著者

宝田 晋治 宮城 磯治 東宮 昭彦

出版者

特定非営利活動法人 日本火山学会

雑誌

日本火山学会講演予稿集 2018 (ISSN:24335320)

巻号頁・発行日

pp.116, 2018 (Released:2019-03-06)

被引用文献数

1

著者

小園 誠史

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.66, no.3, pp.135-146, 2021-09-30 (Released:2021-10-29)

参考文献数

16

著者

宮城 磯治 東宮 昭彦

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.47, no.6, pp.757-761, 2003-01-08 (Released:2017-03-20)

参考文献数

16

被引用文献数

3

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We developed a new thermometer that uses color of volcanic ashes. A series of heating experiments for basaltic ashes under the atmospheric condition provided a quantitative relationship among color, heating temperature, and heating duration. The higher the heating temperature, the more the redness in color of heated ash. We applied the relationship to estimate heated temperature of the ash that was underlying below or contact with a cauliflower-shaped volcanic bomb ejected from the Miyakejima volcano on 18 August, 2000. The estimated temperature was about 390℃ for the ash underlying 1 cm below the volcanic bomb, and 550℃ for the ash in contact with the bomb. Numerical heat transfer calculations for the volcanic bomb on the ash layer suggested that temperature of its center at the time of landing is about 1,000℃. This is the first concrete evidence that the bomb was essential material and that the 18 August eruption was phreatomagmatic.

著者

井田 喜明 山岡 耕春 渡辺 秀文

出版者

特定非営利活動法人 日本火山学会

雑誌

火山.第2集

巻号頁・発行日

vol.33, pp.S307-S318, 1988

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Various features of the eruption that began on November 15, 1986 in Izu-oshima volcano are examined to infer the underground magmatic activities and the mechanism of the eruption. A massive dike intrustion that is assumed to have happened at the same time as the fissure eruption cannot explain the seismicity, deformation and other evidence consistently. Another preferable model that gives a systematic explanation of the available data is proposed as follows. A magma reservoir was situated at a depth of about 5 km below a NW (north-western) flank of Izu-Oshima volcano. This magma reservoir supplied magma to the summit crater through a well-developed vent, and caused the first summit eruption under an enhanced NW-SE compressive component of the tectonic stress. As the magma reservoir deflated with the discharge of magma in this summit eruption, a compressive stress increased in the neighboring area centered at the northern rim of the caldera. The stress finally fractured this area with intense seismicity, and produced fissures. Along these fissures, the magma that had penetrated into interstital space between rocks effused explosively with bubbling of steam. The magma had been more or less cooled and chemically differentiated in the interstitial space so that the ejecta from this fissure eruption was more felsic. The deflation of the magma reservoir due to the summit and fissure eruption resulted in a significant subsidence of the NE part of the island. Strain associated with opening of the volcanic fissures was transmitted through a strike-slip fault to the SE part of the island, and caused a local extensional stress and graben there.

著者

鈴木 毅彦

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.40, no.3, pp.167-176, 1995

参考文献数

26

被引用文献数

4

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So-called kazanbaido which means volcanic-ash-soil in a literal translation overlies surfaces and hill slopes in most area of the Japanese island. In 1960's, the kazanbaido with massive structure and brown color was recognized as residual soil (not transported soil) which was originated from pyroclastic deposits. Recently, most studies regard the kazanbaido as soil formed through the accumulation of dispersal tephra, eolian dusts from the Asian continent and local eolian dusts. In this study, the author discusses the source of the material constructing kazanbaido on the basis of the pattern of change in its thickness (Fig. 1). The kazanbaido treated here has accumulated during the last 50,000 years in central Japan. Thickness of the kazanbaido distributed along the Japan Sea coast and in the south part of the Shizuoka Prefecture is less than 1 m. Source of the kazanbaido seems to be a lot of fine distal air-fall deposits which derived from distant volcanoes, a long-range transported eolian dust from the Asian continent, and local eolian dust from the adjacent non-vegetated area. Kazanbaido thicker than 2 m distributes in the South Kanto and North Kanto areas. Increase in the thickness of the kazanbaido in these areas is most likely caused by depositions of tephras derived from near volcanoes. Two main depositional processes of accumulation of the thick kazanbaido are as follows. One is frequent accumulation of a minor air-fall deposit associated with a small-scale eruption, which does not form stratification because of the small volume of each deposit. The other is accumulation of secondary tephras, which are derived from the slope of a volcano through wind transportation. Change in thickness in the Kanto area suggests that the former is more significant than the latter.

