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.31, no.4, pp.287-288, 1986-12-26

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. 第2集 (ISSN:04534360)

巻号頁・発行日

vol.30, no.1, pp.45-47, 1985-04-01

著者

久野 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:04534360)

巻号頁・発行日

vol.13, no.3, pp.123-130, 1968-12-01

被引用文献数

1

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Andesitic and dacitic lavas form a certain kind of autobrecciated structure upon entering into the water instead of forming the pillow structure common in basaltic lavas. Such lavas consist of angular, polyhedral blocks ranging in size from a few meters to several centimeters in diameter cemented by comminuted fragments of the same material or by sediments. Matrix of palagonite is sometimes present. Individual blocks are compact and are often traversed by joints which divide them into still smaller polyhedral blocks. In blocks larger than 0.5m., which are usually angular in outline and sometimes spheroidal, closely spaced joints roughly perpendicular to the surface of the blocks are developed, indicating their quenching against the water. In the Pleistocene volcanoes of Izu Peninsula and Hakone, no such subaqueous autobrecciated lavas have been found even along the present sea coast. This fact implies that they have never been uplifted since the beginning of the Pleistocene or have been partly submerged because of the elevation of the sea level since the end of the glacial period.

著者

澤田 可洋 Andal C. Marzan D.

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, 1980-12-01

著者

澤田 可洋

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

中禮 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.29, no.2, 1984-07-01

著者

高橋 正樹

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.143-144, 1981-07-01

著者

中村 一明

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

著者

宇平 幸一 永福 順則 山本 博二 横山 博文 荒木 卓次

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, pp.S36-S44, 1984-12-28

被引用文献数

1

---

A swarm of earthquakes, precursory indication of the eruption, began to be recorded at Miyakejima Weather Station at 1358 on 3 October, 1983, although none was recorded at any other seismic station of JMA until the onset of the eruption. On the other hand, another swarm of earthquakes that resumed after the onset of the eruption was caught by seismographs around Miyakejima. Precursory earthquakes were grouped into two types, i.e., high frequency earthquakes and low frequency ones, according as their predominant frequencies were higher than 2.5 Hz or not. It is unpromissing to try to determine hypocenters of precursory events, but, both the first motions of 5 high frequency earthquakes and the particle motions of 2 low frequency ones in the horizontal plane inidicate that their sources were located to the SW of the seismograph, probably on the island. Gradually increasing continuous tremors started immediately after the earthquake at 1522 which had a predominant frequency of about 1.4 Hz from initial motion through coda. The following continuous tremor had almost the same predominant frequency. Major eruptive activity probably began with this low frequency earthquake. The magnitudes of two large precursory earthquakes were estimated to be about 3.0 by applying the relation between the magnitudes of post-eruption earthquakes and their maximum amplitudes or duration times of vertical component at Miyakejima Weather Station. However, this estimation was not appropriate because earthquakes of such size were large enough to be recorded at seismic stations other than Miyakejima. The seismograph at the sea bottom off Omaezaki (named "TK1OBS" in the seismological bulletin of Japan Meterological Agency), about 180 km W of Miyakejima, detected post-eruption earthquakes of magnitude about larger than 2.5, but did not record any pre-eruption earthquakes. The background noise on 3-4 October had remained at a similar level of 0.02 milikine, which corresponds to the expected maximum velocity of the vertical component on TK1OBS when an earthquake of magnitude 2.4 occurs at Miyakejima. Therefore, precursory earthquakes seem to be of magnitude less than 2.4.

著者

水上 武 茂木 清夫 平賀 士郎 宮崎 務

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.2, no.2, pp.77-90, 1957-12-30

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Volcano Sakura-zima resumed explosive eruption in its summit crater after a long repose on Oct. 13. 1955, and is still active up to the present (Oct. 1957). In order to throw a light on the relation between explosive eruptions and volcanic earthquakes, we applied to this volcano the same method of seismometrical observation as being carried out in Volcano Asama. As the result, we observed four types of volcanic earthquakes originating from Sakura-zima: Namely, 1) volcanic earthquakes of the A type, 2) volcanic earthquakes of the B type, 3) earthquakes accompanied by explosive eruptions and 4) volcanic pulsation of continuous train (or harmonic tremor). On the basis of the seismometrical observation at four or six stations, we determined localities of these earthquakes of the four types. As the result, it was made clear that the epicentral area of the B type earthquakes, the explosion earthquakes and the volcanic pulsation agree with the locality of the active crater on the summit, and the A type earth quakes are originated from deeper part of the volcano. From the illustration of seismic activity and explosive eruption in Fig. 5, it seems that frequency of the B type earthquakes harmonizes with the eruptive activity. After precise examination of the development of the mentioned phenomena, we find that marked swarms of the B type earthquakes preceed in many cases to respective swarms of explosive eruption by ten or fifteen days. However, the problem is not always simple. It is neccessary to continue the observation not only in active state of the volcano but also in its calm state.

著者

水田 敏夫 小畑 正明 江上 桂子

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.249-262, 1990-07-02

被引用文献数

3

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Morphology, abundance and vertical distribution of vesicles were studied in a thick (40-60 m) andesitic lava flow, that lies in the underground of Kumamoto City. The vesicles are frozen bubbles that were fomed in the molten lavas at the time of its eruption. The lava can be divided into three zones: (1) an upper vesicular zone (2) a middle non-vesicular and compact zone and (3) a lower, thinner vesicular zone. The vesicles in the upper zone are elongated vertically, probably due to bouyancy-driven ascent of the bubbles, and those in the lower zone are flattened and elongated horizontally, that may be ascribed to a viscous shear flow at the bottom of the lava flow. Size distribution of the vesicles typically display nearly the log-normal distribution. Abundance, the mean size and the number density of the vesicles are greater in the upper zone than in the lower zone. Such vesicle distribution pattern is consistent to the hypothesis that the lava originally contained abundant bubbles when it was poured on the ground and then the bubbles started to ascent in the lava. Vesicles in the lower zone were the bubbles trapped by the advancing cooling front from the bottom surface of the lava. Bubbles that have escaped from the cold trap below have been accumulated in the upper zone and have been frozen in the lava upon cooling from the top surface. Mass balance calculation, however, indicates that much of the bubbles that were originally present in the lava, have been escaped through the lava surface. A dynamic cooling model was, therefore, proposed, that is to say, in the presence of surface flow in the lave during its cooling, impermeable lava crusts may not be maimtained so that gas bubbles may leak out of the lava into the air.

