Substantial accumulation rates on a glacier avalanche cone from time-lapse photogrammetry and field measurements

Avalanches are critical contributors to the mass balance and spatial accumulation patterns of mountain glaciers. While gravitational snow redistribution models predict high localized accumulation, these predictions lack field validation due to the difficulty of monitoring highly dynamic avalanche cones. Here, we present two years of high-resolution monitoring of a large avalanche cone in the accumulation area of Argentière Glacier (French Alps). To capture these dynamics, we employed a multi-sensor approach: Uncrewed Aerial Vehicle (UAV) surveys and a time-lapse photogrammetry array consisting of 7 low-cost cameras deployed ∼ 1 km away from the cone. Point clouds and Digital Elevations Models were produced at a two-week resolution using Structure-from-Motion photogrammetry. Methodological validation shows that while side-looking time-lapse photogrammetry captures the overall elevation changes, it tends to underestimate them compared to UAV data, with biases up to 1.8 m and precisions of 2–6 m. Despite these uncertainties, our results reveal extreme spatial variability in accumulation. The top of the cone is the most active zone, exhibiting elevation changes of ∼ 30 m annually corresponding to a local annual mass balance reaching 23 ± 4 m w.e. in 2023 and 16 ± 4 m w.e. in 2024. We identify a topographical threshold for snow storage: the upper cone fills early in the season until reaching a critical slope of ∼ 35°, after which subsequent avalanches bypass the cone's apex to deposit mass at the cone's base. From May onwards, mass redistribution is further modulated by the development of surface channels. Our findings demonstrate that time-lapse photogrammetry is a viable tool for monitoring dynamic glacier surfaces and provide rare empirical evidence of the dominant role avalanches play in the local glacier mass budget.