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 (Released:2017-03-20)
参考文献数
14
被引用文献数
2

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 6,000m3 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 (20×5m2) 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 S02(<30ppm) and H2S(<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
岸上 冬彦 小坂 丈予
出版者
東京大学地震研究所
雑誌
東京大學地震研究所彙報 (ISSN:00408972)
巻号頁・発行日
vol.33, no.1, pp.153-161, 1955-06-25

1953年7月26日箱根早雲山において山津波が発生し,人員及び建造物に対して相当の損害をあたえた(第1図).我々は7月29日, 31日, 8月5日及び11月11日に現地を調査する機会を得たので,その結果を報告する.
著者
小坂 丈予 平林 順一 吉田 稔 鎌田 政明 松尾 禎士 小沢 竹二郎
出版者
岡山大学
雑誌
重点領域研究
巻号頁・発行日
1987

1.全国の火山地域における噴気ガスの化学成分測定とその変化:一 今年度は本邦における有珠, 十勝, 雌阿寒, 樽前, 北海道駒ヶ岳, 旭岳, 秋田駒ヶ岳, 秋田焼山, 鳴子(潟沼), 那須, 草津白根, 富士(河口湖), 木曽御岳, 伊豆大島, 雲仙岳, 霧島, 桜島, 開聞(うなぎ池)などの諸火山について, 噴気ガスの噴出温度, 化学成分, 噴出量や速度などを測定し, 特に火山活動の消長と噴気ガスの成分変化との関係を求められた.2.諸火山の噴気孔ガスの化学的研究から判明した2, 3の事実:- 今年度の調査結果から判明したことのうち2, 3の例について挙げると, 有珠火山に於いては, その化学組織と同位体組成の次時間変化から, その最高値より出口温度の最高値の方が約2年遅れて出現することが判った. また秋田焼山の叫沢の噴湯はその酸素・水素同位体比の測定などから山頂の噴気ガスと低温の地下水との混合後に与熱されて噴出した特殊な湧出過程であることや, また今回活動が活発化した雌阿寒岳ではフッ素/塩素比の明らかな増加が見られ逆に活動の沈静化が進んでいる大島ではこの値の低下が認められた.3.大気中に放出された火山ガスの滞留状況と災害についての調査研究:- 1986年5月に火山ガス中毒死亡事故の発生した秋田焼山叫沢に於いて, 大気中に滞留している火山ガス濃度の分布状況は, ガス発生地点の位置, 発生濃度, 温度, 地形, 気温, 風向等に密接に関係することを確かめ, 現在でもところにより250ppm以上の滞留濃度を示すことがあるのが確かめられた. 同じくガス中毒事故のあった草津白根山殺生河原や, その他桜島, 木素御岳などでも同様大気中に拡散した火山ガス濃度の経時変化を測定した.4.研究の問題点と今後の展望:- 火山ガス災害の発生源である火山噴気ガスの濃度・発生量等の予測と, 大気中への拡散後の地形・気象条件との関係についてより詳細な調査が必要である.
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

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
小坂 丈予 小沢 竹二郎 松尾 禎士 平林 順一 大隅 多加志
出版者
Tokyo Geographical Society
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.94, no.6, pp.551-563, 1985-12-25 (Released:2009-11-12)
被引用文献数
5 4

The temperature of fumarolic gas ranged from 100 to 128 °C. These gas usually contained few HCl and SO2, and contained a small amount of H2S. These facts indicated that acidic gas components were absorbed into the aquifer during the cause of ascent. Hot springs may be classified into three types according to their chemical composition : 1) volcanic thermal water type ; 2) sea water type ; and 3) type of mixture of 1 and 2.δD and δ18O of waters collected from this island are high. The rocks from Iwo-jima are all trachy andesite with the SiO2 content of 54-58 %, and with the Na2O+K2O content of 9-10 %.
著者
森本 良平 小坂 丈予 羽鳥 徳太郎 井筒屋 貞勝 浦部 和順 高橋 春男 岡田 義光 平林 順一 伊佐 喬三 磯部 宏
出版者
Tokyo Geographical Society
雑誌
地学雑誌 (ISSN:0022135X)
巻号頁・発行日
vol.77, no.5, pp.255-283, 1968-10-25 (Released:2009-11-12)
参考文献数
25
被引用文献数
3 3