著者

荒牧 重雄

出版者

特定非営利活動法人 日本火山学会

雑誌

火山.第2集 (ISSN:24330590)

巻号頁・発行日

vol.8, no.3, pp.110-113, 1963-12-25 (Released:2018-01-15)

著者

堀田 耕平 髙橋 秀徳 本田 裕也 剣持 拓未

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.68, no.2, pp.83-89, 2023-06-30 (Released:2023-07-27)

参考文献数

21

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Leveling surveys were conducted in Jigokudani valley, Tateyama volcano, since 2015. Subsidence was revealed to have started in 2017‒2018 when a new crater was formed at southwestern area of Jigokudani. Subsidence kept until 2020. During the one-year period from September 2020 to September 2021, ground of Jigokudani was revealed to have re-uplifted. We applied five types of deformation sources (Mogi-type spherical, finite spherical, penny-shaped, rectangular tensile fault and prolate spheroid sources) to the detected deformation. Using the grid search method and the weighted least squares method, we searched the optimal combination of the parameters of each model. Based on the c-AIC value, the penny-shaped deformation source was the best model among them. A penny-shaped inflation source with a radius of 375 m was located including southeastern area of Jigokudani valley where violent fumarole activities have been continued. Its depth was 50 m from the surface. The pressure change in the source of +0.8 MPa yields its volume change of +4800 m3. Inflation of the gas chamber beneath Jigokudani valley might have started due to increase in accumulation of volcanic gas/fluid or decrease in fumarolic activity.

著者

松本 恵子 コンウェイ クリス 畑 真紀 伊藤 久敏 岩橋 くるみ 片岡 香子 森田 雅明 西原 歩 三反畑 修 渡部 将太 山﨑 誠子 長谷川 健

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.68, no.2, pp.115-123, 2023-06-30 (Released:2023-07-27)

参考文献数

7

著者

三反畑 修 綿田 辰吾 佐竹 健治 金森 博雄 Luis Rivera Zhongwen Zhan

出版者

特定非営利活動法人 日本火山学会

雑誌

日本火山学会講演予稿集 2020 (ISSN:24335320)

巻号頁・発行日

pp.6, 2020 (Released:2021-02-01)

著者

南 裕介 伊藤 順一 草野 有紀 及川 輝樹 大場 司

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.68, no.2, pp.39-57, 2023-06-30 (Released:2023-07-27)

参考文献数

39

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Akita-Yakeyama Volcano is an active stratovolcano located on Northeast Honshu island, Japan. Recent eruptive activity has occurred on the flank of the volcano in May 1997 and in the summit crater (Karanuma vent) in August 1997. These events indicate that Akita-Yakeyama Volcano has a high potential for future eruptions. In order to better understand the hazards posed by Akita-Yakeyama Volcano, this study focused on the modern explosive activity of Akita-Yakeyama during the last 6000 years. The authors conducted field observations and excavation surveys at outcrops, whole-rock chemical analysis, volcanic glass chemical analysis, and radiocarbon dating for intercalated paleosol layers. As a result, at least nine layers of pyroclastic fall deposits derived from Akita-Yakeyama during the last 6000 years were recognized, ranging from Volcanic Explosivity Index (VEI) levels of 1 to 2. In chronological order, the major pyroclastic fall deposits consist of AKY8 (45th to 47th century BC), AKY7 (10th to 29th century BC), AKY6 (2nd to 8th century BC), AKY5 (1st century BC to 2nd century AD), AKY4 (5th to 9th century AD), AKY3 (1678 AD), AKY2 (1892 AD), AKY1 (1951 AD) and 1997 eruption ejecta. The decreasing proportion of juvenile materials in eruptive deposits over the last 6000 years is consistent with a reduced magma contribution. It indicates that the development of the hydrothermal system is likely to play an important role in future eruption scenarios for Akita-Yakeyama Volcano.

