Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Primary tephra layers can provide isochrons in a stratigraphic sequence. Such isochrons are powerful tools in terms of correlation and chronology of strata, and they constrain a chronological framework for geology, geomorphology, archaeology and palaeo-environmental studies in the Neogene to Quaternary. However, reworking processes can re-distribute tephra materials in both time and space, so that a given tephra can form a new discrete layer later in the depositional sequence, or it can be distributed in low concentrations (no visible layers, i.e., crypto-tephras) over a range of different stratigraphic horizons. The present study, based on sedimentological, petrographical, and geochemical analyses of reworked tephras in Japan, evaluates the duration and persistence of reworking and the tephra mobilisation and delivery to watersheds. Furthermore, it discusses how a unique isochron can be constructed from tephra distribution in a sedimentary sequence. Examples presented here are from fluvial and deltaic sequences in the Japanese Quaternary, which contain several visible tephra layers and a certain amount of tephra materials from multiple sources at different stratigraphical horizons. In the Niigata Plain, 5.4 ka Numazawako tephra material continued to be reworked for more than 4000 years after the eruption of Numazawa volcano, and was re-deposited as reworked pumice grains consisting of a "visible" tephra layer in delta front deposits. Mixed tephra materials originating from an earlier eruption of Numazawa volcano and eruptions from other calderas were also identified. In the Tsugaru Plain, post-2.5 ka subsurface deposits have > 10% glass shards content throughout the sequence. Glass shards were derived from several different tephra materials, such as those from the most recent eruption of Towada volcano (AD 915), and earlier caldera forming eruptions (30 ka, 15 ka). Some of the glass shards probably originated from erosion of exposed Pliocene pyroclastic bedrock. Thus, tephra reworking processes in alluvial to shallow marine settings can continue long after an eruption has ended, and can persist even during inter-eruptive (i.e., background sedimentation) periods. As tephra reworking involves complicated processes, careful observation and interpretations are necessary to evaluate whether tephra materials can truly provide an isochron for the strata in which they are found to exist. (C) 2015 Elsevier Ltd and INQUA. All rights reserved.

DOI： 10.1016/j.quaint.2015.03.022

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

This study reports on geomorphic and sedimentary evidence for a gigantic breakout flood from Towada caldera, Honshu Island, northeast Japan, as observed along the Oirase River downstream from the outlet of the caldera lake. A number of features of the Oirase River are inconsistent with its present discharge, including the occurrence of 1) hanging valleys and a horseshoe-shaped waterfall in the upstream gorge area, 2) boulder bars and scattered flood boulders, 3) a dry valley at a high elevation in the gorge, and 4) a large fan (the Sanbongi fan) in the downstream area of the river. The Sanbongi fan is composed of thick, lithic-rich hyperconcentrated flow deposits that include pumice clasts derived from the 15 ka Towada-Hachinohe ignimbrite and well-rounded meter-sized (and outsized) boulders derived from bedrock of welded ignimbrite. The deposits are entirely aggradational, with no major channels, indicating the absence of a major hiatus during sedimentation. The depositional facies also indicate that a single sheet-like flood event deposited the sediment within the Sanbongi fan area. Based on the age of the Sanbongi fan, the flood occurred between 15 and 12 ka, after eruption of the Towada-Hachinohe ignimbrite. The most probable water source for the flood is Towada caldera lake, as suggested by landforms and sediments along the lake outlet. A paleohydrological analysis indicates that at least 6 km(3) of water was released from the caldera at a peak discharge of >2 x 10(4) to 3 x 10(5) m(3) s(-1) during the breakout flood. Although the Sanbongi fan was previously considered to be a "normal" alluvial fan that formed during a stage of low-stand sea level, the present results show that the formation of the fan was closely related to a catastrophic flood from Towada caldera rather than perennial fluvial activity, climate change, or a change in relative sea level. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.geomorph.2010.08.006

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Volcanic activities can create cataclysmic hazards to surrounding environments and human life not only during the eruption but also by hydrologic remobilisation (lahar) processes after the cessation of eruptive activity. Although there are many studies dealing with the assessment and mitigation of volcanic hazards, these are mostly concentrated on primary eruptive processes in areas proximal to active volcanoes. However, the influence of volcaniclastic resedimentation may surpass the impacts of primary eruptive activity in terms of both extent and persistence, and can ultimately result in severe hazards in downstream areas.
Examination of the volcaniclastic successions of non-marine Pliocene-Holocene sedimentary basins in Japan has revealed hydrological volcaniclastic sedimentation in fluvial and lacustrine environments hundreds of kilometres from the inferred source volcano. Impacts on these distal and often spatially separated basins included drastic changes in depositional systems caused by sudden massive in fluxes of remobilised pyroclastic material. Typical volcaniclastic beds comprise centimetre-to decimetre-thick primary pyroclastic fall deposits overlain by metre- to 10s of metres-thick resedimented volcaniclastic deposits, intercalated in sedimentary successions of non-volcanic provenance. The relatively low component of primary pyroclastic fall deposits in the volcaniclastic beds suggests that: 1) potential volcanic hazards would be underestimated on the basis of primary pyroclastic fall events alone; and 2) the majority of resedimented material was likely derived from erosion of non-welded pyroclastic flow deposits in catchment areas rather than remobilisation of local fallout deposits from surrounding hillslopes.
The nature, distribution and sequence of facies developed by distal volcaniclastic sediments reflect the influence of: 1) proximity to ignimbrite, but not directly with the distance to the eruptive centre; 2) ignimbrite nature (non-welded or welded) and volume; 3) temporal changes in sediment flux from the source area; 4) the physiography and drainage patterns of the source area and the receiving basin, and any intervening areas; and 5) the formation of ephemeral dam-lakes and intra-caldera lakes whose potential catastrophic failure can impact distal areas. Models of the styles and timing of distal volcaniclastic resedimentation are thus more complicated than those developed for proximal settings of stratovolcanoes and their volcaniclastic aprons and hence present different challenges for hazard assessment and mitigation. (C) 2009 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.sedgeo.2009.04.016

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：GEOLOGICAL SOC AMER, INC  

Numazawa volcano in northeast Japan erupted most recently at ca. 5 ka, forming a 2-km-diameter caldera and emplacing at least 4 km(3) of valley-confined ignimbrite. The ignimbrite dammed the Tadami River to a depth of >100 inn, temporarily impounding >1.6 km(3) of water. Overtopping of the barrier triggered breaching and catastrophic release of the dam lake. Pyroclastic material redeposited by the ensuing flood is widely distributed along the Tadami and Agano Rivers in deposits tens of meters thick as far as the coastal Niigata Plain >150 km downstream of the volcano. Evidence for damming and flooding found along the rivers includes (1) fine-grained, thinly laminated lacustrine deposits upstream of the pyroclastic blockage; (2) 30-m-thick, pumiceous debris-How and hyperconcentrated-flow deposits that show continuous sedimentation with no major hiatus downstream of the volcano; (3) fine-grained slackwater deposits at tributary river mouths; and (4) large flood boulders that form lags on stripped ignimbrite surfaces and younger terrace surfaces, or cropping out within hyperconcentrated-flow deposits. Paleohydraulic estimation techniques indicate a peak discharge of 30,000-50,000 m(3)/s at the breach point. Burial of Neolithic Jomon settlements by flood and volcaniclastic aggradational deposits at distal locations indicates that such indirect volcanogenic hazards are significant, even where direct primary consequences of volcanic eruptions are minor or absent.

