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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]

Debris flows occurred very often in Guxiang gully, one tributary of Palongcangbu since 1950s. Debris flows were investigated and the volume of debris flows have been caculated since 1953. This paper collected 60-years data of accumulation rates of loose sediment in the upstream of the narrow sections of the gully with relationships of debris flows magnitude. Sediments changes in the upstream of the narrow gully section are compared with channel incision, debris flow activity and motions. The data of the sediment accumulations and its debris flow events provide insights into narrow gully section controls and debris flow dynamics. Acceleration in debris flow events was recorded between the 1950s and 1980s, compared with a decrease in debris flow events since the 2000s. The narrow gully section has always formed as a dam for sediment accumulation. The loose material accumulations rates have remained quite small and sediment is not enough to support the frequent debris flows since 2000. On the contrary, sediments accumulated in the upstream of the narrow section due to large earthquake in 1950 were the sources of debris flows. There was not a clear coupling between accumulation rates of sediment and the frequency-magnitude debris flows in the 1950s and 1980s. On the contrary, a clear link between accumulation rates of sediment and the frequency-magnitude debris flows exists since 2000. In the debris flow events since 2000, debris flows in the gully are both controlled by the rainfall and narrow section of the gully. In this paper we have considered the dynamics of many debris flow events in the upstream and downstream of the narrow gully section. The sediments accumulation in the upstream of the narrow section of the gully created as a dam, which was depending on the accumulated sediment volume and the width of the narrow section. The accumulation of sediment in the upstream of the narrow section could affect its longitudinal morphology and add the longitudinal gradient, which caused a perturbation of debris flow dynamic in the gully.Key Word: debris flow; narrow section; consolidation; intermittent motion; additional gradient [ABSTRACT FROM AUTHOR]

The Dadu River Basin (DRB) is an important economic corridor on the Chuanxi Plateau. The DRB is located in the highly changeable terrain of the eastern Qinghai-Tibet Plateau and is often threatened by debris flows. To mitigate the damage of debris flow disasters to the construction and operation of large infrastructures such as railways, roads and hydropower stations in the DRB, it is necessary to evaluate debris flow susceptibility. The connectivity of potential material sources (CPMS), which proxies the possibility of potential material transfer from the source to the outlet, was calculated using an improved index of connectivity, excess topography and brittle fracture index to identify and quantify debris flow susceptibility. The results show that the IC and the gully scale have a Logartihmic function in the DRB, in which IC decreases as the catchment area increases. In 3967 gullies of the Dadu River and its tributaries, the total connectivity of potential material sources (TCPMS) could be used to distinguish between debris flow gullies and non-debris flow gullies (AUC = 0.748). The TCPMS and average connectivity of potential material sources (ACPMS) were used to classify the scale and activity intensity of the 2398 debris flow gullies into four levels. The moderate- and high-activity intensity and large- and extra large-scale debris flows are mainly distributed in Danba, Luding and Kangding. The results of this study provide reference and evidence for the identification and evaluation of debris flow susceptibility. • A new method for assessing debris flow susceptibility based on potential material sources and sediment connectivity. • The quantitative relationship between the scale of debris flow and conditioning factors. • The contribution of excess topography was considered. [ABSTRACT FROM AUTHOR]