Abstract
In Hokkaido, landslides are hitherto believed to occur not so frequently when Compared with the other' part of Japan. However, in recent years, landslides and allied phenomena were observed at many places, as human activities such as railroads, highway or other construction works go further into the undeveloped areas of this island.
They occur at various geologic horizons from the so-called Paleozoic group up to the present deposits and igneous rocks from basic to acidic nature, Tha most abundant accidents occur in Miocene. marine sediments which Consist of mudstone with intercalation of tuffite that easily decompose into clay, and. also in Cretaceous marine sediments consist of mudstone with frequent thin alternation of sandstone, Serpentinite bodies which intruded into Crotaceous formations slide very often in various parts of central Hokkaido when they suffered from weathering.
From the view point of geologic structure, they appear in large extent in faulted zones, particularly when accompanied by intensely faulted belt or high-throw fault. They also occur in area of homoclinal structure even in gentle dip when faced toward downslope. This is paticularly true when rivers or seawaves cut foot of the slidable area. Various other common factors in lndslide, i.e. lithologic, structural and topographic, are also recognized in Hokkaido, and most of them are combined together to Cause slide. Among them, in usual case, Climatic factors, particularly seasonal or unusual precipitation take important role in landslide.
