Meltwater influences on deep stick‐slip icequakes near the base of the Greenland Ice Sheet

Abstract

We detected over 11,000 stick-slip icequakes near the base of the western margin of the Greenland Ice Sheet using a 17-seismometer array. These icequakes have negative (i.e., very small) moment magnitudes and, according to similarities in their waveforms, group into over 100 distinct clusters distributed beneath our 3 × 3 km study area. Some clusters were active for several weeks, while others have burst-like episodes lasting 1-6 days only. Some clusters correlate with subglacial water pressure measured within a nearby moulin. For these clusters, we observe high water pressure concurrent with many small yet numerous stick-slip icequakes and periods of lower water pressures with larger, less frequent icequakes. These patterns might change over time and are not common to all clusters. We explain these observations that the stick-slip icequakes are located at sticky spots at the interface of the ice sheet with the glacier bed that consists of basal till characterized by different connectivity to the subglacial drainage system. Because the till's frictional strength depends on its pore pressure, variations in subglacial water pressure can either weaken or strengthen the bed; this explains the variation in seismic moments and interevent times. Our results suggest that seismogenic stick-slip motion is an integral part of the flow mechanism in the ablation zone in western Greenland, which is highly sensitive to the configuration of the local subglacial drainage system. Stick-slip motion may therefore play a key role in the relationship between climate-induced changes of surface runoff and ice sheet dynamics.

Greenland subglacial drainage evolution regulated by weakly connected regions of the bed

“…The low hydraulic connectivity that differentiates these regions from the rest of the distributed system may be due to local bed geometry causing smaller cavity orifices or the presence of low hydraulic conductivity till. Indeed, extensive subglacial till has been identified at FOXX21, and stick-slip ice motion observed seismically is associated with spatially differing connectivity of till23. More generally, both modelling4849 and observations2150 have argued for the existence of significant amounts of till underlying marginal regions of the GrIS.…”

“…recently described direct observational evidence that even where channelization occurs, it is unable to explain lowering ice speed during late summer. At the extensively studied drill site FOXX in western Greenland41420212223 (Fig. 2a), water pressure in moulins feeding subglacial channels showed little change during the latter part of the melt season, yet velocities were observed to decrease over this same time period (Fig.…”

Cryoseismology

“…Roeoesli et al [] recently reported the first seismogenic stick‐slip events beneath the Greenland Ice Sheet. The seismic monitoring network was located on a relatively slow‐flowing (0.27 m d −1 ) part of the ice sheet.…”

Seasonal Variability in Regional Ice Flow Due to Meltwater Injection Into the Shear Margins of Jakobshavn Isbræ

“…There have been a few efforts focused on the impact of infiltrated surface meltwater on ice stream dynamics. Roeoesli et al () found a short‐term increase in surface velocity correlated with an increase in subglacial water pressure. Additionally, Joughin et al () documented a short‐duration surge in Ryder Glacier over a 7 week period due to drainage of a large supraglacial lake during the 1995 melt season.…”