MECHANISM OF GIANT LANDSLIDES FROM LONGYANGXIA VALLEY TO LIUJIAXIA VALLEY ALONG UPPER YELLOW RIVER

This paper is based on the types of giant landslides and their relevant distribution from Longyangxia valley and Liujiaxia valley along the upper Yellow River.It investigates the relationship between the giant landslides and the evolution of Yellow river.The Gonghe,Guide and Xunhua basins experienced erosion and deplanation due to water during the B section of Kunhuang tectonic movement(~0.8Ma B.P).On the other hand,the field from Lijiaxia valley to Gongboxia valley and eastern Duolonggou near Longyangxia valley experienced denudation.The Gonghe tectonic movement of ~125kaB.P.caused that Yellow River cut through this study area,and shaped several high and steep slopes along the Upper Yellow River,which included the early rapid downward erosion with the maximum eroseion of ~30~50kaB.P.at Jianzha Basin and the later intermittent erosion.The early rapid downward erosion triggered the early high-speed giant landslides and the later intermittent erosion triggered the later climate-driven giant landslides.Therefore,the staged ed erosion of Upper Yellow River caused by tectonic uplift is the principle reason for occurrence of giant landslides.Earthquake and clogging river are triggers for occurrence of giant landslides in the study area.Above all,the mechanism of giant landslides from Longyangxia valley to Liujiaxia valley along the upper Yellow River includes three types: earthquake-triggered giant landslides; banks rebuilding-triggered giant landslides; and climate-triggered giant landslides.