PRELIMINARY STUDY ON CHARACTERISTIC AND MECHANISM OF SUPERLARGE LANDSLIDES IN UPPER YELLOW RIVER SINCE LATEPLEISTOCENE

The coupling mechanism between landslide and climate change is one of the hot topics in the landslide study in recent years.This paper studies the paleolandslides and present landslides that occurred in the upper Yellow River since latePleistocene. The characteristics of spatial and temporal distribution of the landslide and the coupling relationship between landslide active periods and climate changes and the climate changedriven mechanism of landslide are analyzed in detail. It is found that: (1)the landslide development is closely related to the climate changes. Most landslides are developed in warm and wet periods such as the marine oxygen isotopic odd stages. Rapid and continuous climatic fluctuation periods usually are also the highfrequency active periods of landslide. (2)There are 205 landslides distributed from Liujia Gorge to Longyang Gorge in the main stream of upper Yellow River. The total volume of residual deposits is 781108 m3. There are 15 superlarge landslides located the main steam,which accounts for 73% of the total landslides. 3)There are three active periods of Paleolandslides and debris flows in the region from Longyang Gorge to Liujia Gorge of Yellow River. Landslides in the first active stage have the OSL age of 18～21 kaBP. Their volume is more than 5108 m3. They are developed on the 3rd～4th fluvial terraces of Yellow River. Landslides in the 2nd active stage have the OSL age of 4～9 kaBP. Their volume is between 1～5108 m3. They are developed on the 2nd fluvial terraces of Yellow River. The present landslides are in the 3rd active stage. Their volume is between 05～1107m3. They are developed on the 1st fluvial terraces of Yellow River. The study shows that the Gonghe tectonic movement caused the region uplift and in turn strong downcutting erosion occurred along the river to form 300～600m steep slopes. In addition,the rapid climatic fluctuation in the LGM induced the landslide development in the first stage. During the 3～8 ka BP. of Holocene Optimal,strong monsoonal rainfall and a large of melted snow and ice converged into Yellow River,which led the landslide development of the second stage. The present landslides were mainly trigged by the human activities．