Roles of Landslides to the Landform Development
a landslide survey in the northern mountain district of Nagano Prefecture
1982 Volume 19 Issue 1 Pages 1-8
Details
1982 Volume 19 Issue 1 Pages 1-8
The geological structure of the Japan islands is complicated. The crustal movement is active and the relative relief of the mountainous areas is conspicuous. The mountainous areas reflect the existence of faults, the relative hardness of rock and the upheaval of the ground. The striking development of the structural relief and the tectonic relief is sometimes seen. The landslide is a kind of landform process which proceeds rapidly. The landslides in the mountainous areas accelerate the development of the slope landform; the response to the structural relief is rapid. We have surveyed the landslides occurred at the Tertiary zone in the northern mountainous districts of Nagano Prefecture and have summarized the following interesting characteristics.
(a) The formation of gentle slopes in the mountain side is accelerated by the occurrence of landslides. The formation of gentle slopes is noticeable in the folding areas, in the back slope of homoclinal ridges and in the surroundings of monadnock areas composed of the Tertiary pyroclastic rocks. Repetition of landslide occurrence forms the rounded wavelike gentle-slopes in the mountain side. The wavelike gentle-slopes produced in this manner are the unique ones which are not formed by the river erosion process due to the common running water.
(b) In the rock slide areas, abnormal landforms are often produced by the movement of the huge rock and soil mass. Sometimes, large cracks run across the ridge behind the mountain side and part of a mountain mass including the ridge slides. And the deformation process in the surroundings of the sliding rock and soil mass is abnormally accelerated.
(c) The most important in surveying the ground structure of the sliding area is to decide whether the landslide in question are primary or secondary. The landslides in the landform with the character of (a) are often secondary and those in the landform with the character of (b) are usually primary.
