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Hiromitsu TANIGUCHI
Article type: Article
1980 Volume 25 Issue 4 Pages
217-229
Published: December 01, 1980
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In the present study, the thicknesses of the hydration layers along the cracks in the glassy groundmass of Kdzu-shima rhyolite were measured on thin sections, and the results are shown in histograms. The histograms show a single or more peaks which give the true thickness of the hydration layer. The thickest peak is considered to be related to the original emplacement of the lava flow, and the other to the episodes after the emplacement. Based on this assumption, the relations between the peaks and the geological evidences were examined. The main results are summarized as follows : On the basis of analyses of the histograms some knowledges about the episodes were found including lava emplacement, which give the cracks accompanied by hydration layer. It was also found that the absolute ages of those episodes might be estimated from the above-mentioned analyses.
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Tutomu SUGlURA, Ryuichi SUGISAKI, Yoshihiko MIZUTANI, Minoru KUSAKABE
Article type: Article
1980 Volume 25 Issue 4 Pages
231-244
Published: December 01, 1980
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Ontake Volcano suddenly began to erupt on its south-western flank near the summit at 05
h20
m on Oct, 28, 1979, forming several new craters and ejecting large amounts of volcanic ash and steam. Up to that time, the volcano had been believed to be dormant, though there were weak geothermal activities at a part of the south-western flank of the volcano, Jigokudani. This paper reports some results obtained by preliminary examination of volcanic ashes, thermal waters and gases collected on and around Ontake Volcano during the early stage of eruptive activity. The volcanic ashes are homogeneous in chemical and mineralogical compositions, and similar in chemical composition to the pre-historic volcanic ashes. The ashes contain pyrite, anhydrite, cristobalite and clay minerals. The sulfur isotopic equilibrium temperature is estimated to be about 400℃ for pyrite-anhydrite pairs in the volcanic ashes. The estimated temperature is apparently too high for the temperature of phreatic explosion. The interpretation of this isotopic data remains unsettled. The thermal waters collected from the boiling pools in craters are enriched in D and
18O. The isotopic enrichment is probably caused by evaporation of water at the surface of boiling pool. The hydrogen and oxygen isotopic data also suggest that spring waters issuing around Ontake Volcano are meteoric in origin. Nigorigo Hot Spring, about 4 km north-west of Ontake Volcano, showed significant increases in the concentrations of major dissolved chemical components soon after the eruption, but since then no significant change in chemical and isotopic composition has been observed
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Tatsuhiko WADA, Shigetomo KIKUCHI, Hiroyasu ONO
Article type: Article
1980 Volume 25 Issue 4 Pages
245-253
Published: December 01, 1980
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On the 6th of September, 1979, the explosive eruption happened at the 1st crater of Naka-dake, the only active crater of Volcano Aso. The eruptive energy amounts to 5x10
18 erg. The distribution of ejecta was particularly shaped, that is, in a butterfly pattern. Moreover, the ground motions at several observing points arranged near the crater were predominant in horizontal and transversal component. These observed results suggest us that two openings were formed at the crater bottom and generated a force of single couple type.
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Kazuaki NAKAMURA
Article type: Article
1980 Volume 25 Issue 4 Pages
255-269
Published: December 01, 1980
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Rift zones are characteristic features of Hawaiian volcanoes. They are long narrow zones of flank fissure eruptions but are distinct from ordinary flank eruption sites on stratovolcanoes in that eruptions, and therefore dike intrusions, occur repeatedly at the same general place for a long time and thus cause a considerable amount of lateral spreading. This spreading should somehow be accomodated. Moreover, the stress field should remain the same after accomodation in order for a new dike to intrude in the same orientation. The current spreading episode in Iceland (BJORNSSON et al., 1979) between North American and European plates revealed that the sequence of events in the spreading process is similar to that observed for Hawaiian volcanic activities. This implies that the process of plate separation and accretion is nothing but the activity of rift zones. Constructional plate boundaries may be regarded as composed of a chain of rift zones and associated feeding polygenetic centers. Room necessary for repeated dike intrusion is supplied in the case of spreading centers, by the lateral motion (separation) of lithosphere over asthenosphere. In the case of Hawaii, sliding of the volcanic edifice over a deep sea sediment layer may be the analogous mechanism such as appears to have occurred during the 1975 Kalapana earthquake, as studied by ANDO (1979) and FURUMOTO and KOVACH (1979). Kalapana earthquake had been anticipated by SWANSON et al. (1976) as one of the repeated steps as the east rift zone has continuously dilated. Thus, the primary cause for the long, well developed rift zones of Hawaiian volcanoes may be in the existence of thick enough oceanic sediments serving as a potential sliding plane beneath the volcanic edifices. Lack of rift zones in Galapagos shields which grew over the young ocean floor with rough topography is consistent with this view.
