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:04534360)

巻号頁・発行日

vol.32, no.1, pp.57-72, 1987-04-30

被引用文献数

3

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Lake Nyos is a maar-type volcano formed by phreatomagmatic eruption along the fissure. The rock is weakly alkaline olivine basalt very rich in crustal xenoliths and mantle-derived spinel-lehrzolite nodules. Stratiied surge deposits made of scoria and ash drape the pre-Cambrian(?) granitic basement along the lake shore. Lake Nyos is a part of Cameroon Volcanic Line which contains many fields of monogenetic volcanoes. Among them is another maar-type crater lake Monoun, which erupted similar lethal gas(CO_2) in 1984 and killed 37 people. The rocks of these young monogenetic volcanoes range from weakly to strongly alkaline basalts and basanitoids. The older(Tertiary?), plateau-forming basalts which constitute immediate basement are also alkaline basalts and basanitoids.

著者

村山 広道 鎌田 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.21, no.3, 1976-12-15

著者

日下 部実

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.32, no.1, 1987-04-30

著者

荒牧 重雄 海野 進 橋本 光男

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.2, pp.187-188, 1983-07-01

著者

諏訪 彰

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.16, no.2, pp.103-106, 1971-12-01

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A mixed eruption took place at Medake, biggest central cone of the composite volcano Akita-Komagatake, in 1970-71. This is the first magmatic eruption of the volcano in the historical age. All the former eruptions on record were phreatic explosions. The new lava is andesite, though older lavas of the central cones are basalts.

著者

岡崎 紀俊 田中 和夫 三品 正明

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.35, no.4, pp.375-388, 1990-12-28

被引用文献数

1

---

Surveys of magnetic total intensity and gravity were conducted to reveal the underground structure of Medake, one of the central cones in the cadera of Akita-Komaga-take Volcano, from which about 1.42 million m^3 of lavas flowed in the period of 1970-1971 eruption. Magnetic and gravity anomalies obtained show some characteristic features suggesting the subsurface structure. Long wave length magnetic anomalies show that Me-dake is composed of uniformly magnetized volcanic rocks, lavas and scoriae, On the other hand, short ones found at the summit of Me-dake indicate there is a body with reversal or weaker magnetization than the surroundings. The distribution of the Bouguer anomalies is characterized by a narrow area of higher values of anomalies at the summit and a trend of higher values in northwest of Me-dake and lower ones in southeast. The latter suggests the basement structure of the caldera. The former implies an exislence of more dense intrusive rocks under the ground surface. Both centers of short wave length magnetic anomaly and of the narrow area of higher value of gravity locate at the same place about 100 m northeast of the 1970 crater on the summit. Judging from the topographic features, this place is one of the old craters. To interpret magnetic and gravity anomalies, numerical analyses for demagnetization model and for more dense intrusion model with various shapes were carried out independently. Finally, magnetic anomalies can be expained by a demagnetized vertical pentagonal prism, of which size is 80 m in N-S, 150 m in E-W and 300 m in thickness and of which top is at the depth of 5-10 m. Gravity anomalies can be interpreted by a more dense vertical rectanglar prism, of which size is 30 m×110 m×300 m and the top is at 15 m deep. The zones of high ground temperature and fumaroles are found at the surroundings of the 1970 crater and the area of the higher gravity anomalies. The fumarolic area preceding the 1970 eruption was found at north of the crater. We can infer the processes of the 1970 eruption by using the interpreting subsurface model of Me-dake and the distribution of fumaroles. At the first stage of eruptive activity in 1970, magma intruded into northeast of the 1970 crater. At the second, most of magma passed through the vent conncted with the crater and flowed out. Small quantity of magma remained in the narrow part at northeast of the crater make the present magnetic and gravity anomalies and fumaroles.

