地学雑誌
Online ISSN : 1884-0884
Print ISSN : 0022-135X
ISSN-L : 0022-135X
77 巻 , 5 号
選択された号の論文の3件中1~3を表示しています
  • 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
    1968 年 77 巻 5 号 p. 255-283
    発行日: 1968/10/25
    公開日: 2009/11/12
    ジャーナル フリー
    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.
  • 阪口 豊
    1968 年 77 巻 5 号 p. 284-310
    発行日: 1968/10/25
    公開日: 2009/11/12
    ジャーナル フリー
    The author studied morphometrically the characteristics of the height distribution of many mountains over the world by using large scale topographic maps. From the data obtained, the author illustrated newly devised hypsographic curves using semi-logarithmic paper.
    Morphogenetic movement is discontinuous up-warping, which total amount of uplift during each cycle of movement ranges from several hundreds to two thousands meters, when we see height of mountain with hecto meters level. Total amount of uplift during one cycle of movement is not significantly different between orogenic zones and continental masses. The essential difference between both regions on the morphogenetic movement may be that of the duration of the stage of standstill after a quick uplift of the early stage of a cycle of movement.
    The hypsographic curve is an assemblage of several partial exponential curves. There is no mountain consisting of only one exponential curve. The contact points of the partial exponential curves are made every uplift.
    These points are conserved at the same level, until each point coincides to a summit of mountain as a result of erosion.
    From this law, the author inferred that every mountain is transformed by two different manners, that is, logarithmic parallel retreat and logarithmic rotating lowering of the “graded profile”. The latter appears in the lowest “graded profile”, and the former in the other ones. This inference was proved by the characteristics of the vertical distribution of the degree of dissection of a mountain.
  • 森本 良平, 小坂 丈予
    1968 年 77 巻 5 号 p. Plate1-Plate2
    発行日: 1968/10/25
    公開日: 2009/11/12
    ジャーナル フリー
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