawa B1 pyroclastic flow deposit is consistent with the distribution of the Yoshidaguchi cones that contain scoriaceous materials and lava from 2150 to 3000m elevation. Therefore, we conclude that the collapse progressed from a low to high elevation in the vent generation area. The Takizawa B2 pyroclastic flow deposit, which has the same depositional structure as the Takizawa B1 pyroclastic flow deposit, contains a lower temperature, lithic-rich bottom layer and a high-temperature, ash-rich upper layer. The transition of the depositional textures and temperatures indicates the collapse occurred from the outer to inner parts of the scoria cones.

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Sakurajima volcano is the most active volcano in Japan. The Yokoyama core (JMA-V44) was drilled on the western foot of this volcano in 2009. This core consists of volcanic soil (0 to -1.30m in depth), volcanic fan deposits (-1.30 to -49.60m), marine sediments (-49.60 to -59.60m), non-welded normal-graded dacite pumice lapilli tuff (PFD1; -59.60 to -69.34m), marine sediments (-69.34 to -73.22m), and weakly-to-non welded dacite pumice lapilli tuff (PFD2; -73.22 to -100.60m). Geochemical features of essential pumice in PFD1 coincide with ones of the 12.8-ka Sakurajima-Satsuma tephra (P 14), that is the largest product of Sakurajima volcano in 11km³ of volume and erupted at the beginning of the Younger Kitadake stage. On the other hand, essential pumice in PFD2 differs from the products of Sakurajima volcano in major and trace element contents. PFD2 pumice has lower Ti, P and heavy REE contents than Sakurajima ones. PFD2 presumably belongs to basement formations of Sakurajima volcano and Aira caldera and topographically forms the wall of Aira caldera.

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北海道南西部の有珠山東方に分布する有珠上長和テフラ(Us-Ka)は,下部の軽石層と,上部の細粒火山灰層からなる.軽石層は安山岩質の軽石と石質岩片からなり,軽石のSiO₂量は61-62wt.%である.火山灰層は火山豆石を含み,マグマ水蒸気噴火により形成されたことを示す.Us-Kaテフラは,洞爺湖中島起源のNj-Osテフラを覆い,有珠外輪山溶岩に覆われる.テフラ直下の土壌層は18-19cal ka BPの放射性炭素年代値を示す.テフラの層厚と最大粒径は有珠山に向かって増大し,有珠山から噴出したことを示すUs-Kaテフラは,約18-19kaの爆発的噴火により形成され,この噴火は有珠火山の先駆的な活動であると考えられる.有珠山は,安山岩質の爆発的噴火により活動を開始し,玄武岩質溶岩(有珠外輪山溶岩)を噴出して成層火山を形成した.この成層火山の山体崩壊後,珪長質マグマの噴出により溶岩ドーム群を形成した.

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The Asosan core (JMA-V40) was drilled at a site 1.2km WSW of Nakadake crater, Aso Volcano in 2009. The core consists of the following nine units: 1) alternating beds of ash-fall deposits and buried soil layers (0-3.49m in depth); 2) alternating beds of ash including Nakadake N2 scoria (N2S; 1.5ka) (3.49-4.46m); 3) scoria-fall deposits from Kishimadake scoria cone (4ka; 4.46-9.00m); 4) a basaltic andesite lava (lava 1, 9.00-23.72m); 5) alternating beds of ash, soils and lahar deposits including the Kikai Akahoya tephra (K-Ah; 7.3ka) (23.72-31.00m); 6) a basaltic andesite lava (lava 2, 31.00-76.11m); 7) lahar deposits (76.11-86.47m); 8) a basaltic andesite lava (lava 3, 86.47-91.64m); 9) lahar deposits (91.64-100.00m). The three lavas recognized in units 4, 6 and 8 are quite similar in lithofacies, petrography and major element composition (SiO₂=52.1-53.4wt.%). This suggests that at least two compositionally homogeneous basaltic andesite lava flows were erupted from Nakadake Volcano around 8-5 cal ka and another similar one erupted somewhat earlier, but still in Holocene time.

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We developed a discrete element model to describe extrusion of middle-high viscous lava at the surface. We set the viscosity of magma at 10⁷ to 10¹⁰Pa s for the numerical simulations and arbitrarily set the rising velocity to be constant to the bottom of the conduit, as an extrusion model of magma. The conditions under which the lava dome or lava flow will form depend on not only the viscosity of the magma but also its rising velocity in the conduit. The velocity at which the lava dome is formed is dependent on the viscosity of magma, with magma of lower viscosity requiring higher rising velocity in order to form a dome. The inside structure of the lava dome is a concentric circle and is similar to those formed in previous analogue experiments.

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