Comparative Study on the Runoff Process of Granite Drainage Basins in Korea and Mongolia

Dissected erosional surfaces are widely distributed in the western part of Korea (e.g. Icheon, Chungju, Jecheon, Seosan). The deposits with thickness of less than 2m occur on the smooth bedrock surface are composed of poorly sorted subangular gravels with less than 20cm diameter. However, only weathered mantle of granites without the gravel layer are observed at some outcrops. The results of grain size analysis of deposits of Icheon district revealed that the characteristic of the gain size distribution is very similar with the results of sheetflood deposits presented by Blair (1999) in the Death Valley. Loess layer with buried soil layers of MIS7 covers the sheetflood deposits. The loess layer implies that the sheetflood deposits occurred before MIS7 based on the typical Loess sequences presented by Naruse et al.(2003). On the other hand, the climate of Korean Peninsula in MIS2 was very dry and cold (Yoon and Hwnag, 2003) by pollen analysis. This is because Yellow Sea was completely emerged during the MIS2(e.g. Sau\ito, 1998). So, it is thought that the climate in Korean Peninsula of not only MIS2 but also other glacial ages such as MIS8 was similar with present Mongolian climates. Tanaka et al.(2005) pointed out that Hortonian overlandflow occurs in grass vegetated granite basin in Mongolia. Therefore, dissected piedmont gentle slopes in the western Korea were possibly formed by sheetflood erosion during probably MIS8 as pediment widely distributed in Mongolia.