長野県北部山地における浅層型地すべりの機構と地形特性

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A number of landslides occur in the northern mountain districts of Nagano Prefecture which consists of the Tertiary layers. Most of landslides in those districts (over 90%) are the type of shallow layer slides, the slide surfaces of which lie within 10 meters in depth. These shallow layer slides have not drawn attention of the public, because the damages done by shallow layer slides are usually small in scale. However, since slide areas are used as cultivated fields and the lives of inhabitants of mountain villages are maintained by cultivating arable land in the slide areas, countermeasures for landslides are essential for protecting the lives of the inhabitants. In the shallow layer slide areas, the mass movement occurs gently and intermittently in groups: in consequence, landforms peculiar to shallow layer slide areas are formed and the landforms are fairly different from those of rock slide areas which are accompanied with fierce slides.In this report, the occurrence mechanism of shallow layer slides and the landform characteristics of shallow layer slide areas are investigated based on the actual examples. In the shallow layer slides areas, the boundaries, between sliding areas and non-slide areas are ambiguous. The topside slide scarps and the side slide scarps are not, in many cases, formed and ponds and ditch-like depressions are not created in the down side of slide scarps. And the whole landform shows an undulating mountain slide which has several swelled soil mass similar to closed shells. Such a landform expands gradually to do damage to the surrounding villages but does not spread rapidly to damage severely those villages. The shallow layer slides occur in the mountain districts consisting of the Tertiary mudstone basement rock. Since the continued slide movements make mountain sides gentle, the shallow layer slide areas are generally gentler in slope than the non-slide areas. The mountain sides without landslides are generally steep in slope and utilized as woodlands. On the contrary, the mountain sides with landslides are gentle in slope and used as vegitable fields or paddy fields.
社団法人日本地すべり学会の論文

長野県北部山地における浅層型地すべりの機構と地形特性

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