Stone Movements on the Vegetation-free Slope in a Nivation Hollow

Abstract

Downslope stone movements were measured on Iide Mountaines from 1977 to 1979. Painted stones were set along the experimental lines on the nonvegetated and debris-mantled slope, with gradient between 21° and 36°, in a nivation hollow near the peak of Mt. Iide (Fig. 1 and Photo 1). After the first setting on October, 1977, displacements of the painted stones were measured repeatedly on September, 1978 and September, 1979.These measurements revealed that each painted stone was moved 0 to 170cm for a year, and that on each experimental line the movements of the stones, including standing ones, averaged between 0.1 and 3.0cm per year (Table 1). If the stone was moved, generally speaking, the smaller the stone is, the farther likely to be moved.At some part predominant in fine materials on the experimental lines, especially on the lines 4 and 5, almost all the stones moved somewhat uniformly in small range (below 5cm/yr. in general). On the other hand, some stones often displaced 10cm or more in some tiny rills across the experimental lines. Some great displacements were also found apart from the rills. Small range movements are perhaps due to solifluction, and rather large range movements are due to rill-wash and/or sheet-wash.At the experimental lines 6 and 7 where crevasses often happen in snow-patch during the ablation season, the painted stones were lost except one probably because of complete destruction of the experimental lines due to snow creep. At the lines 1-5, on the contrary, stone movements dragged by snow creep have not been recognized.