DOI： 10.1130/B26159.1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：GEOLOGICAL SOC AMER, INC  

The Pliocene Mushono tephra bed, central Japan, is characterized by fluvio-lacustrine volcaniclastic resedimentation at distal locations from the volcanic source. Sedimentary responses to an explosive eruption are well recorded in the resedimented Mushono tephra bed. Immediately after the eruption, large volumes of primary volcaniclastic material were reworked from proximal areas and discharged into the distal basin. Overloading of fluvial systems by pyroclastic debris resulted in the development of low-sinuosity active fluvial channel systems that carried sediment-laden, hyperconcentrated flows. The fluvial system flowed into a lake more than 150 km from the inferred source location, resulting in delta formation and progradation. Primary pyroclastic fall deposits are only a few centimeters thick but are overlain by reworked volcaniclastic deposits more than 5 m thick, which show coarsening-upward successions representing fluvio-lacustrine deltaic progradation. The reworked succession consists of six sedimentary facies, which can be interpreted as prodelta, mouth bar, distributary-channel, hyperconcentrated-flow, interdistributary-lowland or floodplain, and slump deposits. Rounded, cobble-sized pumice clasts in prodelta and distributary-channel deposits and thick, reworked deposits imply that the majority of resedimented volcaniclastic material was derived from voluminous proximal ignimbrite, rather than thin, fine-grained distal fallout ash material. Vertical facies changes are concordant with a decrease in sediment yields with time. Lateral facies distributions correspond to episodic influxes of volcaniclastic sediments that controlled the morphology of discrete fluvio-lacustrine deltas. The distal sedimentary response to an explosive silicic eruption is thus clearly recorded in vertical and lateral facies distribution of reworked volcaniclastic sediments.

DOI： 10.1130/B25379.1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：BLACKWELL PUBLISHING LTD  

The Ebisutoge-Fukuda tephra (Plio-Pleistocene boundary, central Japan) has a well-recorded eruptive style, history, magnitude and resedimentation styles, despite the absence of a correlative volcanic edifice. This tephra was ejected by an extremely large-magnitude and complex volcanic eruption producing more than 400 km(3) total volume of volcanic materials (volcanic explosivity index=7), which extended more than 300 km away from the probable eruption centre. Remobilization of these ejecta occurred progressively after the completion of a series of eruptions, resulting in thick resedimented volcaniclastic deposits in spatially separated fluvial basins, more than 100 km from the source. Facies analysis of resedimented volcaniclastic deposits was carried out in distal fluvial basins. The distal tephra (approximate to100-300 km from the source) comprises two different lithofacies, primary pyroclastic-fall deposits and reworked volcaniclastic deposits. The resedimented volcaniclastic succession shows five distinct sedimentary facies, interpreted as debris-flow deposits (facies A), hyperconcentrated flow deposits (facies B), channel-fill deposits (facies C), floodplain deposits with abundant flood-flow deposits (facies D) and floodplain deposits with rare flood deposits (facies E). Resedimented volcaniclastic materials at distal locations originated from unconsolidated deposits of a climactic, large ignimbrite-forming eruption. Factors controlling inter- and intrabasinal facies changes are (1) temporal change of introduced volcaniclastic materials into the basin; (2) proximal-distal relationship; and (3) distribution pattern of pyroclastic-flow deposits relative to drainage basins. Thus, studies of the Ebisutoge-Fukuda tephra have led to a depositional model of volcaniclastic resedimentation in distal areas after extremely large-magnitude eruptions, an aspect of volcaniclastic deposits that has often been ignored or poorly understood.

DOI： 10.1046/j.1365-3091.2002.00445.x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

An extremely large magnitude eruption of the Ebisutoge-Fukuda tephra, close to the Plio-Pleistocene boundary, central Japan. spread volcanic materials widely more than 290,000 km(2) reaching more than 300 km from the probable source. Characteristics of the distal air-fall ash (> 150 km away from the vent) and proximal pyroclastic deposits are clarified to constrain the eruptive style, history, and magnitude of the Ebisutoge-Fukuda eruption.
Eruptive history had five phases. Phase 1 is phreatoplinian eruption producing > 105 km(3) of volcanic materials. Phases 2 and 3 are plinian eruption and transition to pyroclastic how. Plinian activity also occurred in phase 3, which ejected conspicuous obsidian fragments to the distal locations. In phase 5, collapse of eruption column triggered by phase 4. generated large pyroclastic how in all directions and resulted in more than 250-350 km(3) of deposits. Thus, the total volume of this tephra amounts over 380-390 km(3). This indicates that the Volcanic Explosivity Index (VEI) of the Ebisutoge-Fukuda tephra is greater than 7. The huge thickness of reworked volcaniclastic deposits overlying the fall units also attests to the tremendous volume of eruptive materials of this tephra.
Numerous ancient tephra layers with large volume have been reported worldwide, but sources and eruptive history are often unknown and difficult to determine. Comparison of distal air-fall ashes with proximal pyroclastic deposits revealed eruption style, history and magnitude of the Ebisutoge-Fukuda tephra. Hence, recognition of the Ebisutoge-Fukuda tephra, is useful for understanding the volcanic activity during the Pliocene to Pleistocene, is important as a boundary marker bed, and can be used to interpret the global environmental and climatic impact of large magnitude eruptions in the past. (C) 2001 Elsevier Science B.V, All rights reserved.

DOI： 10.1016/S0377-0273(00)00300-0

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.jvolgeores.2022.107685

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Fuji Technology Press Ltd.  

