[MIS20-P05] Probable glacier detritus found at downstream site of the Yokoo moraines in the northern Japanese Alps: its geological characteristics and implications
Keywords:glaciations, the Last Glacial age, late Pleistocene, till, Japanese Alps
Around the upper reach of Azusa River in the northern Japanese Alps, the lowest position of a glacier snout during the late Pleistocene was known as the Yokoo-Iwagoya moraines (ca. 1700 m ASL). We revisited this widely-accepted concept of paleoglaciations in the Japanese Alps and newly found poorly-sorted angular to subangular rock clasts from the site lower than Yokoo-Iwagoya moraines (ca. 1400 m longitudinal and 50 m vertical). Rock clasts are composed of Quaternary igneous rocks that are never distributed around Yokoo. We concluded that those rock clasts were transported by a valley glacier from the higher slopes of Mount Yari-Hotaka Massif around 2800–3000 m ASL. Depositional ages of the clasts are still unknown but the Marine Isotope Stage 4 was probable.