Historical Reconstruction Of Glacial Debris Flow Disaster Based On Tree Ring Response

Glacial debris flow in Yarlung Zangbo River Basin has large scale and high density,which has caused great damage to transportation,water conservancy,minerals and ecology.Compared with debris flow initiated by rainfall,glacier debris flow has the characteristics of stronger destructive force and longer flow duration.Reconstructing the temporal and spatial distribution of glacial debris flow events can provide engineering parameters such as scale and outbreak frequency for debris flow control.This paper selects the huge thick moraine undercut erosion debris flow gully（Guxiang gully）,ice avalanche induced debris flow gully（Tianmo gully）,landslide undercut debris flow gully（Zhamunong gully）and barrier lake outburst debris flow gully（Pailong gully）in the Yarlung Zangbo River Basin as the research object,and uses the damage tissue,growth inhibition and release of tree rings in the gully and fan to reconstruct the main gully debris flow and landslide and debris flows in branch in the main gully in the past 40 years;The flow range of debris flow is discussed from the aspects of tree growth disturbance intensity;The occurrence time and flow range of main gully debris flow,internal landslide and branch gully debris flow without historical records are further analyzed through W_it index,and the following conclusions are preliminarily obtained:（1）The accuracy of debris flow outbreak time reflected by tree chronology is related to the scale of debris flow.Too large scale of debris flow will lead to the elimination of disaster historical memory of disturbed trees,which is not conducive to the dating of debris flow events before the large-scale disasters.（2）Tree ring growth disturbance has a lag effect on the response to glacial debris flow.The lag time in Yaluzangpo River Basin is 1-3 years,and the larger the scale of debris flow,the longer the lag time.（3）The sensitivity of tree ring growth inhibition/release and trauma to debris flow disaster is related to tree age.Young trees under 20 years old are more sensitive to debris flow events and can record debris flow events more sensitively.（4）Many branch debris flows in the gully and landslides in the main gully will interfere with the dating of debris flow events in the main gully,but the branch debris flow and main gully landslide events occurring at the same time as the main gully debris flow will increase the wit index,which is conducive to the dating of debris flow disaster events in the main gully.（5）The sediment deposition in the barrier lake formed by debris flow blocking the river will also disturb the growth of tree rings,but the disturbance intensity is far lower than the impact of fan sediment deposition on tree disturbance.The disturbance of tree rings in the barrier lake can also indirectly reflect the occurrence time and scale of debris flow blocking the river.