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Takaaki FUKUOKA, Kunihiko KIGOSHI
Article type: Article
1971 Volume 15 Issue 3 Pages
111-119
Published: February 01, 1971
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The date of volcanic ejection can be determined by the measurements on the state of radioactive disequilibrium between ionium and uranium in a mineral separated from the ejecta. The approach to the radioactive equilibrium state is shown in Fig. 1. From this figure we can conclude that the ionium dating requires uranium and thorium isotopic analysis on two different kinds of minerals. In order to make accurate dating, higher contents of uranium and thorium, and big difference of U/Th activity ratios in these minerals are desirable. In Table 2, contents of uranium and thorium, and U/Th activity ratios in minerals separated from pumice of Torihama pyroclastic flow in southern Kyushu are shown. In this example zircon and glass were most suitable for ionium dating. The results of ionium dating for volacnic ejecta, which are shown in Table 3, were in good agreement with the
14C ages and with the ages estimated from mass color of zircons except
14C age on pumice (PmI) of Ontake volcano. The zircons separated from pumice of Hijiori pyroclastic flow and PmI were not on the isochrones (Fig.3). This means that these zircons were not simultaneously crystallized with other minerals. Possible ways of introduction of these zircons in pumice are discussed in connection with the measured Io/Th and U/Th activity ratios.
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Ichio MORIYA
Article type: Article
1971 Volume 15 Issue 3 Pages
120-131
Published: February 01, 1971
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Mt. Akagi is a Quaternary volcano situated in the northwestern margin of the Kanto Plain, Gunma Prefecture. This is a conical volcano with a small caldera (2-4 km across) at the summit. The history of this volcano is divided into three stages as follows : (1) the older stratovolcano (2) the younger stratovolcano (3) the central cone. In the first stage a great deal of andesite lavas effused, accompanied with considerable volumes of scoria falls and flows, as the result a cone about 2500m high above sea level and about 60 cubic kilometers in volume was formed. Through the second stage paroxysmal activities were dominant erupting pyroclastic falls and flows about 40 cubic kilometers in volume. Just before the third stage the small caldera was formed in the summit of the younger stratovolcano composed of loose pyroclastic materials. In the caldera two dacite dome lavas extruded. The domes are underlain by the Kanuma pumice fall deposit which is correlated with the upper Musashino loam (several ten thousand years B.P.) and overlain by the Itahana pumice fall deposit (10000-20000 years B.P.). So it is presumed that the activity of Akagi Volcano was finished by 20000-30000 years B.P.
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Takeo SUZUKI
Article type: Article
1971 Volume 15 Issue 3 Pages
132-139
Published: February 01, 1971
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Compressive strength of natural welded-tuff and artificial welded-tuff was measured. The artificial welded-tuff was made by slight welding of natural welded-tuff by a sintering method. Both welded-tuffs made of same material showed same compressive strength for the same porosity. In view of the above facts the most reasonable conclusion is that the structure of the artificial welded-tuff is equal to that of the natural one, and therefore, the sintering equation (Eq. 1 in the text.) is available for the studies of natural welded-tuff.
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Y. Tomatsu
Article type: Abstract
1971 Volume 15 Issue 3 Pages
140-
Published: February 01, 1971
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Y. Oba
Article type: Abstract
1971 Volume 15 Issue 3 Pages
140-
Published: February 01, 1971
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S. Ando
Article type: Abstract
1971 Volume 15 Issue 3 Pages
140-141
Published: February 01, 1971
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J. Ossaka, K. Urave, Y. Ohira, M. Kasai
Article type: Abstract
1971 Volume 15 Issue 3 Pages
141-
Published: February 01, 1971
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H. Nakagawa, K. Oide, S. Oike, T. Matsuyama, O. Nanasaki, N. Chuman, H ...
Article type: Abstract
1971 Volume 15 Issue 3 Pages
141-
Published: February 01, 1971
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S. Oike, H. Nakagawa, T. Matsuyama, O. Nanasaki, T. Ishida
Article type: Abstract
1971 Volume 15 Issue 3 Pages
142-
Published: February 01, 1971
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H. Satoh
Article type: Abstract
1971 Volume 15 Issue 3 Pages
142-
Published: February 01, 1971
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A. Suwa, M. Watanabe, S. Kanazawa, Y. Sawada, S. Kasiwabara, T. Kuriha ...
