北海道松前半島南部の地形発達-統計的手法による階段状地形の解析の一つの試み-

概要

論文の詳細を見る
In the southern part of the Matsumae Peninsula, a set of terraces spreads at the basal part of the mountain mass and some stepped erosional surfaces are recognized at the middle and the higher parts of it. The author approaches to the physiographic development of the mountain mass by means of analysis of the hypsometric curve and some characteristic curves of first-order streams such as the headwater-density, the confluence-density, the first-order stream-density and the mean-slope-distribution of first-order streams. Each of these curves is a kind of time-series and all of them are composed of four cycles, respectively. According to the fact, the mountain mass is divided into four zones in altitude as follows; the first zone : the part higher than 725 m, the second zone : the_part of 425 m to 725 m, the third zone : the part of 125 m to 425 m, and the fourth zone : the part lower than 125 m. There are three stepped erosional surfaces to be correlated with each of them from the first zone to the third zone and the set of terraces is distributed in the fourth zone. The distribution-pattern of these zones resembles to that of piedmont treppen. Moreover, it is deduced that the river networks have four cyclic developments corresponding with these zones from the consideration of the relationships between these curves. Therefore, each of these zones is presumed to have been formed during a long standstill of the erosional baselevel and is to be called the “geomorphic formationzone”. On the other hand, the river networks have been formed individually at every geomorphic formation zone and the first-order stream-density curve shows four cyclic changes corresponding to the zone. From the above-mentioned observation, the author inferres that each of the geomorphic formation zones has been conserved for a long time, for the mountain mass is transformed by the river erosion in the manner of the parallel retreat. And in this case, in a geomorphic formation zone, the original surfaces of the upper and the lower parts of it are remarkably destroyed and that of the middle part are mostly preserved. From the examinations of the relationships between these geomorphic formation zones and geology, the author thinks that the first zone was formed during the period from the Miocene to the later Pliocene, the second zone at the end of the Pliocene, the third zone during the former Pleistocene and the fourth zone has been formed during and after the later Pleistocene. The fourth zone is mainly consisted of the set of terraces which have distinct original surfaces. This fact means that these terraces are formed under the different conditions in crustal movement and the mechanism of land-form formations from that of the topographies existing in the middle and the higher parts of the mountain. Consequently, it is suggested that some of the phenomena which are induced or deduced from the researches of these terraces are the peculiar ones during and after the later Pleistocene.
社団法人東京地学協会の論文

北海道松前半島南部の地形発達-統計的手法による階段状地形の解析の一つの試み-

スポンサーリンク

概要

著者

関連論文

スポンサーリンク