地理学評論
Online ISSN : 2185-1719
Print ISSN : 0016-7444
52 巻 , 4 号
選択された号の論文の5件中1~5を表示しています
  • 太田 陽子, 平川 一臣
    1979 年 52 巻 4 号 p. 169-189
    発行日: 1979/04/01
    公開日: 2008/12/24
    ジャーナル フリー
    能登半島の海成段丘を調査して,第四紀中・後期における古地理の推移と地殻変動を考察した.能登半島の海成段丘は,高位からT, H, M, Lの4群に大別され,さらにTは7段,Hは4段,Mは3段に細分される.M1面は最も連続的に分布し,貝化石と海進を示す厚い堆積物とを伴う広い面で,最終間氷期の海進(下末吉海進)に形成されたと考えられる.M1面より高位に約10段もの海成段丘があるので,その分布から,能登半島の大部分が更新世中期以降の離水によって生じたものであるとみられる.M1面の旧汀線高度ば北端の110mから南部の20mまで,全体として南下り,富山湾側への緩い低下を伴う傾動が推定される.しかし,半島全体が一つの傾動地塊をなすのではなく,1辺10~20km,それぞれが南下りの傾動を示す数個の小地塊の集合からなっている.M1面とそれより古期の段丘の傾動の量はほぼ等しいので,各地塊の傾動はM1面形成後に活発になったと考えられる.北端部での平均隆起速度は1m/1,000年となる.
  • 大内 俊二
    1979 年 52 巻 4 号 p. 190-198
    発行日: 1979/04/01
    公開日: 2008/12/24
    ジャーナル フリー
    In Japan, most of rivers on alluvial fans are bounded by the artificial levees, which may affect or change fluvial processes of the rivers. In order to properly analyze the present stages in the development of alluvial fans, it is necessary to know differences of fluvial characteristics before and after building artificial levees.
    Assuming that a present river bed shows the present fluvial characteristics and the other part of the fan surfaces shows the former fluvial characteristics before building artificial levees, low-water channel patterns were investigated using airphotos and the maximum grain sizes of fan deposits were measured in the field on Oi, Tetori, Kurobe, and Joganji alluvial fans in the central Japan.
    Low-water channels on the present river beds show a braided pattern, and have directions of the flows along the artificial levees. The former low-water channels before the build of artificial levees, shown on the fan surfaces, also have a braided pattern and their main directions of the flows are radial from the fan apex (Fig. 1). Comparing the present low-water channels with the older, the former has a larger sinuosity than the latter. Intersect-ing angles of the low-water channels show the same tendency (Table 1).
    At the same distances from the fan apexes, the maximum grain sizes on the present river beds are larger than those on the other part of the fan surfaces or the former river beds (Fig. 2).
    These differences might come from the changes of river conditions or fluvial processes. In this study, examined are the three possible causes, that is, basin transitions by forest cuttings or landslides, artificial reformations of the river beds, and boundings of rivers by artificial levees.
    After due considerations, the author concluded that the main cause of changing the flu-vial characteristics was the builds of artificial levees or fixing of river channels. Because the artificial levees bound the course of flows, the river can not completely adjust their morphologies or fluvial characteristics under given conditions. Especially under a flood with a given volume, flood flows may be concentrated in the present river bed by artificial levees and the velocity of the flood or the tractive force may be much higher than that in the river bed without artificial levees.
    This study indicates that effects of artificial levees can not be neglected in order to analyze processes of alluvial fan formation or histories of alluvial fan development in Japan with considering the present river processes.
  • 海津 正倫
    1979 年 52 巻 4 号 p. 199-208
    発行日: 1979/04/01
    公開日: 2008/12/24
    ジャーナル フリー
  • 1979 年 52 巻 4 号 p. 209-211,215
    発行日: 1979/04/01
    公開日: 2008/12/24
    ジャーナル フリー
  • 1979 年 52 巻 4 号 p. 214
    発行日: 1979年
    公開日: 2008/12/24
    ジャーナル フリー
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