著者

中田 節也

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.61, no.1, pp.199-209, 2016-03-31

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Deterministic eruption scenarios may mislead taking countermeasures for coming hazards. Preparing the event tree covering all phenomena which may happen in future eruptions even with low probability for the volcano is important not only for forecasting eruptions but also for disaster prevention. Eruption event trees can be prepared in various concepts, for example, eruption type, scale, hazard type, impact direction or area and so on. The probability tree is the event tree equipped with probabilities for the branches. Probability trees by USGS and European scientists include the cumulative trees, trees based on scientists' elicitation and Bayesian trees. Introduction of the eruption event trees into the Japanese volcanologist community began around 2009. Then, event trees were prepared for Izu-Oshima, Miyakejima, Sakurajima, Usu, and Izu-Tobu volcanoes. Reasons for branching and time scales of events were also discussed and shown on the event trees together with probabilities. The event tree for Sinabung volcano, Indonesia, as an example of lava dome-forming eruptions was drawn in 2011, based on the geological study. On-going lava dome/flow eruption at this volcano just followed the most probable scenario. For Sakurajima volcano, a conceptual event tree was drawn for understanding the anomalies controlling the eruption scale.

著者

萬年 一剛

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.48, no.6, pp.425-443, 2003-12-25

被引用文献数

3

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Hakone volcano is situated at the northern tip of the Izu-Mariana volcanic arc in eastern Japan, and area that is both tectonically and volcanically active. Fumarolic activity is observed a.t post-caldera cone volcanoes within the caldera, and the northern extension of the Kita-Izu fault, the source of a M7.3 earthquake in 1930 (Kita-Izu earthquake), traverses the southern part of the caldera. Although there is no historical record of eruptive activity, many intense earthquake swarms have been reported since 1786 within the caldera. In this study, literature on earthquake swarms in 1917, 1920, 1933-35, 1943, 1944, 1953, 1959-60 are re-examined to reveal detailed development of the activity, seismic intensity and the epicentral region of these events. Two epicentral regions are recognized; the central cones region (1), and the southern part of the caldera (2). Earthquake swarms in (1) are often accompanied by rumblings and the main shock is not distinct; successive earthquakes are felt almost continuously during the peak of activity. On the other hand, earthquake swarms in (2) are rarely accompanied by rumblings and have obvious sequence of foreshocks, a mainshock and aftershocks. The largest earthquakes in the swarms in (2) are larger than those in (1). The two epicentral regions are both on the northern extension of the Kita-Izu fault system. Differences in the style of earthquake swarm activity in regions (1) and (2) may be due to differences of the geology and the source depth. Correspondence between fumarolic activity in the solfataras at central cone volcanoes and seismic activity was not observed except for the 1933-35 swarm. Most of the earthquake swarms at Hakone volcano are therefore probably tectonic earthquakes on the Kita-Izu fault system rather than being related to hydrothermal or magmatic activity within the caldera. Earthquake swarms at Hakone appear to have been rare before 1917, and except for 1786, no historical records exist even though one of the most important highways in Japanese history passed across the volcano. An interpretation that attributes the earthquake swarms since 1917 to foreshocks and aftershocks of the 1930 Kita-Izu earthquake would broadly explain the frequency of earthquake swarms at Hakone volcano since the early twentieth century.

著者

宮縁 育夫

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.55, no.5, pp.219-225, 2010

参考文献数

17

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Komezuka Volcano, located in the northwestern part of the post-caldera central cones of Aso Volcano, SW Japan, is a basaltic monogenetic volcano comprising a scoria cone (370-380m in basal diameter; 80m in height) and lava flows (10.5km²; 5×10⁷m³). We obtained ¹⁴C ages of 3,070±40 years BP from a buried soil below silty ash underlying Komezuka lava, which corresponds to 3,370-3,210cal years BP, and 2,760±40 years BP (2,950-2,770cal years BP) from a soil above silty ash overlying Komezuka lava. The age of soil below the lava suggests that the eruption age of Komezuka Volcano is about 3,300cal years BP. The eruption age is consistent with the age of Ojodake Volcano (3,600cal years BP) whose lava underlies Komezuka lava. In the northwestern part of the post-caldera central cones, Late Holocene monogenetic volcanic activity commenced with sub-plinian eruptions and lava extrusion from Kishimadake Volcano at approximately 4,000cal years BP, followed by sub-plinian eruptions and lava extrusion from Ojodake Volcano at 3,600cal years BP, and ceased with strombolian eruptions and lava extrusion from Komezuka Volcano at 3,300cal years BP.

