Glacial Expansion during the Early Stade of the Last Glacial Period on Mt. Tateyama, Central Japan

抄録

This paper reconstructs the flow directions and extent of glaciers on the western slopes of Mt. Tateyama (3, 015m asl) in central Japan from distribution, materials, and facies of two glacial sediments and related deposits. The timing of the larger glacial expansion during the Last Glacial period is then discussed on the basis of their stratigraphic relationships with dated tephras such as K-Tz (95 to 90 ka), Tt-E (ca. 70 ka), and DKP (52 to 50 ka), The wider glacial extension occurred and deposited the Jodosawa Gravel during Murodo Stade I (95 to 70 ka) in MIS 5b to 4 (marine oxygen isotope stage 5b to 4). In this substade, the glaciers extended from the non-volcanic Tateyama Main Ridge onto the flat surface of the pyroclastic flow deposits erupted from the Tateyama Volcano, and overflowed to the north from the basin. The glaciers eroded the pyroclastic flow deposits during Murodo Stade I, and extended to at least 2, 300m asl. Between Murodo Stades I and II, the glaciers were forcefully melted by the pumice fall erupted from the Tateyama Volcano, and temporarily retreated upstream. During Murodo Stade II (70 to 50 ka) in MIS 4 to early MIS 3, the snout of glaciers readvanced to about 2, 350m asl, and deposited the Murodo Gravel. The glacial readvance was restored in size soon after the pumice fall had finished.