The lahars are one of the most hazardous volcanic phenomena causing the third greatest causalities among the volcanic hazards since the 16th century worldwide. Lahars can flow down a long distance and cause tremendous disaster at the foot of volcanoes often beyond the areas of primary volcanic impacts of pyroclastic fall and pyroclastic density currents. Therefore, the research on lahar history of active volcanoes approaching from an analysis of a geological record in distal volcanic regions is significant for lahar hazard risk evaluation. Zao volcano has high risks of future eruptions, because volcanic tremors have been detected since 2013. The presence of a crater lake at the summit area, and steep slopes at the high altitude of Zao indicates high potential energy for future lahars, if triggered by an eruption starting underneath the crater lake. This study firstly reports the existence of lahar deposits at the western foot of Zao and discusses the depositional features and the origin of these as well as the lahar hazard risk at this volcano. The lahar deposits were exposed during the archaeological excavation of the Fujiki ruin, western foot of the Zao volcano. Two major lahar units, L1 and L2, were recognized. Based on the ¹⁴C dating and stratigraphic relationships, the ages of units L1 and L2 were estimated to be <ca. 4.0 and ca. 4.6 cal ka, respectively. The lithology, granulometry, and componentry features of the lahar deposits revealed the depositional features and the source materials. The upper part of L1 (L1-1) unit and lower part of L2 (L2-2) unit were deposited from a hyperconcentrated flow, whereas, the lower part of L1 (L1-2) unit and upper part of L2 (L2-1) unit were formed by a debris flow. The sources of both units were phreatomagmatic eruption products that may have erupted shortly before the lahar events. This implies that these eruptions were the most plausible trigger for the lahars. These results suggest that lahar risk will increase especially after the phreatomagmatic eruptions as well as phreatic eruptions, even in the western foot of this volcano.

DOI： 10.20965/jdr.2022.p0736

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DOI： 10.5026/jgeography.131.339

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Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.jvolgeores.2020.107001

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Tokyo Geographical Society  

GNSS data analyses reveal that recent large inland earthquakes in the Northeast (NE) Japan occurred in strain concentration zones. Seismic low-velocity anomalies, indicative of mechanically weak materials (weak zones), are estimated below the strain concentration zones at depths corresponding to the lower crust. Such crustal structures with weak zones have been formed as an accumulation of tectonic movements and igneous activities since early Miocene. Volcanic activity in the NE Japan during the Late Cenozoic Era can be subdivided into three prominent stages: continental margin volcanism stage, back-arc basin opening stage, and island-arc volcanism stage. The crustal structure of the NE Japan arc is characterized by many rift structures and large transcurrent faults formed during the back-arc basin opening stage, and by many large caldera volcanoes formed during the island-arc volcanism stage. The relationships among mechanically weak crustal structures, present strain localizations, earthquake distributions, and geological characteristics including rift structures, large transcurrent faults, volcanic belts, and caldera volcanoes, are clarified using various geophysical data such as gravity anomalies, seismic velocity structures, strain rates, and epicenter distributions. The results show that strain concentration zones and inland earthquake epicenters have close spatial relationships with geological structures such as rift boundary faults, large transcurrent faults, caldera structures, and volcanic belts. It can be interpreted that fluids migrating upwards from lower crustal weak zones below rifts, volcanic belts, or calderas, effectively weakened the crust due to its high pore fluid pressure, and caused earthquake ruptures under horizontal compression.

DOI： 10.5026/jgeography.129.529

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Volcanic fans and volcaniclastic aprons (ring plains) developed at the foot of a volcano preserve the products of high-discharge, sediment-laden lahar flows that originate from a volcano. Geological and geomorphological features of a volcanic fan are important for discussing the flow characteristics and history of far-reaching flows such as lahars. The present study focuses on volcanic-fan deposits at the northern base of Chokai Volcano in northeast Japan. The authors conducted geomorphological analysis, excavation survey at the distal part of the volcanic fan, sedimentary facies analysis, radiocarbon dating, and historical document analysis to understand the flow characteristics and history of far-reaching lahars in relation to changes in the depositional processes and their triggering volcanic activity. Geological observation by manual trenching and coring revealed that the volcanic fan is composed mainly of a series of lahar deposits formed by at least five large lahar events. The 14C ages of the lahar deposits and their correlation with historical documents indicate that the large lahars travelled down the volcanic fan at: the 2nd–5th century BCE (L1); 2nd to 4th century BCE (L2); 5th to 7th century CE (L3); 871 CE (L4); and 1801 CE (L5) after the Kisakata debris avalanche (2.5 ka). According to the stratigraphy, ratio of magmatic fragments and hydrothermally altered material content in the deposits, and correlation with historical documents, these lahar events can be classified into three types in terms of their material source: (1) a cohesive debris flow sourced by the debris avalanche deposit (L1); (2) a non-cohesive lahar by a magmatic eruption (L2, L3, L4, and L5–1 subunit); and (3) a cohesive debris flow by a phreatic eruption (L5–2 subunit). The facies analysis revealed that the different flow behaviors of lahars reflect their sourced volcanic activity. The oldest lahar (L1), incorporating debris avalanche deposit, flowed as hazardous cohesive debris flow; lahars after magmatic eruptions (L2, L3, L4, and L5–1 subunit) tends to be streamflow through the flow transformation of sandy debris flow; and a cohesive lahar (L5–2 subunit) by a phreatic eruption tends to be of small scale. These results indicate that the characteristics of a lahar depend largely on causal volcanic activity.

DOI： 10.1016/j.jvolgeores.2019.106661

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DOI： 10.1016/j.jsames.2018.12.016

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publisher：日本第四紀学会  

DOI： 10.4116/jaqua.57.65

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DOI： 10.23917/forgeo.v31i1.3977

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© 2016, © Emerald Group Publishing Limited. Purpose – The purpose of this paper is to present a concurrent implementation of sustainable inventory for the UNESCO World Heritage sites of Bat, Al-Khutm and Al-Ayn in the interior of Oman. Design/methodology/approach – A digital heritage inventory (DHI) was developed through an action research to realize demands of the local agent and to co-design the solution. The Ministry of Heritage and Culture of Oman, the local agent, demanded to have archaeological information of the sites shared with foreign expeditions, which had worked at the sites for decades, for efficient heritage management, scientific research, outreach, and education. To this end, the Bat Digital Heritage Inventory (BatDHI) was implemented by a combination of network-access-ready database application, open source geographical information systems, and a web-based map service to incorporate and visualize previous works, which were concurrently cross-checked and updated by ground-truth surveys. Findings – The online inventory made it possible to update information during archaeological fieldwork in real time and accelerated the decision-making process in heritage management by prompt data updates and visualization. Research limitations/implications – The DHI is extendable for other sites or regions. It should also be considered to install Arches, an open-source suite of digital heritage inventories. Practical implications – The BatDHI was implemented through the action research mentioned in the design/methodology/approach section and yielded the implications mentioned in the findings section. Originality/value – This paper is a challenging application of transdisciplinary approach to the sustainable heritage management, in which researchers and societal stakeholders collaborate for co-design of research agendas, co-production of knowledge, and co-dissemination of outcomes.

