Pub Date : 2021-12-25DOI: 10.5026/jgeography.130.783
Yasushi Daita, T. Ohba, Muga Yaguchi, Takao Sogo, M. Harada
Earthquake swarms have occurred with volcanism repeatedly at Hakone volcano in Kanagawa prefecture, Japan. In 2015, a phreatic eruption took place about two months after the start of an earthquake swarm. Hakone volcano is a popular tourist destination. If it is possible to forecast at the early stages of an earthquake swarm whether or not an eruption will occur, the forecast could contribute to preventing disasters involving tourists. At Hakone volcano, increases in the ratio of components (CO2 /H2S) contained in the volcanic gas from fumaroles were observed in synchronization with earthquake swarms and ground deformation in 2013 and 2015. Similar increases in CO2 /H2S ratio were also observed in 2017 and 2019, although the increases in the CO2 /H2S ratio in 2017 and 2019 were not as sharp as those in 2013 and 2015. Furthermore, the maximum values of the CO2 /H2S ratio in 2017 and 2019 were lower than the values in 2013 and 2015. These differences in the CO2 /H2S ratio may be related to the limited and smaller scale of volcanic activity in 2017 and 2019 relative to 2013 and 2015. Another explanation for the difference is a possible irreversible change in the underground structure of the Owakudani area, which is a geothermal area around Hakone volcano, because the phreatic eruption took place in the Owakudani area in 2015. During all four seismically active periods in 2013, 2015, 2017, and 2019, the CO2 /H2S ratio decreased simultaneously with decreases in the number of volcanic earthquakes. The lower limit of CO2 /H2S ratios after the peak of the CO2 /H2S ratio time series was about 20 in all periods. This implies that subsequent unrest would not start until the CO2 /H2S ratio drops to about 20. The CO2 /H2S ratio might be an effective tool for forecasting activity at Hakone volcano. During the active periods in 2013, 2015, 2017, and 2019, extensions * 神奈川県環境科学センター ** 東海大学理学部化学科 *** 気象庁気象研究所火山研究部 **** 神奈川県温泉地学研究所 * Kanagawa Environmental Research Center, Hiratsuka, 254-0014, Japan ** Department of Chemistry, School of Science, Tokai University, Hiratsuka, 259-1292, Japan *** Department of Volcanology Research, Meteorological Research Institute, Japan Meteorological Agency, Tsukuba, 305-0052, Japan **** Hot Springs Research Institute of Kanagawa Prefecture, Odawara, 250-0031, Japan 地学雑誌 Journal of Geography(Chigaku Zasshi) 130(6)783796 2021 doi:10.5026/jgeography.130.783
{"title":"Volcanic Activity Forecast Based on Volcanic Gas Composition of Hakone Volcano, Japan: Utilization for Volcanic Disaster Prevention","authors":"Yasushi Daita, T. Ohba, Muga Yaguchi, Takao Sogo, M. Harada","doi":"10.5026/jgeography.130.783","DOIUrl":"https://doi.org/10.5026/jgeography.130.783","url":null,"abstract":"Earthquake swarms have occurred with volcanism repeatedly at Hakone volcano in Kanagawa prefecture, Japan. In 2015, a phreatic eruption took place about two months after the start of an earthquake swarm. Hakone volcano is a popular tourist destination. If it is possible to forecast at the early stages of an earthquake swarm whether or not an eruption will occur, the forecast could contribute to preventing disasters involving tourists. At Hakone volcano, increases in the ratio of components (CO2 /H2S) contained in the volcanic gas from fumaroles were observed in synchronization with earthquake swarms and ground deformation in 2013 and 2015. Similar increases in CO2 /H2S ratio were also observed in 2017 and 2019, although the increases in the CO2 /H2S ratio in 2017 and 2019 were not as sharp as those in 2013 and 2015. Furthermore, the maximum values of the CO2 /H2S ratio in 2017 and 2019 were lower than the values in 2013 and 2015. These differences in the CO2 /H2S ratio may be related to the limited and smaller scale of volcanic activity in 2017 and 2019 relative to 2013 and 2015. Another explanation for the difference is a possible irreversible change in the underground structure of the Owakudani area, which is a geothermal area around Hakone volcano, because the phreatic eruption took place in the Owakudani area in 2015. During all four seismically active periods in 2013, 2015, 2017, and 2019, the CO2 /H2S ratio decreased simultaneously with decreases in the number of volcanic earthquakes. The lower limit of CO2 /H2S ratios after the peak of the CO2 /H2S ratio time series was about 20 in all periods. This implies that subsequent unrest would not start until the CO2 /H2S ratio drops to about 20. The CO2 /H2S ratio might be an effective tool for forecasting activity at Hakone volcano. During the active periods in 2013, 2015, 2017, and 2019, extensions * 神奈川県環境科学センター ** 東海大学理学部化学科 *** 気象庁気象研究所火山研究部 **** 神奈川県温泉地学研究所 * Kanagawa Environmental Research Center, Hiratsuka, 254-0014, Japan ** Department of Chemistry, School of Science, Tokai University, Hiratsuka, 259-1292, Japan *** Department of Volcanology Research, Meteorological Research Institute, Japan Meteorological Agency, Tsukuba, 305-0052, Japan **** Hot Springs Research Institute of Kanagawa Prefecture, Odawara, 250-0031, Japan 地学雑誌 Journal of Geography(Chigaku Zasshi) 130(6)783796 2021 doi:10.5026/jgeography.130.783","PeriodicalId":45817,"journal":{"name":"Journal of Geography-Chigaku Zasshi","volume":null,"pages":null},"PeriodicalIF":0.3,"publicationDate":"2021-12-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43410278","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-12-25DOI: 10.5026/jgeography.130.719