Unusual uplift of the land was found about an insular active volcano Iwo-jima, Ogasawara archipelago, 1, 200 km south of Tokyo. Remarkable retreat of shore line was revealed by reviewing topographic maps and aerophotographs of the island. Some upward movements of the island are to be one of the most principal reasons of the retreat. As the clear evidences of the upheaval of the land, following phenomena were observed by the writers who investigated the island five times from 4th July to 23rd August 1968 : a) Sunken vessels and a landing craft have emerged on the western coastal beach of the island : b) Faults and cracks appeared on the abandoned run-way of the former Japanese Navy in the central part of the island ; c) Coastal reef emerged on the sea to connect off shore islet with the island ; d) New coastal terraces were formed on the sand beaches ; e) Fresh living corals were exposed on the sea.Results of the investigations are enumerated as follows : 1) About 8 m upheaval of the land since 1953-4 was revealed by levelling survey at the western coast of the island. 2) Amount of uplift observed on the above-mentioned run-way is smaller in its central part than in both terminals, maximum vertical displacement of the fault being 3 m. 3) Tide gauge installed at the western rocky coastrecorded slight relative down of sea level but further observation should be continued without disturbance by typhoon to obtain more reliable data. 4) No expected microseisms were recorded on the high sensitive electro-magnetic seismographs except 2 or 3 per day. 5) Temperature of the fumarolic gases were 95-123°C, 10-25°C higher than that observed in 1935. In spite of the rise in temperature, gases of so called high temperature type, such as sulphur dioxide and halogens, were not contained. 6) Composition of the sublimates also accords with these results of chemical analyses of the gases. 7) Content of each main component element and its ratio to other ones is quite variable in several hot springs whose pH values range from 2.1 to 6.8. 8) Analcite was identified by X-ray and DTA analyses in the tuff forming Moto-yama, an eastern main flat cone of the island. Genetic condition of the mineral inferred from its chemical composition may indicate submarine eruption of the volcano. 9) Three weak zones were recognized by the present investigations in addition to the two ones previously reported by Tsuya. Thus three are arranged radially through the center of the eastern main cone and the two are arranged concentrically around the foot of the same cone. From these weak zones phreatic explosions are expected in future, if they occur. 10) Nothing more than mere weak phreatic explosion was recorded through the historic activity of the volcano. Artificial filling up of the vent, such as the pavement of the surface often causes the small explosion at fumarole. 11) Submarine eruption recently found at the sea bottom, about 5.4 km NNE of the South Sulphur Island, about 50 km south of the island did not occur recently but must have repeated rather stationarily.According to the present investigations, no remarkable magmatic explosion could be expected except those small phreatic ones, same one of which has often occurred on the island. Chemical composition of the gases does not indicate any approach of hot magma to the surface.
著者
吉田 稔 小沢 竹二郎 小坂 丈予
出版者
公益社団法人 日本化学会
雑誌
日本化学会誌(化学と工業化学) (ISSN:03694577)
巻号頁・発行日
vol.1972, no.3, pp.575-583, 1972-03-10 (Released:2011-05-30)
参考文献数
58

薩摩硫黄島火山の高温噴気孔周辺に青色の火山昇華物が見られる。この鉱物は無定形で変質物上にごく薄く付着しているので常法による同定は困難である。著者らはおもにその化学的性質を検討することにより,本鉱物がモリブデンブルー(M。(V)とMo(斑)の混合水湘酸化物)であることを確認した。一方,低温噴気地帯にはモリブデナイトが見いだされ,X線回折法と化学分析により同定した。日本各地の火山の火山ガスと火山岩のMo含量を求めた。薩摩硫黄島の高温の噴気孔ガスは凝縮水1Z中0.3~7,hngMoを含む。低温のものや他の火山のガスにはMoは検出されなかった。火山岩のMo含量はo.5~3.4μ9/9であった。上記のデータと熱力学計算の結果から,これらの鉱物の生成機構をつぎのように推定した。水酸化物かオキシバ冒ゲン化物として高温の火山ガスにより運ばれたMoが出口での温度低下と酸素分圧の増加によりモリブデンブル_として沈積する。また,雨水に溶けて低温地域に運ばれたモリブデンブルーが硫化水素と反応してモリブデナイトを生じる。
著者
小坂 丈予 平林 順一 山本 雅弘 野上 健治
出版者
日本自然災害学会
雑誌
自然災害科学 (ISSN:02866021)
巻号頁・発行日
vol.17, no.2, pp.131-154, 1998-08-31
参考文献数
24
被引用文献数
3

Volcanic gas disasters around active volcanoes all over Japan have occurred 27 times and 45 people have been killed since 1950. Configuration of the ground near fumarolic areas and weather conditions are the principal factors in gas accidents. Making gas-hazard maps, setting of restricted zones and installation of automatic alarm system with continuous monitoring are effective measures to prevent volcanic gas disasters. Knowledge of toxicity of volcanic gases and first aid are also helpful in reducing volcanic gas disasters.
著者
小坂 丈予 小沢 竹二郎 酒井 均 平林 順一
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.28, no.1, pp.59-74, 1983
被引用文献数
6 1