著者

高橋 良 鈴木 隆広 大森 一人

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.67, no.4, pp.453-469, 2022-12-31 (Released:2023-01-30)

参考文献数

49

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In active geothermal areas, subsurface high-temperature thermal waters occasionally cause phreatic (hydrothermal) eruptions without any direct input of mass and energy from magma. So, understanding subsurface hydrothermal systems is critical to improving mitigation strategies for such hazards. The Noboribetsu geothermal area in Kuttara volcano, southwestern Hokkaido, has had repeated phreatic eruptions through the Holocene. In this study, to reveal the hydrothermal system beneath this geothermal area, we investigate (1) the chemical and isotopic compositions of thermal waters and fumarolic gases and (2) the characteristics of hydrothermally altered rocks in phreatic ejecta and around thermal water discharge areas. The chemical and isotopic features of the thermal waters indicate that the hydrothermal activity in this area is attributable to a deep thermal water with a Cl concentration of approximately 12,000 mg/L and a temperature>220 °C. The hydrothermally altered pyroclastic rocks in the phreatic ejecta often include vesicles filled with smectite, chlorite, and Ca-zeolite, implying that a low-permeability clay cap consisting of these minerals exists in the subsurface and impedes the ascent of the deep thermal water. The deep thermal water ascends partly to the shallow subsurface, causing separation of the vapor phase containing CO2 and H2S due to boiling, and the liquid phase discharges as neutral NaCl-type waters. In addition, absorption of the separated vapor phase by groundwater, with oxidation of H2S, leads to the formation of steam-heated acid-sulfate waters, which cause acid leaching and alunite precipitation in the shallow subsurface. The Hiyoriyama fumaroles are derived from the vapor separated from the deep thermal water at 140 °C. Phreatic (hydrothermal) eruptions in the Noboribetsu geothermal area are assumed to have occurred due to rapid formation of a vapor phase caused by a sudden pressure drop of the deep thermal water. Because such eruptions are likely to occur in this area in the future, we should perform efficient monitoring using the constructed model of the hydrothermal system.

著者

小山 真人

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.50, no.Special, pp.S289-S317, 2005-12-20 (Released:2017-03-20)

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A critical review was made on public communication/education of knowledge and information about volcanoes and their risk in Japan. Volcanic process can socially be divided into four periods: dormant, pre-emergency, emergency, and restoration/rehabilitation periods. For better mitigation of disasters during all these periods, knowledge and information about volcanoes should enough be shared among volcanologists, officials, and residents around volcanoes. Psychologists well studied the methodology of decision-making and public communication under various risks and many of the results can be applied to volcanic risk. Many volcanologists, however, do not well know the achievements by psychologists. Several Japanese volcanological terms, which have been traditionally used in the public information/education, are ambiguous and have potential for misunderstanding. Journalists often distort the information from volcanologists. The internet may provide a better place for direct risk-communication between volcanologists and residents around volcanoes. Volcanologists should systematically survey the residents and know what method of public communication is the best for sharing risk infomation. The author summarizes the present status of the Japanese system for risk evaluation and announcement during volcanic crises and reviews the problems, which were exposed during the recent volcanic crises in Japan. The author also reviews the status of risk education using hazard maps and/or other methods, which include outreach programs for citizens and schoolchildren.

著者

無盡 真弓

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.67, no.3, pp.389-399, 2022-09-30 (Released:2022-10-27)

参考文献数

62

著者

鈴木 由希

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.67, no.3, pp.409-423, 2022-09-30 (Released:2022-10-27)

参考文献数

33

著者

小林 哲夫

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.67, no.3, pp.335-350, 2022-09-30 (Released:2022-10-27)

