Preliminary Study of Paleoflood of Last Glacial Maximum in Upper Reaches of the Yellow River

It is well known that paleoflood predictions must base on its occurrence. But our available records do not provide long enough temporal scale for identification and grasp the emergence law of flood events. So it is very important and necessary to discuss the characters of floods during the characteristic climatic period using geological records. The flood record of Lanzhou Yinchuan reach in upper Yellow River reveals 106 flood events, with a frequency of 53 per ka, during 20 to 18 ka including 18 complex floods superposed by multiple flood peaks. These paleoflood probably belonging to ice slush floods are associated with abrupt and extreme climatic oscillation and instability of this stage. The high frequency of these paleoflood is consistent with high lake surface of western China in course of last glacial maximum. It is neither in accordance with the monsoon theory nor different from the climatic feature of eastern areas typical of cold and dry climate. This indicates the climate complexity and particularity of western China.