We newly identified tephra layers sandwiched by soil layers between AD 1663 (Kanbun age) and 1769 (Meiwa age) tephras at several sites on the northwestern flank of Usu volcano. The layers consist of pumice fall, ash fall and pyroclastic surge deposits. The presence of soil layers were confirmed by their carbon and nitrogen analysis. Petrographical and geochemical features of the pumice from newly recognized tephra largely differ from those of 1663 eruption, and are similar to those of 1769 one. However, on the basis of modal volume and chemical compositions of phenocrystic minerals, it can be possible to distinguish the pumice from those of the 1769 eruption. Considering the thickness of soil layers, the eruption would occur at around end of 17^th century. We name the eruption as the pre-Meiwa eruption, because petrological features of the pumice is similar to those of 1769 (Meiwa). The eruption was generated by distinct magma from other historic eruptive magmas. The sequence of the tephra suggests that the eruption started with phreatic eruptions followed by magmatic eruption to form plume. In the climactic stage, pyroclastic surge occurred with the formation of plume and its activity ended with phreatic eruptions. The finding of the pre-Meiwa eruption could provide important information to reveal not only relationship between eruption and dormancy but also evolution of magma systems.

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The previous eruption history of Fuji volcano has been re-examined by new 100 radiometric carbon ages. The major unconformity between Ko-Fuji and Shin-Fuji volcanoes of Tsuya (1968, 1971) was caused by the edifice collapse resulting in the Tanukiko debris avalanche at about Cal BC 18,000. Voluminous effusion of basalt lava flows in the older ejecta of Shin-Fuji volcano (Tsuya, 1968, 1971) had started at about Cal BC 15,000 and continued until about Cal BC 6,000. Deposition of black soil layer between the Older and Younger Fuji tephra layers of Machida (1964, 1977) started at Cal BC 8,000. After several thousands years quiescent time, basaltic eruptions in the middle ejecta of Shin-Fuji volcano (Tsuya, 1968, 1971) had restarted at about Cal BC 3,600 and thin lava flows had piled up as the central volcanic cone, until about Cal BC 1,700. The eruption style of the volcano changed into explosive basaltic eruptions from the summit and the flank at about Cal BC 1,500; the S-10 to S-22 scoria fall deposits were generated in this first half period of the younger ejecta of Shin-Fuji volcano (Tsuya, 1968, 1971). Also, basaltic pyroclastic flows cascaded down the western flank at about Cal BC 1,500, Cal BC 1,300, Cal BC 1,000 and Cal BC 770. The last summit explosive eruption (S-22) occurred at about Cal BC 300. Immediately after the S-22 eruption, basaltic fissure eruptions had repeated at the flanks until the 1707 Hoei eruption. New data suggest that the Fudosawa, Nissawa and Suyama-tainai lava flows in the southern flank are historical products at about Cal AD 1,000.

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Kikai Caldera, 17 km wide and 20 km long, is a Quaternary volcano located, nearly submerged, in the East China Sea, southern Kyushu. Two volcanoes, Iwo-dake (a rhyolitic volcano) and Inamura-dake (a basaltic volcano) on Satsuma Iwo-jima Island at the marginal part of this caldera, were formed after the great caldera-forming eruption of 6.5 ka known as the Akahoya Eruption. We made a geological study to understand the eruptive history of Satsuma Iwo-jima Island after the caldera formation. The volcanic activity in the island after the Akahoya Eruption is divided into three main stages and ten sub-stages based on volcanic edifice development and tephra deposits; the old Iwo-dake stage (stage OIo-I-II), the Inamura-dake stage (stage In-I-IV), and the young Iwo-dake stage (stage YIo-I-IV). The old Iwo-dake stage was initiated by phreatomagmatic eruptions and pumice fallout (stage OIo-I), followed by the effusion of rhyolitic lava with continuous ejection of ash and lithic fragments, resulting in building up an old volcanic edifice (stage OIo-II). In the stage OIo-II, intermittent explosive eruptions also occurred. The Inamura-dake stage is characterized by the effusion of basaltic lava flows and scoria-cone building (stage In-I-II). After that, at the western foot of the cone, phreatomagmatic explosions occurred (stage In-III) and andesitic lava flow effused (stage In-IV). In the young Iwo-dake stage, the explosive eruption occurred at the beginning (stage YIo-I), followed by the effusion of multiple rhyolitic lava flows from the summit crater and the formation of hyaloclastite in shallow sea that made up the marine terrace (stage YIo-II). During the past 1000 years, the volcanic activity changed to intermittent ones with pumice and bomb fallout (stage YIo-III-IV). Total phenocryst contents of the Iwo-dake lavas increased up to 8 vol.% through the young stages. The magma of the young Iwo-dake stage is different from that of the Akahoya Eruption and the old Iwo-dake stage, bordered by the Inamura-dake stage.