参考文献数

90

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In the Kikai caldera, a major caldera-forming eruption, the Akahoya eruption (Ah eruption), occurred at 7.3 cal ka BP. It started with a plinian eruption (K-KyP), accompanied by a small intra-plinian Funakura pyroclastic flow (K-Fn). In the second eruptive stage, large Koya pyroclastic flow eruption (K-Ky) occurred, which covered the southern part of Kyushu with widespread co-ignimbrite ash (K-Ah (c)). These series of pyroclastic materials are collectively called Kikai-Akahoya tephra (K-Ah (T)). It has been thought that the Akahoya tsunami (Ah tsunami), occurred in connection with the Ah eruption. However, in outcrops below 50 m elevation in the proximal area of the caldera (~60 km), the K-Ah (T) was either replaced by Ah tsunami deposits of various sedimentary facies or completely eroded away by the same tsunami. The largest tsunami was therefore estimated to be due to the collapse of the caldera rim, which occurred some time after the end of the Ah eruption. On the other hand, in the Yokoo midden at Oita city, approximately 300 km from the caldera, it was considered that the K-Ah (c) was deposited immediately above the sandy tsunami deposit. However, the parent material of these distal Ah tsunami deposit is presumed to be K-Ah (r), which was transported and deposited from hinterland to the estuary, and was then incorporated and redeposited by the subsequent striking Ah tsunami. That is, the particles in the tsunami can be interpreted as separating and settling into two different layers, i.e. the basal sand layer and the upper K-Ah (r) set as the same tsunami deposit, due to differences in density. This interpretation is also supported by the chemical analyses of volcanic glass. Thus, the erosion and deposition either proximal or distal area of the caldera indicate that the largest Ah tsunami occurred some time after the Ah eruption. The caldera rim shows a double depression structure which was formed during the Ah eruption, and there are many channel structures on the caldera rim that suggest intense seawater movement. It is therefore highly probable that the sudden collapse of caldera wall after the Ah eruption is the cause of the tsunami, together with the run-up height near the caldera. However, it is not possible to estimate the time until the collapse that caused the Ah tsunami.

著者

馬場 章 藤井 敏嗣 吉本 充宏 千葉 達 渋谷 秀敏

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.67, no.3, pp.351-377, 2022-09-30 (Released:2022-10-27)

参考文献数

36

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Mt. Hoei (Hoei-zan) is a protuberance on the southeastern flank of the Fuji volcano, Japan. The lateral cone was formed during the Hoei eruption in AD 1707. However, the geological map of the Fuji volcano assigns the material of the protuberance to an older unit in the Hoshiyama Stage (100 to 17 ka); this is because the Akaiwa deposits around the summit have been altered in the same manner as rocks in the Hoshiyama Stage. This assignment has led to a model, unique in the context of modern volcanology, in which Mt. Hoei is an uplifted bulge caused by the intrusion of degassed magma that occurred at the time of the eruption; it thus led us to reinvestigate the geology of Mt. Hoei for the first time since Tsuya (1955). In addition to a geological survey, we obtained paleomagnetic directions from the Akaiwa and fallout deposits in the Goten-niwa erosional valley at the base of Mt. Hoei and compared the former with directions from the spatter cone that formed in the first Hoei crater during the final stage of the Hoei eruption. All the directions agreed well with each other and the archeomagnetic directions reported as corresponding to AD 1707, clearly indicating that the Akaiwa is not a part of the Hoshiyama Stage. We also performed petrographic and whole-rock chemical analyses of the deposits and found a gradual upward compositional change from dacite to basalt corresponding to the distal tephrostratigraphic units Ho-I to Ho-IV. This result shows that the Akaiwa deposits corresponded to the rocks of unit Ho-III, and both paleomagnetic and petrologic investigations strongly suggest that the former formed contemporaneously with the eruption. Therefore, the protuberance is not a bulge caused by the magmatic intrusion but a pyroclastic cone from the Hoei eruption.

著者

寺井 邦久

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.67, no.3, pp.319-333, 2022-09-30 (Released:2022-10-27)

