Micro-topographic Analysis of Snow covered Mountain Slopes by Aerial Photographs

Abstract

The main purpose of this paper is the presentation and discussion of the basic concept used to analyze the micro-topographic elements of mountain slopes as one of the fixed conditions governing the occurrence of snowslides and avalanches, by means of aerial photographic interpretation. In order to investigate the micro-topographic elements of slopes systematically, the method of landform classification, which was developed by T. Nakano (Nakono, 1952) and has been widely applied for land survey in Japan, is introduced and discussed. Further-more, micro-topographic elements are considered in connection with micro-climatic conditions such as surface wind direction and solar radiation intensity that govern the distribution pattern of snow depth and snow conditions in a small area. The elements witch can be interpreted by the analysis of aerial photographs are shown in Table 2.A preliminary study based on this method has been carried out on approximately 50 slopes along the national railways passing through a region of heavy snowfall in Central Japan, on which large avalanches are known to have occured. Some results obtained by this study are; the slope type favouring the occurrence of avalanches is east or south facing, shaped like a cirque wall, have a steep gradient with the concave profile in horizontal and longitudinal section, and most of these slopes are almost free from soil and vegetation (especially forest) cover.Judging from this preliminary investigation, the method discussed in this paper leads to the identification of slopes on which avalanches can be expected.