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

本研究旨在阐明大雪山冰川地貌和末次冰期古环境研究较少的晚第四纪冰川和冰缘环境。在研究期间，能够厘清部分冰川的分布和晚冰期的古环境。首先，在石笠河的上游支流石笠泽河中发现了某种冰川沉积物，推测末次冰期第一亚期冰川已扩张至海拔1050m附近。在石kari河干流海拔980m附近，发现了具有剪切构造的较古老的冰下坡地。接下来，在大雪山东侧的仙台附近的平顶山脊（海拔1360米）上发现了一块被认为是不稳定的巨石（长轴4米以上）。被认为是冰下碛物的沉积物也分布在巨石附近，这可能表明大雪山平顶脊被冰川广泛覆盖。此外，在大雪山南缘的富村山附近也发现了冰川地貌和沉积物，并根据富村山火山形成历史推测了末次冰期第一亚期冰川的扩张区域。另一方面，在末次冰期约3万年前，石笠河因火山活动而淤积，形成了古大雪湖（古大雪湖）。湖相沉积物放射性碳测年表明，该湖一直持续到全新世初。此外，在属于不连续多年冻土带的高寒地区，继续进行气象调查，对冰缘环境进行了定量把握。

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.