The Outer Zone of S. W. Japan consists of Kui Peninsula, Southern Shikoku and Southern Kyushu.The purpose of this paper is to describe the distribution of intermontane basins and coastal plains inrelation to the up and down warping and volcanic activities during the Quaternary.
The distribution of intermontane basins and coastal plains, with its marked regional and localvariation, mainly shows the different varieties of upheaval movements. There are few intermontanebasins in Kui Peninsula, the east and the north of the mountains of middle Shikoku, and in the KyushuMountains, where upheaval movements are rather small.
There are topographic and geologic axes extending from west to east, in parallel with the MedianTectonic Line and the island are in Outer Zone. Sub-topographic axes are at right angles to the mainaxes;
i.e. N-S.
The main axes were fromed by gentle up and down warping by a push from the south. Thedistribution of intermontane basins and coastal plains in western Shikoku and eastern Kyushu havebeen controlled by the slow up and down warping.
When a river has intermontane basins, a considerable part of the large, heavier gravel which istransported from the upper reaches is deposited in the basins while only sand, silt, clay and small-sizegravel is allowed to continue on its way. This is one of the important reasons that there are few wideplains in the Outer Zone.
The eruptions of Quaternary volcanoes have influenced the basin floor and coastal Landformdevelopment. We have found volcanic ash formation (Akahoya ash which dates back to 6, 300 y. B. P.) in the boring cores of the coastal bay head alluvial plains in the Outer Zone. Ash layers overlaymarine silt and clay formation with a thickness of 1 to 9m.
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