Preliminary Study On The Glacial And Temperature Conditions Of Terminal Moraine Dam Glacier Lake Outburst In Tibet

Glacier lake is widely distributed in the high altitude mountain areas of the world, such as the Himalayas,the Alps,Central Asia,North America,the United Kingdom,Peru, etc. In recent years, due to the impact of global warming, glacier melting accelerated, glacier lake outburst disasters occur frequently.Tibet has the most of the glacier lake in China, at the same time it is the most serious disaster area affected by glacier lake outburst,from 1935 to 2013,24 glacier lake of Tibet have been happened outburst 28 times. As the glacier lake outburst occurred in the remote mountain area,the geological environment is complex and harsh, and it's sudden outbreak,difficult to observe,has become one of the common disasters in Tibet mountain area, brings a serious threat to local people's life and property safety.And the glacier lake outburst floods rapid erosion glacial deposits,slope and gully bed material source,vulnerable to the formation of debris flow,namely the glacier lake outburst debris flow, causing greater harm.Therefore,to strengthen the formation of glacier lake outburst,movement and disaster mechanism research has a very important theoretical and practical significance for the accurately evaluate the stability of the lake,reduce or avoid occurrence of glacier lake outburst, protect the safety of people's lives,and reduction of all kinds of economic losses.The formation of glacier lake outburst is closely related to the factors of glacier lake's trailing edge glacial condition and external temperature, temperature is trigger condition,glacial condition is potential condition for glacier lake outburst.Predecessor's study on glacial and temperature conditions were more limited to qualitative description,quantitative research were rarely simple and rough, lack of more in-depth and more detailed feature analysis on individual glacier lake,did not give a quantitative discriminant model.So far,according to the monitoring and early warning of glacier lake outburst are mainly concentrated in temperature, comprehensive study on several conditions was not considered. This paper is mainly in the case of Tibet's glacier lake outburst disaster,we selected 11 outburst lake and the surrounding 51 not outburst lake as the research object. First of all,we separately study the effects of glacial on outburst in each glacier lake through which we obtained the glacial discriminant model, and then we explore the effect of temperature through which we got the temperature discriminant model. Through comprehensive analysis of these two model, we obtained a composite factor discriminant model of glacier lake outburst.Eventually we apply the topographic discriminant model to Almaty in Kazakhstan,Tronador in Argentina,Zhongyu Village in Tibet and Himalayas in Bhutan to verify, very good results are achieved.The main conclusions are as follows:(1) In the event of glacier lake outburst in Tibet,ice avalanche and glacial landside are the main reason of outburst,which is closely related to the slope of glacier tongue, aspect of glacier,area of glacier.The cause of the ice avalanche and glacial landside as the temperature change,so the effect of temperature factor on the glacier lake outburst is also crucial.After the glacier lake outburst,downstream movement outburst flood is likely to evolve into glacier lake outburst debris flow if encounter a sufficient source of material.(2) This article select the slope of glacier tongue(a), aspect of glacier(6),area of glacier(A) as the topographic factor of glacier lake outburst,and then make the slope factor S=tan(a), aspect factor C=sin(?),area factor A=A0/A*. Through the comprehensive analysis on slope factor(S), aspect factor (C) and the area factor(A),we get a comprehensive topographic model:R= S+0.5C+0.05A,it can well represent the glacier lake outburst glacial conditions.(3) Through the above studies of glacier lake outburst occurred in Tibet, we conclude that the critical terrain conditions is:R>Cr.That is to say when in case of the same temperature condition, the topographic R-factor must be greater than a certain value can the glacier lake outburst.(4) On the base of formation mechanism of glacier lake outburst,select T7(7 days temperature sum before outburst),To(effective accumulated temperature),Ty2(anteced-ent temperature) as the temperature factor of glacier lake outburst.Through the comprehensive analysis on the three factors,we get a comprehensive temperature factor:T*=T0+0.5T7+0.8Ty2.Finally the comprehensive temperature factor divided by the average temperature of Ty we get a critical temperature discrimination model it can well represent the glacier lake outburst temperature conditions.(5) Analysing the correlation of the topographic R-factor and the temperature T-factor, we get a comprehensive P-factor of glacier lake outburst that its expression is factor model can better reflect the possibility of glacier lake outburst.(6) Using the T-factor model in the glacier lake outburst disaster of Almaty in Kazakhstan,Tronador in Argentina,Zhongyu Village in Tibet and Himalayas in Bhutan,the difference in temperature is not considered, we get a good verification result. So the studies on glacier lake outburst model has universal applicability.