抄録
Recently some of palynologist, ecologist and also climatologist have suggested that in Japanese islands it was dry in the Last Glacial Age and wet in late- and post-Glacial Ages. This climatic change was considered to have been mainly brought by the turning into heavy snow. In this paper the author investigated this hypothesis from the viewpoint of climatic geomorphology. He examined especially the age and environments of the formation of fossil periglacial slopes, nivation hollows and mountain oligotrophic bogs. Results are summarized as follows:
1. On high mountains in central Japan, except the northernmost part of the Northern Japan Alps there are developed wide fossil periglacial slopes which are covered with coarse blocks and vegetation. They are thought to have been formed in the Last Glacial Age under the cold climatic conditions. If it was snowy in Glacial Age, the formation of these slopes might have been impossible. So it is considered that there was little snow in the Last Glacial Age except the northernmost part of the Northern Japan Alps.
2. In the snowy high mountains of the Japan Sea side, there are many nivation hollows. They are divided into two types. One, wide and shallow type and the other; narrow and deep type. Though the latter is now being formed, the former is fossil type and the latter is situated in the former. From this fact the author guessed the change of snowfall from little to heavy. Perhaps during the Last Glacial Age it snowed little, but under the cold climatic conditions shallow and wide nivation hollows were formed. However, since late Glacial Age it became warmer and warmer, and snow melting was accelerated. So nivation hollows became fossil. But on account of increasing snowfall, deep snow banks were born on a part of fossil nivation hollows. Such parts were thought to have been developed into new nivation hollows. This estimation supports the above-mentioned hypothesis.
3. To know the age of the beginning of heavy snowfall, the author examined the age of the beginning of deposition of peat in mountain oligotrophic bogs which were located around the present nivation hollows. The ages center in 12, 000-7, 000y.B.P. and 4, 100-3, 300y.B.P., Peats of the latter age are thought to have been deposited owing to the delay of snow melting caused by the little lowering of temperature. But peats of the former age are thought to have been born on account of heavy snowfall. Perhaps in the mountainous region of the Japan Sea side snowfall increased since 12, 000y.B.P. and became as present in about 7, 000y.B.P.,
4. On Mt. Kisokomagatake in the Central Japan Alps, there exist small nivation hollows which were born on fossil periglacial slopes. This means possibility of increasing of snowfall on the high mountains of Pacific Ocean side in Holocene.
