Drivers of Flow Channel Formation on Snow Surfaces: Rain versus Melt-Water – A Case Study in the Austrian Alps

Flow channels on the snow surface are a common phenomenon frequently observed and reported to avalanche warning services. An accurate interpretation of field observations and an understanding of the underlying physical processes are crucial for the assessment of snowpack stability. Flow channel formation is typically associated with rain-on-snow (ROS) events and is often interpreted as an indicator of the approximate elevation of the snow line, a key factor in forecasting wet-snow avalanche activity and the formation of crusts and crust-related weak layers. However, recent observations of flow channel development, without significant liquid precipitation, challenge the assumption that ROS events are the sole cause of their formation.

In this study, we quantitatively compare liquid water input into the snowpack from melt processes to the amount of rain during a documented flow channel formation event. Using a combination of field observations, energy balance calculations and model simulations, we demonstrate that, at least in our case study, meltwater was the predominant driver of flow channel formation. Our results indicate that more than 97% of the total liquid water input originated from melt, while rain contributed only roughly 2%. These findings highlight the need for a revised interpretation of flow channel formation, suggesting that meltwater-driven flow channels may be more significant than previously assumed.