Homoclinal Structure Research Articles

Landslides and Allied Phenomena in Hokkaido, Japan

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.

Streamlining of the Carolina Bays

Ground-water studies in the area of the Carolina bays have revealed a singularly consistent set of subsurface conditions when considered collectively. These conditions, apparently related to the origin of the bays, are (1) the presence of distinctly bedded clays in which at least one bed of limestone occurs, the limestone being generally less than 25 feet thick and less than 150 feet below land surface; (2) a remarkably simple homoclinal structure, ideally suited for artesian conditions, especially in the uppermost beds; (3) solution under artesian rather than water-table conditions in the near-surface bed of limestone, resulting in slow but regular removal of mineral constituents during the long periods since deposition of the soluble beds. The hypothesis advanced is that solution in a near-surface artesian aquifer composed of limestone resulted in subsidence of overlying clay into this aquifer, thus forming a normal sink. This condition was followed by streamline ground-water flow around this relatively impervious clay obstruction, leading to increased rate of solution and subsidence in the down-gradient side of the area. The slow, continuous streamline flow of ground water around the impermeable clay enlarged the dissolved area into an ellipsoid or, more generally; into an ovoid, the more pointed end of which is down-gradient. The hypothesis of streamline origin apparently accounts for genetic features of the bays. Sand rims that characterize parts of some bays are shown to be superimposed features, not requiring explanation under this hypothesis.