Permafrost and Ground Ice Occurrences at Oketo, Hokkaido.

在北海道奥户市卡诺科湖附近斜坡上的永久冻土存在点进行了地电阻率调查。在那个地点，沉积物中的地面冰在之前的挖掘中暴露出来。电阻率调查的目的是通过探测地电阻率值的不连续来扩大分布范围。结果表明，沉积物中的高电阻率区与已存在的地面冰体相吻合。挖掘地冰时在钻孔中进行的长期测量表明，在1米至5米深的土层中存在永久冻土层。由于最近气候变暖的趋势，永久冻土层趋于变薄。为了比较Oketo等低海拔地区的永久冻土与大越山典型高山永久冻土的存在，在研究期间进行了大量的实地调查。在存在典型高山永久冻土的地点也进行了地电阻率调查。在此基础上建立了冻土厚度与地电阻率剖面的相关性。在该地点观测到与高山永久冻土带有关的地形，称为palsa。通过钻孔试验和地电阻率垂直剖面测量，获得了帕尔萨的内部构造。在palsa遗址进行钻孔取样，所得样品进行了花粉分析和碳定年分析。结果表明，各层间沉积始于末次冰期和暖间冰期。

Geo-electric-resistivity survey was conducted at the site of permafrost existence on the slope near Lake Kanoko, Oketo, Hokkaido. At that site, ground ice among the sediments was exposed by the previous excavation. The resistivity survey aimed to extend the distribution area by detecting the discontinuity of ground resistivity values. As the results, the high resistivity area in the sediments coincided with the per-existed ground ice body. The long term meaurements in the bore hole which was made at that time of excavation of ground ice indicate the permafrost existence in the layers between 1meter and 5 meter deep. By recent trend of warm climate, this permafrost layers tend to thin.To compare permafrost existence at low altitude area such as Oketo with typical alpine permafrost at Mt. Daisetsu, intensive field surveys were conducted during research periods. The geo-electric-resistivity surveys were also made at the site where typical alpine permafrost existed. Correlation between permafrost thickness and geo-electric-resistivity profiles was made based on the results. The haved topography related to alpine permafrost occurrence named as palsa was observed at that site. The internal structure of palsa was obtained by means of bore hole test and vertical profiling of geo-resistivity survey.Bore hole sampling was made at the site of palsa and obtained samples were subjected to pollen analysis and carbon dating analysis. The results indicated that the sedimentation initiated to last glacial ages and warm interglacial period interval was observed among the layers.