Kiso-Ontake Volcano erupted suddenly on the 28th of October, 1979. The eruption started forming ten new craters on the southern flank of the volcano's summit. This paper deals with geochemical study on its volcanic activity after the eruption. The ratio of Cl to S was found to be high in the water-soluble components of the volcanic ash. The content of SO<sub>2</sub> was larger than that of H<sub>2</sub>S in the volcanic gas. According to these observations and considering the sulfur isotopic ratio, the under ground temperature was estimated to be higher than 250℃, while that at the orifice was measured to be as low as 90℃. These facts and seismic observation indicate that magma was not elavated to a sarrow part, but that only high temperature-gas, which was separated from the magma, came up rapidly along the crack, and then rushed into the mud reservoir near the surface, where a large amount of water was evaporated, following the eruption caused by prompt increase of pressure. At an early stage of the eruption, the content of Cl<sup>-</sup> was larger than that of SO<sup>2</sup><sub>4</sub> in spring and pond waters, which were in contact with the fumarolic gases at the summit, but its relation was reversed later. This has been explained by the absorption of HCl, which had been contained in the volcanic gas at the early stage, into the water phase near the summit. From 1980 to 1982, the outlet temperature of fumarole increased to 108-145℃. However, the ratio of SO<sub>2</sub> to H<sub>2</sub>S reduced rapidly, which indicates the decrease of temperature at depth. Therefore, the increase of the temperature of the fumarole is thought to be caused due to the decrease of cooling effect by ground water, because water was evaporated by the continuation of the eruptive activity. Recently no significant changes have been observed in temperature and chemical compositions of volcanic gas, suggesting that the activity will remain to be low for the time being.
著者
小坂 丈予 小坂 知子 平林 順一 大井 隆夫 大場 武 野上 健治 木川田 喜一 山野 眞由美 油井 端明 福原 英城
出版者
日本地球化学会
雑誌
地球化学 (ISSN:03864073)
巻号頁・発行日
vol.31, no.2, pp.119-128, 1997
被引用文献数
7

Geochemical study on Yugama, a crater lake at Kusatsu-Shirane volcano, has been conducted since 1966. Amounts of various cationic species in Yugama water started increasing around 1981, slightly before the phreatic eruptions in 1982-1983, and kept increasing until 1985. In 1986, they turned to decrease and at present restore their former levels before the eruptions. The concentration of sulfate ion showed a secular change similar to those of cationic species, but no such variation was observed for chloride ion even during the 1976 and 1982-1983 eruptions. However, it started increasing in 1989. A high correlation between the concentrations of chloride and hydrogen ions suggests an increasing influx of hydrogen chloride from the deep volcanic systems under the lake. A Cl<sup>-</sup>-SO<sub>4</sub><sup>2-</sup> is an excellent monitor of the variation in volcanic activity at Kusatsu-Shirane volcano; all of the three past activities since 1966, i.e., the high-level subsurface activity in 1968, the eruption in 1976 and the eruptions in 1982-1983, showed a reverse secular change with time in the Cl<sup>-</sup>-SO<sub>4</sub><sup>2-</sup> plot. This could be attributable to the function of Yugama water as a condenser of volatiles released underground.
著者
野上 健治 吉田 稔 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.38, no.3, pp.71-77, 1993-08-15
参考文献数
10
被引用文献数
6

薩摩硫黄島東温泉沿岸では温泉水と海水とが様々な比率で混合した結果,極微細なSiO_2-Al_2O_3-Fe_2O_3-H_2O系の低結晶質沈殿物が生成しており,海面が様々な色調を呈している.これらの変色海水について,母液及び沈殿物のSi-Fe-Al_3成分の化学組成及び生成条件,特にpHとの関係について検討を行った.その結果,沈殿物の化学組成は温泉水と海水との混合溶液のpHに強く依存し,pHが2前後では沈殿物中のFeの割合は低いが,pHが3〜5の範囲ではFeの割合が相対的に高くなる.更にpHが上昇するとAlの割合が相対的に高くなる.また変色海水の色調はpHが2前後の時は透明から乳白色であるが,pHが3〜5の時には黄褐色である.更にpHが上昇すると色調は再び白色系になり,沈殿物中のFeの割合によって色調が変化する.これらに対して,各採取地点における沈殿物と母液との混合物の化学組成は東温泉から湧出している温泉水のそれと殆ど同じであり,見かけ上沈殿の生成過程においてSi,Fe,Alの3成分は分別していない.
著者
岸上 冬彦 小坂 丈予
出版者
東京大学地震研究所
雑誌
東京大学地震研究所彙報 (ISSN:00408972)
巻号頁・発行日
vol.33, no.1, 1955-03
被引用文献数
3

1953年7月26日箱根早雲山において山津波が発生し,人員及び建造物に対して相当の損害をあたえた(第1図).我々は7月29日, 31日, 8月5日及び11月11日に現地を調査する機会を得たので,その結果を報告する.The earth-flow of 1953 at Sounzan was studied, and the results are summarized as follows: 1. The earth-flow reached about 2 km distant eastward from its source with a maximum width of nearly 140 m, and the total volume of flowed earth and stones was estimated at 700,000 m3.