Preliminary Investigation on the Kinetic Characteristics of the Glacial Debris Flows in Tianmo Valley, Tibet Plateau, China.

Glacial debris flows occurring on the Tibetan Plateau consistently result in significant property damage and loss of human life. A comprehensive field investigation was conducted in Tianmo valley along the Sichuan‐Tibet Highway to reveal the dynamics of a debris flow that occurred on 11 July 2018. Furthermore, a depth‐averaged multiphase debris flow model was proposed and employed to reconstruct the characteristics of the debris flow. The model derivation, implementation, evaluation, and application were presented to demonstrate its performance. The Voellmy model was chosen because it adequately accounts for both basal frictional effects and the entrainment phenomenon. The entrainment processes, the ice melting, and the lubrication effect, were also taken into consideration. Based on the numerical results combined with field investigation data, the kinetic characteristics of the glacial debris flow were analyzed. The Tianmo valley has a small area, but the volume and erosion rate of debris flows were much larger than that of two‐phase debris flows in the same location due to ice melting. The simulation results demonstrated that the glacial debris reached a peak velocity of 20 m/s. Additionally, the volume of the debris flow increased by 50% due to the erosion over a short runout distance of approximately 4,000 m. This increase was a result of the high velocity and abundant entrainment sources on the slope. This study aims to improve understanding of the high velocity and destructive potential of debris flows in the Tianmo valley. Plain Language Summary: Debris flows frequently affect people or infrastructure due to their large volumes and high velocities. A detailed field investigation was taken in Tianmo valley, Tibet Plateau, China in this paper to reveal the dynamics of debris flow hazard chains. In addition, an optimized numerical model was proposed and used to analyze the kinetic characteristics of a glacial debris flow that occurred on 11 July 2018. The basal friction, debris erosion, and ice melting were taken into account in the numerical simulation. Based on the numerical results combined with field investigation data, the kinetic characteristics of the glacial debris flow were obtained. Simulated results indicated that the movement process of a glacial debris flow moved approximately 4,000 m, reaching a maximum velocity of 20 m/s and 50% more materials through erosion along its path. It is expected that this study can help to better understand the significant destructive force in the Tianmo valley and establish evacuation and rescue plans for communities in Tibet Plateau. Key Points: The kinetic characteristics of a glacial debris flow in Tibet were investigatedAn optimized depth‐averaged multiphase debris flow model was derived, implemented, and evaluatedThe Tianmo debris flow exhibited high velocity, large volume, and high erosion rates due to ice melting and sufficient entrainment sources [ABSTRACT FROM AUTHOR]