The Japanese Coastline

Abstract

The writer in this paper gives his interpretation of the irregularities in the Japanese shoreline. 1. The japanese coastline with special reference to the pacific coast. Under this heading the writer states that the irregular coasts in Japan are limited to regions composed of hard rock, while back of a smooth coast we generally find Neogene or other soft rocks. Fig. I shows the distribution of the shore-line irregularity _??_ in Japan (text fig. A). Table 1 and fig. 2 show the relation of the shore-line irregularity to the kind of rocks that constitute the coast. 2. Drowned valleys, and the age of their formation. writer discusses the formation of drowned valleys, and concludes that the drowned valleys that are found distributed on the pacific coast were formed during very late Pleistocene or very early Alluvium. 3. The Sakisima and other coasts. 4. Subsidence during early Alluvial age. In this paragraph, the writer explains that the Japanese Islands had an extraordinary outline in early Alluvial age. The Japanese shore-line was very irregular on account of subsidences, and quite different from the present coastline. Many evidences are given of early Alluvial drowned valley conditions in the smooth Japanese coasts today. Since that stage, marine erosion and progradation gradually lessened the irregularities, forming smooth coast lines. This smoothing down process took place faster in coasts made up of soft rocks than in those of hard rock. 5. On regional crustal movements. In this paragraph, regional crustal movement is inferred from the Alluvial regional subsidence in the Japanese Islands already mentioned. The writer distinguishes this kind of crustal movement from Prof. Gakuro Imamura's earth wave. 6. Recent crustal movement in the Japanese Islands. The crust deformations determined by means of precise geodetic surveys are treated. According to these surveys, the Japanese Islands have slowly upwarped during the last ten years or so. Fig. 4 and 5 show examples of this recent upwarped deformation along the levelling route across the Japanese ma'n island and the kii Peninsula. 7. Interpretation of the early Alluvial subsidences. The wrier consider that the Japanese arc was formed during the Quaternary by this kind of crust deformation through certain endogenetic agencies. The peripheries of the island subsided relatively to the backbone districts of Japan. This is illustrated in Fig. 10. It is therefore concluded that the Alluvial subsidence of the Japanese coast might have partly been caused by this kind of crust deformation. 8. Development the Japanese coast line. In discussing the development of the present Japanese coastline, the writer concludes that it cannot well be explained without references to the hardness of the rocks and the late Quaternary crustal movement.