迫川沿岸の地形

概要

論文の詳細を見る
The Ichihazama and the Nihazama rivers originate in the back-bone range of Tohoku, run through hilly area of Pleistocene Pyroclastic-flow deposits, and reach the Snauma lowland in the northern part of the Sendai plain.The results of the authors study on the river terraces and hills along these rivers arc as follows;1) The geomorphological surfaces are classified as in Fig. 1, and the relation between terraces and the lacustrine deposits is shown in Figs. 8, 9 and 10.2) The western part of the hills is composed of dacite and tuff of Pleistocene (Kitamura 1956) and the hilltops in the eastern part of it are covered comformably with gravel bed (Hanzawa, Kitamura 1957). Fujiwara (1958) suggested that the hill surface is subdivided into two levels covered with different gravel layers without detailed description and mapping.The present author has acertained that the eastern part of the hills consists of the remnant surface of terraces in two levels: the upper one 70 to 90m, and the lower 40 to 50m above sea level. The upper covers comformably the pumiceous tuff in the lower half of the middle reaches as was reported by Hanzawa and Kitamura (1957) and others, while in the upper half the surface of pumiceous tuff is terraced and the older alluvium underlies a lower level terrace surface in dendritic pattern. The longitudinal pattern of the older alluvium is shown schematically in Fig. 7. The levels of deposition and erosion on these two, therefore, are about 70m and 50m above sea level.3) The upper Tsukidate surface is distributed widely in the middle reaches. The surface was reported hitherto as that of fluvial origin, however it is fill terrace formed at the time of the high sea level at the hieght less than 20m above sea level. Fujiwara (1958) suggested an uplift of the surface near Tsukidate by means of drainage pattern analysis. The author presumes that the terrace-building was influenced by a regression of sea, and in the development there may have been a tectonic movement.4) Oide (1964) reported that certain deposits upvalley a gorge in the upper reaches of the Ichihazama river is lacustrine deposits lain in a lake basin produced by an uplfit of gorges of Miocene andesite. In his opinion the barrier is shown with the site of present gorges. Imaizumi (1966) supported his opinion. The present author thinks that the lacustrine deposits was lain through violent accumulation of voluminous sandy tuff in a short time, for the deposit scarcely shows lamination and has nodules, erected stumps and pisolite particles in non-stratified material. The heavy-mineral analysis reveals that the lacustrine deposits are same as the Kitagawa formation (dacite and its tuff) and the uppermost volcanic ash on the terrace and hill surfaces along the Eai river.5) The gentle slopes of erosion cut terraces under-lain with so-called lacustrine deposits in the upper reaches of the Ichihazama river. Some of their lower flanks may have been buried beneath the alluvial plain surface in the middle reaches. Drift wood in the so-called lacustrine deposits was dated 27, 000±1, 700yrs B. P. by C-14 method (Oide 1964). Its form is very much akin to cryopediment (Wako 1960).

迫川沿岸の地形

スポンサーリンク

概要

論文 | ランダム

スポンサーリンク