DOI： 10.1108/JCHMSD-01-2016-0005

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Hole U1395B, drilled southeast of Montserrat during Integrated Ocean Drilling Program Expedition 340, provides a long (>1 Ma) and detailed record of eruptive and mass-wasting events (>130 discrete events). This record can be used to explore the temporal evolution in volcanic activity and landslides at an arc volcano. Analysis of tephra fall and volcaniclastic turbidite deposits in the drill cores reveals three heightened periods of volcanic activity on the island of Montserrat (approximate to 930 to approximate to 900 ka, approximate to 810 to approximate to 760 ka, and approximate to 190 to approximate to 120 ka) that coincide with periods of increased volcano instability and mass-wasting. The youngest of these periods marks the peak in activity at the Soufriere Hills volcano. The largest flank collapse of this volcano (approximate to 130 ka) occurred toward the end of this period, and two younger landslides also occurred during a period of relatively elevated volcanism. These three landslides represent the only large (>0.3 km(3)) flank collapses of the Soufriere Hills edifice, and their timing also coincides with periods of rapid sea level rise (>5 m/ka). Available age data from other island arc volcanoes suggest a general correlation between the timing of large landslides and periods of rapid sea level rise, but this is not observed for volcanoes in intraplate ocean settings. We thus infer that rapid sea level rise may modulate the timing of collapse at island arc volcanoes, but not in larger ocean-island settings.

DOI： 10.1002/2015GC006053

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Recent studies hypothesize that some submarine slides fail via pressure-driven slow-slip deformation. To test this hypothesis, this study derives pore pressures in failed and adjacent unfailed deep marine sediments by integrating rock physics models, physical property measurements on recovered sediment core, and wireline logs. Two drill sites (U1394 and U1399) drilled through interpreted slide debris; a third (U1395) drilled into normal marine sediment. Near-hydrostatic fluid pressure exists in sediments at site U1395. In contrast, results at both sites U1394 and U1399 indicate elevated pore fluid pressures in some sediment. We suggest that high pore pressure at the base of a submarine slide deposit at site U1394 results from slide shearing. High pore pressure exists throughout much of site U1399, and Mohr circle analysis suggests that only slight changes in the stress regime will trigger motion. Consolidation tests and permeability measurements indicate moderately low (similar to 10(-16)-10(-17)m(2)) permeability and overconsolidation in fine-grained slide debris, implying that these sediments act as seals. Three mechanisms, in isolation or in combination, may produce the observed elevated pore fluid pressures at site U1399: (1) rapid sedimentation, (2) lateral fluid flow, and (3) shearing that causes sediments to contract, increasing pore pressure. Our preferred hypothesis is this third mechanism because it explains both elevated fluid pressure and sediment overconsolidation without requiring high sedimentation rates. Our combined analysis of subsurface pore pressures, drilling data, and regional seismic images indicates that slope failure offshore Martinique is perhaps an ongoing, creep-like process where small stress changes trigger motion.

DOI： 10.1002/2015JB012061

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Volcanic edifice collapses generate some of Earth's largest landslides. How such unloading affects the magma storage systems is important for both hazard assessment and for determining long-term controls on volcano growth and decay. Here we present a detailed stratigraphic and petrological analyses of volcanic landslide and eruption deposits offshore Montserrat, in a subduction zone setting, sampled during Integrated Ocean Drilling Program Expedition 340. A large (6-10km(3)) collapse of the Soufriere Hills Volcano at similar to 130ka was followed by explosive basaltic volcanism and the formation of a new basaltic volcanic center, the South Soufriere Hills, estimated to have initiated <100years after collapse. This basaltic volcanism was a sharp departure from the andesitic volcanism that characterized Soufriere Hills' activity before the collapse. Mineral-melt thermobarometry demonstrates that the basaltic magma's transit through the crust was rapid and from midcrustal depths. We suggest that this rapid ascent was promoted by unloading following collapse.

DOI： 10.1002/2015GL064519

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.4116/jaqua.54.21

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DOI： 10.4116/jaqua.54.31

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

IODP Expedition 340 successfully drilled a series of sites offshore Montserrat, Martinique and Dominica in the Lesser Antilles from March to April 2012. These are among the few drill sites gathered around volcanic islands, and the first scientific drilling of large and likely tsunamigenic volcanic island-arc landslide deposits. These cores provide evidence and tests of previous hypotheses for the composition and origin of those deposits. Sites U1394, U1399, and U1400 that penetrated landslide deposits recovered exclusively seafloor sediment, comprising mainly turbidites and hemipelagic deposits, and lacked debris avalanche deposits. This supports the concepts that i/ volcanic debris avalanches tend to stop at the slope break, and ii/ widespread and voluminous failures of preexisting low-gradient seafloor sediment can be triggered by initial emplacement of material from the volcano. Offshore Martinique (U1399 and 1400), the landslide deposits comprised blocks of parallel strata that were tilted or microfaulted, sometimes separated by intervals of homogenized sediment (intense shearing), while Site U1394 offshore Montserrat penetrated a flat-lying block of intact strata. The most likely mechanism for generating these large-scale seafloor sediment failures appears to be propagation of a decollement from proximal areas loaded and incised by a volcanic debris avalanche. These results have implications for the magnitude of tsunami generation. Under some conditions, volcanic island landslide deposits composed of mainly seafloor sediment will tend to form smaller magnitude tsunamis than equivalent volumes of subaerial block-rich mass flows rapidly entering water. Expedition 340 also successfully drilled sites to access the undisturbed record of eruption fallout layers intercalated with marine sediment which provide an outstanding high-resolution data set to analyze eruption and landslides cycles, improve understanding of magmatic evolution as well as offshore sedimentation processes.

DOI： 10.1002/2014GC005652

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Language：Japanese   Publisher：特定非営利活動法人 日本火山学会  

Chokai volcano is an andesitic stratovolcano in northeast Japan. The collapse of parts of the volcano occurred about 2500 years ago, and formed the Kisakata debris avalanche deposits. The post-2.5 ka fan (partly volcaniclastic apron) deposits are largely distributed in north to northwestern foot of the volcano. The fan deposits consist of several lithological/sedimentological units, however, most of their geological, sedimentological, and geomorphic characteristics have not been examined in previous studies. This paper, therefore, aims at understanding of geomorphology and depositional processes of these lahar deposits and mineralogical component changes in relations with different sources. Field survey in the upstream and observation of a trench in the downstream area revealed that the fan deposits consist of more than 16 units, which are composed of debris flow, hyperconcentrated flow and streamflow facies; most of them were deposited by lahar events. The lahar deposits have total thickness of 30 m, and overlie the Kisakata debris avalanche deposit. In proximal areas (with steep to moderate slopes), lahars flowed down as debris flows. Whereas in the distal area (with very gentle slopes), the lahars were transformed into hyperconcentrated flow and/or stream flows commonly, although some of them reached to the distal area with a debris flow nature. Clasts of the lahar deposits comprise altered and fresh andesites, mudstones and sandstones. Proportions of altered andesite clasts to total clasts decrease upwards in stratigraphic sequences. Matrices of the lower eight units are composed of grayish-blue clay and are different from those of the upper eight units, which are composed of brownish yellow volcanic sand. The stratigraphic variation in the matrix component is consistent with the change in matrix mineral assemblage, possibly reflecting changes in the source materials from Chokai volcano.