Article type: Abstract
1971 Volume 15 Issue 3 Pages
142-143
Published: February 01, 1971
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K. Tanaka, S. Hori, M. Kasahara
Article type: Abstract
1971 Volume 15 Issue 3 Pages
143-
Published: February 01, 1971
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Takeshi Ohguchi
Article type: Abstract
1971 Volume 15 Issue 3 Pages
143-
Published: February 01, 1971
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Z. Suzuki, M. Kasahara, S. Ueki
Article type: Abstract
1971 Volume 15 Issue 3 Pages
144-
Published: February 01, 1971
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M. Kasahara
Article type: Abstract
1971 Volume 15 Issue 3 Pages
144-145
Published: February 01, 1971
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K. Chihar, K. Osawa
Article type: Abstract
1971 Volume 15 Issue 3 Pages
145-
Published: February 01, 1971
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T. Ishikawa
Article type: Abstract
1971 Volume 15 Issue 3 Pages
145-146
Published: February 01, 1971
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O. Oshima
Article type: Abstract
1971 Volume 15 Issue 3 Pages
146-
Published: February 01, 1971
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M. Kono, S. Aramaki
Article type: Abstract
1971 Volume 15 Issue 3 Pages
146-
Published: February 01, 1971
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K. Mimura, U. Fujimoto, T. Hyuga, S. Ichikawa, S. Kawachi, M. Taneichi
Article type: Abstract
1971 Volume 15 Issue 3 Pages
146-147
Published: February 01, 1971
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T. Miyazaki, N. Gyoda, S. Hiraga
Article type: Abstract
1971 Volume 15 Issue 3 Pages
147-
Published: February 01, 1971
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T. Ishikawa, Y. Katsui, T. Nakamura
Article type: Abstract
1971 Volume 15 Issue 3 Pages
147-148
Published: February 01, 1971
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Article type: Abstract
1971 Volume 15 Issue 3 Pages
148-
Published: February 01, 1971
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T. Fukuoka
Article type: Abstract
1971 Volume 15 Issue 3 Pages
148-
Published: February 01, 1971
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H. Kurasawa, K. Ono, H. Hattori
Article type: Abstract
1971 Volume 15 Issue 3 Pages
148-149
Published: February 01, 1971
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K. Ono
Article type: Abstract
1971 Volume 15 Issue 3 Pages
149-
Published: February 01, 1971
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N. Yamada, K. Kawada, T. Morohashi
Article type: Abstract
1971 Volume 15 Issue 3 Pages
149-150
Published: February 01, 1971
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T. Ui
Article type: Abstract
1971 Volume 15 Issue 3 Pages
150-
Published: February 01, 1971
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S. Taneda
Article type: Abstract
1971 Volume 15 Issue 3 Pages
150-
Published: February 01, 1971
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I. Iwasaki, T. Ozawa, M. Yoshida, K. Yamaya
Article type: Abstract
1971 Volume 15 Issue 3 Pages
150-151
Published: February 01, 1971
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T. Ishikawa
Article type: Abstract
1971 Volume 15 Issue 3 Pages
151-
Published: February 01, 1971
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K. Yagi
Article type: Abstract
1971 Volume 15 Issue 3 Pages
151-
Published: February 01, 1971
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Y. Oki, H. Hirano
Article type: Abstract
1971 Volume 15 Issue 3 Pages
152-
Published: February 01, 1971
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K. Noguchi, Y. Aikawa
Article type: Abstract
1971 Volume 15 Issue 3 Pages
152-
Published: February 01, 1971
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N. Isshiki
Article type: Abstract
1971 Volume 15 Issue 3 Pages
152-153
Published: February 01, 1971
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[in Japanese]
Article type: Abstract
1971 Volume 15 Issue 3 Pages
153-
Published: February 01, 1971
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T. Wada, K. Kamo, H. Ono, Y. Sudo
Article type: Abstract
1971 Volume 15 Issue 3 Pages
153-154
Published: February 01, 1971
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K. Nishi
Article type: Abstract
1971 Volume 15 Issue 3 Pages
154-
Published: February 01, 1971
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Y. Tomoda, K. Kobayashi, K. Kitazawa, J. Segawa
Article type: Abstract
1971 Volume 15 Issue 3 Pages
154-155
Published: February 01, 1971
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T. Minakami
Article type: Abstract
1971 Volume 15 Issue 3 Pages
155-
Published: February 01, 1971
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N. Fujii, M. Osako, I. Kaneoka
Article type: Abstract
1971 Volume 15 Issue 3 Pages
155-
Published: February 01, 1971
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T. Suzuki
Article type: Abstract
1971 Volume 15 Issue 3 Pages
155-156
Published: February 01, 1971
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K. Sato
Article type: Abstract
1971 Volume 15 Issue 3 Pages
156-
Published: February 01, 1971
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N. Ueno, I. Kaneoka, M. Ozima
Article type: Abstract
1971 Volume 15 Issue 3 Pages
156-
Published: February 01, 1971
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I. Kaneoka
Article type: Abstract
1971 Volume 15 Issue 3 Pages
156-157
Published: February 01, 1971
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I. Kaneoka, M. Ozima
Article type: Abstract
1971 Volume 15 Issue 3 Pages
157-
Published: February 01, 1971
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T. Ui
Article type: Abstract
1971 Volume 15 Issue 3 Pages
157-
Published: February 01, 1971
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B. Iwasaki, T. Katsura
Article type: Abstract
1971 Volume 15 Issue 3 Pages
157-158
Published: February 01, 1971
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Y. Aoki, T. Yukutake, K. Nakamura
Article type: Abstract
1971 Volume 15 Issue 3 Pages
158-
Published: February 01, 1971
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I. Yokoyama
Article type: Abstract
1971 Volume 15 Issue 3 Pages
158-
Published: February 01, 1971
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