The Aoso volcano is one of the representative stratovolcanoes of the Aoso-Osore volcanic zone in the northeast Japan arc. The volcanic activity of the Aoso volcano can be classified into two stages; the stages are separated by a caldera collapse event. The volumes of the products are 3.6 km3 (earlier stage) and 0.8 km3 (later stage). During the initial part of the earlier stage, thin lava flows (olivine orthopyroxene clinopyroxene basaltic andesite, SiO2=54.7-55.3%), block and ash flows (olivine bearing orthopyroxene clinopyroxene andesite, SiO2=57.9-58.5%), and thick lava (orthopyroxene clinopyroxene andesite, SiO2=59.0-59.9%) were extruded. The products construct either a conical shaped stratovolcano or series of stratovolcano. After that, scoria flows (orthopyroxene clinopyroxene andesite, SiO2=60.2%) and pumice flows (quartz orthopyroxene clinopyroxene hornblende andesite, SiO2=62.1-62.3%) spewed out, which might have caused the caldera at the top of this volcano. All the rocks during this stage can be plotted as linear lines on the co-variant diagrams. During the initial part of the later stage, pyroclastic rocks (olivine bearing hornblende orthopyroxene quartz dacite, SiO2=68.2-69.8%) were erupted, and lava domes grew. The lava domes can be separated into two types. One consists of clinopyroxene bearing orthopyroxene quartz dacite (SiO2=66.6-67.0%), whilst the other is clinopyroxene orthopyroxene dacite (SiO2=64.4-66.8%). All the eruptive rocks of this stage characteristically include mafic inclusions (quartz olivine bearing basaltic andesite and andesite, SiO2=53.8-57.5%). Each type of lava dome displays a distinct chemical trend in the covariant diagrams. All of the later stage products have higher SiO2 contents than the earlier stage products. Some of the later stage products, especially the pyroclastic rocks, were not plotted on the extrapolated lines of the trend drawn by the earlier stage products.
Mn-rich mineral paragenesis containing Mn-winchite, Mn-aegirine-augite, and Mn-rich garnet (calderitic spessartine) is found in hematite-rich siliceous schists from the Sanbagawa metamorphic belt in the Kanto Mountains. Chemical composition of amphibole widely changes with compositional layers in a siliceous schist; Mn-winchite in aegirine-augite+garnet+hematite+quartz layer, actinolite in hematite+calcite+quartz layer, and Mn-cummingtonite in hematite+quartz layer.
Bandai volcano is located in the southern part of Tohoku-Honshu arc, Japan, and has been active from about 300 ka. Most recently, the volcano erupted in 1888 and the phreatic eruption caused volcanic body collapse and produced huge debris avalanche deposit. Here we present new data of the tephrochronology and volcanic geology of Bandai volcano and discuss its growth history. The tephra-loam association in this area consists of the Hayama and the Mineyama Loam Formations. Sixty-three layers of tephra are recognized in the Mineyama Loam Formation, and seventy-seven layers of tephra in the Hayama Loam Formation. The volcanic activity is classified into seven stages based on tephrochronology: Stage 1: 300 ka≤(presumed age), Stage 2: 300-280 ka, Stage 3: 250-230 ka, Stage 4: 170-85 ka, Stage 5: 75-57 ka, Stage 6: 36-28 ka, Stage 7: 24-0 ka. Pyroxene andesite lavas and tephras are eruptions of Bandai volcano throughout its activity, and more than 13 large avalanche deposits are found in Stages 2, 5, 6, and 7 including 1888 debris avalanche. Modes of eruptions were almost sub-plinian with lava effusions from Stages 2 to 3, whereas sub-plinian was subsequently followed by vulcanian with lava effusions from Stages 5 to 7. Sub-plinian eruptions occurred in the earliest phase of Stages 5, 6, and pumice falls with occasional pumice flows were associated. Stage 4 consists of two eruption types. Large debris avalanches were commonly produced related with the sub-plinian eruption, except for 1888 eruption. Bandai volcano is a complex of at least five stratocones, and resurge of volcanic activity caused collapse of pre-existed volcanic body. This cyclic feature is considered to be the behavior of the volcano.