Fossil Periglacial Morphology in Chugoku Mountains

Abstract

In Chugoku mountains, the writer found patterned grounds and block stream originated in the last glacial age in several places.Patterned grounds develop on gentle crest-slopes, which are higher than 1, 100 metres above the sea level and gentler than 28 degrees. And on the slope, steeper than 15 degrees, steps develop in several places. These patterned grounds cut Sanbeyama pumice and are covered with Daisen volcanic ashes.Block streams are located at the upper part of the mountain slopes (1, 150-900 metres). These block streams are originated from Felbsburgen above them. The form of these block streams are very similar in this mountain. A block stream at the upper part of the Hibayama, the largest one in the mountains, is 300 metres long, 40-30 metres wide at least. The slope of this block stream is 34-30 degrees. Diameter of blocks of the block stream is 1.5-1 metres, in rare occasions 4 metres. And at the lower part of the block stream, these are small boulders (30-20 centimetres in diameters), but deficient of matrix. These blocks are broken with the fracture planes. Covered with bushes, it is proved that the block streams do not move under the present climate.