GROUND-BASED RADAR INTERFEROMETRIC MEASUREMENTS OF THE TERMINUS REGION OF HELHEIM GLACIER (SOUTHEAST GREENLAND)

Interferometric radar is a robust tool for measuring small displacements, having relevant applications to a variety of engineering and scientific disciplines. While radar interferometry is not new to glaciological study, prior estimates from space-based radar are generally limited to satellites with short orbital periods or tandem paths in order to avoid aliasing or decorrelation of the radar phase that can result from large displacements. This study applies ground-based radar interferometry to the terminus region of Helheim Glacier in southeast Greenland. During a ~42-hour observation period, radar data were collected with one-minute intervals, thus facilitating estimates of ice velocity from one minute to the next. Line-of-sight displacements were converted to true vector displacements using flow directions indicated by glacier morphology. Average velocities for the observation session along a mid-flow transect indicate that the terminus moves at ~3 cm/min down-fjord, whereas upstream flow proceeded more slowly at ~1 cm/min. – hence, an extensional flow in the lower glacier. Immediately adjacent to the terminus, the ice mélange flows at a comparable rate (~3 cm/min.); farther down the fjord, the melange velocity slows to ~1 cm/min. Velocity time-series along the glacier and in the mélange document long-period (diurnal and semi-diurnal) signals that likely correspond with tidal forcings. Additionally, short period variations may correspond with ice responses to processes such as calving at the terminus. The observed rates of melange displacement relative to ice flow at the terminus suggest that a cohesive mélange may be important to prevent rapid ice stream progression down-fjord. Furthermore, comparisons of the timing of velocity variations near the terminus also suggest that mélange buttressing may be an important control on the stability of the terminus of Helheim Glacier.