Volume 89 (1980) Issue 6 Pages 319-335
Movement types and intensity of surface processes were investigated on the slopes above the forest line of Mt. Shirouma-dake (2, 933 m. a. s. 1., 36°45'N, 137°45'E). The slopes studied are vegetation-free or sparsely vegetation covered ones that are mantled with rubble layers (thin layers of rock fragments).
There are six types of slow mass movement operating on the rubble slopes talus creep, frost creep, needle ice creep, gelifluction, rapid solifluction, and a movement derived from snowpack creep. Rapid mass movement processes such as rockfalls, debris flows, and rolling down of stones often occur, but only a small amount of the materials is moved. Running water, supplied by rainfall and melting of snow and ground ice, carries the debris. While the amount of the materials moved by wash are not so large on the rubble slopes, the channel erosion is one of the important processes on the nivational rubble slopes that are covered by the long lasting snowpatches. The particle movement by wind and the transport in solution are probably insignificant on the study slopes.
Relative vertical mass transfer in unit area that is a geomorphic work of process is estimated for a quantitative comparison of process intensity. The processes acting on the slopes are grouped as following five process sets according to their rates and types of the movements. I) Periglacial process set with low raet. II) Periglacial process set with medial rate. III) Nivational process set with low rate. IV) Nivational process set with medial rate. V) Nivational process set with high rate. The slow mass movements cover over 75 percent of the total mass transfer of the periglacial process set. The value of the slow mass movements of the nivational process set, however, is limited less than 75 percent of the total value and the remainder is mostly comprised in value of channel erosion. While the periglacial process sets occur on the periglacial rubble slopes that are put under the snow free dry conditions throughout the year, the nivational process sets occur on the nivational rubble slopes. The rate of these process sets vary according to the differences of the climatic environments, slope forms and gradients, and slope materials ; size of the surface material and thickness of the rubble layer. Among them the slope materials perform the important role. The process sets with low rate (less than 3.0× 103m· t/ Km2·yr.) correspond with the processes occurring on the slopes which are mantled by the boulder size debris. The process sets with high rate (over 6.0 × 103m·t/ Km2·yr.) occur both on the nivational slope with steep gradients and the nivational slopes covered by fine materials.