Observation of recent surges of Vatnajökull, Iceland, by means of ERS SAR interferometry

Recent surges of two outlet glaciers of the Vatnajökull ice cap, Iceland, Were observed using European Remote-sensing Satellite (ERS) synthetic aperture radar (SAR) tandem interferograms floor 12 different dates between December 1995 and January 2000. ERS SAR interferometry provided new information on the temporal and spatial variations in surface velocity during surges, after fieldwork became impossible. The area affected by the surge and therefore by increased basal sliding was delineated. The migration of flow divides oil the ice cap during a surge was described. At Sylgjujökull, a western outlet glacier covering an area of 175 km², the fully developed surge and its abating phase were studied. Over a period of > 2 years after December 1995, the ice motion decreased steadily, with initially the highest velocities and subsequently the most pronounced decrease in velocity at the glacier terminus.The surge of Dyngjujökull, a northern outlet glacier covering an area of 1040 km², reached its maximum in 1999/2000. Slow acceleration over an area of about 200 km² was first observed between March 1996 and January 1997. The interferogram from January 1999 shows a well-developed surge area, covering 210 km². This area more than doubled by January 2000, with maximum velocities reaching > 7 m d ¹. Between January 1997 and January 2000, the flow divide between Dyngju- and Skeioarárjökull shifted 16 km to the south. The investigations indicate that a surge cycle on these glaciers spans several years, with slowly increasing motion over an extended area in the bcginning, and more pronounced velocity changes during the active surge phase lasting 1-2 years.