水系の発達からみた線状凹地と崩壊・地すべりとの関係 [in Japanese] Linear Depressions as a Sign of Landslides with Respect to the Development of Channel Systems [in Japanese]
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赤石山地南部の5地域を対象に, 線状凹地の存在する稜線区間とそれに隣接する線状凹地のない稜線区間の稜線両側斜面の谷密度を比較した結果, 線状凹地存在区間の斜面では, 水流のある谷の発達が悪く, 化石谷が多いことがわかった。この原因として, 線状凹地形成の原因となる岩盤クリープなどの山体変形により引張応力場となる山体上部の地盤が緩んで, 降水流出のうち地下水浸透分が大きくなるためと考えられる。これは線状凹地下方斜面への地下水供給の増大をもたらし, 下方斜面での崩壊・地すべり発生の原因となるとみなされる。
Linear depressions are the graben-like landform on the crest slopes with multiple ridges or up-hill facing scarps. Deep-seated gravitational slope deformation (sagging) has been considered as the main cause of such depressions. The relation between formation of linear depressions and landslide occurrences are investigated with respect to the development of channel systems.<br>Drainage density of channelways and abandoned channelways are compared in two cases of the slopes with and without linear depressions, Here abandoned channelways are the shallow dry valleys covered with detritus transported from lateral slopes after past stream erosion. Though the drainage density of channelways is lower on the former slopes than on the latter, that of abandoned channelways indicates to the contrary.<br>Groundwater conductivity on the upper part of mountain slopes is thought to become high in the tension zones caused by deep-seated gravitational slope deformation. Consequently increased share of groundwater flow in total discharge in the tension zones prevents the development of channelways and promote that of abandoned channelways. Because groundwater infiltration is the main cause of landslides, linear depresions are considered to be a sign of landslide occurrences on the flank slopes.
- Annals of The Tohoku Geographycal Asocciation
Annals of The Tohoku Geographycal Asocciation 48(1), 33-41, 1996-03-15
The Tohoku Geographical Association