Snow particle motion in process of cornice formation

Abstract

Snow cornices are a common snow pattern in cold regions, and their fracture and collapse can easily trigger avalanches. Despite numerous observations and experimental simulations on their formation process, the microscopic mechanism of their initial stage of formation remains unclear. In this paper, based on wind-tunnel experiments and high-speed photography, experimental studies on the trajectory of particles surrounding the snow cornice were carried out. The experiment results reveal the distinct differences in particle size, impact velocity, and impact angle between the surface and edge of a cornice. The findings show that edge-deposited particles are generally smaller and more dendritic, attaching mainly through low-velocity saltation and mechanical interlocking, while surface deposition is dominated by larger and faster particles. The different probability distributions of impacting velocities and angles in these two regions are attributed to variations in airflow and local cornice topography. Both surface and edge regions, however, exhibit a characteristic vertical impact velocity threshold of 2-2.5 m s-1, which is the dominant parameter governing particle adherence or rebound. A static adhesion model incorporating particle morphology parameters for edge deposition was developed and experimentally validated, confirming its effectiveness in predicting the influence of particle size and shape on adhesion thresholds. Overall, this research reveals the micro-dynamics underlying initial cornice growth, providing a theoretical basis for avalanche modeling and infrastructure protection in alpine environments, as well as offering a methodological and mechanical framework for studying snow and ice adhesion in both natural and engineered systems.