K. Mannen, Y. Yukutake, R. Doke, D. Hirata
Owakudani, the eruption center of the 2015 eruption of Hakone Volcano, is one of the most popular tourist destinations in Japan, attracting more than three million visitors every year. However, the new crater created by the eruption is only 200 m from an area where tourists stroll (e.g., Mannen et al., 2018). Moreover, several craters that are assumed to have been the sources of ancient phreatic eruptions much larger than the 2015 eruption have been recognized near Owakudani using topographic and geological analyses (e.g., Yamaguchi et al., 2021). On the other hand, a slight inflation of the volcanic edifice and an increase in seismic activity, as observed before the 2015 eruption, are not rare in Hakone volcano. Indeed, they have been occurring once every few years since 2001. Because sightseeing at Owakudani is valuable for the local economy, it is not practical to designate the area as restricted every time seismic activity increases. Consequently, it is important to understand the processes of volcanic eruptions and to evaluate the imminence of an eruption in order to minimize economic losses, while ensuring the safety of tourists and residents. In addition to analyzing the 2015 eruption, the Hot Springs Research Institute of Kanagawa Prefecture, which has been engaged in research on Hakone volcano for many years, has been surveying the latest studies related to phreatic eruptions to consider the direction of future research on volcano monitoring. Activities include publishing a special issue in an international journal named Earth, Planets and Space (Mannen et al., 2019) and hosting domestic and international workshops on phreatic eruptions (Abe, 2019; Man nen and Kato, 2020). This special issue contains presentations given at the International Workshop on Phreatic Eruption Mechanisms, which was co-organized with the Kanagawa Prefectural Museum of Natural History in January 2020 with support from local companies and organizations, the Town of Hakone, and the Tokyo Geographical Society, as well as papers based on subsequent research. The contents of the special issue are as follows. Yukutake and Mannen (2021) summarize the latest research on hydrothermal systems, which are largely responsible for the occurrence of phreatic eruptions. In this review, they focus on the formation of low-permeable layers in hydrothermal systems. The shallow impermeable layer is formed of clay minerals generated by hydrothermal alteration, and can be detected with magnetotelluric surveys as low resistivity bodies. The deeper impermeable layer is thought to be formed by silica precipitation, 地学雑誌 Journal of Geography(Chigaku Zasshi) 130(6)719723 2021 doi:10.5026/jgeography.130.719
Owakudani是2015年箱根火山爆发的喷发中心，是日本最受欢迎的旅游目的地之一，每年吸引300多万游客。然而，火山喷发产生的新火山口距离游客漫步的区域只有200米（例如，Mannen等人，2018）。此外，通过地形和地质分析，在Owakudani附近发现了几个被认为是比2015年火山喷发大得多的古代潜水喷发源的火山口（例如，Yamaguchi等人，2021）。另一方面，2015年火山爆发前观察到的火山建筑轻微膨胀和地震活动增加在箱根火山并不罕见。事实上，自2001年以来，这种情况每隔几年就会发生一次。由于Owakudani的观光对当地经济很有价值，因此每次地震活动增加时都将该地区指定为限制区是不现实的。因此，重要的是要了解火山爆发的过程，并评估火山爆发的紧迫性，以最大限度地减少经济损失，同时确保游客和居民的安全。除了分析2015年的火山喷发，多年来一直从事箱根火山研究的神奈川县温泉研究所一直在调查与潜水喷发有关的最新研究，以考虑未来火山监测研究的方向。活动包括在一本名为《地球、行星和太空》的国际期刊上发表特刊（Mannen et al.，2019），并举办关于潜水喷发的国内和国际研讨会（Abe，2019；Mannen和Kato，2020）。本特刊包含在2020年1月与神奈川县自然历史博物馆联合举办的潜水喷发机制国际研讨会上发表的演讲，以及基于后续研究的论文。该研讨会得到了当地公司和组织、箱根镇和东京地理学会的支持。特刊的内容如下。Yukutake和Mannen（2021）总结了热液系统的最新研究，热液系统是潜水喷发发生的主要原因。在这篇综述中，他们专注于水热系统中低渗透层的形成。浅层不透水层由热液蚀变产生的粘土矿物形成，可以通过大地电磁测量作为低电阻率体进行探测。更深的不可渗透层被认为是通过二氧化硅沉淀形成的，地学雑誌 地理杂志（Chigaku Zasshi）130（6）719723 2021 doi:10.5026/jgeography.130.719
