Glacial and Periglacial Landforms around Mt. Kasaga-take, Northern Japanese Alps

In the last two decades, the Last Glacial paleoenvironment of the Japan Islands based on glacial and periglacial geomorphology has been actively discussed. However, positive correlations between glacial and periglacial stages in the identical region have not been made in previous studies in Japan. The purpose of this study is to clarify historical development of glacial landforms and fossil penglacial smooth slopes around Mt. Kasaga-take (Fig. 1), northern Japanese Alps, and to correlate glacial and periglacial stages.<br> On the basis of the distribution of glacial landforms recognized by aerophoto-interpretation (Figs. 2-4), five glacial stages, Kasaga-take I, II, III, IV, and V stages, in order from the oldest to the youngest, are classified in the study area. Glacial landforms of Kasaga-take stage I consist of dissected troughs and trough edges in the valley. Those of stages II and III are composed of fresh cirques and glaciated valley walls. Landforms of stage IV are very fresh cirques. Glaciated slopes of stage V are the most fresh and are located on part of the cirques of stage IV. Average altitude of the glacial terminus in each stage is estimated as follows: Kasaga-take stage I, below 1, 700m a. s. l.; stage II, about 2, 000m a. s. l.; stage III, 2, 400m a. s. l. on the windblown side (western side) and 2, 200m a. s. l. on the lee side (eastern side); stage IV, disappearance on the windblown side and 2, 420m to 2, 600m a. s. l. on the lee side; stage V, 2, 630m to 2, 720m a. s. l. on the lee side (Fig. 5 and Table 1). The older four stages can be correlated to glacial stages in the Uchikomi-dani Valley (Hasegawa, 1992), located on the northern flank of Mt. Kasaga-take: Kasaga-take stage I, Ichino-sawa stage (early stage of Last Glacial period); Kasaga-take stage II, Futamata stage (first glacial advance in late stage of Last Glacial period, 25, 000 y. B. P.) ; Kasaga-take stage III, Migimata stage (Last Glacial Maximum); Kasaga-take stage IV, Kitakenkoku stage (Late Glacial). It is possible that Kasaga-take stage V, youngest one, is correlated to Neoglaciation.<br> Fossil periglacial smooth slopes around t. Kasaga-take are inclined from 20 to 30 degrees on average, and thickness of the surface materials is 0.5 to 3m. They are classifid into debris slopes, composed of angular gravels with fine matrix, and block slopes, composed of angular boulders without matrix. The fabric of the periglacial slope materials is parallel to the slope direction (Fig. 8). Formative stages of the fossil periglacial smooth slopes are defined to three stages: Older Stage 1, Older Stage 2, and Younger Stage, in order from oldest to youngest. The definitions of Younger Stage and Older Stage 2 are based on the topographical and vegetational characteristics; the continuous risers of large-scale solifluction sheets exist on the lower limit of the younger slopes and present forest limits are also located on the same positions (Figs. 7 and 11). These characteristics are identical to the chronological features of fossil periglacial smooth slopes clarified in the Chichibu mountains (Shimizu, 1983; Shimizu and Suzuki, 1994) and Mt. Hayachine-san (Shimizu, 1994). On the other hand, the definition of Older Stage 1 and Older Stage 2 are based on the stratigraphic sequence of penglacial slope materials and Aira-Tn Volcanic ash (AT; about 24, 000y. B. P.: Fig. 9). The lower limit of the slope in each stage is located about 1, 800m a. s. l., about 2, 000m a. s. l. and 2, 400-2, 500m a. s. l., from older to younger, respectively. Moreover, from the stratigraphic sequence of Kikai-Akahoya volcanic ash (K-Ah; 6, 300y. B. P.) in the surficial layers of the periglacial slope materials around the main ridge (Fig. 10), it is clarified that wind-beaten bare grounds interfingered to Pinus pumila scrubs expanded more in the Neoglaciation than in the present time.