GLACIAL AND PERIGLACIAL ENVIRONMENTAL CHANGES IN LATE QUATERNARY IN THE DAISETSUZAN MOUNTAINS, CENTRAL HOKKAIDO

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It is the purpose of this research to clarify the glacial and periglacial environments in the late Quaternary in the Daisetsuzan Mountains where glacier landforms and paleoenvironment of last glacial stage have been hardly studied. Within the research period, it was able to clarify the distribution of some glaciers and the paleoenvironment of late glacial stage. First, in the Ishikarizawa River, the upper tributary of the Ishikari River, some kind of glacial sediments were found, and it was presumed that the glacier had expanded to near the altitude of 1050m in the first substage in the last glacial stage. Furthermore, near the altitude of 980m along the Ishikari River main stream, the older subglacial till with shearing structure was discovered. Next, a boulder (major axis of 4m or more) believed to be one of erratics on the flat-topped ridge (altitude of 1360m) near Ginsendai on the eastern side of the Daisetsuzan Mountains was discovered. The sediment considered to be a subglacial till is also distributed near the boulder, and it may be suggested that flat-topped ridges of the Daisetsuzan Mountains were widely covered with glaciers. Moreover, glacial landforms and sediments were recognized also around Mt Tomuraushi-yama of the southern Daisetsuzan Mountains, and the expansion areas of the glaciers in the first substage of the last glacial stage were presumed from relation with the history of Tomuraushi-yama volcano formation.On the other hand, Ishikari River dammed up by the volcanic activity about 30,000 years before in the last glacial stage, and consequently paleo-lake Daisetsu (Ko-Daisetsuko) was formed. Its expansion range became clear and radiocarbon dating of lacustrine sediments showed that the lake continued till the beginning of Holocene.In addition, in the alpine zone belonging to a discontinuous permafrost zone, the weather survey is continued and the periglacial environment has grasped quantitatively.