{"title":"Overview of the Special Issue “Mechanism of Phreatic Eruptions and Challenges for Eruption Forecasting: Latest Advances and Volcanic Disaster Prevention”","authors":"K. Mannen, Y. Yukutake, R. Doke, D. Hirata","doi":"10.5026/jgeography.130.719","DOIUrl":"https://doi.org/10.5026/jgeography.130.719","url":null,"abstract":"Owakudani, the eruption center of the 2015 eruption of Hakone Volcano, is one of the most popular tourist destinations in Japan, attracting more than three million visitors every year. However, the new crater created by the eruption is only 200 m from an area where tourists stroll (e.g., Mannen et al., 2018). Moreover, several craters that are assumed to have been the sources of ancient phreatic eruptions much larger than the 2015 eruption have been recognized near Owakudani using topographic and geological analyses (e.g., Yamaguchi et al., 2021). On the other hand, a slight inflation of the volcanic edifice and an increase in seismic activity, as observed before the 2015 eruption, are not rare in Hakone volcano. Indeed, they have been occurring once every few years since 2001. Because sightseeing at Owakudani is valuable for the local economy, it is not practical to designate the area as restricted every time seismic activity increases. Consequently, it is important to understand the processes of volcanic eruptions and to evaluate the imminence of an eruption in order to minimize economic losses, while ensuring the safety of tourists and residents. In addition to analyzing the 2015 eruption, the Hot Springs Research Institute of Kanagawa Prefecture, which has been engaged in research on Hakone volcano for many years, has been surveying the latest studies related to phreatic eruptions to consider the direction of future research on volcano monitoring. Activities include publishing a special issue in an international journal named Earth, Planets and Space (Mannen et al., 2019) and hosting domestic and international workshops on phreatic eruptions (Abe, 2019; Man nen and Kato, 2020). This special issue contains presentations given at the International Workshop on Phreatic Eruption Mechanisms, which was co-organized with the Kanagawa Prefectural Museum of Natural History in January 2020 with support from local companies and organizations, the Town of Hakone, and the Tokyo Geographical Society, as well as papers based on subsequent research. The contents of the special issue are as follows. Yukutake and Mannen (2021) summarize the latest research on hydrothermal systems, which are largely responsible for the occurrence of phreatic eruptions. In this review, they focus on the formation of low-permeable layers in hydrothermal systems. The shallow impermeable layer is formed of clay minerals generated by hydrothermal alteration, and can be detected with magnetotelluric surveys as low resistivity bodies. The deeper impermeable layer is thought to be formed by silica precipitation, 地学雑誌 Journal of Geography(Chigaku Zasshi) 130(6)719723 2021 doi:10.5026/jgeography.130.719","PeriodicalId":45817,"journal":{"name":"Journal of Geography-Chigaku Zasshi","volume":null,"pages":null},"PeriodicalIF":0.3,"publicationDate":"2021-12-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44410681","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-12-25DOI: 10.5026/jgeography.130.731
Y. Yukutake, K. Mannen
A phreatic eruption is a phenomenon in which water near the surface expands rapidly due to magma-supplied heat, ejecting the surrounding rocks. Recent studies of conceptual models, subsurface structures, pre-eruption processes, and eruption processes of phreatic eruptions are reviewed. These eruptions often occur in volcanoes with well-developed hydrothermal systems, where a low electrical resistivity layer is found near the surface using magnetotelluric surveys. The low resistivity layer indicates a low-permeability structure that acts as a pressure-confining cap on the hydrothermal system. In the brittle-ductile transition zone above deep magma, a sealing structure associated with quartz crystallization develops. Volcanoes with open conduits that connect magma reservoir and surface crater also have the potential for phreatic eruptions. A low-permeable sealing structure in the shallow part of the conduit plays an important role in eruptions of this type of volcano. Phreatic eruptions are prepared by an imbalance in the hydrothermal system, which is caused by increases of heat, volcanic gases, and fluids from the deep magma reservoir, and are triggered by depressurization of the aquifer due to the breakdown of the cap/sealing structure. In recent years, eruptive processes have been modeled using data from broadband seismograms and tiltmeters near vents. At Ontake, Hakone, and Aso volcanoes, slow crustal movements or very low-frequency earthquakes were observed just prior to phreatic eruptions. These phenomena result from crack opening due to the rapid vaporization of liquid water. Incremental seismic activities, low-frequency earthquakes, and expansion of volcanic edifice, and geochemical changes in volcanic gases and hot springs are identified as long-term eruption precursors. These precursors reflect the supply of new magma, related changes in volcanic gases, and increased fluid pressure in shallow hydrothermal systems. Several new techniques for monitoring volcanoes to detect temporal changes in resistivity, crustal deformation, and chemical composition of hot springs and groundwater have been developed for forecasting eruptions.
