Journal of Geography (Chigaku Zasshi)
Online ISSN : 1884-0884
Print ISSN : 0022-135X
ISSN-L : 0022-135X
Volume 89 , Issue 6
Showing 1-6 articles out of 6 articles from the selected issue
  • Shuji IWATA
    1980 Volume 89 Issue 6 Pages 319-335
    Published: December 25, 1980
    Released: November 12, 2009
    JOURNALS FREE ACCESS
    Movement types and intensity of surface processes were investigated on the slopes above the forest line of Mt. Shirouma-dake (2, 933 m. a. s. 1., 36°45'N, 137°45'E). The slopes studied are vegetation-free or sparsely vegetation covered ones that are mantled with rubble layers (thin layers of rock fragments).
    There are six types of slow mass movement operating on the rubble slopes talus creep, frost creep, needle ice creep, gelifluction, rapid solifluction, and a movement derived from snowpack creep. Rapid mass movement processes such as rockfalls, debris flows, and rolling down of stones often occur, but only a small amount of the materials is moved. Running water, supplied by rainfall and melting of snow and ground ice, carries the debris. While the amount of the materials moved by wash are not so large on the rubble slopes, the channel erosion is one of the important processes on the nivational rubble slopes that are covered by the long lasting snowpatches. The particle movement by wind and the transport in solution are probably insignificant on the study slopes.
    Relative vertical mass transfer in unit area that is a geomorphic work of process is estimated for a quantitative comparison of process intensity. The processes acting on the slopes are grouped as following five process sets according to their rates and types of the movements. I) Periglacial process set with low raet. II) Periglacial process set with medial rate. III) Nivational process set with low rate. IV) Nivational process set with medial rate. V) Nivational process set with high rate. The slow mass movements cover over 75 percent of the total mass transfer of the periglacial process set. The value of the slow mass movements of the nivational process set, however, is limited less than 75 percent of the total value and the remainder is mostly comprised in value of channel erosion. While the periglacial process sets occur on the periglacial rubble slopes that are put under the snow free dry conditions throughout the year, the nivational process sets occur on the nivational rubble slopes. The rate of these process sets vary according to the differences of the climatic environments, slope forms and gradients, and slope materials ; size of the surface material and thickness of the rubble layer. Among them the slope materials perform the important role. The process sets with low rate (less than 3.0× 103m· t/ Km2·yr.) correspond with the processes occurring on the slopes which are mantled by the boulder size debris. The process sets with high rate (over 6.0 × 103m·t/ Km2·yr.) occur both on the nivational slope with steep gradients and the nivational slopes covered by fine materials.
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  • Shizuo SHINDOU
    1980 Volume 89 Issue 6 Pages 336-347
    Published: December 25, 1980
    Released: November 12, 2009
    JOURNALS FREE ACCESS
    Following the groundwater discharge control which was enforced in 1961 in the urban area of Tokyo Metropolis, the Metropolitan Government prohibited, from 1972 on, the drilling of deep wells in the suburban area (Santama district) and gave guidance in reducing the discharge of the existing wells.
    As a result, the groundwater level has been showing a gradual recovery. This tendency is not a local one but is recognized throughout the Santama district.
    Such a phenomenon cannot be readily judged whether it is merely a temporary state or it indicates a net rise of water level due to supply from rivers or from unconfined groundwater, but it will provide a good opportunity for knowing the behavior of confined groundwater.
    The present paper is made up of a part of the results of the investigation in the Musashino district and in the urban area of Tokyo Metropolis. This research was carried out by the request from the Environmental Pollution Bureau of the Metropolitan Government.
    In part I of this paper the author described an outline of hydrogeological condition of the Musashino district as a background of the study.
    In part II he mentioned the characteristics of annual change of groundwater level due to artificial impact and he showed some interpretations about groundwater recharge mechanism in short term.
    In III he clarified large scale recharge mechanism which is induced by long term discharge.
    In part W he showed two kinds of piezometric surface contour map based on the geological horizon of aquifer (one is Tokyo group and the other is Kazusa group), and then he clarified that water level difference between the upper and lower parts increases throughout the district with the increase of groundwater utilization.