著者

都司 嘉宣 上田 和枝

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

巻号頁・発行日

vol.1996, no.2, 1996-11-05

著者

安井 真也 富樫 茂子 下村 泰裕 坂本 晋介 宮地 直道 遠藤 邦彦

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.43, no.2, pp.43-59, 1998-04-30

被引用文献数

4

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A large amount of pyroclastic materials (ca. 1.7 km^3) was erupted during the 1707 eruption of Fuji Volcano. Variety of lithic fragments has been recognized in the pyroclastic fall deposits, namely, accessory and accidental lava fragments, gabbros, and granitoids. A great variety of petrologic features is observed in gabbroic fragments consisting of olivine gabbro norite, gabbro norite, troctolite and anorthosite. The gabbros are divided into O, P and F groups on the basis of modal ratios of olivine, plagioclase and Fe-Ti oxide. O group mainly consists of plagioclase and olivine with minor amounts of pyroxenes and Fe-Ti oxide. O group is considered to have been adcumulated in the lower part of magma chamber because of their high depletion in incompatible elements, their well-sorted grain size and sedimentary structure. P group is composed of plagioclase, pyroxenes and minor amounts of olivine and Fe-Ti oxide. F group is similar to P group, but is enriched in Fe-Ti oxide. P and F groups are orthocumulates and may be solidified in the upper part and margin of magma chamber or dike because of their porphyritic texture. Such a variety of gabbros may correspond to the difference in location of the single gabbroic body beneath Fuji Volcano. The estimated source magma of the gabbros is similar to the basalt of Fuji Volcano in chemical and mineralogical compositions indicating that they are cognate origin. Chemical compositions of olivine and pyroxenes become magnesian and those of plagioclase become calcic with the decreasing of bulk-rock FeO^*/MgO ratio. It suggests that they are the products of continuous fractional crystallization. The magma of the 1707 eruption could have come up from under the gabbroic body, which was the solidified basaltic magma chamber, and have caught and brought the rocks from the gabbroic body up to the surface as cognate xenoliths during the eruption.

著者

山元 孝広 高田 亮 石塚 吉浩 中野 俊

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.2, pp.53-70, 2005-05-20

被引用文献数

5

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The previous eruption history of Fuji volcano has been re-examined by new 100 radiometric carbon ages. The major unconformity between Ko-Fuji and Shin-Fuji volcanoes of Tsuya (1968, 1971) was caused by the edifice collapse resulting in the Tanukiko debris avalanche at about Cal BC 18,000. Voluminous effusion of basalt lava flows in the older ejecta of Shin-Fuji volcano (Tsuya, 1968, 1971) had started at about Cal BC 15,000 and continued until about Cal BC 6,000. Deposition of black soil layer between the Older and Younger Fuji tephra layers of Machida (1964, 1977) started at Cal BC 8,000. After several thousands years quiescent time, basaltic eruptions in the middle ejecta of Shin-Fuji volcano (Tsuya, 1968, 1971) had restarted at about Cal BC 3,600 and thin lava flows had piled up as the central volcanic cone, until about Cal BC 1,700. The eruption style of the volcano changed into explosive basaltic eruptions from the summit and the flank at about Cal BC 1,500; the S-10 to S-22 scoria fall deposits were generated in this first half period of the younger ejecta of Shin-Fuji volcano (Tsuya, 1968, 1971). Also, basaltic pyroclastic flows cascaded down the western flank at about Cal BC 1,500, Cal BC 1,300, Cal BC 1,000 and Cal BC 770. The last summit explosive eruption (S-22) occurred at about Cal BC 300. Immediately after the S-22 eruption, basaltic fissure eruptions had repeated at the flanks until the 1707 Hoei eruption. New data suggest that the Fudosawa, Nissawa and Suyama-tainai lava flows in the southern flank are historical products at about Cal AD 1,000.