{"title":"Observations of Hydrothermal System and Preparatory Process of Phreatic Eruption: Recent Developments and Future Prospects","authors":"Y. Yukutake, K. Mannen","doi":"10.5026/jgeography.130.731","DOIUrl":"https://doi.org/10.5026/jgeography.130.731","url":null,"abstract":"A phreatic eruption is a phenomenon in which water near the surface expands rapidly due to magma-supplied heat, ejecting the surrounding rocks. Recent studies of conceptual models, subsurface structures, pre-eruption processes, and eruption processes of phreatic eruptions are reviewed. These eruptions often occur in volcanoes with well-developed hydrothermal systems, where a low electrical resistivity layer is found near the surface using magnetotelluric surveys. The low resistivity layer indicates a low-permeability structure that acts as a pressure-confining cap on the hydrothermal system. In the brittle-ductile transition zone above deep magma, a sealing structure associated with quartz crystallization develops. Volcanoes with open conduits that connect magma reservoir and surface crater also have the potential for phreatic eruptions. A low-permeable sealing structure in the shallow part of the conduit plays an important role in eruptions of this type of volcano. Phreatic eruptions are prepared by an imbalance in the hydrothermal system, which is caused by increases of heat, volcanic gases, and fluids from the deep magma reservoir, and are triggered by depressurization of the aquifer due to the breakdown of the cap/sealing structure. In recent years, eruptive processes have been modeled using data from broadband seismograms and tiltmeters near vents. At Ontake, Hakone, and Aso volcanoes, slow crustal movements or very low-frequency earthquakes were observed just prior to phreatic eruptions. These phenomena result from crack opening due to the rapid vaporization of liquid water. Incremental seismic activities, low-frequency earthquakes, and expansion of volcanic edifice, and geochemical changes in volcanic gases and hot springs are identified as long-term eruption precursors. These precursors reflect the supply of new magma, related changes in volcanic gases, and increased fluid pressure in shallow hydrothermal systems. Several new techniques for monitoring volcanoes to detect temporal changes in resistivity, crustal deformation, and chemical composition of hot springs and groundwater have been developed for forecasting eruptions.","PeriodicalId":45817,"journal":{"name":"Journal of Geography-Chigaku Zasshi","volume":null,"pages":null},"PeriodicalIF":0.3,"publicationDate":"2021-12-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43571824","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
箱根火山2015年喷发中心的大涌谷，是国内屈指可数的每年有300万游客到访的观光地，但由于这次喷发而新产生的火山口，距离游客散步的区域只有200米左右（例如，Mannen et al.，2018）。另外，在大涌谷附近，发现了多个火山口地形（例如山口等，2021），认为是比2015年喷发规模更大的水蒸气喷发的供给源。因此，在喷发前采取限制入内等防灾行动从保护人命的观点来看是极其重要的。另一方面，箱根火山山体的轻微膨胀和地震活动的活跃化并不一定是罕见的现象，2001年以后以几年一次的频率发生。因此，在每次活跃的时候进行经济损失大的限制是很难的。为了保护游客和居民的生命，采取最小化经济损失的火山防灾对策，理解喷发过程，评价喷发的紧迫度是很重要的。长年从事箱根火山研究的神奈川县温泉地学研究所，在分析2015年喷发的同时，根据上述问题意识，在英文杂志Earth、Planets and Space上编辑了特集号（Mannen et al.，2019），通过研究集会的实施，为了探讨今后的研究和火山监视的方向性，努力收集必要的知识（安部，2019；万年·加藤，2020）。本特集号收录了在当地企业·团体、箱根町以及东京地学协会的资助下，于2020年1月与神奈川县立生命之星·地球博物馆共同举办的“关于水蒸气喷发机制的国际沃克商店”上进行的演讲，以及以之后的研究为基础的论文。行竹·万年（2021）整理了与水蒸气喷发的发生有很大关系的热水系统的见解的综述中，着眼于热水系统中发展的难透水层，在浅部由于变质粘土矿物的发展，在深部由于二氧化硅的结晶而形成难透水层，列举了关于各个难透水层的观测事例。浅部的难透水层由热水变质产生的粘土矿物形成，作为低比电阻体，通过电磁探测检测出特集号“水蒸气喷发的机理和火山喷发预知的课题—最新的见解和火山防灾—”卷头言
{"title":"Preface for the Special Issue “Mechanism of Phreatic Eruptions and Challenges for Eruption Forecasting: Latest Advances and Volcanic Disaster Prevention”","authors":"K. Mannen, Y. Yukutake, R. Doke, D. Hirata","doi":"10.5026/jgeography.130.725","DOIUrl":"https://doi.org/10.5026/jgeography.130.725","url":null,"abstract":"箱根火山 2015年噴火の噴出中心となった大涌 谷は,年間 300万人の観光客が訪れるとされる 国内有数の観光地であるが,この噴火で新たに生 じた火口は,観光客が散策する領域からわずか 200 mほどしか離れていない(例えば, Mannen et al., 2018)。また,大涌谷の近傍には,2015年 噴火よりもはるかに大規模な水蒸気噴火の給源と なったと考えられる火口地形が複数認められる (例えば, 山口ほか, 2021)。こうしたことから, 噴火前に立入規制などの防災行動をとることは人 命保護の観点からきわめて重要である。一方,箱 根火山では山体のわずかな膨張や地震活動の活発 化は必ずしも珍しい現象ではなく,2001年以降 は数年に 1度の頻度で発生している。