Effects of subglacial geothermal activity observed by satellite radar interferometry

We use one day Synthetic Aperture Radar (SAR) interferograms from data of the Earth Remote Sensing Satellites ERS-1 and ERS-2 to study ice how and uplift of two surface depressions within the Vatnajokull ice cap, Iceland. The ice cauldrons are created by melting at subglacial geothermal areas. Meltwater accumulates in a reservoir under the cauldrons over 2 to 3 years until it drains in a jokulhlaup under the ice dam surrounding the reservoir. The ice surface in the depressions drops down by several tens of meters during these draining events but rises again, as ice flows into the depressions, until a jokulhlaup occurs again. Using SAR interferograms we quantify an uplift rate of about 2 to 18 cm/day within the jokulhlaup cycle varying with the surface slope of the depressions. The uplift rate is high during the first months after a jokulhlaup when the cauldron is relatively deep with steep slopes, but the uplift rate decreases as the cauldron is gradually filled. A simple axisymmetric model simulating the ice-flow into one of the depressions describes quantitatively the filling rate of the cauldron and qualitatively the shape of the ice flow field. The best-fit model has an ice flow law parameter Ao that is about one order of magnitude lower than typically estimated for temperate glaciers.