Formation Mechanism Of Glacial Debris Flow In Bomi,Tibet

Glacier debris flow is a natural geological phenomenon which closely related to glacial movement.It is often considered as typical geo-hazards in alpine regions with the characteristics of sudden outburst,fast flow,strong impact ability,long-distance running and difficult to predict in general.Bomi is located on the northeast of the eastern Himalyan Syntaxis where have complex crustal movements,strong tectonic activity and development of oceanic glaciers.The glacial debris flows is the main geological disaster in this region caused by the complex geological conditions,which is a tremendous threats to local people’s lives and their property security.It is also a huge challenge of local foundation construction,such as road,railway and electrical transportation equipments.The detailed study of glacial debris flows and modern glaciers in Tibet’s Bomi region is based on the data from documents of previous research,videos of remote sensing and field survey.First,this article summarized characteristics and relations of glacial debris flows formation conditions.Then it analyzed the formation mechanism and development model of typical glacial debris flows.Last,it discussed the overall mechanism of glacial debris flows in the basin.This acquires the following points:1.There are numerous glacial debris flows in Tibet’s Bomi region.According to the 2016 survey,there are 25 glacial debris flows in the region,which are mainly distributed in the downstream canyon of the Pallon Tsangpobasin.There are 13large-scale glacial debris flows,5 medium-sized ones,5 small ones,and 2 giant ones.The research area has developed the largest oceanic glaciers in China.According to the survey results,there are a total of 86 glaciers in the study area,with a total glacial area of 133.35 km~2and glacial reserves of 8451.3×10~6m~3.2.The formation conditions of glacial debris flows can be subdivided into three major categories:hydrothermal conditions,source conditions,and topographic conditions.Various types of conditions affect each other independently and restrict each other,and various types of conditions show significant differences on both sides of the river basin.(1)The hydrothermal condition is the trigger factor of the glacial debris flow,divided into two aspects:temperature and precipitation.The effect of temperature is a long-term concept that affects the evolution of glaciers;The impact of precipitation is a concept of a short-term scale,which is mainly concentrated between July and September each year.And the glacial debris flow has a certain lag in response to hydrothermal conditions.(2)The source condition is the material basis of the glacial debris flow.Its material composition,reserves,recharge methods,and recharge position largely control the nature of the glacial debris flow.(3)The terrain condition is a necessary condition for the formation of glacial debris flow,in which the basin shape mainly affects the catchment capacity of the gully and the movement of the glaciers in the upper reaches of the gully;the longitudinal ratio of the gutter controls the accumulation of source and the circulation of the water source;The longitudinal profile of the channel has a comprehensive effect on the formation and distribution of debris flow.(4)Each condition shows differences in the north and south banks of the basin.For example,The south bank of the basin receives more precipitation and is less affected by temperature,while the northern shore of the basin is in the opposite situation;the north bankvalley has more conditions for producing moraines soil;the south bank valleys are mostly in the shape of“willows”,while the north bank valleys are mostly“funnel”.These differences will lead to different development characteristics and formation mechanisms of the glacial debris flows on the north and south banks of the basin.3.In this paper,combined with previous research progress,through analysis and discussion of the typical glacial debris flow in the study area,summed up their respective genetic mechanisms,and summarized the three glacial debris flow genesis mechanism model.Type I:Fractures developed at the front of the glaciers lead to the collapse of glaciers.The meltwater under the glaciers accelerates the collapse of the ice,allowing the ice to move rapidly downstream.During the movement,the ice body is fragmented and transformed into fluids to bring about a great capacity to start the source material in the channel to induce the glacial debris flow pattern.Type II:In the early period,under the erosion of glacial meltwater and slow rainfall,increase the moisture content of the hail and other sources in the channel.And under the spur of heavy rainfall,glacier melting water and rainwater form a runoff to carry out the liquefaction start of the loose material in the channel to eclipse,and accelerate the rush out in the“smooth”circulation area.Type III:The channel is formed by channeling the channel body and blocking the channel to form a dam body.After the material in the dam has accumulated to a certain amount,the dam breach will cause a mud flow pattern.4.The formation mechanism of the 25 glacial debris flows in the study area is basically among these three types,but the genetic mechanism of glacial debris flows on the south and north sides of the basin varies.In summary,the outbreak patterns of glacial debris flows on the south bank of the basin are mainly Type II and Type III;the north shore of the basin is mainly Type I and Type III.