Late Quaternary Slope Development of Valley-head Area in the Northern Margin of the Kitakami Mountains, Northeastern Japan

Abstract

This paper discusses the slope development of valley-head area in the hills around Karumai, northern margin of the Kitakami Mountains, where tephrochronological method is applicable. Each valley head area is classified into six micro-landform units, and the relation between slope profiles and slope surface deposits is investigated by digging a lot of pits. These profiles (Figs. 5, 8) reveal the change of slope processes since the late Last Glacial as follows.In the Full Glacial, almost all slope in this area including “Crestslope” and “Upper sideslope” suffered surface denudation under periglacial conditions, although small surface slides occured on steep sideslopes in part. In the Late Glacial, surface denudation became weaker as warming climatic condition, and the both slope units were stabilized before HP fall (12-13×103yr. B. P.). On the other hand, the stabilization of “Lower terrace-like gentle slope”, that is valley bottom in the Last Glacial period, took place in the time between HP fall and NbP fall (8.6×103yr. B. P.). This stabilization is a consequence of the formation of “Lower sideslope”, that is provided by increase in precipitation.