The following proximal deposits of andesitic composition in Asama-Maekake Volcano and Asama-Kurofu Volcano were compared: 1) Kama-yama, 2) Upper Maekake-yama, and 3) Upper Sennin-iwa. The 1783 and 1108 eruptions formed Kama-yama and upper Maekake-yama, respectively. The upper Sennin-iwa, which is exposed on the collapsed caldera wall, was formed before the large-scale sector collapse approximately 24,000 years ago. Most of these deposits are piles of multiple welded pyroclastic rocks that form the topography of pyroclastic cones. Massive parts exhibit densely welded features such as fiamme and a eutaxitic texture under a microscope. These deposits are also associated with Plinian pumice fall deposits on the distal area, indicating that the intense pyroclastic fall formed these welded pyroclastic cones in the proximal area during the eruptions. Therefore, syn-Plinian fountaining is considered to have occurred in these cases. Kama-yama is a simple, small-scale truncated cone and occupies the dish-shaped crater of Maekake-yama. A thick, densely welded pyroclastic rock that is exposed on the crater wall forms the central part of the cone. On the other hand, upper Maekake-yama is a large truncated cone extending in the east-west direction. The complex topography and geology around upper Maekake-yama suggest that it is a composite of pyroclastic cones and that it collapsed at least twice during the 1108 eruption. The upper Sennin-iwa is a remnant of a pyroclastic cone, judging from its topography. It is considered to be less proximal than the other two examples. However, it consists of densely welded pyroclastic rocks with interbedded non-welded pumice fall deposits. Various factors, including the distance from the eruptive source, depositional rate, and fountain height, may have generated the variations in the occurrence among the proximal deposits observed in this study.

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Volcano databases of Japan and the world are reviewed to determine the present status of the databases and future course of action to make them more useful and relevant for volcanic hazard risk mitigation and related scientific endeavors. The reviewed volcano databases in Japan are the (1) National catalogue of the active volcanoes in Japan (fourth edition), (2) Volcanoes of Japan, (3) Database of Quaternary volcanic and intrusive rock bodies in Japan, (4) Image database for volcanoes, (5) Catalogue of Quaternary volcanoes in Japan, (6) Database on volcanic hazard maps and reference material, (7) visualization system for volcanic activity (VIVA ver. 2), (8) Volcanic activities in Japan (JMA), (9) Database of submarine volcanoes in Japan, (10) Hayakawa's one million-year tephra database, (11) Basic information links of Japanese volcanoes, (12) Atlas of tephra in and around Japan, and (13) Inventory of Quaternary outcrops. On the other hand, the reviewed volcano databases in the world are the (1) Volcanoes of the world (Smithsonian VGP), (2) Volcanic global risk identification and analysis project (VOGRIPA), (3) WOVOdat, (4) Significant volcanic eruption database, (5) Volcanic ash advisory database, (6) Global volcanoes locations database, (7) Volcanic eruption database, (8) Volcano hazards program, (9) Volcano deformation database, (10) Collapse caldera database, (11) Vhub, (12) Michigan Tec. volcanoes page, (13) Volcano world, (14) Nordic volcanological center, (15) ASTER volcano archive, (16) EarthChem, (17) Volcanic disaster and incidents database, (18) Damaging volcanoes database, (19) Global volcano hazard frequency and distribution database, and (20) Global database of composite volcano morphometry. The Asia-Pacific region global earthquake and volcanic eruption risk management (G-EVER) consortium is promoting the (1) Volcanic hazard assessment support system, (2) Asia-Pacific region earthquake and volcanic hazard information system, and (3) Indonesia volcano information system. Furthermore, the Coordinating Committee for Geoscience Programmes in East and Southeast Asia (CCOP) and Geological Survey of Japan (GSJ) started the Geoinformation Sharing Infrastructure for East and Southeast Asia (GSi) project. The future version of the volcano databases will be developed based on the aforementioned volcano databases, current advances in information technology and internationally accepted standards.

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Statistical treatment of volcanic eruptions clearly shows the regularity of power law between the frequencies and the scales not only in the global scale but also in regional and individual volcano scales. However, ancient smaller eruption events tend to be not recorded, compared with recent data. In the log frequency-VEI plot, incompletely normalized frequency which ignores the time-dependent nature of the database, provides a gentler regression line than when the data time-dependence is considered; that is, the former reflects low numbers of small eruptions insufficiently recorded. The slopes of the regression lines are similar, irrespective of area scales. This regularity may help our understanding about the potential of future large eruptions in not only individual volcanoes but also caldera regions. Volcanic activity in Japan has been quiet recently; no VEI 4 eruptions occurred after the early 20th Century, and no VEI 5 eruptions did since the middle 18th Century. Considering the regularity of volcanic eruptions in the arc scale, it is likely that Japan will experience these large eruptions near future.

