Meander and Tectonic Movement in the Area along the Middle Stream of the Kamo River in Ehime, Shikoku Island, Japan

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  • 伊予西条・加茂川中流域の蛇行地形と地殻変動
  • イヨ サイジョウ カモガワ チュウリュウイキ ノ ダコウ チケイ ト チカク ヘンドウ

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Abstract

The purpose of this study is to make clear how the one-sided meandering channels of the Kamo River were formed in the middle stream in the steep escarpment (so called "the Ishizuchi fault scarp"). The steep escarpment is mainly composed of metamorphic rocks and partly of the Izumi group which is enclosed by the Okamura fault in the north-western part of the steep escarpment. The thick shutter zone of the Median Tectonic Line (MTL) runs between the two different rocks. It dips northward at the angle 30 to 40 degree. Kamo River streams almost along the shutter zone of MTL, which is weak in resistance against erosion. The conclusion of this study is as follows: The valley of the Kamo River is a fault line valley. The shutter zone dipping northward favored the stream of the Kamo River deepening, shifting the channel northward and meandering northward. The rocks of Izumi group which are weaker in resistance against erosion than the metamorphic rocks, have urged to shift the channel. The tributaries of the Kamo River from the southern steep escarpment supplied so much water that they prompted Kamo River to shift or make it meander northward. Finally, Kamo River made basin-like valleys by meandering. The basins by northward meandering were once filled with gravel by tectonic movement tilting this area northward, but the terrace surfaces of gravel again began to be erosed into lower terraces, caused by general uplift in the steep escarpment. This point of view makes us able to explain the whole landforms in this area. This suggests that the steep escarpment was formed by active warping but not by a single fault movement and the following retreat by erosion. The front of warping uplift is the active Okamura fault.

Journal

  • GEOGRAPHICAL SCIENCES

    GEOGRAPHICAL SCIENCES 62 (4), 221-236, 2007

    THE JAPANESE SOCIETY FOR GEOGRAPHICAL SCIENCES

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