Elevation changes (1949-1995) of Black Rapids Glacier, Alaska, derived from a multi-baseline InSAR DEM and historical maps

We have constructed a new digital elevation model (DEM) of the 1995 surface of Black Rapids Glacier, a surge-type glacier in the central Alaska Range, using ERS-1/-2 repeat-pass interferometry. We isolated the topographic phase from three interferograms with contrasting perpendicular baselines. Numerous phase-unwrapping errors caused by areas of poor coherence were corrected in all three interferograms, using a novel, iterative, semi-automated approach that capitalizes on the multi-baseline nature of the dataset. Comparison of our DEM with a 1949 US Geological Survey DEM and with 1973-95 ground survey data shows the gradual return of Black Rapids Glacier to a pre- surge hypsometry following a surge in 1936/37. Maximum elevation changes along the glacier center line in the ablation and accumulation areas are, respectively,-249 and +63m (-5.4 and +1.4ma-1). Maximum elevation changes of survey points at nearby locations are-4.9ma-1 (1975-84) and +0.5ma-1 (1975-85). Center-line thickening of +62m between 1949 and 1995 (+1.4ma-1), just above the Loket tributary in the upper part of the ablation zone, indicates dynamic thickening following the 1936/37 surge.