参考文献数

27

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This paper presents a revised stratigraphy of the volcanic rocks, pyroclastic materials, and marine deposits transitional from the Pre-Unzen to Unzen volcanoes during the period of 1.9-0.3 Ma in the southern part of Shimabara Peninsula, Kyushu. The geological units, in ascending order, include the Kazusa Formation, Mejima Formation, Minami-Kushiyama Formation, Hojodake basalt, Saishoji Formation, Otani Formation, Kita-Arima Formation, Suwanoike basalt, Ideguchi Formation, Tonosaka andesite, Takaiwasan andesite, and Older Unzen volcanic fan deposits. Among these units, Saishoji and Kita-Arima Formations are shallow marine sediments deposited during a quiet period of volcanic activity, and the Otani Formation, an exotic marker tephra, is intercalated between them. In this study, these formations are newly defined as the Uppermost Kuchinotsu Group (1.0-0.6 Ma), and the Upper Kuchinotsu Group (1.9-1.0 Ma) and Older Unzen volcano (0.6-0.3 Ma), were defined as two active volcanic periods separated by the quiet period (Uppermost Kuchinotsu Group). The continuity of activity ages and similarities in rock chemistry imply that the Suwanoike basalt, Tonosaka andesite, Takaiwasan andesite, and Older Unzen volcanic fan deposits were associated with the Older Unzen volcano. This means that Older Unzen volcano become active after the quiet period of 1.0-0.6 Ma. The Ideguchi Formation, also an exotic marker tephra, and the Otani Formation were excluded from the volcanic activity in this area. The eruption sources of these exotic tephras could have been derived from other regions in Kyushu, but the source was not identified in this study.

著者

東宮 昭彦

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.67, no.2, pp.195-205, 2022-06-30 (Released:2022-07-28)

参考文献数

47

著者

柴田 翔平 長谷川 健

出版者

特定非営利活動法人 日本火山学会

雑誌

火山 (ISSN:04534360)

巻号頁・発行日

vol.67, no.2, pp.149-169, 2022-06-30 (Released:2022-07-28)

参考文献数

48

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We studied the 40 ka Kp I eruption deposits of Kutcharo volcano to unravel its eruption sequence and generation mechanisms. Previous studies have suggested that Kp I is the youngest caldera-forming eruption in this volcano and is characterized by large-scale phreatomagmatic activity. We divided Kp I eruption deposits into 7 units (Units 1~7, in ascending order). Units 1~6 consist of alternating thin pumice and thick fine ash layers. Units 1, 3, and 5 are pumice falls (totaling 1.6 km3), while Units 2, 4, and 6 are ash falls (totaling 52.2 km3) with abundant accretionary lapilli. Stratigraphically higher ash fall units are larger in volume, finer in grain size, and more widely distributed (e.g., Units 2, 4, and 6 are 0.2 km3, 13 km3, 39 km3 respectively). Unit 7 is a climactic ignimbrite (76 km3) that subdivides into lower (Unit 7-L), and upper (Unit 7-U) parts based on the pumice size and the existence of a lithic concentration zone (LCZ).Considering its wide dispersion, high fragmentation, and existence of abundant accretionary lapilli, Unit 6 can be considered to have been deposited by a “phreatoplinian style” eruption. Even though the ejected magma volume increased during the eruption of Unit 1 to 6, interaction between ascending magma and ground water caused maximum explosivity during the eruption that deposited Unit 6. Highly fragmentated magmas might have promoted vaporization and mixing with surface (lake) water to form the buoyant eruption column of Unit 6 eruption phase. Unit 7 is the most voluminous and the richest in lithic fragments at the LCZ, suggesting caldera collapse that generated a climactic pyroclastic flow.In addition to glass shards of bubble wall and pumiceous types, Kp I eruption deposits also commonly contain flake-, and blocky-shaped glass shards produced by phreatomagmatic (quenching) fragmentation. For both types of glass shards to have been generated, part of the ascending magma would have interacted with ground water before and/or during the magmatic fragmentation (vesiculation) that generally occurs below a depth of approximately 1,000 m in felsic H2O-saturated magma systems. In conclusion, a large and deep (~1,000 m) aquifer in the former caldera basin was sustainably supplied with ground water through the conduit system. Generation of the phreatoplinian eruption seems to have been controlled by a plumbing where conduits penetrated the huge aquifer of a pre-existing caldera structure that preserved/hosted a large amount of external water.

著者

早川 由紀夫 荒牧 重雄 高田 亮 浅岡 伸之 金子 隆之 津久井 雅志 岸 智 山下 茂 野原 状 平田 由紀子 小山 真人 白尾 元理 川辺 禎久

出版者

特定非営利活動法人 日本火山学会

雑誌

火山.第2集 (ISSN:24330590)

巻号頁・発行日

vol.32, no.3, pp.259-262, 1987-10-15 (Released:2018-01-15)