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The Shirataki obsidian-rhyolite field (Shirataki Geopark, Hokkaido) contains many outcrops of densely compact obsidian layers of excellent quality. The Shirataki obsidian lavas (SiO₂=76.7-77.4 wt.%) were erupted at ca. 2.2 Ma and formed a monogenetic volcano comprising 10 obsidian-rhyolite lava units. The thickness of the units ranges from 50 to ＞ 150m, and each unit comprises a surface clastic zone, an upper dense obsidian zone, an upper banded obsidian zone, a central thick rhyolite zone, a lower banded obsidian zone, a lower dense obsidian zone, and a lower clastic zone. The dense obsidian is ＞ 98% glass with microlites of mainly magnetite and plagioclase, and rare plagioclase phenocrysts. Obsidian and rhyolite within single lava flows have similar bulk-rock compositions and number density of microlites, although the rhyolite contains glass with perlitic cracks and a large amount of crystalline material (spherulites and lithophysae), while the dense obsidian contains 0.4-0.8 wt.% H₂O. These geological and petrological features indicate that the formation of obsidian and rhyolite layers in the lava units was controlled mainly by the timing of the vesiculation and degassing of magmas, in addition to the cooling effect.

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The 30 ka caldera-forming eruption of Ohachidaira in central Taisetsu volcano, Hokkaido, produced Plinian pumice-fall and pyroclastic-flow deposit that contain juvenile products of pumice, scoria, and banded pumice. We reconsidered the eruption history of the caldera-forming eruption on the basis of combined geological and petrological data. The pyroclastic-flow deposits are classified into two types based on petrological features: Hb-type and Px-type. We identified three representative outcrops of the main deposit types at the foot of Taisetsu volcano: the Oiwa outcrop of an Hb-type pyroclastic flow, the Obako outcrop of a Px-type pyroclastic flow and a Plinian pumice fall, and the Tenninkyo outcrop where a Px-type pyroclastic and an Hb-type pyroclastic flows are recognized in the upper and lower parts, respectively. We analyzed the glass compositions of juvenile pumices as means of discriminating the two types of pyroclastic-flow deposit and estimated the flow directions and distribution of the two types of pyroclastic flow. The Hb-type pyroclastic-flow deposit is distributed in north-westerly and south-westerly directions. On the other hand, the Px-type pyroclastic-flow deposit is distributed in north-easterly and south-westerly directions. There might be more than a few hundred years interval between the Hb-type and Px-type pyroclastic flows.

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Take tephra occurs on the northern slope of Kitadake cone, which is one of the main edifices of Sakurajima volcano, Southwest Japan. It is the products of the last eruption of Kitadake at 5,600 cal BP, and the bulk volume is 3 estimated at 0.03 km³. The tephra forms two different lithofacies: stratified facies and massive facies. The stratified facies are alternating beds of thin pyroclastic flow deposits and pumice fall deposits, whereas the massive facies are composed of thick pyroclastic flow deposits. The total thickness of the stratified facies reaches 1 m, and thin small pyroclastic flow deposits contain accretionary lapilli. In contrast, massive facies are more than 10 m thick and contain abundant pumice clasts set in a fine matrix. The thick pyroclastic flow deposits constituting massive facies are mostly welded within 2.2 km from the summit crater of Kitadake. At the vicinity of the summit of Kitadake, densely welded pyroclastic rocks are formed agglutinates. It occurs as secondary flowage at near the altitude of 500 m. At least two cycles of massive facies and stratified facies can be confirmed in Take tephra. These facts suggest that multiple intra-plinian flows were generated by partial collapses of the sustained plinian eruption column. The presence of accretionary lapilli in stratified facies indicates that an interaction of magma and water occurred during the last eruption of Kitadake cone.

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It is very important for reconstructing volcano eruptive history to identify paleosols interbedded between tephra layers because they indicate dormant or gentle periods of volcanoes. However, it is difficult to recognize paleosols around volcanoes dominating long-term small ash-emitting activity for a long time. Gain-size, total carbon content and phytolith analyses and measurement of soil hardness of paleosols and fine-grained tephra layers (ash-fall deposits) were undertaken at a proximal (4 km) and a distal (11 km) sites of active Nakadake crater, Aso Volcano (southwest Japan) whose activity is characterized by small ash eruption, to discuss effective discrimination between paleosols and tephras using their physical and chemical properties. Paleosols were finer grained than tephra layers at the proximal site whereas there was no distinct difference in grain size between them at the distal site. Since Holocene tephras tended to be more consolidated than the paleosols, hardness may be an effective indicator to distinguish paleosols from tephras only in the Holocene. Although Holocene paleosols had higher total carbon contents than the tephras, both paleosols and tephras in the late Pleistocene contained extremely low carbon. Phytolith concentrations of paleosols were significantly higher than those of tephras both in the Holocene and late Pleistocene. Therefore, phytolith analysis is a useful method to divide into paleosols and tephras even at distal sites although the analysis is needed a practiced technique.

