Annals of the Tohoku Geographical Association
Online ISSN : 1884-1244
Print ISSN : 0387-2777
ISSN-L : 0387-2777
A Geomorphologic Land Classification Map Indicates an Active Fold of the Shonai Plain, Northeast Japan
Sumiko KUBO
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JOURNAL FREE ACCESS

1991 Volume 43 Issue 3 Pages 188-194

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Abstract

Shonai Plain is located in the lower reach of the Mogami River, which flows into the Japan Sea in Northeast Japan. The Amarume Anticline, where Amarume and other oil fields are located, runs from north to south in the eastern part of the plain. Deformations of the plain surface are seen as evidences of an active fold on this plain.
During the revision of the “Geomorphologic Land Classification Map of the Shonai Plain illustrating features of flooding and soil liquefaction” (Oya et al., 1982, 1989), it was found that the Amarume Anticline influenced the river courses in the Shonai Plain. By studying historical maps based on a geomorphologic land classification map, I found that the Mogami River has changed its course repeatedly within a entrenched meandering belt of the river along the Amarume Anticline from 17th century to the present. The relative height of a natural levee from the former Mogami river bed is 2.65m along the anticline. Furthermore, the Aizawa River, a small tributary which flows into the Mogami River near Sagoshi, is entrenching the alluvial surface of the plain with its relative height of 4.5m. The Kyoden River from Mt. Haguro shows an incised meander along the Amarume Anticline. These phenomena descrived above can be used to determine the existence of an active fold—Amarume Anticline.
Geomorphologic land classification maps serve many purposes. For example, one was used to determine the site of bridge at the Brahmaputra-Jamna River by Oya (1979). Geomorphologic land classification maps can also be used to indicate the presence of an active fold. Moreover, they illustrate how river cources change with time.

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