DOI： 10.18940/kazan.60.1_1

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Language：Japanese   Publisher：一般社団法人 日本地質学会  

DOI： 10.5575/geosoc.2015.0035

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Language：Japanese   Publisher：特定非営利活動法人 日本火山学会  

Previously known lahar deposits along the Sukawa River, western slope of Adatara volcano, consist of at least 7 muddy (cohesive) units and were formed during the last 2500 years. This paper reports stratigraphy, chronology and depositional processes of the newly found lahar units that were deposited older than 2500 years ago. ^<14>C dating for wood fragments within lahar deposits and intercalated paleosol layers indicates that at least 18 lahar events occurred in the area during the last 14000 years. The newly found lahar units comprise 10 muddy matrix-rich units and one bouldery gravel unit. The muddy matrix-rich units are very poorly sorted with pebble to cobble sized andesite clasts and hydrothermally altered clasts. Bouldery gravel unit is filled with sandy matrix and composed of clasts with oxidized rind locally. Bulk chemistry of these lahar units indicates that high sulfur content in the muddy units whereas Fe_2O_3 content is higher in the bouldery gravel units. The muddy units are derived from syn- or post-eruptive lahars in relations with phreatic eruptions or degradation of hydrothermally altered source rocks nearby the Numanotaira crater at the summit. The bouldery unit distributed farther downstream may have resulted from a non-cohesive debris flow or an outburst flood from the crater or a volcanically dammed upstream area. The presence of oxidized clasts indicates that during traveling, the watery flow entrained clasts which were exposed on a gravelly riverbed in an inter-eruptive period. The two types of lahar deposits show flows with different characteristics (cohesive and non-cohesive) that originated from Adatara volcano. Proximal eruptive units in the summit area sometimes can be degraded easily and overprinted by other eruptive units that result in a paucity and difficulty in understanding the precise eruption history of a volcano. Therefore, approaching from analysis of distally deposited lahar units will give a hint to assess not only a lahar trigger but also the types, frequency and volume of volcanic eruptions.

DOI： 10.18940/kazan.60.4_461

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Association for Quaternary Research  

DOI： 10.4116/jaqua.53.323

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Association for Quaternary Research  

DOI： 10.4116/jaqua.53.265

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Association for Quaternary Research  

DOI： 10.4116/jaqua.53.229

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Marine sediments around volcanic islands contain an archive of volcaniclastic deposits, which can be used to reconstruct the volcanic history of an area. Such records hold many advantages over often incomplete terrestrial data sets. This includes the potential for precise and continuous dating of intervening sediment packages, which allow a correlatable and temporally constrained stratigraphic framework to be constructed across multiple marine sediment cores. Here we discuss a marine record of eruptive and mass-wasting events spanning similar to 250 ka offshore of Montserrat, using new data from IODP Expedition 340, as well as previously collected cores. By using a combination of high-resolution oxygen isotope stratigraphy, AMS radiocarbon dating, biostratigraphy of foraminifera and calcareous nannofossils, and clast componentry, we identify five major events at Soufriere Hills volcano since 250 ka. Lateral correlations of these events across sediment cores collected offshore of the south and south west of Montserrat have improved our understanding of the timing, extent and associations between events in this area. Correlations reveal that powerful and potentially erosive density-currents traveled at least 33 km offshore and demonstrate that marine deposits, produced by eruption-fed and mass-wasting events on volcanic islands, are heterogeneous in their spatial distribution. Thus, multiple drilling/coring sites are needed to reconstruct the full chronostratigraphy of volcanic islands. This multidisciplinary study will be vital to interpreting the chaotic records of submarine landslides at other sites drilled during Expedition 340 and provides a framework that can be applied to the stratigraphic analysis of sediments surrounding other volcanic islands.

DOI： 10.1002/2014GC005402

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Association for Quaternary Research  

DOI： 10.4116/jaqua.53.175

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Association for Quaternary Research  

DOI： 10.4116/jaqua.53.111

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DOI： 10.4116/jaqua.53.103

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Luminescence dating has been applied to scoria and lahar deposits from Somma-Vesuvius, Italy. Samples include scoria from the AD472 and 512 (or 536) eruptions and lahar deposits. In order to find a stable luminescence signal which is less affected by anomalous fading, infrared stimulated luminescence (IRSL) signals at elevated temperatures after bleaching with IR at 50 degrees C (termed post-IR IRSL; pIRIR) were tested at different preheat and elevated stimulation temperatures. The fading rates of both IRSL and pIRIR signals reduced dramatically with increasing preheat and pIRIR stimulation temperatures. A pIRIR signal measured at 290 degrees C after a preheat at 320 degrees C (60 s) and an IR stimulation at 50 degrees C (100 s) was selected to calculate the equivalent dose (D-e). The gamma spectrometry results indicate that the U-series nuclides are not in equilibrium and there is a large Ra-226 excess. The dose rates and ages were calculated by assuming a Ra-226 excess (over its parent Th-230) at deposition, and that this unsupported excess then decayed to the present level. The resulting luminescence ages of the two scoria samples agreed with the expected ages, and the ages of the lahar deposits indicate that they are associated with the AD1631 eruption. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.quageo.2013.10.005

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPRINGER INT PUBLISHING AG  

Onshore-offshore geophysical studies conducted on Martinique have identified major flank collapse events of Montagne Pelee that generated large submarine mass wasting deposits. Here, we evaluate the preconditioning factors involved in the deformation and failure of marine sediments related to volcano-flank collapse events. We use core logging, sedimentological and geotechnical data of the upper 200 m of core at sites U1397, U1398, U1399 and U1400 drilled during the Integrated Ocean Drilling Program (IODP) expedition 340, west of Martinique. We find that the low hydraulic conductivity of hemipelagic sediment causes low rates of dewatering of turbidites and tephra layers allowing excess pore fluid pressures to persist at depth. Overpressure generation was likely enhanced during major flank collapses, leading to low shear strength and subsequent deformation of large volumes of marine sediments, as found at Site U1400.