したがっ て,活発化のたびに経済的な損失の大きい規制を 行うのは難しい。観光客や住民の生命を守りつ つ,経済的な損失を最小化する火山防災対応をと るためには,噴火にいたる過程を理解して,噴火 の切迫度を評価することは重要である。箱根火山 の研究に長年従事している神奈川県温泉地学研究 所では 2015年噴火の解析を行うことと並行して, 上のような問題意識に基づいて,英文誌 Earth, Planets and Spaceでの特集号編集や(Mannen et al., 2019),研究集会の実施を通じて,今後の 研究や火山監視の方向性を検討するために必要な 知見の集約に努めている(安部, 2019; 萬年・加藤, 2020)。本特集号は,地元企業・団体,箱根町お よび東京地学協会の助成を受けて,2020年 1月 に神奈川県立生命の星・地球博物館と共催で実施 した「水蒸気噴火のメカニズムに関する国際ワー クショップ」で行われた講演や,その後の研究を 基にした論文を収録する。 行竹・萬年(2021)が,水蒸気噴火の発生に 大きく関わる熱水系に関する知見を整理した総説 では,熱水系に発達する難透水層に着目し,浅部 では変質粘土鉱物の発達による,深部ではシリカ の晶出による難透水層が形成されるとし,それぞ れの難透水層に関する観測事例を列挙している。 浅部の難透水層は熱水変質で生じる粘土鉱物によ り形成され,低比抵抗体として電磁探査で検知で 特集号「水蒸気噴火のメカニズムと噴火予知への課題 ─最新の知見と火山防災─」巻頭言","PeriodicalId":45817,"journal":{"name":"Journal of Geography-Chigaku Zasshi","volume":null,"pages":null},"PeriodicalIF":0.3,"publicationDate":"2021-12-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43719236","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-12-25DOI: 10.5026/jgeography.130.831
K. Mannen
― 831 ― Abstract Hakone volcano has been in an active phase since 2001, as implied by frequent volcanic unrest every 2 5 years, with each accompanied by deep inflation （ 6 10 km ） , increase of deep low-frequency events （ DLFEs ） at a depth of ~20 km, increase of CO 2 /H 2 S ratio in fumarole gas, and surge of volcano tectonic earthquakes （ VT; < 6 km deep ） . A series of episodes of volcanic unrest culminated in a small phreatic eruption （ erupted volume; ~100 m 3 ） in 2015; however, lesser unrest in terms of seismic activity occurred in 2017 and 2019. Recent studies on crustal structures based on seismic tomography indicate a magma chamber 10 20 km beneath the volcano, which might be connected to a large magma chamber beneath Fuji volcano, approxi-mately 30 km NW of Hakone. Interestingly, the DLFEs beneath Hakone volcano seem to take place in a high attenuation zone that connects the magma chambers. Deep inflation beneath Hakone volcano, however, is clearly located at a shallower location than the magma chamber of Hakone. The increases of CO 2 and He within the fumarole of Hakone during its unrest may indicate degassing of magma at depth. The maximum fumarole temperature after the eruption and constraints on subsurface temperature （ ~200°C at 400 m deep indicated by the mineral assemblage and ~370°C at 4 km below sea level where is the lower depth limit of VT ） imply a vapor-dominated hydrothermal system in the volcano from the bottom of the cap structure （ ~100 m deep ） to a depth of possibly 2 4 km. Such a vapor-dominated system may allow rapid transfers of magmatic gases and their emission from the fumarole area in the very early phase of volcanic unrest, as was observed. Hakone lacks long period events （ LF ） and volcanic tremors, which are common at many active volcanoes. Because such events are considered to be related to fluid migration, the vapor-dominated system can be attributed to their absence in Hakone. An estimation of the water mass balance implies that the amount and rate of inflation in the hydrothermal system are comparable to those emitted from the fumarole area in pre-eruptive calm periods. Thus, continuous inflation at depth can be explained by crystal depositions from the hydro thermal fluid. The high temperature of steam emitted in the fumarole area after the eruption indicates destruction of the container of the hydrothermal system, which also caused the lower VT activity and CO 2 /H 2 S
{"title":"Magma-hydrothermal System of Hakone Volcano","authors":"K. Mannen","doi":"10.5026/jgeography.130.831","DOIUrl":"https://doi.org/10.5026/jgeography.130.831","url":null,"abstract":"― 831 ― Abstract Hakone volcano has been in an active phase since 2001, as implied by frequent volcanic unrest every 2 5 years, with each accompanied by deep inflation （ 6 10 km ） , increase of deep low-frequency events （ DLFEs ） at a depth of ~20 km, increase of CO 2 /H 2 S ratio in fumarole gas, and surge of volcano tectonic earthquakes （ VT; < 6 km deep ） . A series of episodes of volcanic unrest culminated in a small phreatic eruption （ erupted volume; ~100 m 3 ） in 2015; however, lesser unrest in terms of seismic activity occurred in 2017 and 2019. Recent