Seasonal and spatial variations in ice velocity, South-West Greenland

We used satellite offset tracking and synthetic aperture radar interferometry (InSAR) to investigate seasonal and spatial variations in ice velocity in South-West Greenland. The study area covers approximately 10 000 km2 of the south-western ice sheet margin and includes 6 land-terminating glaciers. We processed about 50 pairs of European Remote Sensing (ERS) synthetic aperture radar (SAR) images using offset tracking and 7 image pairs using SAR interferometry. The offset tracking technique was applied to 35-day repeat-track pairs from 1992-1998, while the InSAR image pairs (1-day repeat) were acquired during 1995 and 1996. The results reveal a clear seasonal pattern of velocity variation for all the 6 glaciers, with significantly higher ice velocities occurring from May to September compared to the rest of the year. The summer speed-ups vary between 50 and 200 % and are believed to be caused by routing of surface meltwater to the glacier base, leading to enhanced glacial sliding. Altitudinal variations in ice velocities were also observed, with summer speed-ups generally starting earlier at locations close to the ice sheet margin compared to the colder higher elevation areas.