地理学評論 Ser. A
Online ISSN : 2185-1735
Print ISSN : 0016-7444
57 巻 , 10 号
選択された号の論文の5件中1~5を表示しています
  • 吉川 虎雄
    1984 年 57 巻 10 号 p. 691-702
    発行日: 1984/10/01
    公開日: 2008/12/25
    ジャーナル フリー
    Landforms are shaped by tectonic movement and sculptured by denudational processes. Davis (1899) deduced landform development by denudational processes, postulating prolonged stillstand of a landmass following rapid uplift, but W. Penck (1924) emphasized that land forms were formed by tectonic and denudational processes proceeding concurrently at different rates. These two distinctive views of tectonics and denudation in geomorphology have been discussed many times, but actual conditions of these processes have rarely been assessed quantitatively.
    Schumm (1963) and Bloom (1978) estimated modern rates of uplift to be much greater than those of denudation, and supported to some extent the Davisian assumption of rapid uplift of a landmass, which allowed little denudational modification of the area during the period of uplift. Recent geomorphological study has achieved many excellent results concerning tectonic and denudational processes and their products, but landform development by concurrent tectonics and denudation has scarcely been investigated intensively.
    As a result of the author's estimate in Japan (Yoshikawa, 1974), modern rates of uplift are generally greater than those of denudation, but denudation rates are greater than or approximately equal to uplift rates in high mountains of Central Japan and on the Pacific slope of Southwest Japan; in these mountains both rates are usually of the order of 1mm/yr. These mountains have been rapidly uplifted and intensely denuded in the Quaternary. Landform development of these mountains, therefore, should be explained not by the Davisian scheme, but by the Penckian.
    When a landmass is uplifted at a constant rate, the area increases its relief with uplift, being sculptured by rivers. Denudation rates become greater and approach uplift rates. Ultimately both rates become equal, and steady-state landforms in dynamic equilibrium of uplift and denudation are accomplished, as far as the landmass is continuously uplifted at the constant rate (Plirano, 1972, 1976; Ohmori, 1978). Landform evolution by uplift and denudation, therefore, can be divided into the following three stages; (1) the developing stage that landforms approach steady state by concurrently proceeding uplift and denudation, (2) the culminating stage that steady-state landforms are maintained in dynamic equilibrium of uplift and denudation, and (3) the declining stage that landforms are reduced down to sea level by denudation when uplift ceases. Landform evolution passes through these three stages in different duration periods according to various rates of uplift and denudation as well as duration periods of uplift.
    Supported by the interpretation that erosion surfaces fragmentarily distributed in Japanese mountains are remnants of peneplains in previous cycles, the Davisian scheme of landform development has survived in Japan, where active uplift and intense denudation have proceeded concurrently in recent geologic time. It was, however, clarified in the upper drainage basin of the Waiapu River, northeastern North Island, New Zealand, that erosion surfaces in the hills, about 500 to 700m above sea level, were formed nearly at the present height probably by periglacial processes and fluvial transportation of debris in the last glacial age (Yoshikawa et at., in preparation). This suggests that there is a possibility that a considerable part of erosion surfaces in Japanese high mountains is also of the similar origin.
    Geomorphological study in tectonically active and intensely denuded regions, such as Japan, will produce invaluable information of landform evolution by concurrent tectonics and denudation. This will contribute to further development of geomorphology.
  • 北畠 潤一
    1984 年 57 巻 10 号 p. 703-719
    発行日: 1984/10/01
    公開日: 2008/12/25
    ジャーナル フリー
    大阪平野の北部丘陵地における1945~1979年間の住宅地化の地域的展開と,その原地形の小地形的環境をメッシュ法を用いて計測・解明した.
