Abstract
We have found a large-scale landslide in a hilly mountainous area of Kikonai Town, southern Hokkaido, by recent aerophotographs. Through previous aerophotographs of the landslide area, we can determine that the landslide occurred after June 23 and before July 27, 1988. Further investigation into the aerophotographs of ca. 1948, 1959, 1973, 1976, 1988 has revealed that the landslide has a historical movement related with cutting of needle-leaf forests (man-made cedar forest). In addition, we have researched the landslide in the field and analyzed the landslide volume in comparison between the maps made through aerophotographs in 1959 and those in 1988. As the results, the landslide is geologically dip-slipping within a clayey rhyolitic tuff and was triggered by upheaval of groundwater level in the old landslide, followed by considerable high precipitaion in June and July, 1988.
