Abstract
The Large-scale landslide of Mt. Shichimen is located in Hayakawa town, southwest region of Yamanashi Prefecture, and adjacent to the Itoigawa-Shizuoka tectonic line. It has been reported that this landslide was triggered by the Tokai earthquake which occurred in 1854, Ansei period. However, the newly disclosed historical documents show that this landslide took place before Ansei period. Although Mt. Shichimen has been introduced as one of the large-scale landslides so far, it might be considerable that Mt. Shichimen has become present geographical feature due to the small or medium-scale collapses triggered by the earthquakes occurred past and erosion of the slope surface caused by freezing and thawing. The climate that is appropri-ately cold at night and has an abundance of sunlight in winter season, makes frequent repetition of freezing and thawing possible at the crushed slate zone in Mt. Shichimen. According to the analysis of the aerial photo survey, the annual depth of erosion in Mt. Shichimen may be roughly estimated in the range of 5-50 cm, the value of which fluctuates due to the climate condition of a year and micro geographical features. And more than a half of this erosion would occur in the winter season.
