Evolution of Ice Mélange Motion During Periods of Terminus Quiescence

Variations in the strength of ice mélange, a dense matrix of icebergs and sea ice retained in many proglacial fjords, has been proposed as a key process influencing the stability of tidewater glaciers in Greenland [Straneo et al., 2013]. Several observational studies have shown that variations in ice mélange characteristics often precede changes in speed and calving rates along glacier termini. A full understanding of the resistance provided by ice mélange, and therefore its impact on glacier stability, requires knowledge of its granular rheology. Toward this goal, we present unique terrestrial radar interferometry (TRI) observations of the ice mélange at Jakobshavn Isbræ, Greenland that was acquired at very high spatial (meters) and temporal (minutes) resolution during summer 2012. Data was collected over a 15-day period, during which several large calving events occurred. Previous work [Peters et al., 2015] described the dynamic jamming of the ice mélange that was observed during calving events. Here, we focus on the more gradual evolution of the ice mélange during periods of terminus quiescence. We look at variations in velocity and strain rate and consider how glacier motion, ocean currents, tides, and wind affect motion of the ice mélange. Our aim is to provide the most comprehensive study of ice mélange rheology to date.