地理学評論
Online ISSN : 2185-1719
Print ISSN : 0016-7444
ISSN-L : 0016-7444
37 巻, 3 号
選択された号の論文の4件中1~4を表示しています
  • 中山 正民, 三浦 敏彦
    1964 年 37 巻 3 号 p. 115-130
    発行日: 1964/03/01
    公開日: 2008/12/24
    ジャーナル フリー
    河川における磨滅・運搬過程を知る一方法として,安倍川・大井川・木曽川・長良川・物部川・揖斐川・庄川・手取川・犬上川・日野川の10河川における平野部分で,数種の32~16mm礫を用いて,円形度を測定し,その変化及び原因の考察を行なつた.
    各河川とも,円形度の変化は礫質によつて異り,石灰岩礫は急激に円形化するのに,チャート礫はほとんど円形化が進まず,岩質による磨滅に著しく差異のあることを示す.また花崗岩・粘板岩・頁岩等は,その剥離性質のため,分裂・粉砕作用を受けやすい.
    最も多くの河川に存在する砂岩礫を用いて,円形化の原因を考察すると,河床勾配の急な河川ほど,急激なことがわかる.しかし,流域面積に比して,河川幅員の非常に広い大井川では,平均円形度は上流から下流へかけてほとんど変らず,礫の磨滅に対して,乱流が大きな役割をはたしていることを示す.
    礫の重量が減少する割合は河川の性質・運搬距離・礫質などによつて異るが,円形度を利用した推定結果では,わが国の河川砂礫は,一般的には渓口までで7%, 礫の分布限界あるいは河口まで9%程度減少するようである.さらに,これを基とした粒径変化に含まれる磨滅作用の割合は,平野部分では2%ほどで,残りの98%は篩分作用によるものと考えられる.
    円形度の変化から,磨滅作用に対する岩石抵抗の関係を求めると,チャート・石英斑岩・流紋岩・砂岩・花崗岩・頁岩・粘板岩・石灰岩の順に弱くなる.
  • 新井 正
    1964 年 37 巻 3 号 p. 131-137
    発行日: 1964/03/01
    公開日: 2008/12/24
    ジャーナル フリー
    温帯および寒帯の湖沼においては,夏期にいちじるしい水温躍層(変水層)が形成される.躍層の深さは湖沼の広さによつて異なり,日本附近ではD=6L 1/3で示される.この関係にもとづいて,湖沼の熱貯留および表面熱収支の大きさも湖沼の広さの関数として表現することができる.この報文では上記の各項に関する計算結果を示し,また躍層形成の条件についても簡単な考察をのべる.
  • 山内 秀夫
    1964 年 37 巻 3 号 p. 138-146
    発行日: 1964/03/01
    公開日: 2008/12/24
    ジャーナル フリー
    In order to investigate the cause of local variation in sea cliff retreat, the author surveyed the sea cliffs along the Pacific coast of Ohmika, Haranomachi City in Fukushima Prefecture, Japan (Fig. 1). Throughout this coast of 3 kilometers in length, we find sea cliffs with a height of 5 to 25 meters. Most of them are 20 meters high cutting a marine terrace, but some of them at the northern part are found on a side of another lower fluvial terrace, which is about 5 meters high. An obtuse angled cape divides this coast into two: northern and southern parts (Fig. 2).
    Judging from the old (1912) and the recent (1959) maps of this area, it is possible to recognize a clear difference of the land area lost between the northern and southern parts (Fig. 4). The southern part showed more loss than the northern one, though the former has a wider beach in general. Moreover, there is a difference in type between the northern and southern cliff profiles (Fig. 3). The northern cliffs are almost everywhere characterized by a vertical bluff just like a wall showing a smooth face. Deep sea-caves at their foot and narrow stepped platforms in the middle of the cliff profiles also can be seen at some places in thenorthern part. On the other hand, the southern cliffs are rough and vertical at the lower part and also quite steep, but not vertical, at the upper. There are no sea-caves but shallow notches at their foot. Wave-cut benches could be seen at the foot of the cliffs in the southern part.
    As regards to the fallen debris at the foot of these cliffs in the southern part, a large amount of all sizes having fresh faces and sharp edges are to be found. On the contrary, in northern part, there are less debris but most of them are larger and well-rounded.
    As for the geology of this coast, they consist generally of sand and gravel deposits at the upper, a sandy mudstone layer at middle and lower (Fg.5). At the southern part, this sandy mudstone layer is divided into two by an inserted unconsolidated stratum of sand, and this sandy stratum locates just at the foot of the southern cliffs, The middle and lower parts of the northern cliffs consist of only homogeneous mudstones.
    To know one of the resisting powers of these strata against wave attack, the author measured hardness for every stratum on the southern and northern cliffs by using a penetrometer, an instrument for measuring soil consistency (Tab.2). The strikes and intervals of the joints in the mudstone layers are also important factors for destruction of the cliffs by storm waves. In the southern part, the strikes are oblique to the present shoreline. On the contrary, the strikes of the northern cliffs are parallel to the shoreline.
    Other factors concerned with destruction of these cliffs such as wave, wind (Fig.7) and shallow water topography (Fig.6) were also examined, but the author considered that they are not so much concerned with the difference of cliff retreat as geological factors in this coast are.
    Finally it was proven that the main cause of local variation in cliff retreat, and cliff profiles between the northern and southern parts on this coast depend mainly upon the geological factors, such as differences in stratigraphy, joints in mudstone layers and hardness of strata on this coast.
  • 1964 年 37 巻 3 号 p. 147-161_2
    発行日: 1964/03/01
    公開日: 2008/12/24
    ジャーナル フリー
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