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The eruptive activity of Torishima volcano is divided into three stages; the stratovolcano stage, the caldera-forming stage and the central cone stage, respectively. Volcanic rocks of the stratovolcano stage are characterized by basalt containing abundant plagioclase phenocrysts. The chemical variation of this stage in oxide-oxide diagrams can be explained basically by addition of plagioclase and moderate removal of mafic minerals. Volcanic rocks of the caldera-forming stage are characterized by olivine-bearing dacite. Their whole-rock compositions lie on a straight line between the rhyolitic glass and the stratovolcano basalt with MgO=8wt.%. They also show different Ba/Zr and Nb/Zr ratios from stratovolcano-stage basalts, indicating contamination of crustal materials. So they were most likely to be formed by magma mixing of basaltic magma and rhyolitic melt formed by partial melting of mafic lower crust. Volcanic rocks of the central cone stage are classified into two groups; Komochi-yama basalts and Io-yama basaltic andesites, respectively. Io-yama basaltic andesites make a tholeiitic trend with stratovolcano-stage basalt in SiO₂ vs FeO^*/MgO diagram and have higher TiO₂ and FeO^* contents than other volcanic stages. On the other hand, they lie on a mixing line between caldera-forming-stage dacite and stratovolcano-stage basalt in Zr vs Ba/Zr and Nb/Zr diagrams. Therefore, their magmatic evolution can be explained by two processes; (1) TiO₂ and FeO^* enrichment by additional fractional crystallization of stratovolcano-stage basalt, (2) magma mixing between caldera-forming-stage dacite and differentiated magma with higher TiO₂ and FeO^*content.

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Advances in calorimetric measurements for magmatic liquids in the recent two decades are reviewed. This paper summarized previously reported values of heat capacities of silicate glasses and liquids and heats of fusion of minerals. Some of the values for heats of fusion are recalculated using the recently reported heats of vitrification and more reliable heat capacities of solids compared with those previously used. Heats of mixing of silicate liquids are also re-examined using excess enthalpies of glasses, heat capacities of end-members, excess heat capacities of liquids and recalculated values of heats of fusion. Excess enthalpies of pseudobinary silicate liquids are generally within ±30kJ/mol and mostly +5～-10kJ/mol. Although the excess enthalpies reach only 3-10% of enthalpies of fusion, those cannot be ignored, because liquidus temperatures and compositions of minerals are greatly affected by small excess enthalpies. Based on the compilation of the excess enthalpies by direct and indirect measurements, we found that interactions among network-forming oxides (SiO₂, NaAlO₂, KAlO₂), network-modifying oxides (CaO, MgO) and intermediate oxide (CaAl₂O₄) control the excess enthalpy of silicate liquid. As a preliminary test for generalized prediction of enthalpy of magmatic liquids, regular solution parameters for K₂O-Na₂O-CaO-MgO-Al₂O₃-SiO₂ liquids are determined using compiled calorimetric enthalpies using a least square method. Finally, Adam-Gibbs theory for viscosity and configurational entropy of silicate liquid are reviewed. In order to express Gibbs free energy of magmatic liquids, the following studies will be required in future : (1) measurements of excess heat capacity by drop calorimetry for liquids including interactions between NaAlO₂, KAlO₂ and CaO, MgO, (2) measurements of excess enthalpy by solution calorimetry and relative enthalpy by drop calorimetry for Fe-bearing multicomponent glasses and liquids, and (3) determinations of entropy of mixing and configurational entropy by systematic viscosity measurements for multicomponent silicate liquids.

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中部日本, 諏訪地方に分布する後期鮮新世から前期更新世にかけての膨大な火山岩類は塩嶺火山岩類と呼ばれている.筆者らは塩嶺火山岩類最上部を構成する霧ヶ峰火山の火山岩から2つのK-Ar年代を測定した.既知の層序・年代値と新たに得られた年代値をまとめると霧ヶ峰火山の活動期間はおよそ1.3〜0.75Maである.さらに, 霧ヶ峰火山に覆われる追分火山性地溝帯が主に約0.85Maに形成された可能性が明らかになった.既知の塩嶺火山岩類の研究と今回得られた年代値をあわせると塩嶺火山岩類の主な形成時期は約1.5～0.75Maであり, これは諏訪地方に近接した前期更新世における八ヶ岳火山の活動時期と同じである.つまり, 前期更新世の諏訪・八ヶ岳地域において, 広い地域(800km²)に膨大な体積の噴出物を形成した火山活動がおきたと考えられる.

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