集水域の地形・地質条件による扇状地の分類

DOI Web Site 被引用文献2件

書誌事項

タイトル別名
  • CLASSIFICATION OF ALLUVIAL FANS IN JAPAN BY TOPOGRAPHICAL AND GEOLOGICAL DATA OF DRAINAGE BASINS
  • シュウスイイキ ノ チケイ チシツ ジョウケン ニヨル センジョウチ ノ ブン

この論文をさがす

抄録

The ratios of drainage basins with alluvial fans to all basins show two reliable peaks around 100 km2 and 500 km2 in the Japanese Islands (Fig. 1). The conditions of the alluvial fan formation were analyzed by interpretation of the peaks.<br> The bedrock lithology of drainage basins favourable for the formation of fans is plutonic rocks, tuffs, agglomerates, and metamorphic rocks (Table 2) . In such basins debris flows are considered to have frequently occurred in Japan. The drainage basins smaller than 250 km2 in area with alluvial fans are dominantly occupied by these rocks (Fig. 4). Furthermore, it has been pointed out that drainage patterns of basins smaller than 200 km2 in area are simple in Japan (Fig. 6), and that such basins provide the large specific peak discharge (Fig. 5). By taking all these factors into consideration, it can be stated that the detritus deposited by the debris flow on the river bed in the mountain is transported to the valley mouth at a stretch by the flood flow, and that alluvial fans are composed of such detritus. Paticularly, in the drainage basins around 100 km2 in area, the markedly high ratio of drainage basins with fans to all basins is considered to be attributed to the frequent occurrence of the flood.<br> In the drainage basins larger than 200 km2 in area, the specific peak discharge is not high due to the complicated drainage patterns, but the total discharge is high enough to bring about the flood frequently. The wider the drainage basins are, the weaker the influence of the lithology on the formation of the alluvial fan (Table 3), It may be inferred that the bedload in the mountain are transported to the valley mouth by a number of floods and that the formation of an alluvial fan is a result of deposition by a stream which has swinged its channel to and fro over the accumulation material. This idea is supported by the fact that alluvial fans have been extensively formed in actively uplifted areas, i.e. Central Japan (Fig. 7), where sediments yield is very abundant. As the drainage basins become wider, the discharge and occurrece of floods increase. However, the ratios of basins with alluvial fans to those larger than 500 km2 in area decrease with the increase of area. This suggests that the coarser sediments cannot be transported to mountain fronts by the rivers due to gentle gradients and are mostly deposited in montane basins (Table 4).<br> In the drainage basins around 200 km2 in area the debris on the river bed is considered to be rarely reansported to the valley mouth at a stretch by the flood flow. After the transpotation has happened, the next flood flow appears to erode the debris deposited at the mountain front, because of a relatively small quantity of bedload in spite of large discharge. Consequently, it is difficult for the drainage basins around 200 km2 in area to form alluvial fans except the smaller ones (Fig. 2).

収録刊行物

  • 地理学評論

    地理学評論 55 (5), 334-349, 1982

    公益社団法人 日本地理学会

被引用文献 (2)*注記

もっと見る

キーワード

詳細情報 詳細情報について

問題の指摘

ページトップへ