A. STUDY OF THE LACUSTRINE TERRACES OF LAKE INAWASHIRO

Abstract

In this paper the writer describes the torographic features of lacustrine terraces around Lake Inawashiro. The Lake is situated at the southern foot of Mt. Bandai, a famous volcano in Japan. A river flowing over a mud-flow district is the northwestern outlet of the lake. According to the writers observations, many terraces consisting of “Paleo-Lake Inawashiro beds”, accumulations of later diluvium or early alluvium, are found along the rivers. These terraces containing diatom. fossils which are only found along lake shores. The distribution of these lacustrine terraces indicates, therefore, that the level of the lake were higher than at, present. The maximum. height appears to have been 535 meters above sea level while the present lake level is 514 meters. This inferred heigit of the level of Paleo-Lake Inawashiro suggests that the lake was made by the damming action of two volcanoes, Mt. Bandai and Mt. Nekoma, and after that the lake water flowed down to the Aizu Basin fromn tine lowest part of Paleo-Lake Inawashiro. That part is Onohara which is composed of the mud-flow “Okinajima-oshidashi”; this mud-flow was not formed by the volcanic activity which formd the present cones of the two volcanos. The general altitude of Onohara, which the writer got by measuring summit levels, is 540 meters above sea level. That altitude generall ycoinci-des with the heights of the lacustrine terraces around the lake. The existence of many drowned valleys on the bottom of the lake, the charaeter of knick points on the river beds of inflowing rivers which were ex, ased by the lowering of the lake level, and the distribution of earthenwares articles of pre-historic age are further evidences used by the writer.