Glacial rebound near Vatnaj?kull, Iceland, studied by GPS campaigns in 1992 and 1996

Since about 1920 the Vatnaj?kull ice cap in Iceland has experienced a significant retreat, corresponding to a volume reduction of more than 180 km3. With two GPS campaigns in 1992 and 1996 along the southern border of the glacier preliminary results reveal land uplift rates of 1–6 mm/yr, after a one-parameter (bias) fit with recent earth rheology models. The best fit model suggests that the lithosphere in the area is about 30 km thick and the viscosity of the asthenosphere 5 × 1018 Pa s. The rms fit of uplift rate at all GPS sites is ±1.4 mm/yr. As the GPS data alone cannot provide the absolute uplift rates, the one-parameter fit to the theoretical modelling implies that the absolute rates were estimated by the matching of the GPS data and model. The resulting uplift rate at station H?fn (1 mm/yr) is not consistent with two independent sources, and we therefore conclude that further GPS epoch and permanent GPS site data are needed to confirm the present geodynamic processes near Vatnaj?kull.