DOI： 10.1007/978-3-319-00972-8_7

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Association for Quaternary Research  

Twelve tephra beds (NB1 to NB12) are identified in peaty bog sediments on the summit of Mt. Naebasan, central Japan. Radiocarbon data from the sediments shows that the peaty deposits and tephra beds were deposited during the Holocene. On the basis of petrographic characteristics, refractive index, and chemistry of glass shards, the following correlation with previously reported tephras is suggested : NB3 tephra with Kikai-Akahoya tephra mixed with Myoko-Akakura tephra ; NB8 with Kusatsu-Shirane-Kumakura pumice ; NB10 with Kusatsu sp1-3 tephra ; NB11 with Myoko-Otagirigawa tephra ; and NB12 with Koyaike volcanic ash group C. Glass shard chem- istry suggests that the remaining uncorrelated tephra layers were probably derived either from Asama, Kusatsu-Shirane, Myoko, or Niigata-Yakeyama volcanoes.

DOI： 10.4116/jaqua.52.241

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Language：English   Publishing type：Research paper (international conference proceedings)  

Luminescence dating has been applied to volcanogenic outburst flood sediments (Takuma gravel bed) from Aso volcano, Japan, and tephric loess deposits overlying the gravel bed. The poly-mineral fine grains (4-11 μm) from loess deposits were measured with pulsed optically stimulated luminescence (pulsed OSL) and post-IR infrared stimulated luminescence (pIRIR) methods, whereas the Takuma gravel bed containing no quartz, was measured with IRSL and pIRIR methods using sand sized (150-200 μm) plagioclase. The loess deposits date back at least to ∼50 ka by consistent IRSL, pIRIR and pulsed OSL ages from the lowermost part of the loess deposits from one section. The ages obtained from the bottom part of the other loess section are not consistent each other. However, we consider that the pIRIR age (72±6 ka) which showed negligible anomalous fading is most reliable, and regard as a preliminary minimum age of the Takuma gravel bed. The equivalent doses (De) for the plagioclase from the Takuma gravel bed have a narrow distribution and the weighted mean of the three samples yield an age of 89±3 ka. This age is in agreement with the last caldera-forming eruption of Aso volcano (∼87 ka) and it is likely that the pIRIR signal has not been bleached before the deposi-tion. IRSL dating without applying pIRIR using small aliquots was also conducted, however, the IRSL signal shows no clear evidence of an additional bleaching during the event of outburst flood from the caldera lake. © 2013 Silesian University of Technology, Gliwice, Poland. All rights reserved.

DOI： 10.2478/s13386-013-0135-4

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Association for Quaternary Research  

Drastic changes in the sedimentary environment occurred during the Heian Period (AD 794 to 1192) in the central Tsugaru Plain. Observation of sedimentary facies in trenches of the excavated Jusanmori archaeological site, one of the largest village of the middle Heian Period (around AD1000) in this area, as well as data from subsurface sediments at 21 sites obtained by hand auger, have revealed an extensive distribution of volcaniclastic sands (lahar deposits) abruptly overlying organic-matter rich (peaty) silt and peat in the area. Radiocarbon ages from the peaty silt, mineral compositions, and shape and refractive index of volcanic glass shards show a sudden sedimentary facies change from peaty silt to volcaniclastic sand in the early Heian Period. The volcaniclastic sand bed contains a high proportion of glass shards derived from the Towada-a tephra (AD 915 erup-tion of Towada volcano). This indicates that pre-eruptive low-energy wetland to floodplain in the central Tsugaru Plain was inundated by lahar after the AD915 eruption. The Baegdusan-Tomakomai tephra fall (B-Tm tephra : ∼AD 930 to 940) overlying the lahar deposits implies the termination of the lahar event within decades.<br>In the central Tsugaru Plain, many archaeological sites appear above the horizon of the volcaniclastic sand bed (i.e., lahar sediments after the 915 eruption). This is probably because the extensive sandy plains formed by lahar events were preferable places to settle for Heian people and eventually caused an increase in habitants in the area.

DOI： 10.4116/jaqua.51.317

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Using temperature gradients measured in 10 holes at 6 sites, we generate the first high fidelity heat flow measurements from Integrated Ocean Drilling Program drill holes across the northern and central Lesser Antilles arc and back arc Grenada basin. The implied heat flow, after correcting for bathymetry and sedimentation effects, ranges from about 0.1 W/m(2) on the crest of the arc, midway between the volcanic islands of Montserrat and Guadeloupe, to &lt;0.07 W/m(2) at distances &gt;15 km from the crest in the back arc direction. Combined with previous measurements, we find that the magnitude and spatial pattern of heat flow are similar to those at continental arcs. The heat flow in the Grenada basin to the west of the active arc is 0.06 W/m(2), a factor of 2 lower than that found in the previous and most recent study. There is no thermal evidence for significant shallow fluid advection at any of these sites. Present-day volcanism is confined to the region with the highest heat flow.

DOI： 10.1029/2012GC004260

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The Towada Caldera Volcano is located between the prefectures of Aomori and Akita - Northeast Honshu Island, Japan. The caldera, today filled by a lake, has produced 15,000 years ago a complex eruption emplacing an ignimbrite topped by the lake outburst flood deposit, through which the present Oirase River erodes. This flood deposit has shaped the geomorphologic feature named Sanbongi Fan, on which Towada City extends. This flood event hypothesis is mainly based on sedimentological and geomorphological evidences of floods mainly from outcrops retrieved from the Sanbongi Fan area. Because of the lack of extended outcrops - typical of the Japanese environment - the present paper has therefore put the theory to the test using GPR (Ground Penetrating Radar) radargram extending along a 640 m length. The GPR used for the survey was a Pulse-ekko-Pro with 50 MHz antennas, and the software Reflex was used to process the data. The radargrams have displayed a sole unit, which the GPR could not penetrate. It can be interpreted as the ignimbrite. On top of this deposit a series of subhorizontal layers, with the alternation between a backset and a foreset extends between 5 m and 3 m depth. Above 3 m, the units are regular and subhorizontal. The deposit is also characterized by the extensive presence of boulders, which are located along three bands: (1) on top of the ignimbrite; (2) in the units deposited by the outburst flood, between 3 and 5 m depths; (3) and in the units close to the surface, although part of these punctual elements are most certainly anthropogenic. Compared with the outcrops, the present research confirms that the material located above the ignimbrite material have been deposited by the outburst flood, creating large-sheet patterns, which have transported boulders. These sheets display backset and foreset patterns, depending on the position of the deposit, indicating flow pulsation or surges under a 'high-energy-flow' condition. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jvolgeores.2012.04.009

