山地の勾配と隆起速度(<特集>数値地形図の技術と応用)

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概要

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• How does steepness of mountain slopes depend on geology and uplift velocity? We checked this statistically using DEMs and grid maps of geology and uplift velocity. The gradient was defined along drainage line on the ortho- hexagonal DEM, of which side length was 30 meters, and original resolution was ca. 50×50 m-DEM. 162,444,468 gradients were measured in the eastern part of Honshu Island (east from 135°E line), and 10% values in frequent distribution were chosen as representative values for each category of geology and uplift velocity. The grid map of geology were categorized by rock types and absolute geological ages, of which original was the 250 m-resolution Geological Map of Japan. The grid map of uplift velocity was compiled mainly from displacement of age-known terrace topographies (Fujiwara et al, 2004). The heights of upraised shore lines at the 5 e isotopic stage were referred to just velocity of uplift for 100,000 years. In inland areas, height differences of fluvial terrace topographies formed at the same stage of the previous climatic cycle were referred. The spatial resolution of this map is fairly rough (20×20km) but only available data at present. Main results are as follows: 1) Slope gradient reaches a constant value for elapsed time 1.7Ma in the case of volcanic rocks, in other words, after that the gradient does not depend on the time. 2) In the case of sedimentary rocks, it takes about 7Ma, but it is hard to differentiate the effect of time itself and progressive hardening of rocks with time. 3) Sedimentary (older than 22Ma), volcanic (older than 7Ma), plutonic, metamorphic and accretionary prism rocks (basalt, limestone and chert) give almost the same gradient value, in other words, it is not apparent in the rock control. This statistical result indicates that properties of weathered material layer are more effective than rock property itself under temperate and humid environments of the Island. 4) Statistically by uplift velocity, the slope gradients are decided, in other words, it means that the higher uplift velocity, the steeper and higher mountains appear in the Island located in the mobile belt of tectonics.

• 日本地形学連合の論文
• 2008-01-25

著者

• 野上 道男

  日本大学文理学部

関連論文

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• 特集:数値地形図の技術と応用
• 地形特徴による谷頭の定義(第15回日本情報地質学会講演会講演要旨)
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• 河川縦断形発達の拡散モデルについて
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• 地形発達に関する数値シュミュレーションの構想
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• 気候値メッシュデータと期間を合わせた河川流量データによる流域水収支モデルの高精度化
• 実蒸発散量の推定と地球植生フェノロジー
• 流域地形発達シミュレーションのスキーム

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