都城盆地の地形発達 : とくに蛤良軽石流堆積後

概要

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The geomorphological surfaces distributed in Miyakonojd Basin can be classified into four groups, namely M1, M2, L1 and L2 Surfaces. M1 Surface is the depositional surface of upper pumice flow (Aira pumice flow) called “Shirasu” that was dated back to 16, 000 to 20, 000 years B.P. during the last glacial stage. M2 Surface is the depositional one of pumiceous sand and gravel. L1 Surface is subdivided into Surfaces L1-1 and L1-2 a (they are shown as LI Surface inclusively in all illustrations). The former is the erosional surface, mainly distributes in the western and southern part of the basin. The latter is in the eastern paxt of the basin and is the depositional surface of the gravel bed that was supplied from Minaminaka Mts. L2 Surface is a group of small surfaces and is consisted of gravel bed. This surface was formed in ca. 6, 000 years B.P., during the Postglacial transgression. The welded part of upper pumice flow has main effect on the geomorphological develop- ment of the Miyakonojô Basin. It is supposed that there was an effect of the eustatic rise of sea-level simultaneously. It may be considered that the geomorphological development of this basin is a process to recover the equilibrium of Ôyodo River, which is lost by the deposition of upper pumice flow and by the eustatic rise of sea-level in late Quaternary.
東北地理学会の論文