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

Few of the Japanese Pliocene to early Pleistocene tephra beds have been correlated to their source volcanoes, mainly because of the rapid degradation of proximal ejecta after eruptions. The present paper discusses the source areas of non-marine, distal tephra beds intercalated in the Plio-Pleistocene Second Setouchi Supergroup, central Japan, by focusing on the facies and thickness variations of both pyroclastic fall deposits and fluvially reworked deposits. Many of the examined tephra beds have thick (1—10 m) reworked/resedimented portions, indicating the transportation and deposition of tephra material by fluvial activity—a significant process during tephra bed formation. The tephra beds are divided into the following types based on the ratio of the thickness of the primary fall part to that of the reworked part: A-type, tephra consisting mainly of reworked part; B-type, reworked part dominant; C-type, fall part dominant; and D-type, tephra consisting mainly of fall part. The presence of pumice pebbles and cobbles in an A-type bed suggests the tephra was derived mainly from the resedimentation of ignimbrite emplaced by the nearest source volcano. The C- and D-type beds indicate eruptive activity at distant volcanic areas, with the consequence that the alluvial area received ashfall only. The present results indicate that 15 of the examined tephra beds were derived from large ignimbrites, and 5 from southern Kyushu or Tohoku (mainly distal ashfall). Thus, the sedimentology of distal resedimented tephra beds provides important clues (although indirect) to the source area, eruptive style, history, magnitude, and paleogeographical background of ancient tephras and eruptions.

DOI： 10.5575/geosoc.2011.0024

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

The Echigo Plain, which faces the Sea of Japan in northeast Japan, is a typical coastal plain with numerous sand dunes. We examined the sedimentology of pumiceous sediments (lahar deposits) in the Agano River area of the Echigo Plain, derived mainly from a large-scale dam-break flood after the Numazawako eruption (about 5 ka), using an existing borehole dataset and facies analysis of sediment cores.<br>The lahar deposits show different sedimentary facies in coastal areas versus the shallow marine environment. Coarse-grained pumiceous sediments (5—8 m thick) are interpreted to have been deposited under the delta front or in a delta plain environment in a coastal area. Sandy silt deposits (pro-delta facies), including pyroclastic material (horizons of concentrated volcanic glass shards and heavy minerals), are distributed in the shallow sea area.<br>The large volumes of volcaniclastic sediment delivered during the flood event induced the rapid progradation of the delta system in the Agano River region. The deposition of volcaniclastic sediments in the shallow sea also caused progradation of the delta system and changed the coastal landforms along the margin of the Echigo Plain.<br>The flood event resulted in an increase in the progradation rate of the depositional system from 0.9 to 2.5 km per 1000 years. An understanding of large-scale pyroclastic resedimentation can contribute to evaluating and predicting the volume of sediment discharge and the nature of hazards created by a volcanogenic flood and its aftermath in an alluvial plain setting.

DOI： 10.5575/geosoc.117.483

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Language：Japanese   Publisher：The Geological Society of Japan  

DOI： 10.5575/geosoc.116.S49

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：TAYLOR & FRANCIS LTD  

It has been suggested that the sustainability of turbidity currents is derived from self-sustainment of the flow. This self-sustainment can be realized through the process of acceleration of the current as it increases its own density due to the incorporation of sediment eroded from the substrate. Although self-sustaining turbidity currents have been predicted theoretically, experimental turbidity currents to date have all been net-depositional decelerating flows. We report here the results of experiments on self-sustaining turbidity currents. In order to produce non-depositional flows, we modeled the sediment using two types of plastic particles with densities that were much lower (1.3 and 1.5 g/cm(3)) than that of silicielastic sands. After the bed was covered with sediment, a mixture of sediment and water was injected to produce a turbidity current at the upcurrent end of the flume. As a result, some experimental flows showed acceleration, and measurements using siphons revealed that the sediment concentration of the flow increased downcurrent, so indicating a trend toward self-sustaining turbidity currents.

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Language：Japanese   Publisher：日本地質学会  

DOI： 10.5575/geosoc.113.12.XIX_XX

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DOI： 10.3720/japt.71.337

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Association for the Geological Collaboration in Japan  

DOI： 10.15080/agcjchikyukagaku.59.1_3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：日本堆積学会  

The volcanic, lacustrine fan-delta deposits in the Pleistocene Lower and Middle Formations of the Yachiho Group, central Japan commonly include debris-flow and hypercon-centrated-flow deposits in the upper fan-delta-plain facies. The hyperconcentrated-flow deposits are recognized by its characteristics and depositional organization with debris-flow and streamflow deposits. Hyperconcentrated-flow deposits usually coexist with cohesionless debris-flow deposits. This indicates that the generation and depositional processes of hyperconcentrated flow are closely related to cohesionless debris flow in the volcanic fan-delta setting. A depositional organization comprising cohesionless debris-flow deposits, hyperconcentrated-flow deposits, and normal streamflow deposits, in ascending order, is commonly observed. This organization indicates the longitudinal segmentation of the composite flows. Cohesionless debris flow preceded dilute hypercon-centrated flow followed by a streamflow that segregated from the initial debris flow.

DOI： 10.4096/jssj1995.59.17

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Osaka City University  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

Stratigraphic horizon of the Km3 tephra layer intercalated in the lower part of the Kitaura Formation, Akita Prefecture, Japan, is located above the calcareous nannofossil datum plane 11 (1.65Ma). The Km3 tephra layer, approximately 1m thick, is mainly composed of volcanic glass shards with minor amounts of plagioclase, quartz and biotite. On the basis of the stratigraphic position, lithofacies, petrographic characteristics and chemical composition of glass shards, the Km3 tephra layer is correlated to the Om-SK110 Tephra (1.65Ma). By this result, it is clarified that the Km3 tephra layer was transported more than 450km away from its probable volcanic center situated in the Hida Mountain Ranges, central Honshu Island.

DOI： 10.5575/geosoc.108.11_761

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Other Link： http://hdl.handle.net/10191/17815

Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publisher：地学団体研究会  

The Plio-Pleistocene Osaka Group, consisting of gravel, sand and mud with intercalation of several tens of volcanic ash layers, has been considered as fluvial to shallow bay sediments. The volcanic ash layer examined in this study is located at Tondabayashi City, southern Osaka, and can be correlated to Sayama volcanic ash layer by lithofacies and petrographic characteristics including mineral composition, heavy mineral composition, and refractive index of volcanic glass. This ash layer is intercalated in the mud layer interpreted to be bay floor deposits. The volcanic ash layer consists of five units namely unit I, II, III, IV, and V, which range in thickness from 1 to 4 centimeters. The unit I is composed of coarse sand to medium sand sized volcanic materials, and shows normal grading. The basal boundry is comformable. The depositional process of the unit I is derived from direct pyroclastic air fall deposition. The unit II, III and IV are composed of very coarse sand to silt sized volcanic materials, show normal grading with parallel- and cross-lamination and form incomplete Bouma Sequence (e.g. Ta, Tb, Tc, Td). These units show laterally discontinuation and changes of thickness and basal boundaries are erosive. Mud clasts included in unit II and III are divided into two types. One is white and is composed of silt sized volcaniclastics, and the other is black to dark gray and consists of non-volcaniclastic materials. Both mud clasts are interpreted as rip up clasts. These characteristics are suggestive of a turbidite, and therefore, the depositional process of the unit II, III and IV is derived from resedimentation by turbidity current on the bay floor rather than from direct pyroclastic air-fall deposition. The unit V consists of alternating beds of thin volcanic materials and mud layers. This unit is the distal facies of turbidites.

