The Geomorphological Structure of the Mihara Alluvial Plain on Awaji Island, Hyogo Prefecture
1982 Volume 34 Issue 3 Pages 138-150
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1982 Volume 34 Issue 3 Pages 138-150
The development of the landforms in the Mihara Alluvial Plain is summarized as follows:
STAGE 0 (before about 22, 000y. B. P.)
The coarse materials were deposited in the valley of dissected Terrace I.
STAGE I (about 18, 000y. B. P.)
The alluvial fans were dissected by the rivers, and then Terrace II was formed.
STAGE II (about 7, 500y. B. P.)
When the sea invaded landward and it passed the location immediately below the present shoreline, the sea-level rose to -13m (T. P.).
STAGE III (about 6, 400y. B. P.)
The sea-level rose still more, and the sea invaded landward further. In this time, four main rivers did not join each other but flowed separately into the sea. Consequently, from this stage to the following stages, several characteristic landforms correspoding to the environmert of each river basin were formed.
STAGE IV (about 2, 600y. B. P.)
The inner bay changed into a lagoon because the sea-level fell and sandbars were formed. As the humic silt deposited in the fresh water environment existed about -60cm (T. P.) at point o, the author estimates that the sea-level fell below -60cm (T. P.).
STAGE V (Recent Age)
After the “early Kofun era” (the 4th C. A. D.), the occurrence of floods became more frequent, and the floodloam was deposited rapidly. Then, present landforms were completed. The landform classification map is drawn based on the development of landforms (Fig. 9). Each landform unit is arranged according to the time necessary for each landforming process and the geomorphological dendrogram is completed (Fig. 10). Finally, the Mihara Alluvial Plain is classified as follows: 3 surfaces in the order of 104 years, 7 zones are in the order of 103 years and 16 units in the order of 102 years or lers.
