箆岳丘陵における高位侵蝕谷と地形発達

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The Nonodake Hill is an isolated hill surrounded by the alluvial Sendai Plain. It is consisted of two-storied erosional surfaces, the Nonodake (180-220m) and the Ishibotoke (100-140m) surfaces, which cut the bedrock of alternating Miocene breccia and conglomerate, Pliocene tuffaceous sandstone and shale formations. On the Ishibotoke surface, wide open and concavesloped valleys belonging to a former cycle of erosion are preserved. In these valleys the Ishibotoke surface appears as a rolling surface with low interfluves and gently concave profiles of slopes. Along the northern foot of the hill, a dissected terrace, the Osato surface (30-40 m), is distributed. The following conclusions are obtained from the geomorphological analysis of the hill : 1) After the erosional surfaces with the concave-sloped valleys had been formed, there arose a tilting upheaval which lifted the northern part of the area more than the southern. 2) As a consequence the erosion was rejuvenated and the uplifted block suffered the dissection in the form of retreating knickpoints in the dissecting valleys, then the concave-sloped valleys and the rolling surface diminished to be preserved partly near valley heads and divides. Some tributaries of the concave-sloped valleys were captured by the younger streams. 3) Through the last tilting movement emerged the Osato terrace surface, which was also dissected later. 4) Recent transgression which was common to whole Japan spread into this area and the dissecting V-shaped valleys were transformed into Solthin-kerbtal as are seen today. 5) The asymmetrical drainage pattern and topographic profile in the hill are attributed endogenetically to the tilting movements, and exogenetically to the existence of steep scarp at the northern fringe by the lateral erosion of the Hazama river, and proceeded rejuvenation in the southern area of the hill.
東北地理学会の論文

箆岳丘陵における高位侵蝕谷と地形発達

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東北地理学会 | 論文

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