Abstract
Most of the reports on landslides have described about the length, width, inclination of the slope and other components which serve to give general information upon the extent of landslide. However, no detailed discussins on the extent of landslide have been made, so far as the author is aware of, except that in the work of F. O. Jones et al. Of the components concerns this paper mainly with the length, width and scarp height components by which some discussions on the development of landslide area are made. These components of each landslide were measured either from topographic maps or from field observations. Twenty six landslides were examined in Higashi-Kubiki and Uonuma Mountains, Niigata Prefecture, where many landslides have occurred.
The length component is the horizontal distance from the toe of the landslide to the crown as taken in the direction of maximum inclination at midsection of the slide. The width component is the average horizontal distance from side to side across the slope of the slide. The scarp height component is the maximum difference in altitude between the foot of the scarp and the crown as taken in the direction of the slope. As the foot of the scarp was frequently obscured by tales deposits, determination of its position was made at the topographic breakpoint. The data of scarp height, therefore, are somewhat low in reliability.
The results obtained are shown in the table and figures.
The conclusions to be drawn are as follows:
(1) A unit landslide (landslide formed by one sliding) seems to be shorter than 240 meters in length.
(2) Landslides range from several decades of meters to 1360 meters in lengh, and their lenght and width tend to be larger as they regress.
(3) At the early stage of the development of landslide its position is at foot of the valley wall slope and the ratio of length to width is smaller than that of the later stage.
(4) The scarp height increases with regression of the landslide. But when the crown of the landslide reaches to the ridge, altitude of the ridge is lowered and so the height of the scarp is reduced again.
