白石川・松川の河岸段丘について

概要

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There are several levels of river terraces at different heights along the course of the Shiroishi-gawa and the Matsu-kawa. The author classifies these levels of river terraces based on his field survey and air photo analysis as shown in Fig. 1. He also explains how the features of terrace surfaces were effected by the volcanic ejecta of the Aoso and the Zao volcanoes, or by the tectonic movement around the area. (1) Along the Shiroishi-gawa and the Matsu-kawa, there are four different levels of terrace surfaces. (2) The terrace surfaces are generally covered with veneers of thin gravel beds. (3) The terrace bedrocks are composed of the Shirasawa Formation, the Matsu-kawa mudflow, and a portion of the Enda Formation. With the exception of the Enda Formation, most of them are composed of volcanic mudflows, and they have an effect on the features of terrace surfaces. (4) As the influence of the volcanic activity, chiefly of the Zao Volcano, a great quantity of debris was supplied into the Matsu-kawa, and recent depositional terraces and a number of fans are constructed with this debris. (5) In the northern part of the surveyed area, the overlain volcanic ash layer is thicker, and it fits with the gentleness of the mountain slopes.
東北地理学会の論文