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Tatsuhiko WADA
Article type: Article
1980 Volume 25 Issue 4 Pages
271-278
Published: December 01, 1980
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Mechanism generating the volcanic tremor of the 1st kind (characterized by period of about 1 sec., and transversally polarized orbit, as firstly pointed out by SASSA (1935)) observed at Aso Volcano, is deduced from the “gas-turbine effect” of high speed gas stream passing through volcanic vent. Assuming the probable length of the vent (500-600 m) and the probable value of s-wave speed (1.0-1 .2 km/sec.), the mechanism is proved to be compatible for almost all natures of the tremor of the 1st kind.
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Osamu MATSUBAYASHI
Article type: Letter
1980 Volume 25 Issue 4 Pages
279-280
Published: December 01, 1980
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Sachio EHARA, Kozo YUHARA, Akira SHIGEMATSU
Article type: Letter
1980 Volume 25 Issue 4 Pages
281
Published: December 01, 1980
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Shigeo ARAMAKI
Article type: Letter
1980 Volume 25 Issue 4 Pages
282-283
Published: December 01, 1980
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Y. Tatsumi
Article type: Abstract
1980 Volume 25 Issue 4 Pages
285-
Published: December 01, 1980
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T. Tohara
Article type: Abstract
1980 Volume 25 Issue 4 Pages
285-286
Published: December 01, 1980
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H. Sato
Article type: Abstract
1980 Volume 25 Issue 4 Pages
286-
Published: December 01, 1980
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K. Shiraki, N. Kuroda, H. Urano, S. Umino, T. Ishii
Article type: Abstract
1980 Volume 25 Issue 4 Pages
286-287
Published: December 01, 1980
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M. Shimazu
Article type: Abstract
1980 Volume 25 Issue 4 Pages
287-
Published: December 01, 1980
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S. Okamura
Article type: Abstract
1980 Volume 25 Issue 4 Pages
287-
Published: December 01, 1980
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A. Fujinawa, K. Aoki
Article type: Abstract
1980 Volume 25 Issue 4 Pages
287-288
Published: December 01, 1980
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T. Yamaguchi
Article type: Abstract
1980 Volume 25 Issue 4 Pages
288-
Published: December 01, 1980
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E. Iwasaki
Article type: Abstract
1980 Volume 25 Issue 4 Pages
288-289
Published: December 01, 1980
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T. Ishii
Article type: Abstract
1980 Volume 25 Issue 4 Pages
289-
Published: December 01, 1980
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K. Uto
Article type: Abstract
1980 Volume 25 Issue 4 Pages
289-290
Published: December 01, 1980
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H. Hiyagon, M. Ozima
Article type: Abstract
1980 Volume 25 Issue 4 Pages
290-
Published: December 01, 1980
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S. Togashi
Article type: Abstract
1980 Volume 25 Issue 4 Pages
290-291
Published: December 01, 1980
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H. Kurasawa, S. Kawachi
Article type: Abstract
1980 Volume 25 Issue 4 Pages
291-
Published: December 01, 1980
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T. Nagao
Article type: Abstract
1980 Volume 25 Issue 4 Pages
291-292
Published: December 01, 1980
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S. Nakada, M. Seno
Article type: Abstract
1980 Volume 25 Issue 4 Pages
292-
Published: December 01, 1980
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T. Soya, Y. Katsui
Article type: Abstract
1980 Volume 25 Issue 4 Pages
292-
Published: December 01, 1980
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K. Okumura, T. Soya, K. Ono, H. Satoh
Article type: Abstract
1980 Volume 25 Issue 4 Pages
