## 2 Physical Model Experiments  
### Experimental Apparatus  
Rock-ice avalanches occur in high-altitude, cold mountain regions, where they typically have long return periods but short durations, making direct field observations challenging. To address this, and drawing on prior laboratory studies of debris flows and mudslides [23; 26], the present study uses flume experiments coupled with high-speed imaging to replicate the shear-scraping phenomena during the motion of rock-ice avalanches, with a focus on understanding the impact of ice debris. The experimental setup was optimized according to the specific conditions of the study. The primary modification involved adjusting the slope of the chute to ensure that the rock-ice avalanche reaches a sufficiently high speed while allowing the basal material to accumulate smoothly in the chute prior to being scraped. The setup consists of both an upper and a lower chute, with adjustable slopes for each, enabling precise control over the experimental conditions. The experimental design did not aim to strictly replicate the characteristics of any specific rock-ice avalanche event. Instead, it focused on investigating how ice debris affects the impact and shear-scraping processes within the flow. The material composition of the experimental model was selected to closely match that of real-world rock-ice avalanches, ensuring that the densities of both ice and rock were consistent with natural conditions (\(\lambda\rho=1\)). Other similarity factors were not considered critical to the investigation of shear-scraping effects. Previous studies on the flow dynamics and impact forces of rock-ice avalanches have similarly emphasized the importance of matching material composition [8; 27; 28].  
This experimental setup consists of four main components: the upper flume, lower flume, accumulation plate, and data monitoring system, as shown in Figure 1. Measuring 1.5 m \(\times\) 0.36 m \(\times\) 0.3 m (length \(\times\) width \(\times\) height), the upper flume's slope can be adjusted between 0\({}^{\circ}\) and 60\({}^{\circ}\) by altering the position of the connecting section. At the top of the upper flume is a material hopper, which is 0.3 m in length, whose door is manually operated to release materials. The effective distance from the hopper door to the junction between the upper and lower flumes is 1.2 m. With dimensions of 1 m \(\times\) 0.36 m \(\times\) 0.3 m (length \(\times\) width \(\times\) height), the lower flume also allows slope adjustment, ranging from 0\({}^{\circ}\) to 35\({}^{\circ}\). It is designed to accommodate the accumulation of scraped material, with horizontal and vertical scale rulers affixed to its sidewalls for recording scraping features. To ensure accurate tracking of the avalanche movement and scraping process, the sidewalls of both the upper and lower flumes are constructed from transparent polycarbonate (PC) panels, while the base is made from hardwood. Situated at the end of the lower flume, the accumulation plate measures 2.3 m \(\times\) 1.2 m and is constructed from standard board material.  
For data monitoring, the system includes a regular camera (Camera 1) and a high-speed camera (FASTCAM MiniX50 Photron, Tokyo, Japan, Camera 2). Camera 1 captures the accumulation of material after the rock-ice avalanche impacts and scrapes the base, while Camera 2 records the avalanche's movement prior to scraping. This allows for the calculation of flow velocity and offers a dynamic view of the scraping process.