There are small mounds near the lake Tashiro-ike in the Kamikochi Valley of Central Mountain National Park. These mounds, over fifty in number, scattered across the valley from west to east on the north side of the lake. Fifty years ago, late Professor K. Oseki, a pioneer of Japanese glaciology, suggested that the mounds may possibly be glacial deposit, but it had not been examined since by any student. The distribution of the mounds is shown in Fig. 2.
The author made a survey of the erosion process and alluvial deposits of this valley, and observed these mounds in autumn of 1968. Fortunately, he saw some cutting places of the mounds by a newly opened path, and collected many andesite gravels which in the same facies of rocks from Yake-dake Volcano. Thus, it will be concluded that the mounds are the landforms made by a mudflow from Yake-dake Volcano, because there are no sources of andesite in this valley except this volcano. The arrangement of are the mounds and the vegetation on them are other evidences. This mudflow once would have dammed the Azusagawa making a small lake. The-remains of this geomorphic episode are found in the shape of longitudinal profile of Azusa-gawa, which is shown in Fig. 1.
