Evolution Characteristics And Formation Mechanism Of The Glacier Avalanche-debris Flow Events In Sedongpu Gully,Yarlung Zangbo River,Tibet

Glacier avalanche-debris flow is a special fluid with high speed,long distance and extremely complex internal structure,which is formed bythe glacier onthe slope ofthe alpine mountain area collapsing and sliding underthe action of gravity.It is converted into kinetic energy by potential energy,disintegrated and moves together with loose materials inthe lower part.It hasthe characteristics of high speed,long sliding distance,frequent turning and high disaster-causing.It not only causes destructive disasters tothe areas alongthe way,but also tends to blockthe main stream to form barrier lakes and cause more secondary disasters.Withthe global temperature generally rising,glaciers inthe Qinghai-Tibet Plateau are seriously degraded,and disasters such as glacial debris flow,glacial lake outburst and glacier avalanche are frequent,causing serious loss of personnel and property,which has attracted extensive attention of scholars at home and abroad.On October 17 and 29,2018,two large-scale glacier avalanche-debris flow events occurred in Sedongpu Gully inthe lower reaches of Yarlung Zangbo River,posing a seriousthreat to residents alongthe line and major water conservancy facilities inthe lower reaches.Therefore,it is of great significance to studythe causes,evolution characteristics and development trend ofthe Ice Quake debris flow in Sedongpugou to ensurethe personal and property safety ofthe people alongthe Yarlung Zangbo River,and to provide reference forthe prevention and control of similar disasters in other areas ofthe Qinghai-Tibet Plateau,especially alongthe Sichuan-Tibet Railway and Sichuan-Tibet Highway.Inthis paper,the Sedongpu gully inthe lower reaches ofthe Yarlung Zangbo River is taken asthe research object.Firstly,the historical debris flow events in Sedongpu gully are analyzed by multi-source and multi-temporal remote sensing images.Secondly,the evolution characteristics ofthe Glacier avalanche-debris flow in Sedongpu gully are studied by interpreting and comparingthe historical remote sensing images.Finally,the influencing factors and genetic mechanism ofthe Glacier avalanche-debris flow inthe Sedongpu gully are analyzed by using temperature,rainfall,seismic data and multi-temporal high-precision digital elevation model data.The main understandings are as follows:(1)There have been at least 8 river blocking events inthe history of Sedongpu Gully,showingthe rule of "active-intermittent-active-intermittent-active",which indicatesthat its activities have Periodicity.(2)From January 4th,1988 to January 19th,2017,the glaciers inthe formation area were relatively stable,with few occurrence of Ice Quake.From January 19th,2017 to January 22th,2018,the glacier area was greatly reduced,resulting in frequent occurrence of Ice Quake and rockfalls,which showedthe characteristics of concentrated time and concentrated area.From December 8th,1969 to November 18th,2013,the moraine inthe shoveling and scraping movement area was slowly accumulating.From November 18th,2013 to October 30th,2018,the movement ofthe moraine intensified and some ofthe moraine slipped on a large scale underthe impact ofthe ice,forming two large-scale river blocking events on October 17th and 29th,2018.(3)The occurrence of Glacier avalanche-debris flow in Sedongpu gully is coupled with factors such as temperature,rainfall and earthquake.The abnormal increase of temperature inthe study area since 2017 andthe serious degradation of glaciers arethe main factors forthe frequent occurrence of recent River blockage events in Sedongpu gully.(4)The process ofthe two river blocking events in October 2018 was: ice-cold start-up→disintegration of ice-disintegration,shovel scrapingthe rocky soil ofthe lower steep slope,shocking and scrapingthe lower platform ice shovel,making it largescale Start → ice collapse body and started hail debris flow movement → debris flow due tothe gentle slope andthe opposite mountain block,gradually silting and blockingthe Yarlung Zangbo River to form a dam and a barrier lake →the dam is gradually increased afterthe dam Eventually,the dam was flooded fromthe relatively low elevation ofthe ditch onthe opposite side ofthe Mizoguchi.