Dynamic Analysis Of The Ice–rock Debris Avalanche In The Langtang Valley Triggered By The 2015 Gorkha Earthquake,Nepal

On April 25,2015 a disastrous rock avalanche that was triggered by the Gorkha earthquake,which buried a touristic village and killed more than 350 people,in the Langtang valley of central Nepal.This was a multiphase avalanche comprising of glacier snow–ice and rock debris mixture,which occurred in multiple stages from different source areas.In this study,the runout and deposition process of the Langtang avalanche were analyzed using a two-phase mass flow model with the r.avaflow software to recreate the flow heights,velocity,and deposition structure and sequence.The simulation results indicated that the duration of the total failure process was 140 sec,and the avalanche flowed with an average velocity of 36 m/s.The interaction between two different stages of the avalanche deflected its path,directing it toward the downstream end of the valley and generating a splashing air blast,which caused significant damage in that direction.Parameter calibration,model performance evaluation,and verification were performed numerically and based on field observations.In addition,a study on the initiation of the landslide is conducted based on the Newmark sliding block concept to determine the initiation times of the various stages of the avalanche.This is done by calculating the factor of safety(FS)of each component landslide and using the criterion FS<1 in the recorded ground acceleration during the Gorkha earthquake.Incorporation of the initiation time into the optimized simulation improved the model accuracy.This study gave insight into the progressive failure mechanisms of the dual-phase and multi-staged avalanche occurring in the snowline regions and explained the path deflections due to the stage interactions.The results provide a reference for hazard zonation in such mountainous regions.