著者

西村祐一 宮地直道

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.43, no.4, pp.239-242, 1998-08-31

被引用文献数

1

著者

金子 克哉 伊藤 公一 安部 祐一

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

巻号頁・発行日

vol.2009, 2009-10-10

著者

安井 真也 高橋 正樹 石原 和弘 味喜 大介

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.52, no.3, pp.161-186, 2007-06-29

被引用文献数

3

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The 1914-1915 Sakurajima eruption was the largest eruption in Japan in the 20th century and erupted andesitic magma was about 1.5km^3 DRE (Dense Rock Equivalent) in volume. Pumice fall and lava flows were generated from the fissure vents on the western and the eastern flanks of the volcano and pyroclastic cones were formed around the vents. Eruptive style changed with time. It is divided into three stages. After the initial, vigorous, Plinian eruption of about 36 hours (Stage 1), extrusion of lava associated with intermittent ash-emitting eruptions with or without detonations lasted for about 20 days on both sides (Stage 2), followed by an outflow of lava for more than 1.5 years on the eastern side (Stage 3). Consequently, the vast lava fields, which consist of a number of flow units formed on both sides of the volcano. Some units of lava show evidence of welded pyroclastic origin, suggesting clastogenic lava. In the western lava field, surface blocks characteristically consist of pyroclastic materials which show variable degrees of welding even within a single block. Typical eutaxitic textures and abundant broken crystals are also recognized under the microscope. Some flow units can be traced upstream to a pyroclastic cone. These features indicate that many flow units of lava on the western flank are clastogenic, which were generated by the initial, Plinian eruption of Stage 1. In the eastern lava field, evidence of pyroclastic origin is rarely discernable. However, the content of broken crystals varies widely from 20% to 80% in volume. Most lava flows, which were erupted in Stage 2 associated with frequent ash-emitting eruptions, contain broken crystals more or less than 50%. This fact indicates that magma in the conduit experienced repetitive fragmentation and coalescence due to intermittent explosions prior to outflow. Lava flows of Stage 3 contain much smaller amounts of broken crystals indicating gentle outflow of coherent lava. Relatively large-scale lava deltas developed toward the sea in the eastern lava field. Eyewitness account at that time reports that ocean entry of lava from several points started several months after the beginning of Stage 3. Although small-scale breakouts formed at the flow fronts of some lava on both sides, a large volume of the deltas can not be accounted for by secondary breakouts of ponded lava within the precedent flow lobes. It is considered that lava tube system fed lava to form the lava deltas.

著者

井村 隆介

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.43, no.5, pp.373-383, 1998-10-30

被引用文献数

6

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The eruptive sequence of the An-ei eruption of Sakurajima volcano (1779-1782) is revealed by historical records. From the evening of November 7, 1779 (the 29th day of the 9th month in the 8th year of An-ei), Kagoshima and its environs were shaken frequently. At 11 a.m. of the next day, the water in the wells in the island boiled up, spouting at several points and the color of sea became purple. On the noon of the same day, minor white plumes rose up from the Minamidake summit crater. At about 2 p.m., plinian eruption oecurred at the southern upper slope of Minamidake, and several tens of minutes later, at the northeastern flank of Kitadake. The height of eruption column reached about 12000 meters. It is estimated that a pyroclastic flow was generated at 5 p.m. The plinian eruption climaxed from the evening of November 8, to the morning of next day, and later was followed by emission of lava flows. The activity of the southern craters ceased within a few days, but lava emission from northeastern craters lasted for a long period. On November 11, the lava flow from northeastern craters entered into the sea. Since then, submarine explosions occurred repeatedly off the northeastern coast, and it continued to January 18, 1782. Nine small islands produced by this submarine volcanic activity during a year. Submarine explosions caused small tsunamis on August 6 and 15, September 9, October 3 1, November 9, 1780 and April 11, 1781.

著者

三宅 康幸 小坂 丈予

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.43, no.3, pp.113-121, 1998-06-10

被引用文献数

4

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A steam explosion occurred at about 14:30 JST, February 11th, 1995, in the hot-spring area near Yakedake volcano, central Japan. More than six workers were near the site of the explosion for the road construction, and four of them were buried by the ejected material and killed. A small initial explosion began at the bottom of a 4m deep moat dug by a backhoe and it was followed by the maximum explosion, which ejected about 6,000m^3 of blocks (maximum length is more than 2m) and mud, with steam and volcanic gas. The ejecta contain gravels of welded tuff, granite and mesozoic sedimentary rocks, which are the components of a pyroclastic dike of Pliocene age, and pumiceous lapilli tuff derived from the terrace sediments covering the pyroclastic dike. The explosion caused a landslide from the western cliff and the vent was buried by the slid debris, most of which was blown away by the second explosion. All of these processes took place within a few minutes. A small depression (20×5m^2) on the west of the mound of the ejecta may represent part of the vent; its depth is estimated to be about 60m or more. Gaseous S0_2(<30ppm) and H_2S(<90ppm) were detected at the explosion site for three days after the explosion. The chemical composition of gas collected from the holes drilled after the explosion were nearly same as the gas from the summit crater of the Yakedake volcano. Because a wall-like Low-Q zone is suggested by seismologists beneath Yakedake volcano and the explosion site, it is most probable that there existed a magma beneath the explosion site and that the heat for the explosion was supplied by the magma and gas exsolved from the magma.

