Preliminary investigation and dynamic analysis of a multiphase ice-rock avalanche on July 5, 2021, in the upper Naltar valley, Gilgit, Pakistan

On July 5, 2021, a catastrophic rock avalanche hit an area in the upper Naltar valley, located in northwestern Gilgit, Pakistan. The 14 Mm(3) rock mass flowed down the hillslope and traveled a distance of approximately 5 km. The avalanche killed four people and damaged more than 150 livestock. Based on a field investigation, the event is classified as a dual-phase avalanche comprising glacial ice and rock mass mixtures. In this study, the runout behavior and characteristics of the upper Naltar rock avalanche are analyzed using DAN3D. The simulation results indicate that the propagation process lasted for 140 s, with an average maximum velocity of 32 m/s. The frictional-Voellmy model for the materials in the source and erosion areas produced the best results for DAN3D. Parameter calibration, model performance, and verification were performed numerically and based on field observations. It is hoped that the selected model and parameters will help the relevant agencies understand the propagation process of similar kinds of rock avalanches in the area surrounding the current avalanche, thus improving the hazard zonation in this region.

Automated summary

In this study, the runout behavior and characteristics of the upper Naltar rock avalanche in the Gilgit region of Pakistan were analyzed using the DAN3D model. The simulation results showed that the avalanche lasted for 140 seconds with a maximum velocity of 32 m/s. Through parameter calibration and verification based on field observations, the selected model and parameters are expected to improve hazard zoning in the area.