    新住宅地には,原地形の制約により,多数の坂,段,迂回路,急斜地,崖,陸橋等が存在する.住宅地化は,地形からみた開発適地から不適地へと進行した.それは,住宅地の原地形の起伏量・海抜高度・谷密度を増大し,日向斜面より日陰斜面の開発に向かう過程であり,これらは特に高度成長期以降に顕在化した.きわめて地形が複雑で,海抜高度が高い急傾斜地の開発は,比較的後期に起こり,公共施設の共用可能な既開発地の隣接地か,それと同時進行した開発地域であった.原地形のうち,住宅地化に最も強く影響したのは傾斜方向であり,緩傾斜地においても開発の初期に選択されたものは南向系傾斜地であった.以上の地域的特性は奈良盆地とも類似し,第2次世界大戦後の関西地方における住宅地化の一般的傾向と考えられる.
  • 松本 秀明
    1984 年 57 巻 10 号 p. 720-738
    発行日: 1984/10/01
    公開日: 2008/12/25
    ジャーナル フリー
    本論は東北地方の5地域の海岸平野を例に,そこに形成されている浜堤列の成因と形成時期を明らかにするものである.
    沖積層の露頭観察,堆積物の粒度分析をもとに,過去6,000年間における旧汀線位置・高度の連続的な変化を復元した.その結果,現在を含めて4回の極大をもつ旧汀線高度の上下変動が認められ,これに伴い沖積上部砂層上面に風成・浅海底砂からなる波状の起伏が生じ,その凸部が地表で浜堤列として認められていることが明らかになった.従来,浜堤列は3列に大別されることが多かったが,本論では地表面下に埋没している浜堤列の存在も認められ,各浜堤列形成時の海水準高度は,仙台平野中部地区において,それぞれ+1m, -1.5m, -1m, ±0m (現在)である.
    各海岸平野において個別に求められた浜堤列の形成時期には明らかな同時性が認められ,各列の形成時期は,内陸側から5,000~4,500年前, 3,300~3,000年前, 2,600~1,700年前および800年前~現在であることが明らかになった.
  • 小泉 武栄, 山川 信之, 原 篤, 坂本 里美
    1984 年 57 巻 10 号 p. 739-748
    発行日: 1984/10/01
    公開日: 2008/12/25
    ジャーナル フリー
    Mt. Tairappyo (1, 983m) is a snowy mountain against which the strong winter monsoon blows from the Sea of Japan. Gentle slopes are dominant in this mountain. Due to much snow, tall trees which usually form subalpine conifer forest are not able to grow on the upper part above 1, 600m. Therefore, no subalpine zone exists in this mountain. Instead of tall trees there excel meadows, Sasa fields or scrubs. The result of soil survey in this area showed that the buried peat is widely distributed under the Sasa fields or Graminea-herb meadows. The peat layers are 20_??_30cm thick and are buried under the Kuroboku (Ando) soil or alpine meadow soil (wet type), both with a thickness of about 15cm.
    The accumulation of the present peat is limited at the bottom of nivation hollows. In these hollows snow patches exist till late June or middle July and supply enough melt water. The wide distribution of the buried peat layer indicates that there was an age when the remaining snow existed more widely in summer season as compared with the present. It seems that the delay of the snow melting is due to first the cool climate in that age. Perhaps it was low temperature at that age, especially in summer season. However, that age seems also to have had a heavier snowfall than the present situation. At present heavy snowfall occurs only in the year when the special strong cold waves hit Japan; it occurs in every ten and odd years. At the age when the buried peat layer was formed due to low temperature in winter, the frequency of the heavy snowfall must have increased, so that much snow existed comparing to the present. The buried peat layers probably accumulated owing to the delay of the snow melting caused by the increase of winter snow and the low temperature in summer. The 14C age of the bottom of the buried peat layer was 3, 100 y. B. P., suggesting that this cool and snowy age would correspond to the Neoglaciation.
  • 1984 年 57 巻 10 号 p. 749-756
    発行日: 1984/10/01
    公開日: 2008/12/25
    ジャーナル フリー
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