著者

宇井 忠英 柴橋 敬一

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.20, no.2, pp.51-64, 1975-08-01

被引用文献数

1 3

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Volcanic activity at the snow-capped summit of Mt. Chokai was first noticed by the captain of scheduled airline on March 1, 1974. The activity began with swarm of volcanic earthquakes, succeeded by fumarolic activity and finally explosion took place and a few craters were formed at eastern (late February-early March) and western (late April) foot of 1801 lava dome (Shinzan). The ejecta were exclusively fine-grained air-fall ash and accidental blocks. The blocks, formed the mud flow mixed with melted snow, rushed down the slope of volcanic edifice. Essential materials, such as bombs, air-fall scoria, or lava flows were not erupted. Rapid melting of snow was supposed to have been triggered by the formation of fumaroles caused by ascent of hot magma and associated juvenile gas. Thermal energy consumed for melting and evaporating snow is calculated as 3×10^<21> ergs. Total volume of mud-flow deposit is around 3×10^4 cubic meters, and that of air-fall ash is an order of 10^5 cubic meters. The entire area which showed thermal activity is approximately 700×200 meters, elongated in east-west direction. Distribution of earthquake foci was also trending east-west just passing the prehistoric summit and parasitic vents. Direction of vent alignments is the same for the most volcanoes in northeastern Japan, and is supposed to reflect regional stress field.

著者

田沢 堅太郎

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.1-15, 1984-04-01

---

Izu-Oshima volcano consists mostly of subaerially deposited volcanic products. On the sea cliff, however, the water-laid deposits are intercalated in the O_<42> (about 7, 500 yB.P.) and O_1 (about 1, 500 yB.P.) members of the Older Oshima Group. Layers of coastal gravels are observed in the Y_5-Y_1 (A.D. 1338-the present) members of the Younger Oshima Group near the present coast. These layers show imbricate structure indicating landward flow. They are interpreted as wind-transported from nearby coastal beach. These nearshore deposits were presumably resulted from the variation of the sea level in height. In the O_1 age, lagoons were formed along the coast. In the S_2 age (about A.D. 550), remarkable emergence of the shoreline occurred. After that, the island has kept subsiding gradually.

著者

松本 〓夫 林 正雄 石橋 澄

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, pp.207-208, 1976-12-15

著者

小坂 丈予 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.25, no.2, pp.108-109, 1980-07-01

著者

小坂 丈予 湊 一郎 森 彰 大平 洋子

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.19, no.1, pp.39-40, 1974-07-01

著者

荒牧 重雄 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.3, pp.203-215, 1982-10-01

被引用文献数

9

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A small-scale explosive eruption of Asama volcano lasted from 02 h 25 m to ca. 06 h, April 26, 1982. It produced a thin but far-reaching ash fall bed and very minor pyroclastic flows on the upper slopes. The main axis of ash-fall deposit extended ESE passing Tokyo to reach the Boso Peninsula. Subordinate axis extended toward the southwest to reach Lake Suwa. The wind above 5, 000 m was mainly responsible for the main axis while the low altitude winds produced the subordinate axis as it blew south to southwestwards. The amount of ash fall ranged from more than 300 g/m^2 to 100 g/m^2 at the distance of ca. 10 km from the vent and the total mass erupted was estimated to be about 8 million tons. The ash traveled at an average speed of 12 m/s as far as 200 km from the vent along the main axis. Grain size of the ash regularly decreases clockwise at the distance of about 10 km from the crater reflecting the changing wind direction with altitude. No appreciable change in the medium diameter was found for samples taken in Tokyo (130 km away, Md_φ=3.32) and the one 10 km away (Md_φ=3.26). All samples show marked skewness toward fractions finer than 63 μm suggesting that such fine particles descended in aggregates. Field evidence that in some places ash was incorporated in mud droplets strongly supports this mechanism although it was reported that ash fell apparently in a "dry" state. Ash contained several percent of hydrothermally altered older volcanic materials as well as much water-soluble substances, gypsum, alunite, etc. No clay minerals were found by x-ray diffraction, a fact in strong contrast with the ejecta of 1977-1978 eruption of Usu and 1979 eruption of Ontake volcanoes although both materials had a very similar appearance and clayey physical properties as the present ash. No vesicular, juvenile matelials were identified and the bulk consisted of polyhedral grains of hyalopilitic pyroxene andesite very much similar to recent lavas of Maekawa-yama. No liquid magma but a high-temperature steam jet deep out of the vent may have been responsible for this explosive eruption. High temperature of the erupted material was clearly demonstrated by the glowing deposits observed on the upper slopes immediately after the first phase of eruption. These were mainly laid down by the very small scale pyroclastic flows which overflowed the crater rim and descended for a short distance over the northern and southern slopes.

著者

豊田 純一 柿沢 栄一 木村 政昭

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, 1983-07-01

著者

関根 利守 桂 敬 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.23, no.2, pp.175-176, 1978-07-01

著者

岩淵 洋 浅田 昭 玉木 操

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.295-299, 1989-12