studies on crustal structures based on seismic tomography indicate a magma chamber 10 20 km beneath the volcano, which might be connected to a large magma chamber beneath Fuji volcano, approxi-mately 30 km NW of Hakone. Interestingly, the DLFEs beneath Hakone volcano seem to take place in a high attenuation zone that connects the magma chambers. Deep inflation beneath Hakone volcano, however, is clearly located at a shallower location than the magma chamber of Hakone. The increases of CO 2 and He within the fumarole of Hakone during its unrest may indicate degassing of magma at depth. The maximum fumarole temperature after the eruption and constraints on subsurface temperature （ ~200°C at 400 m deep indicated by the mineral assemblage and ~370°C at 4 km below sea level where is the lower depth limit of VT ） imply a vapor-dominated hydrothermal system in the volcano from the bottom of the cap structure （ ~100 m deep ） to a depth of possibly 2 4 km. Such a vapor-dominated system may allow rapid transfers of magmatic gases and their emission from the fumarole area in the very early phase of volcanic unrest, as was observed. Hakone lacks long period events （ LF ） and volcanic tremors, which are common at many active volcanoes. Because such events are considered to be related to fluid migration, the vapor-dominated system can be attributed to their absence in Hakone. An estimation of the water mass balance implies that the amount and rate of inflation in the hydrothermal system are comparable to those emitted from the fumarole area in pre-eruptive calm periods. Thus, continuous inflation at depth can be explained by crystal depositions from the hydro thermal fluid. The high temperature of steam emitted in the fumarole area after the eruption indicates destruction of the container of the hydrothermal system, which also caused the lower VT activity and CO 2 /H 2 S","PeriodicalId":45817,"journal":{"name":"Journal of Geography-Chigaku Zasshi","volume":null,"pages":null},"PeriodicalIF":0.3,"publicationDate":"2021-12-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49485352","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-10-25DOI: 10.5026/jgeography.130.cover05_01
{"title":"The Tetori Group Exposed at Yunotani, Upstream on the Tedori River in Southwestern Mt. Hakusan","authors":"","doi":"10.5026/jgeography.130.cover05_01","DOIUrl":"https://doi.org/10.5026/jgeography.130.cover05_01","url":null,"abstract":"","PeriodicalId":45817,"journal":{"name":"Journal of Geography-Chigaku Zasshi","volume":null,"pages":null},"PeriodicalIF":0.3,"publicationDate":"2021-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44688698","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-10-25DOI: 10.5026/jgeography.130.633
Haruka Tani, M. Shishikura
We present the detailed distribution of liquefaction during the 1948 Fukui Earthquake in the central part of Fukui City by interpreting air-photographs taken immediately after the earthquake. Comparing this result with the liquefaction hazard map published by Fukui City, the actual distribution of liquefaction is not consistent with the risk assessment. The reason for this contradiction is that because the liquefaction hazard map of Fukui City was evaluated based only on information about the thickness of soft sediments. The results of the current study are also compared with geomorphic classification maps published by Geographical Information Authority of Japan, the land condition map, and the landform classification map for flood control （ the first edition and the updated edition ） , respectively. They show that the liquefaction distribution overlaps with micro-topography such as the former river channel and the natural levee where liquefaction is likely to occur. From these comparison results, the importance of considering micro-topography when preparing a liquefaction hazard map can be recognized, and it is effective to refer to previously published geomorphic classification maps. However, since these maps are created for various purposes and have slightly different interpretations of micro-topography, multiple maps should be integrated to assess liquefaction potential.
