On the quieting of glaciohydraulic tremor

Małgorzata Chmiel , Nicoletta Caldera, Florent Gimbert, Gerrit Olivier, Alberto Guadagnini, Dominik Gräff, Manuela Köpfli, Mauro A Werder, Fabian Walter

The subglacial hydraulic system strongly modulates glacier motion, yet the links between subglacial water flow, basal pressure, and short-lived drainage reorganization remain difficult to observe directly. Seismology can track seismic power generated by turbulent subglacial water flow, known as glaciohydraulic tremor (GHT). At Rhône Glacier, Switzerland, previous observations documented periods of GHT quieting around stick-slip tremor during elevated basal water pressure, but the physical origin of this quieting remained incompletely understood. Here, we combine seismic power analysis, matched-field processing, borehole water pressure measurements, surface velocity, runoff, and hydraulic-potential routing to investigate the origin of GHT quieting. The quieting is strongest in the 10–20 Hz band and recurs across stick-slip episodes, whereas the 6–8 Hz band shows a weaker response. Matched-field processing shows that coherent GHT sources persist during quieting near an inferred subglacial drainage pathway, suggesting reduced hydraulic–seismic coupling rather than disappearance of the hydraulic source. Physics-based hydraulic calculations show that near-complete filling of broad, low-aspect-ratio conduits can increase wetted perimeter and frictional resistance, producing modeled local discharge reductions of ∼20–28% and seismic-power decreases of ∼1.2–1.8 dB. We interpret GHT quieting as a seismic signature of transient drainage reorganization during rising basal water pressure. Our results suggest that localized, transiently flow-limiting drainage elements can redistribute water across the wider subglacial drainage system, modulating basal water pressure and glacier motion well beyond the element itself. More broadly, cryoseismic observations can help identify shortlived changes in drainage-system state, hydraulic resistance, and ice–water coupling beneath glaciers.