On the Landslides and Earth Failures in the Middle Reaches Area of the Himekawa River

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After our investigations of areas along the middle reaches of the Himekawa River, on geologic and topographic features and on the distribution of landslides and earth failures, we co ld find some facts as follows:<BR>1) Most of landslides are distributed on open, deeply dissected erosion-valleys. Slopes of them show a rormal distribution with the mode value of 15°-20°gradient; landslides are intensively concentrated on the mudstone zone of tertiary. We found 86 percent of landslides occurred on the existing earth fault, and those of a large scale often on the effusive rocks areas, accompanied by head failure.<BR>2) Most of earth failure seem to be found, topogrphically, on the younger stage valley, among direct bottom of flat land; and on slopes supporting cap rocks and among ridges. Slopes of those show a normal distribution with the mode value of 45°-50°gradient, intensively on slopes at the foot of a mountain.<BR>3) About landslides and earth failures, we should not overlook human antivities, such as water ways overflowed or destroyed, and rude management of forest land.
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