{"title":"Liquefaction Distribution in the Central Part of Fukui City during the 1948 Fukui Earthquake: Comparison of Micro-topographic Classification Map and Liquefaction Hazard Map","authors":"Haruka Tani, M. Shishikura","doi":"10.5026/jgeography.130.633","DOIUrl":"https://doi.org/10.5026/jgeography.130.633","url":null,"abstract":"We present the detailed distribution of liquefaction during the 1948 Fukui Earthquake in the central part of Fukui City by interpreting air-photographs taken immediately after the earthquake. Comparing this result with the liquefaction hazard map published by Fukui City, the actual distribution of liquefaction is not consistent with the risk assessment. The reason for this contradiction is that because the liquefaction hazard map of Fukui City was evaluated based only on information about the thickness of soft sediments. The results of the current study are also compared with geomorphic classification maps published by Geographical Information Authority of Japan, the land condition map, and the landform classification map for flood control （ the first edition and the updated edition ） , respectively. They show that the liquefaction distribution overlaps with micro-topography such as the former river channel and the natural levee where liquefaction is likely to occur. From these comparison results, the importance of considering micro-topography when preparing a liquefaction hazard map can be recognized, and it is effective to refer to previously published geomorphic classification maps. However, since these maps are created for various purposes and have slightly different interpretations of micro-topography, multiple maps should be integrated to assess liquefaction potential.","PeriodicalId":45817,"journal":{"name":"Journal of Geography-Chigaku Zasshi","volume":null,"pages":null},"PeriodicalIF":0.3,"publicationDate":"2021-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49068379","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-10-25DOI: 10.5026/jgeography.130.707
Tomohito Nakano, Y. Isozaki, Y. Tsutsumi
― 707 ― Abstract U Pb ages of detrital zircons are measured for two sandstones of the Domeki Formation （ Fm ） in the Shimanto belt, western Kochi, which represent bench deposits on the Paleogene fore-arc slope in SW Japan. The results show that both samples are replete with Paleocene and Late Cretaceous zircons, and they have extremely small quantities of pre-Cretaceous grains. This indicates that the provenance of the Domeki Fm was occupied mainly by felsic igneous rocks of the San-in belt in SW Japan, i.e., coeval volcanic arc. The age spectrum of zircons in the Domeki Fm is almost identical to those of coeval sandstones deposited in the main fore-arc basin （ uppermost Izumi Group in the Kii peninsula, and Kanohara Conglomerate/Yorii Fm in Kanto ） . This suggests the ubiquitous supply of terrigenous clastics of the monotonous composition into the Paleocene fore-arc domain, including both the main fore-arc basin at the continent side and minor bench basins at the trench side, for more than 80 km across the arc from the southern margin of the Ryoke belt to the central Shimanto belt. Also confirmed is the stable and continuous deposi-tion of voluminous arc-derived clastics on the fore-arc of SW Japan from the Late Cretaceous to Paleocene for more than 1000 km along the arc. The present data constrain the timings of two large-scale tectonic episodes in Paleogene SW Japan, i.e., the initiation of the Median Tectonic Line between the Ryoke and Sanbagawa belts and the first surface exposure of high-P/T Sanbagawa schists, to have been no earlier than Paleocene/Eocene boundary （ ca . 56
{"title":"New Constraints on the Distributary Pattern of Clastics in Fore-arc and Tectonics in Paleogene SW Japan: U–Pb Ages of Detrital Zircons of the Domeki Formation in the Shimanto Belt, Western Shikoku","authors":"Tomohito Nakano, Y. Isozaki, Y. Tsutsumi","doi":"10.5026/jgeography.130.707","DOIUrl":"https://doi.org/10.5026/jgeography.130.707","url":null,"abstract":"― 707 ― Abstract U Pb ages of detrital zircons are measured for two sandstones of the Domeki Formation （ Fm ） in the Shimanto belt, western Kochi, which represent bench deposits on the Paleogene fore-arc slope in SW Japan. The results show that both samples are replete with Paleocene and Late Cretaceous zircons, and they have extremely small quantities of pre-Cretaceous grains. This indicates that the provenance of the Domeki Fm was occupied mainly by felsic igneous rocks of the San-in belt in SW Japan, i.e., coeval volcanic arc. The age spectrum of zircons in the Domeki Fm is almost identical to those of coeval sandstones deposited in the main fore-arc basin （ uppermost Izumi Group in the Kii peninsula, and Kanohara Conglomerate/Yorii Fm in Kanto ） . This suggests the ubiquitous supply of terrigenous clastics of the monotonous composition into the Paleocene fore-arc domain, including both the main fore-arc basin at the continent side and minor bench basins at the trench side, for more than 80 km across the arc from the southern margin of the Ryoke belt to the central Shimanto belt. Also confirmed is the stable and continuous deposi-tion of voluminous arc-derived clastics on the fore-arc of SW Japan from the Late Cretaceous to Paleocene for more than 1000 km along the arc. The present data constrain the timings of two large-scale tectonic episodes in Paleogene SW Japan, i.e., the initiation of the Median Tectonic Line between the Ryoke and Sanbagawa belts and the first surface exposure of high-P/T Sanbagawa schists, to have been no earlier than Paleocene/Eocene boundary （ ca . 56","PeriodicalId":45817,"journal":{"name":"Journal of Geography-Chigaku Zasshi","volume":null,"pages":null},"PeriodicalIF":0.3,"publicationDate":"2021-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45253395","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-10-25DOI: 10.5026/jgeography.130.653