著者

宮縁 育夫

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.62, no.1, pp.1-12, 2017-03-31 (Released:2017-03-28)

参考文献数

27

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Janoo Volcano (550-750 m in basal diameter;150 m in height) is located in the northwestern part of the post-caldera central cones of Aso Volcano, central Kyushu, southwestern Japan. The volcano had been thought to be a cinder cone composed entirely of scoria-fall deposit and older than 7.3 ka. Fieldwork in and around the volcano has re-examined the detailed tephra stratigraphy and eruption age of Janoo Volcano. A black humic paleosol divides an upper pumice-fall deposit from a lower scoria-fall deposit. The upper pumice-fall deposit shows only two pure pumice bed sections with pumice clasts scattered in a brown massive ash elsewhere in the deposit. The deposit is composed mainly of light gray well-vesiculated dacitic (SiO2=65.4-67.7 wt.%) pumiceous clasts containing biotite phenocrysts, and abundant banded pumices, suggesting a mixture of silicic and mafic magmas. Based on the phenocryst assemblage and age, the pumice-fall deposit is correlated to the Aso central cone pumice 1 (ACP1;4.1 ka), which is the only pumice-fall deposit erupted from Aso Volcano during Holocene time. The lower scoria-fall deposit is more than 30 m thick and constitutes most of the Janoo cinder cone. It includes brownish black to brown well-vesiculated basaltic andesite (SiO2=54.7-55.5 wt.%) scoriaceous clasts and cauliflower bombs with radially arranged cooling joints. The Akamizu lava (SiO2=57-59 wt.%) distributed west of the Janoo cinder cone, whose source was previously unknown, is attributed to Janoo Volcano based on the lava’s petrographic characteristics. A 14C age of 3830±30 years BP, which corresponds to 4.2-4.1 ka, was obtained from the humic paleosol interbedded between the ACP1 and Janoo scoria. The stratigraphy and characteristics of the tephra deposits suggest the following eruption sequence. The initial eruption at Janoo Volcano occurred at 4.9-4.3 ka and was strombolian in style forming the Janoo cinder cone. After lying in repose for a few hundred years, Janoo Volcano erupted again, and produced the ACP1 tephra containing abundant banded pumices and Akamizu lava at 4.1 ka. The southern half of the Janoo cinder cone was destroyed probably by the effusion of Akamizu lava. Volcanic activity forming Kishimadake, Ojodake, Komezuka and Kamikomezuka volcanoes in the northwestern part of post-caldera central cones at 4-3.3 ka was derived from basaltic to basaltic andesite magmas, whereas the eruption products of Janoo Volcano have a wide range in chemistry from basaltic andesite to dacite. Activity of Janoo Volcano is characterized by the presence of a dormant period (a few hundred years), allowing a paleosol to develop on the scoria-fall deposit, before ejection of both mafic and silicic magmas in the late eruption.

著者

黒墨 秀行 土井 宣夫

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.48, no.3, pp.259-274, 2003-07-10

被引用文献数

5

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The Nigorikawa Caldera in southwest Hokkaido, Japan, is 3 km in diameter at the outer rim. Drilling data from 42 geothermal wells of up to -3,000 masl (m above sea level) has been used to study the internal structure of the caldera. Interpretation of the data shows an angular funnel shape, with a wide upper region (3×2.5 km) tapering to a narrower lower region (0.7×0.5 km). The shear zone is the same shape as the caldera, that is, rectangular with a NE-SW elongation. The caldera is infilled with vent-fill material, lake and alluvial deposits, landslide deposits, and post-caldera intrusions. The vent-fill material is a gray, non-welded lapilli tuff and tuff breccia, which homogeneously includes accidental lithics and shattered fragments, which were sheared during pyroclastic eruption, as well as accretionary lapilli occurring up to -824 masl. The vent-fill is intercalated with many lithic bands or lithic dominant zones that dip toward the caldera center. No large fault displacement can be recognized around the caldera wall. The Nigorikawa Caldera was formed ca 12,000 years ago by violent pyroclastic flow eruption, fall-back, and the following subsidence by compaction with degassing.