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Tephra bed occasionally occurs in marine sediment sequence around the volcanic islands such as the Japanese archipelago, and tephra grain is an important component of marine sediments. Spatiao-temporal occurrence and characteristics of marine tephra, however, is not fully understood. This is mainly derived from weak interactions between marine geologists and onshore tephrostratigraphers. Because the deep-sea (pelagic to hemipelagic) muddy sediments have been deposited continuously, collaboration between marine geologists and tephrostratigraphers will give us much more useful information to construct the tephra database.

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The Heian eruption (Eruptive episode A) is the latest activity of Towada Volcano, Northeast Japan that occurred in the 10^th century A.D. The activity comprised both magmatic and phreatomagmatic eruptions, that produced deposits of corresponding faces. It is proved that the Heian eruption started with a magmatic eruption and was followed by a phreatomagmatic eruption, then the magmatic-phreatomagmatic cycle repeated once, and finalized by effusion of a large pyroclastic flow. This eruption sequence is constructed on the basis of our new recognition of the second phreatomagmatic deposits in the proximal area (OYU-4), and correlation of the proximal base surge deposits (OYU-S) with the distal phreatomagmatic deposits (OYU-2). The Towada caldera including the vent of the Heian eruption (Nakanoumi caldera) is known to be abundant water in the Heian Period. The Heian eruption indicates that the magmatic eruption does occur in the existence of abundant water in the early stage of eruption and it migrates into the phreatomagmatic explosion as time passes. This eruption sequence provides evidence that the silicic magma does not necessarily cause phreatomagmatic eruption even in the presence of enough water.

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Geological research on the large-scale eruptions of the Asama-Maekake volcano was carried out by investigating pyroclastic fall deposits such as A (1783 AD), B' (1128 AD), and B (1108 AD). These deposits are mainly composed of pumice layers. In the case of the well-studied 1783 eruption, the most voluminous fall unit A-21 is classified as subplinian from its estimated weight. Ash and lapilli layers composed of lithic fragments also characterize the pyroclastic fall deposits. The particles of these layers are massive and angular to subangular in shape. They are also similar to the particles produced in the recent small-scale eruptions (e.g., 2004 eruption). Most of the recent eruptions, typically vulcanian eruptions, have mainly generated pyroclasts originating from solidified lava in a shallow level of the conduit. The pyroclastic fall deposits of the large-scale eruptions consist of pumice layers and lithic fragment layers, suggesting that intermittent vulcanian and subplinian eruptions occurred in the course of the large-scale eruptions as above. Descriptions and isopach maps of the pyroclastic fall deposits were made as detailed as possible in this study. The distributions of some fall units of the lithic fragment layers of pyroclastic fall deposits B and B' were mappable. These isopach maps show elongated distributions, suggesting the strong effect of wind on dispersal. These lithic fragment layers are composed of coarser grains than those of the recent small-scale eruptions preserved in the ashy soil at all localities. These findings indicate that large-scale vulcanian eruptions occurred in the course of the 12th century eruptions. At present, the 1783 eruption is the only example in the history of the Asama-Maekake volcano for which the temporal variations in the eruptive style and eruptive volume can be discussed with high reliability. Detailed reconstruction of the 1783 eruptive sequence was found to be possible by comparison between the stratigraphy of the eruptive products and information in old documents. The large-scale subplinian eruption that occurred after the intermittent eruptions is considered to be associated with the large-scale clastogenic lava flows owing to vigorous fountaining. On the other hand, little information is available on eruptions before 1783 because of the limited exposure and the availability of few old documents. Although the reconstruction reliability for the eruptions in the 12th century is poor, these eruptions might have occurred with a different sequence from those of the 1783 eruption. The eruptions in the 12th century were characterized by intermittent large-scale vulcanian eruptions after a major pyroclastic eruption in which subplinian pumice falls and pyroclastic flows were generated. This is a major difference from the 1783 eruption. Furthermore, little information, such as the distribution and stratigraphy of the eruptive products, is available for eruptions predating the 12th century owing to the lack of exposure. For instance, although isopach maps of the pyroclastic fall deposits can be prepared, the preparation of an accurate map is difficult for older deposits. Consequently, in the case of the Asama-Maekake volcano, it is not easy to predict the eruptive sequence of future large-scale eruptions on the basis of past eruptions.

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北海道クッタラ火山,登別地熱地域の最も新しい水蒸気噴火堆積物(Nb-a)の調査を行い,その分布域と噴火様式を解明した.調査は登別地熱地域全域の71地点で手掘りトレンチ(深度<90cm)を掘削して行った.水蒸気噴火堆積物は,最大層厚68cmで,変質した岩石片と細粒なマトリクスからなり,有珠山b降下軽石(Us-b,西暦1663年)を覆う.この水蒸気噴火堆積物は,北北西-南南東に伸長する850×1250mの範囲に分布し,その層厚と最大粒径は,複数の爆裂火口(日和山山頂,大湯沼,笠山北,奥の湯,鉄泉池)に向かって増大する.登別地熱地域では,西暦1663年以降(17世紀末～19世紀ごろ),複数の地点で水蒸気噴火が起き,北北西-南南東方向に配列する複数の火口が形成されたと考えられる.

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