M. Matsukawa
The Tetori Group comprises significant Mesozoic （ middle Jurassic early Cretaceous ） marine and terrestrial strata in East Asia. A facies analysis of the group is conducted to reveal the development of the Tetori sedimentary basin. The Tetori Group in the Mt. Hakusan Region is mainly distributed in three areas: the Kuzuryugawa Area in Fukui Prefecture and the Shiramine and Shokawa districts in the Hakusan Area in Ishikawa and Gifu prefectures. Seven lithofacies associations are recognized, which represent the deposition in talus and proximal alluvial fan, gravelly braided river and alluvial fan, sandy braided river, lacustrine delta, estuarine, shoreface, and inner shelf environments. Based on the characters and spatio-temporal distribution of these lithofacies associations across the basin in the three areas, the group is interpreted to have developed in four stages. Stage 1 is represented by the lower part of the Tetori Group in the Kuzuryugawa Area in the southern part of the basin, and shows, in ascending order, talus and proximal alluvial fans, inner shelf, shoreface, and alluvial fan facies. Stage 2 represents the lower middle part of the group in the Shokawa District in the northeastern part of the basin, and shows a change from estuarine, shoreface to inner shelf, and back to shoreface facies. Stage 3 is recognized in the middle part of the group in both the Shiramine and Shokawa districts in the northwestern and northeastern parts of the basin, respectively. Stage 3 was initially formed as talus and proximal alluvial fan, gravelly braided river and alluvial fan, and sandy braided river facies, and was later changed to lacustrine delta, sandy braided river, and gravelly braided river and alluvial fan facies, and back to lacustrine delta and sandy braided river facies in ascending order in the Shiramine District, and was initially formed as estuary and shoreface facies, and was later changed to estuary, lacustrine delta and sandy braided river facies in ascending order in the Shokawa District. Stage 4 is represented by the upper part of the group in all three areas, and shows talus and alluvial fan, gravelly braided river and alluvial fan, and sandy braided river facies. The Tetori basin reflects an upheaval of the basin forming an inter-mountain basin. This supports the hypothesis of a juxtaposition of late Jurassic to earliest Cretaceous accretionary complexes along the eastern margin of the Asia continent during the Hauterivian （ Early Cretaceous ）
{"title":"Sedimentary Environments and Basin Development of the Middle Jurassic–Early Cretaceous Tetori Group in Its Main Area, Central Japan","authors":"M. Matsukawa","doi":"10.5026/jgeography.130.653","DOIUrl":"https://doi.org/10.5026/jgeography.130.653","url":null,"abstract":"The Tetori Group comprises significant Mesozoic （ middle Jurassic early Cretaceous ） marine and terrestrial strata in East Asia. A facies analysis of the group is conducted to reveal the development of the Tetori sedimentary basin. The Tetori Group in the Mt. Hakusan Region is mainly distributed in three areas: the Kuzuryugawa Area in Fukui Prefecture and the Shiramine and Shokawa districts in the Hakusan Area in Ishikawa and Gifu prefectures. Seven lithofacies associations are recognized, which represent the deposition in talus and proximal alluvial fan, gravelly braided river and alluvial fan, sandy braided river, lacustrine delta, estuarine, shoreface, and inner shelf environments. Based on the characters and spatio-temporal distribution of these lithofacies associations across the basin in the three areas, the group is interpreted to have developed in four stages. Stage 1 is represented by the lower part of the Tetori Group in the Kuzuryugawa Area in the southern part of the basin, and shows, in ascending order, talus and proximal alluvial fans, inner shelf, shoreface, and alluvial fan facies. Stage 2 represents the lower middle part of the group in the Shokawa District in the northeastern part of the basin, and shows a change from estuarine, shoreface to inner shelf, and back to shoreface facies. Stage 3 is recognized in the middle part of the group in both the Shiramine and Shokawa districts in the northwestern and northeastern parts of the basin, respectively. Stage 3 was initially formed as talus and proximal alluvial fan, gravelly braided river and alluvial fan, and sandy braided river facies, and was later changed to lacustrine delta, sandy braided river, and gravelly braided river and alluvial fan facies, and back to lacustrine delta and sandy braided river facies in ascending order in the Shiramine District, and was initially formed as estuary and shoreface facies, and was later changed to estuary, lacustrine delta and sandy braided river facies in ascending order in the Shokawa District. Stage 4 is represented by the upper part of the group in all three areas, and shows talus and alluvial fan, gravelly braided river and alluvial fan, and sandy braided river facies. The Tetori basin reflects an upheaval of the basin forming an inter-mountain basin. This supports the hypothesis of a juxtaposition of late Jurassic to earliest Cretaceous accretionary complexes along the eastern margin of the Asia continent during the Hauterivian （ Early Cretaceous ）","PeriodicalId":45817,"journal":{"name":"Journal of Geography-Chigaku Zasshi","volume":null,"pages":null},"PeriodicalIF":0.3,"publicationDate":"2021-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42324793","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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