## 4 Discussion
### Mechanism of Amplified Scraping Effect in Ice-Rock Debris Flows  
As debris particles transition from the initiation zone to the scraping zone, a progressive elongation of the mixed particles is observed. In this physical model experiment, the  
Figure 11: Comparison of the calculated and experimental values of the maximum scraping depth at different ice contents: (**a**) maximum scraping depth: calculated vs. experimental values; (**b**) error between calculated and experimental values of the maximum scraping depth.  
velocity of the leading particles in the debris flow was determined by analyzing frames in reverse, using them as reference points to estimate the pre-scraping velocity. Upon entering the scraping zone, particles begin to accumulate above the scraping area. When the accumulation reaches a certain thickness, it influences the velocity of the leading particles. Therefore, the velocity measurement should be conducted at a location preceding the scraping zone. As depicted in Figure 11a, the flow velocity was quantified by calculating the average speed 30 cm before the scraping zone using high-speed camera footage. Figure 11b presents the correlation between the pre-scraping velocity and ice content.  
As shown in Figure 12b, the pre-scraping velocity of rock-ice avalanches increases progressively with higher ice content. Among the three initial accumulation forms, the mixed configuration yields the highest pre-scraping velocity. Upon opening the material bin valve, the particles at the base of all accumulations begin to move first. In the ice on rock configuration, the rocks initiate movement first, followed by the overlying ice. Due to the higher friction coefficient between the rocks and the base compared to the ice, this configuration exhibits the lowest pre-scraping velocity. In contrast, in the stones on top of ice configuration, the gravel exerts pressure on the underlying ice particles, enhancing gravitational acceleration and consequently increasing the movement speed. As a result, the stones on ice configuration achieves the highest pre-scraping velocity.  
The equivalent friction angle between the particles and the base decreases as ice content increases, while the flow depth of the debris flow correspondingly increases (Table 2). This suggests that the presence of ice reduces friction between the debris flow and the base, enhancing flow depth and other dynamic characteristics, thereby intensifyingscraping effect (Equation (3)).  
Several studies have investigated the factors contributing to the enhanced motion characteristics of rock-ice avalanches. According to the friction-reduction mechanism in these flows, ice particles, being low-friction materials [35], not only reduce friction through their role as a component within the debris but also act as an ice layer that decreases friction with the underlying surface. Furthermore, drum tests have similarly demonstrated that the low-friction properties of ice reduce the resistance between particles and between particles and the substrate [36], thereby enhancing the mobility of the rock-ice avalanche.  
T The physical model experiment, designed to maintain consistent gravitational potential energy in rock-ice avalanches, provided insights into the energy dynamics during both the movement and the scraping processes Specifically, the low-friction characteristics  
Figure 12: Extraction of flow parameters. (**(a)** Illustration of flow velocity extraction; **(b)** relationship between pre-scraping velocity and ice content).  
of ice reduce both the resistance of the debris flow on the chute and the inter-particle friction, thereby decreasing frictional energy dissipation. As a result, a greater proportion of gravitational potential energy is converted into kinetic energy, increasing the energy available for scraping and thus intensifying the scraping effect (Figure 13).