In Situ Snow Avalanche Monitoring and Characterization

Snow avalanches in alpine regions pose significant risks to people and infrastructure. To mitigate these risks, early warning systems based on seismic sensors can provide real-time data on avalanche activity, crucial for avalanche forecasting. Additionally, forecasting and risk management require a thorough understanding of avalanche processes. However, avalanche release mechanism and dynamics are only partly understood due to the multi-physics processes involved, spanning from dynamic crack propagation to granular and turbulent flow. Traditional seismic monitoring systems have relied on far-field signals or sparse point measurements along the flow path, limiting our ability to fully capture the processes at play.

On the one hand, this makes investigating avalanche release very challenging. For example, identifying dynamic fracture propagation through seismic sensors in the near-field is crucial to advance real-time avalanche prediction. On the other hand, far-field measures are often insufficient for effective risk mitigation. Mitigation requires a thorough characterization of avalanche flow regimes and entrainment throughout the entire heterogeneous avalanche path. To address these challenges, we deployed a unique dense array of seismic sensors at the avalanche test site Vallée de la Sionne, Valais, Switzerland, covering the release zone to the runout area. The setup consists of a Distributed Acoustic Sensing (DAS) system interrogating 14 parallel downslope fiber optic lines (~100 m in length, spaced by 2 m) within the release zone at ~2400 m a.s.l., and a quasi linear fiber optic cable down to ~1500 m a.s.l., which follows the avalanche track and covers the entire runout corridor. The ~4 km long cable is embedded beneath the first snow layer, providing innovative in situ measurements of seismic and aseismic signals in the near field. Sampled at 400 Hz, at every 2 m with 4 m gauge length, this deployment represents one of the most comprehensive in situ avalanche monitoring efforts to date.

We present preliminary results from the 2024/2025 season. The avalanches act as moving seismic sources whose far and near-field seismic signals allow us to characterize the spatio-temporal avalanche evolution from release to arrest. We are able to differentiate different flow regimes along the avalanche path, and the grid will potentially capture fracture propagation in the release zone. Our DAS derived information will be benchmarked against concurrent measurements at Vallée de la Sionne which include optical and radar measurements. This makes our setup the ideal field experiment to advance avalanche characterization and lay the groundwork for real-time hazard monitoring with fibre optic cables.