292-293
Published: December 01, 1980
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Y. Oba
Article type: Abstract
1980 Volume 25 Issue 4 Pages
293-
Published: December 01, 1980
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M. Seino
Article type: Abstract
1980 Volume 25 Issue 4 Pages
293-294
Published: December 01, 1980
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H. Watanabe
Article type: Abstract
1980 Volume 25 Issue 4 Pages
294-
Published: December 01, 1980
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H. Yamashita, I. Yokoyama
Article type: Abstract
1980 Volume 25 Issue 4 Pages
294-
Published: December 01, 1980
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I. Yokoyama, H. Ohshima, T. Maekawa
Article type: Abstract
1980 Volume 25 Issue 4 Pages
294-295
Published: December 01, 1980
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E. Miyajima, Y. Nishida, T. Maekawa
Article type: Abstract
1980 Volume 25 Issue 4 Pages
295-
Published: December 01, 1980
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T. Wada
Article type: Abstract
1980 Volume 25 Issue 4 Pages
295-
Published: December 01, 1980
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A. Kubotera
Article type: Abstract
1980 Volume 25 Issue 4 Pages
295-296
Published: December 01, 1980
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T. Suzuki
Article type: Abstract
1980 Volume 25 Issue 4 Pages
296-
Published: December 01, 1980
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I. Moriya
Article type: Abstract
1980 Volume 25 Issue 4 Pages
296-
Published: December 01, 1980
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Y. Nakamura
Article type: Abstract
1980 Volume 25 Issue 4 Pages
296-297
Published: December 01, 1980
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T. Kobayashi
Article type: Abstract
1980 Volume 25 Issue 4 Pages
297-
Published: December 01, 1980
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K. Watanabe
Article type: Abstract
1980 Volume 25 Issue 4 Pages
297-298
Published: December 01, 1980
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H. Kamata, K. Mimura
Article type: Abstract
1980 Volume 25 Issue 4 Pages
298-
Published: December 01, 1980
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K. Sakaguchi, T. Ui
Article type: Abstract
1980 Volume 25 Issue 4 Pages
298-
Published: December 01, 1980
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T. Kumagai, H. Takahashi
Article type: Abstract
1980 Volume 25 Issue 4 Pages
299-
Published: December 01, 1980
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Y. Tanaka, Y. Sawada, M. Churei
Article type: Abstract
1980 Volume 25 Issue 4 Pages
299-
Published: December 01, 1980
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S. Ehara, K. Yuhara, T. Noda
Article type: Abstract
1980 Volume 25 Issue 4 Pages
299-300
Published: December 01, 1980
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S. Ehara, K. Yuhara
Article type: Abstract
1980 Volume 25 Issue 4 Pages
300-
Published: December 01, 1980
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S. Uyeda, T. Watanabe
Article type: Abstract
1980 Volume 25 Issue 4 Pages
300-301
Published: December 01, 1980
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D. Shimozuru, S. Aramaki, T. Ui, T. Takahashi, A. Ono
Article type: Abstract
1980 Volume 25 Issue 4 Pages
301-
Published: December 01, 1980
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S. Aramaki, D. Shimozuru, T. Ui, T. Takahashi, A. Ono
Article type: Abstract
1980 Volume 25 Issue 4 Pages
301-302
Published: December 01, 1980
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Y. Sawada, S. Wakui, M. Komiya
Article type: Abstract
1980 Volume 25 Issue 4 Pages
302-
Published: December 01, 1980
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Y. Ito, C. Kawakami, Clancy Hinrichs
Article type: Abstract
1980 Volume 25 Issue 4 Pages
302-
Published: December 01, 1980
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