Geomorphological Characteristics of Serpentinite Mountains by Two Definitions of Drainage Network

• KOMATSU Yosuke

  Graduate Student, Tokyo Metropolitan University

Bibliographic Information

Other Title

• 谷密度からみた蛇紋岩山地の特性—2種類の谷の定義による評価—
• 谷密度からみた蛇紋岩山地の特性--2種類の谷の定義による評価
• タニ ミツド カラ ミタ ジャモンガン サンチ ノ トクセイ 2シュルイ ノ

Abstract

In Japan, the landforms underlain by serpentinite rocks are characterized by long convex slopes and are known to be distinct from most other lithologies. The geomorphological characteristics of ser-pentinite mountains, however, cannot necessarily be represented by one kind of drainage network. A reexamination of valley identification is necessary because the definition of valley head significantly af-fects studies of landform processes in mountainous terrain. In this paper, drainage densities were meas-ured based on two different definitions of the valley head to quantify the differences in valley land-forms on various lithologies.<br> The two types of drainage networks were identified on a 1: 25, 000 topographical map as follows. All-type valleys were defined as those where topographic convergence at the valley heads could be con-firmed on the map, following Takayama's (1972) method. Deep-type valleys were defined as valleys in which the angle of notched v-shaped contours is less than 90° and the map contour length is long-er than 2mm (actual length 50m), taking the degree of topographic convergence into account. All val-ues of drainage density were measured in second-order drainage basins, and then their average and standard deviation were calculated.<br> The four study areas were in and around the Pin'neshiri, Mukawa-Sarukawa, Oshima, and Oe-yama Serpentinite mountains in Japan. In the Oe-yama area, the drainage density of all-type valleys in moun-tainous terrain underlying three lithologies was in the order of: serpentinite>granite) Paleozoic argillite. In contrast, the drainage density of deep-type valleys was in the order of: granite>Paleozoic argil-lite>serpentinite.<br> These tendencies varied greatly among geologies. In serpentinite mountains, the drainage density of all-type valleys was the highest, while that of deep-type valleys was the lowest. In addition, the ratio of drainage density in deep-type valleys to that in all-type valleys in serpentinite areas was the lowest of all measured areas. Similar results were obtained for the other three areas studied Pin'neshiri, Mukawa-Sarukawa, and Oshima.<br> Using definitions of both deep-type and all-type drainage networks, these drainage densities could be effective in demonstrating geomorphological characteristics. In serpentinite mountains, the correla-tion between stream length and drainage area is lower than for granite and Paleozoic argillite be-cause many large-scale landslide landforms are distributed on the slopes. Based on the results of this study, the author suggests that different landform processes could operate on mountains with differ-ent geomorphometric characteristics because different landform processes produce differences in val-ley landform.

Journal

• Geographical Review of Japa,. Ser. A, Chirigaku Hyoron

  Geographical Review of Japa,. Ser. A, Chirigaku Hyoron 72 (1), 30-42, 1999

  The Association of Japanese Geographers

Keywords

• definition of drainage network
• drainage density
• serpentinite landforms
• deep valley
• shallow valley

Details

• CRID: 1390282680401190784
• NII Article ID: 10002222925
• NII Book ID: AN1016484X
• DOI: 10.4157/grj1984a.72.1_30
• ISSN: 21851735
• ISSN: 00167444
• NDL BIB ID: 4630582
• Web Site: https://ndlsearch.ndl.go.jp/books/R000000004-I4630582
• Web Site: https://www.jstage.jst.go.jp/article/grj1984a/72/1/72_1_30/_pdf
• Data Source:
  • JaLC
  • NDL
  • Crossref
  • CiNii Articles
• Abstract License Flag: Disallowed