DOI： 10.15080/agcjchikyukagaku.55.3_173

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

Hyperconcentrated flow deposit, in the Ebisutoge-Fukuda tephra from Mie Prefecture, is thought to be deposited from dilution of the debris flow. Debris-flow deposit (facies A) is overlain by hyperconcentrated flow deposit (facies B). Typical hyperconcentrated flow deposit (facies B1 ; horizontal bedding part) changes upward into diluted hyperconcentrated flow deposit (facies B2 ; scour and fill structure part). These facies characteristics indicate that the debris flow changed through hyperconcentrated flow into normal streamflow by dilution during flow traveling.

DOI： 10.5575/geosoc.106.897

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Other Link： http://hdl.handle.net/10191/17814

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.5575/geosoc.106.189

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Language：Japanese   Publisher：経済産業省産業技術総合研究所地質調査所  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Association for Quaternary Research  

In the distal areas from Quaternary volcanoes, like the Shikoku, Kinki and Tokai districts of western Japan, studies on terraces have not progressed due to lack of visible volcanic ash. Those studied were mainly approached from the geomorphological point of view, and therefore it is difficult to determine absolute ages and correlations between terraces. In the Suzuka river area, which is located in the west coast area of Ise Bay, there are no reports on terrace deposits with intercalated volcanic ash layers or on the absolute age of terraces.<br>In this study, we took a comprehensive approach, integrating aerial-photo interpretation, investigation on the geology and geomorphic features, and analysis of volcanic glasses which are included in finer deposits overlying the terrace gravels. (Finer deposits here means those mainly consist of eolian deposits and formed after terracing.) The following results were obtained.<br>1. The terraces of the Suzuka river area are classified into five, namely, Otani-ike terrace, Maruoka-ike terrace, Kambe terrace, Seki terrace, and Furu-umaya terrace in descending order of elevation. Kambe terrace is further subdivided into three terraces named Kambe 1, Kambe 2, and Kambe 3. Seki terrace is also subdivided, into Seki 1 and Seki 2.<br>2. Finer deposits overlying terrace gravels can be characterized by their color. At Otani-ike terrace and Maruoka-ike terrace, finer deposits are subdivided into reddish brown, yellowish brown, and dark brown units in ascending order. And at Kambe terrace, finer deposits are subdivided into yellowish brown and dark brown units in ascending order. At both Seki terrace and Furu-umaya terrace, all finer deposits show dark brown to black color.<br>3. At Otani-ike terrace and Maruoka-ike terrace, reddish brown units contain few volcanic glass. The yellowish brown units in Otani-ike terrace, Maruoka-ike terrace, and Kambe terrace include volcanic glasses that can be correlated with Aira-Tn volcanic ash (25-21ka). The blackish units in Otani-ike terrace, Maruoka-ike terrace, Kambe terrace, Seki terrace, and Furu-umaya terrace contain volcanic glasses which derived from Kikai-Akahoya volcanic ash (6.3ka).<br>4. In Seki terrace deposit, one tephra layer was identified with Aira-Tn volcanic ash. A previous study reported intercalation of marine clay in the Kambe terrace deposit. Together with the characteristics of volcanic glasses included in finer deposits, it is clear that Otani-ike and Maruoka-ike terrace deposits were formed before the Last Interglacial, Kambe terrace deposit during the Last Interglacial, Seki terrace deposit during the Last Glacial, and Furu-umaya terrace deposit after the Last Glacial.

DOI： 10.4116/jaqua.36.263

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Language：English   Publishing type：Internal/External technical report, pre-print, etc.  

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Language：Japanese   Publisher：京都大学防災研究所  

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Language：Japanese   Publisher：新潟大学災害・復興科学研究所  

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Language：Japanese   Publisher：新潟大学災害・復興科学研究所  

2013年度の共同研究では，山形県肘折カルデラの約1.2万年前の火砕流噴火を対象として，1）火砕流堆積物と降下テフラ層の層相記載，2）堆積物に含まれる軽石・火山ガラス・鉱物の岩石学的検討，3）地形調査と地中レーダ（GPR）探査に基づき火砕流堆積物および二次堆積物の内部構造と堆積過程を明らかにした．この噴火は背弧域（日本海側）での突発的な火砕流噴火であり，本研究の成果は多雪地域かつ高流量の河川系への災害予測・対策のための基礎資料となる．

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Language：Japanese   Publisher：新潟大学災害・復興科学研究所  

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Language：Japanese   Publisher：新潟大学災害・復興科学研究所  

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Language：Japanese   Publisher：日本堆積学会  

DOI： 10.4096/jssj.71.69

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Language：English  

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Language：Japanese   Publisher：新潟大学災害復興科学センター  

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Other Link： http://hdl.handle.net/10191/5965

Language：Japanese   Publisher：海洋出版  

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Language：Japanese  

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Language：Japanese   Publisher：新潟応用地質研究会  

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Language：Japanese   Publisher：東北大学大学院工学研究科東北地区自然災害資料センター  

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Language：Japanese   Publisher：Niigata University  

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Other Link： http://hdl.handle.net/10191/39267

Language：Japanese   Publisher：Niigata University  

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Other Link： http://hdl.handle.net/10191/39266

Language：Japanese   Publisher：Niigata University  

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Other Link： http://hdl.handle.net/10191/39274

Language：Japanese   Publisher：Niigata University  

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Other Link： http://hdl.handle.net/10191/39260

Language：Japanese   Publisher：Niigata University  

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Event date： 2016

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Language：Japanese  

Catastrophic outburst floods by a breach of volcanic dam or caldera rim tend to be hazardous with voluminous impounded water and loose unconsolidated pyroclastic material. Such extreme floods can travel long distance from the source volcano that ultimately affect landform and hydrology of downstream areas and eventually threaten human life and economy. Tohoku area hosting active volcanoes is susceptible for such a catastrophic flood by dam break as shown by two examples from Numazawa and Towada calderas.

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Event date： 2011

Holocene terrace and meander belt formation in the Tsugaru Plain, North east Japan

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Event date： 2008.9

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Language：English   Presentation type：Oral presentation (invited, special)  

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Language：English   Presentation type：Oral presentation (keynote)  

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Language：Japanese   Presentation type：Oral presentation (invited, special)  

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Language：English   Presentation type：Oral presentation (invited, special)  

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