The Formation Characteristics And Geomorphical Evolution Of The Landslides And Debris Flow Fans In Guide Basin,the Upper Reaches Of The Yellow River

The Guide basin is a Cenozoic graben basin,which is located at the northeast margin of the Tibetan Plateau.Due to the tectonic uplift and Yellow River down-cutting,the geohazards are well developed in the basin.In this paper,the distribution regularities of the landslides and debris flows are analyzed by field survey and high-resolution remote sensing image interpretation.Based on geological drilling,granulation curve comparison,mineral composition test and¹⁴C dating,the formation characteristics and mechanism of typical landslides and debris flows are studied,some main conclusions are as follows:1.Through remote sensing interpretation of 73 landslides and 10 debris flows in the study area,it has been found that most of the landslides are located at the north bank of the Yellow River,showing a linear distribution along the Yellow River's tributaries and the faults,and most of the debris flow fans are located at the eastern part of the basin and the spatial distribution characteristics shows significant difference on the two sides of the Yellow River.6 landslides and 3 debris flow fans were surveyed in detail based on remote sensing interpretation,the landslides are all located at the bank of the Yellow River and its tributaries,so the formation of the them have close relation with the geomorphical evolution of the river valleys.All of the 3 debris flows are located at the eastern part of the basin,on the north bank of the Yellow River,and there are two accumulating sequences of the fans.2.Based on the work of field survey,remote sensing interpretation,granularity characteristics contrastive analysis and ¹⁴C dating,The formation characteristics,period,mechanism and geomorphological evolution process of the Xijitan landslide was studied,some conclusions are as follows:1)The 4 formation stages of this giant landslide is late Pleistocene-early Holocene,5420B.P.,1872A.D.and contemporary age,the inducing factor of stage?and?were climate warming and rainfall,stage?may induced by earthquakes and the stage?is affected by comprehensive factors such as rainfall and human engineering activities.2)The Xijitan landslide stage?is a high-speed and long-distance landslide,which pushed the Yellow river course southwards more than 2 km and changed the Yellow River's flow direction.For this reason,the Yellow River course turned to curving and the erosion to rightbank was enhanced,the river course became broaden and finally the modern river valley formed.3.Based on the work of field survey,geological drilling,granularity characteristics contrastive analysis,mineral composition test and ¹⁴C dating,the formation and evolution process of the Erlian village debris flow fans were studied and some main conclusions are as follows:1)the early debris flow fans at the north bank of the Yellow River formed before 16kaB.P.,as a result of glacial snowmelt water carrying the mud and accumulating besides the river course during Last Glacial Maximum?LGM?,showing that there have been cold-wet climate and more rainfall at the northeastern Tibetan Plateau in LGM.2)The late stage debris flow fans started to accumulate at 8 kaB.P.,and its formation process had close relation with glacial snowmelt water caused by climate warming in early Holocene.Both of the two stages of debris flow fans evolution are affected by climate factors.3)The relationship of the debris flow fans accumulation and Yellow River erosion can be devided into 3 stages:18-16 kaB.P.is the early stage debris flow fans accumulation period,16-8kaB.P.is the erosion period,and 8kaB.P.to present is the late stage debris flow fans accumulating period.4.Based on the study of formation process of Xijitan landslide and Erlian village debris flow,the geomorphical evolution process in Guide Basin is rebuilt,the time sequence is as follows:the early stage Erlian village debris flow fan accumulated?the Yellow River corroded the early stage debris flow fan and Xijitan landslide stage?occurred?the first terrace of Yellow River formed?the late stage of Erlian village debris flow fan accumulated?Xijitan landslide stage?occurred?the modern Yellow River valley formed.