    As the result, he emphasized the following points.
    1. In the early stage of groundwater utilization, recharge for confined groundwater proceeds in the form of compensation for the “elastic strain” in the aquifer which is caused by discharge.
    2. In the stage where the groundwater utilization is fairly advanced, several processes of recharge ndchanism are considered.
    Namely, the recharge in a relatively short period is related chiefly to the vertical movement of flow (in the form of squeeze and leakage), while the recharge in a long period is made in the form of compensation by the flow from the surrounding areas according to hydraulic gradient.
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  • Yoshihiko AKAGI
    1980 Volume 89 Issue 6 Pages 348-360
    Published: December 25, 1980
    Released: November 12, 2009
    JOURNALS FREE ACCESS
    The purpose of this paper is to examine the extent of land deformation through the development of large-scale housing estates and the disasters that will be brought about by this land deformation.
    In the Hiroshima area most new land needed as residential, agricultural or industrial land has been obtained by reclamation of the shallow bay in front of the Hiroshima delta after Hiroshima castle wae built in 1591. But since about 1960 there has been a change in these land uses, that is, large-scale housing estates have been developed in the granitic dissected pediments and hills around the Hiroshima delta.
    The longitudinal lengths of pediments in this area are about 300-2000 meters, and inclinations are about 7-8 degrees in the lower-middle sections of the pediments and 12-15 degrees in the upper section. The inclinations of escarpments behind the pediments are about 26-30 degrees, occasionally 45 degrees. The height of the lower ends of these pediments is about 50 meters above sealevel. These pediments have been dissected by valleys to depths of 50-100 meters. As a result most of the original pediment surfaces have disappeared. It is supposed that the hill lands are dissected pediplains. Most of these dissected pediments and hill lands have been deeply weathered and are readily cut into by bulldozers.
    The large-scale housing estates are reclaimed by the method of cutting spurs and filling valleys, taking into account a balance between the quantities of cut and fill. The mean cut depth of the spurs is about 20 meters.
    The number and area of large-scale housing estates in this area are shown in Table 1. Large-scale housing estate development has been carried out here since 1960, but since the oil crisis development has slowed down. Data was obtained on the area and movement of earth in 15 housing estates in order to calculate the quantities of earth moved artificially for the development of large-scale housing estates in this area (Table 2). The data from which these volumes have been calculated are as follows : 1) The mean depth of cut earth is 10.02 meters; 2) The ratios of cut to fill are almost even both in area and in volume; 3) The area of large-scale housing estates developed or planned to be developed in this area is 3203.7 hectares. Thus the amount of earth moved or planned to be moved in this area is about 160, 000, 000 m3 (1, 600 ha × 10 m). The volume of moved earth per person living in this type of housing estate is estimated at about 500 m3 from a density rate of 100 persons per hectare. The population of Hiroshima area in 1979 was 1, 144, 455. The population growth in this area from 1960-1979 was 489, 250 and about 46% of this consists of people living in this type of housing estate.
    In the Hiroshima area mudflows caused by heavy rainfall have occurred ten times since the beginning of this century. The total number of people killed by these mudflows is 2, 032. All these mudflows occurred in the escarpments behind the pediments, and most of the mudflows ran along the valleys that dissected the pediments. The valleys that have dissected the pediments in the large-scale housing estates are now filled up with artificially moved earth. So if mudflows occur in the escarpments behind the pediments in which large-scale housing estates have been developed the filled parts of the housing estates will suffer heavy damage.
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  • Teiichi KOBAYASHI
    1980 Volume 89 Issue 6 Pages 361-371
    Published: December 25, 1980
    Released: November 12, 2009
    JOURNALS FREE ACCESS
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  • [in Japanese]
    1980 Volume 89 Issue 6 Pages 372-373
    Published: December 25, 1980
    Released: November 12, 2009
    JOURNALS FREE ACCESS
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  • S. IWATA
    1980 Volume 89 Issue 6 Pages Plate1-Plate2
    Published: December 25, 1980
    Released: November 12, 2009
    JOURNALS FREE ACCESS
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