著者

近堂 祐弘 小柳 敏郎 河内 晋平 中川 光弘 鈴木 貞臣 長谷川 榮 山之内 統 川辺 百樹 岸 功志 岡久 保幸

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.34, no.4, pp.360-361, 1989-12

著者

佐々木 龍男 勝井 義雄 熊野 純男

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.26, no.2, pp.113-116, 1981-07-01

被引用文献数

1

著者

勝井 義雄

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:04534360)

巻号頁・発行日

vol.12, no.3, 1967-12-01

著者

勝井 義雄

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:04534360)

巻号頁・発行日

vol.17, no.1, 1972-06-01

著者

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. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.29, no.1, pp.17-30, 1984-04-01

被引用文献数

3

---

"Fuji 1707 Tephra" was thrown out from the three craters on the upper southeast flank of Fuji Volcano on December 16 to 31, 1707 (TSUYA, 1955). It is composed of scoria beds named Ho-II to -IV and lowest two pumice beds named Ho-I. Ho-I and -II are probably originated from the second and the third craters and Ho-III and -IV are from the first crater on the basis of distribution of ejecta and characteristics in apparent densities. Ho-I_a, the lower Ho-I, is studied with respect to its mode of eruption, transportation and sedimentation. This bed is composed of white to pale brownish pumice, and is readily recognizable in the field and traceable over 130 km eastward from the source. Ho-I_a is the Plinian pumice-fall deposit and its volume is calculated to be 0.067 km^3 by the method of "Cross section area" (SUZUKI et al., 1973). The axis of maximum pumice diameters (MP), maximum lithic fragment diameters (ML) and median diameters of grains (Md) run along the southern margin of the distribution area. The same feature is recognized in the apparent density distribution for pumice fragments. More than 130 km eastward from the source, such an asymmetric distribution for MP is preserved. These facts suggest that the eruption column of Ho-I_a was affected by the strong westerlies in the upper atmosphere and the local SW winds in the lower one. The present meteorological data support this interpretation. Consequently, it is concluded that the irregular distribution of this Plinian tephra was originated by the differences in wind direction and velocity due to the altitude.

著者

鎌田 清吉

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.18, no.2, 1973-08-01

著者

津久井 雅志 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:04534360)

巻号頁・発行日

vol.35, no.2, pp.231-248, 1990-07-02

被引用文献数

5

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22,000 years ago, about 100 km^3 of magma erupted from the northrn end of Kagoshima Bay, southern Kyushu. The eruption produced 5 units of pyroclastic deposits; (1) 98 km^3 of airfall pumice (Osumi pumicde fall, OS), (2) 13 km^3 of oxidized, fine-grained Tsumaya pyroclastic flow (TSU), (3) Kamewarizaka breccia (KM) of the new vent-opening and enlargement stage, (4) 250 km^3 of Ito pyroclastic flow (ITO) at the climactic stage, (5) >50 km^3 of co-ignimbrite ash fall (AT ash). Phenocryst mineral assemblage throughout the whole sequence is ubiquitously plag+qtz+opx(Mg#45-60) +mt+il. One exceptional sample (ITO 11c) carries Fe-rich oliv (Fo 26-28) and cpx beside other phases. Fifty-five new XRF analyses of 10 major and 15 trace elements show that the majority of the erupted magma consisted of a remarkably homogeneous, high-silica rhyolite with SiO_2 74-76.5%(H_2O free and 100% normalized). The maximum fluctuation found both in major and trace elements is ±40%. These variations can be explained by the crystal-liquid separation near the roof of the magma reservoir. Mt-il temperatures and opx-mt-qtz pressures show narrow ranges, i e., 770±20℃ and 3-5 kb, respectively. Although the sample ITO 11c shows similar temperature, its calculated pressure is close to 0 kb. The bulk and mineral chemistry and the temperature-pressure estimation suggest that the magma reservoir was not distinctly zoned but was very homogeneous throughout prior to eruption.

著者

藤井 敏嗣

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.29, no.3, pp.245-246, 1984-10-01

著者

藤 一郎 宇井 忠英

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.24, no.2, 1979-07-01

著者

宇都 浩三 小屋口 剛博

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.32, no.3, pp.263-267, 1987-10-15

被引用文献数

1

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. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.29, no.2, 1984-07-01

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. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.25, no.4, pp.305-306, 1980-12-01

著者

荒牧 重雄 柵山 雅則 早川 由紀夫 中村 保夫 巽 好幸

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.26, no.2, 1981-07-01

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. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.27, no.2, pp.174-175, 1982-07-01