著者

宇井 忠英 岡田 弘 三松 三朗 横山 光 池田 武史 川南 恵美子 佐藤 [ツトム] 高橋 祐子 下道 英明 ニュートン ダグラス

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

巻号頁・発行日

vol.2014, 2014-11-02

著者

早川 由紀夫

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.38, no.6, pp.223-226, 1993-12-20

被引用文献数

4 9

著者

津金 達郎 牧野 州明 三宅 康幸 高橋 康

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.51, no.1, pp.49-61, 2006-02-28

被引用文献数

4

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The September 2004 eruptions of Asama volcano, central Japan, ejected essential materials such as pumice with bread crust on September 1st and scoria on September 23rd. The textural and chemical analyses on the materials reveal the crystallization processes in a deep magma chamber and a shallow vent. Two distinct stages of crystallization can be recognized in size distributions and morphology of plagioclase phenocryst and microlite both in the pumice and scoria. First stage (range I ): In a deep magma chamber, pyroxene phenocryst began to crystallize out at 1150℃, and then pyroxene and plagioclase continued to nucleate and grow slowly. Second stage (range II) is divided into two sub-stages for pyroxene or three (range IIa-c) for plagioclase. II a: Magma left the chamber and rose slowly through the vent with ever increasing nucleation rate. II b-c: In a shallow vent beneath the crater, numerous plagioclase microlites like swallow-tailed shape precipitated rapidly under a high undercooling condition induced by decompression. Plagioclase microlite in the pumice and scoria developed a characteristic population density like a bell with a peak at the grain size of 0.003mm, which is interpreted to reflect a decrease in nucleation rate of plagioclase, in response to crystallization and establishment of equilibrium during the time duration when the magma stayed in the vent. Magmatic temperatures estimated from plagioclase-glass equilibrium decreased to 850℃ before the September 1st eruption. The similarity in crystal size distribution of the pumice and scoria implies that they had a common ascent history, although groundmass in the scoria has lower crystallinity than that in the pumice, suggesting that the magma of the Sept. 23rd eruption stood lower in the magma column than the Sept. 1st magma.

著者

佐々木 寿 小林 哲夫

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

巻号頁・発行日

vol.2006, 2006-10-23

被引用文献数

1

著者

中禮 正明 福井 敬一 清野 政明

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:04534360)

巻号頁・発行日

vol.31, no.1, pp.63-64, 1986-04-30

著者

山岡 耕春

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.39, no.4, pp.141-153, 1994-09-20

被引用文献数

2 3

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Relations between activity of volcanic earthquakes in Izu-Oshima volcano and stress and/or strain state around it are investigated. In this paper three kinds of relations are examined during and after the 1986 eruption of Izu-Oshima volcano : (1) How did big earthquakes affect on the volcanic activity of Izu-Oshima? (2) How did the pressure decrease of magma reservoir induce earthquakes around it. (3) How did the dike intrusion induce big earthquakes. The results are as follows : (1) Nine earthquakes of M>5.0 occurred from 1987 through 1990 within the epicentral distance of 100 km from Izu-Oshima volcano. They gave influences on the activity of volcanic earthquakes and/or volcanic tremor when they exerted normal strain of over 10^<-8> on the vertical plane trending N30W. (2) Swarm-like seismic activity in north and western part of Izu-Oshima volcano during the summit eruption is interpreted as an induced swarm due to pressure decrease of magma reservoir. The earthquake swarms occurred both sides of the magma reservoir whose location is estimated from the data of crustal movement. The location of two-lobed earthquake swarm is well explained by a simple model ; infinite two-dimensional elastic medium under differential stress with a circular hole. (3) Large earthquakes accompanied the dike intrusion of 1986 eruption of Izu-Oshima. Two biggest earthquakes occurred at both ends of the dike. A M 5.1 event occurred at the northwestern end and M 6.0 occurred at the southeastern end. Both events may played a role to stop the further propagation of dike intrusion.

著者

小野 晃司 渡辺 一徳 星住 英夫

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.40, no.3, pp.212-213, 1995-07-31