Prediction Research On Crater Lake Break-out Lahar Hazard Of Changbai Mountain

The Tianchi Volcano in Changbai Mountains is one of the international famousvolcanoes which has the highest potentially dangerous to erupted in China. At the topof the Tianchi Volcano in Changbai Mountains has a crater lake with2.04billion m3water in it. Once the volcano erupt again, or other factors lead the crater lake outburst,the lahar will be the main disaster. More important, it is located in the hinterland ofChangbai Mountains area, in the east of Jilin Province, it has been the importantcomponent of Changjitu development and opening-up pilot area and China’s famoustourist area. If large-scale floods and lahar erupted, it would bring serious damage.For those reasons, it has important theoretical and practical value to do the research ofthe Crater lake outburst and triggered mudslides disaster.This article rely on the program of Changbai Mountains’ Early Warning of theEruptions Caused by Secondary Disasters, selected Changbai Mountains volcano’ssecondary debris flow hazards,the type of crater lake outburst, as the research object.After systematic summarized research status of the volcanic secondary debris flowhazards（crater lake outburst type）and analyzed the related research documents, webegin to carry out the field site survey, analysis, sampling and the populationsocio-economic factors’ collecting and collating, taking samples of loose debris todo the experiments of physical mechanical parameters, and summarizing thedistribution and characteristics of the loose material in the study area. Based on theexperimental data and combined with the actual situation of the study area, wedesigned and built a physical simulation test platform to get the debris flow impactfactors cause by the flood impact and the prediction model of hazard range.With helpof numerical simulation software combines physical simulation test to have thenumerical simulation in the study area, such as the outbreak of debris flows, thecourse of the campaign, and accumulation. Master the mechanism and process oflahar’s eruption in study area. Base on the ARCGIS, we exploited the lahar forecastand early warning systems. Made the prediction results display, inquiries and warningcome true. The thesis has made the following main conclusions:1) Firstly, study on the debris loose in the research area. With the means of fieldinvestigation, laboratory experiments, and particle size analysis theory, basicallyidentified the distribution, reserves, as well as the particle size characteristics of the loose debris as the provenance of the volcanic debris flow. Pyroclastic deposits’distribution area can be1262km2,35.38％of the study area, The total amount ofaccumulation estimates more than3km3. Loose debris on the whole of the study areacan be divided into three categories: volcanic falling debris accumulation, pyroclasticflow accumulation and lahar accumulation. The distribution and nature of the varioustypes’ loose debris are significant differences. We focus on the pyroclastic flowaccumulation and lahar accumulation. The average particle size of the loose debris isin-1.5-1.5Ф, the skewness is in0-0.4, the kurtosis is in0.8-1.4, standard deviationhas two obvious centralized region, it has dualism. Frequency curve is given priorityto moderately to sharp a narrow, respectively in the well-sorted and poorly sorted.Depositional environment discriminant value of all sampling points were less than9.8433, corresponding to turbidite sedimentary environment, The energy ofpyroclastic flow to carry substances is relatively large, has fast speed, lahars flowsdownward along the river valley to reach distant, both are of great destructive forces.2) Based on sieve analysis experiments and physical mechanics parametersexperiments, combined with fractal theory gets that pyroclastic flow accumulation andlahar accumulation have significant difference in physical and mechanical properties.Pyroclastic flow accumulation has the characteristics of light weight, high moisturecontent, macropore and so on, while lahar accumulation influenced by other clasticsparticipating and fluviatile transport has little physical property difference betweeneach other. Loose deposit particle size distribution has remarkable linear relation withpercentage content of particle cumulative, with remarkable fractal characteristics.Fractal dimension corresponds to the grain of deposit,the grain is worse when thefractal dimension is higher, the range of the fractal dimension reflects the complexcharacteristics of loose pyroclastic deposits in free organization system, and the loosepyroclastic Grain-size fractal dimension and physical mechanical index of loosematerial have good relativity, it can reflect the differences between index, theGrain-size fractal dimension can be used as the index of loose pyroclastic deposits’quantitative of the physical mechanics character.3) Set up a physical simulation experimental platform, and three main physicalmodel experiments of sediment concentration、demo process from outbreak todepositionin and hazard range about lahar were carried out on the platform. Thefollowing main results had been obtained. The gradient of flume makes significantimpacts on sediment concentration in debris flow. The sediment concentration indebris flow. increase nearly convex and then gently with the increasing of the gradientof flume generally, but it also has the problem of some calculation patterns’empricalcoefficient is not unique. Water source condition (total body water and water sourceflow rate) make less influence on sediment concentration in debris flow, but make remarkable influence on the amount of debris flow and accumulation.4）Under the condition of enough loose material, the length of debris fans isremarkably influenced by flow rate of water source and slope of accumulation area.The length of debris fans and the amount of debris flow outbreak are in close relationand influenced remarkably by the whole water amount and slope of the sink. Thethickness of debris fans is influenced by slope of the sink and accumulation area. Thearea of accumulation is influenced by all the four factors. Under the selected condition,the accumulation area slope, the water amount, and sink slope works effectively.Concentration of debris flow transportation is only remarkably influenced by sinkslope.5）Based on the experiment of debris flow hazard range, established the hazardrange model of debris flows prediction model which based on general regressionneural network model(GRNN).The forecasts’largest error is11.63%, relativeaverage error of prediction result is6.38%, it is not only convenient and high stability,but also have much higher prediction accuracy, it provides possible methods for theforecasts of the hazard warning area of lahar, it can provide reference base to makeplanning for the prevention and reduction of debris flow disaster.6）With the help of laboratory physical model experiments combines numericalsimulation software to simulate the start, movement and accumulation of lahar causedby flood, and analyzing the result of numerical simulation.It has debris flow headphenomenon; The action form of slope erosion is from surface to inside and graduallyinward until debris all washed away;Accumulation form is similar to parabolic typeeffect as a whole.It is provides the measures to study the motion mechanism of lahar.7）Using the software of HEC-RAS can stimulate the range of the type of craterlake outburst flood. Combined with ARCGIS in mapping and inquirying can achievethe forecast of the hazard range of secondary debris flow, the range of flood anddebris flow hazard displayed on the platform of ARCGIS. The tested and appliedresults showed that the measures are simple and feasible and can provide the basisdata service for applying in forecasting lahar.8） Based on the ArcObjects10.0of COM’s GIS components, takes theMicrosoft Visual Studio.NET as its development environment and Visual Basic.net asit’s development language of software, and developed a system of lahar warningbased on GIS. This system mainly consists of the element of geologicalenvironment’s storage、the management of basal Data、input the image display ofharzard area、superimposition analysis of Layer、inrequiring、give early warning toenterprises and so on. It enables the image display of lahar hazardous area、management、 researching、 the economic information layer of superpositionpopulation、analysis, and release early-warning information. Result of application indicates that the system can provide the possibility of actual application after it’supgrade and improvement.