Radar and seismic investigations of an active glacier hydrological system in West Greenland

A hydrologically-active subglacial lake system has been identified near the south lateral margin of Isunnguata Sermia, West Greenland. Differencing time-stamped ArcticDEM strips has revealed multiple anomalies in ice-surface elevation change. A large hydrological drainage event from Isunnguata Sermia in 2015 slowed ice flow for ~1 month and flooded the foreland, depositing up to 8 meters of sediment. Although the proglacial flooding provided evidence that the ice-surface elevation anomalies were likely caused by subglacial water bodies, satellite altimetry cannot provide direct insights into their thickness, structure and properties. Therefore, field-based geophysical measurements, including ground-based radar and active source seismics, were collected during summer 2023 and autumn 2024 to characterise the subglacial hydrological system. 

Radar data were collected in October 2024 using a 10 MHz Blue Systems Integration ice-penetrating radar (IPR) to determine ice thickness and constrain a subglacial hydrological model. 26 km of radar data were collected over two of the ice-surface elevation anomalies. The radar data cross existing airborne IPR transects and point measurements from a phase-sensitive radar (pRES). Active source seismic surveys were performed at three locations over the largest ice-surface elevation anomaly: 1) anomaly centre, 2) anomaly southern edge, and 3) between the anomaly centre and southern edge, where bright basal reflections had been identified from radar observations. Seismic data were acquired with a hammer and plate source and 48 100 Hz vertical component geophones in a 94 m-long spread at a geophone spacing of 2 m. 

Our radar results show that the ice-surface elevation anomalies overlie complex subglacial topography on the southern sidewall of the large over-deepened trough beneath the Isunnguata Sermia trunk. Across the largest surface anomaly, ice thickness varies between 380 m to 600 m. The seismic data shows a negative polarity at the ice-bed interface, coincident with a subglacial topographic low. This indicates an acoustically soft basal material, which could represent water or water-saturated sediment. Scattering and diffraction hyperbola in the radar data arise from a complex englacial structure, which have implications for attenuation of radio and sound energy. 

These observations provide new insights into the glaciology and hydrology of an important West Greenlandic outlet glacier and highlight the complexities associated with active glacier hydrological systems and their geophysical characterisation.