Seismic evidence for storage-release events of glacier discharge affecting proglacial bedload transport

The dynamics of proglacial areas strongly depend on the interplay between glacier discharge and sediment transport. While most investigations focus on relatively long time scales (i.e. daily and seasonal variations), glacier discharge can exhibit short-lived fluctuations potentially influencing proglacial bedload transport. To address such dynamics, we investigated water discharge from the Rutor Glacier (Italy) and proglacial bedload transport at high temporal resolution by integrating seismic monitoring with direct measurements during the 2022 and 2023 ablation seasons. Bedload transport was continuously estimated using the STA/LTA algorithm. Our analysis reveals the presence of 60 abrupt drops followed by peaks in seismic power mostly occurring at a sub-hourly time scale, and ~850 periodic seismic power peaks (mean periodicity of 12 min) typically clustered around the maximum glacier discharge of ~30 days. We associate these events with short-lived variations of glacier discharge resulting from temporary storage and release of meltwater. We explain the abrupt drops and peaks with transient blockage due to ice damming at the front and/or collapse of subglacial conduits followed by water overtopping. On the other hand, we hypothesize that periodic water pulses could be related to a siphon-like mechanism of the subglacial drainage system oscillating around a near-critical condition. Direct bedload measurements and the STA/LTA estimations reveal that the proglacial area is strongly sensitive to such events, with the mobilization of high amounts of sediments regardless of the daily meltwater-driven hydrograph. Our results stress the usefulness of seismic methods to investigate the link between glacier dynamics and proglacial processes.