Morphogenetic Environments of Japanese Mountains in the Late Quaternary

Abstract

Japanese mountains have been elevated at the rate of 0.5-2.0mm/year in the global climatic flactuations during the mid-late Quaternary, and the geomorphic processes acted on the mountain slopes have also been alternated with climatic changes as well as uplift of the mountains.Changes of the morphogenetic environment of the late Quaternary in Japanese mountains are considered by means of palaeoglacier curve (Emiliani, 1978) compared to snow line and timberline (Lower limit of periglaciation) fluctuation curve in the mountainsand superposed the growth rates of the mountains on it (Fig. 1).Judging from fig. 1 the rapidly uplifted high mountains have been successively placed in periglacial environment since the middle Pleistocene, and lee side mountains of the snow bearing winter westeries were glaciated in the last glaciation and probably penultimate glaciation. Snowy, wind ward mountains near Japan Sea coast were possibly glaciated not only in the last two glaciations but also earlier ones. Evidences of penultimate glaciations are found in some mountains mainly in the snowy Japan Sea slope.Intermediate mountains of 1000-2500m (lower than 1500m in Hokkaido) in hight were situated in the periglacial environment during the last glaciation. Vast block slopes were developed under permafrost conditions in the less snow-covered mountain slopes especialy in northen and eastern Hokkaido at the time. On the contray, snowy mountains were dissected by snow-patch erosion and snow avalanche, and debris derived from slopes were transported by rapid streams fed by snow meltwater to the piedmont and alluvial fans developed there.Low mountains less than 1000m in hight have not yet been placed in periglacial environment. Low relief erosion surfaces or initial surfaces of mountains are most widely distributed in these low mountains and secondly in the block covered intermediate mountains and secondly in the block covered intermediate mountains due to feeble fluvial activity. Morphogenetic environments in Japanese mountains during the last glaciation are compiled as Fig. 3.