GLACIAL LANDFORMS AND ACCUMULATION TERRACES AROUND MT. CHOGATAKE, THE NORTHERN JAPANESE ALPS, CENTRAL JAPAN

Abstract

The Pleistocene glacial landforms in the Northern Japanese Alps have been studied by many researchers, and the existence of several glacial stades, ranging from 60, 000 to 10, 000 years B. P., has been proposed by Kobayashi (1958), Iozawa (1962, 1972), Koaze et al. (1974), Fukai (1975) and Ono (1980). The glacial extent and the valley filling before 60, 000 years B. P. have been little recognized. This paper describes the glacial landforms and the accumulation terraces before 60, 000 years B. P., located along the River Karasu, at the eastern part of Mt. Chogatake in the Northern Japanese Alps. At Chogatake Cirque, a rather dissected old cirque at the eastern side of Mt. Chogatake (2, 664 m), the cirque bottom, situated about 2, 000 m in altitude, is partly eroded away by the dissection of the River Chozawa. In this area, the present writer found out two sets of terminal moraines: the Honzawa and the Mameuchi Moraines (Fig. 5). The former, located 1, 600 m high, indicates the Pleistocene maximum glacial extension along the Hon-zawa Valley, and the latter, located at a height of 1, 900 m on the frontal edge of the Chogatake Cirque, shows a recessional feature. Along the downstream of the River Karasu, five accumulation terraces develop which are classified into Terraces I to V in this paper (Fig. 8). Terrace II which extends to the Honzawa Moraine on the terrace profile (Fig. 9), consists of fluvioglacial deposits judging from the sedimentary facies. The pumice fall deposits of Tateyama Volcano (DPm) are intercalated in the periglacial deposits covering the gravel of Terrace II. The pumice fall deposits of the EPm or OPm are intercalated in the periglacial deposits cover-ing Terrace III (Fig. 7). In view of the presumed age of the DPm fall, a stage of glacial extension and accumu-lation terracing (Tarrace II) in this area should be one of the cold periods before 100, 000 years B. P.. This glacial stage is named here the Chogatake Glacial, which can be divided into two stades, judging from the existence and location of the two terminal moraines. After the Chogatake Glacial, a periglacial environment seems to have governed this area during the period between 60, 000 and 35, 000 years B. P., on the basis of the presumed age of the EPm and OPm. Almost no glaciation occurred around the Chogatake Cirque, although the existence of a glacial stade of this period is widely recognized in other parts of the Northern Japanese Alps by many researchers (Fig. 10).