| Summary: | Iceberg calving is a major component of glacier mass ablation that is not well understood due to a lack of detailed temporal and spatial observations. For better understanding, it is critical to examine processes occurring on the time scale of calving processes, sub-daily to sub-hourly. Current satellites are not able to observe the same location at time scales small enough to measure sub-daily phenomena. This research aims to increase the temporal resolution of ice speed and elevation measurements during the calving season to allow for analysis of short-term variations that are otherwise unobserved. We measure glacier speed and surface elevation at 3-minute intervals using a portable radar interferometer at three marine-terminating glaciers in West Greenland over two summer field campaigns. We detect diurnal variations in glacier speed caused by tidal height changes that propagate far inland, the effect of which varies by glacier but are consistent with simple models where basal stress is tidally modulated. We find no speed up from ice shedding off the calving face or the detachment of floating ice blocks, as expected. We detect a 30% speedup within a few hundred meters of the ice front that persists for days when calving removes full thickness grounded ice blocks. Within one ice thickness from the calving front, we detect strain rates 2 to 3 times larger than observable from satellite data, which has implications for studying iceberg calving as a fracturing process, in particular to select an appropriate value of the threshold tensile stress necessary for ice cliff failure.
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