Using UAV-based 4D GPR to investigate the seasonal and interannual evolution of englacial and subglacial drainage

Meltwater routing through englacial and subglacial drainage systems exerts a fundamental control on glacier dynamics, water resources, and related hazards, yet detailed observations of these systems and their temporal evolution remain scarce. In this study, we present uncrewed aerial vehicle (UAV)-based four-dimensional (4D) ground-penetrating radar (GPR) measurements that resolve seasonal and interannual changes in near-terminus glacier hydrology at unprecedented spatial resolution.

We conducted repeated high-density 3D GPR surveys at the Otemma Glacier (Swiss Alps) during four field campaigns (August 2022; June, August, and October 2023). A dedicated 3D processing workflow combining reflection-based imaging of the glacier bed with coherence-based diffraction imaging of englacial scatterers enables comparison of drainage structures across surveys. The GPR results are interpreted alongside complementary observations, including dye tracing experiments, UAV photogrammetry, time-lapse imagery, and a targeted steam drill validation.

Our results reveal a drainage system composed of both persistent and dynamically reorganizing components. Subglacially, one major conduit remains stable across years and shows signs of increasing hydraulic efficiency, while a second conduit is partly rerouted. Englacially, several channels are observed in similar locations across years, indicating structural persistence, whereas other features appear transient. Seasonal drainage evolution is evident, and we observe direct coupling between englacial and subglacial drainage systems manifested by co-evolving structural changes.

These observations demonstrate the potential of UAV-based 4D GPR to capture glacier hydrological dynamics and provide critical constraints for models of meltwater routing and ice dynamics under a changing climate.