Land uplift near Vatnajokull, Iceland, as observed by GPS in 1992, 1996 and 1999

Warming of the climate in the 20th century has been manifested by an ablation of Europe's largest ice cap, Vatnajokull in Iceland. The thin elastic lithosphere and the low-viscosity asthenosphere are responding to the reduction in mass by current land uplift in the vicinity of the ice cap suggested to be of the order of 5-10 mm yr(-1): lithosphere thickness and asthenosphere viscosities compatible with these values have been inferred. From our repeated GPS epoch campaigns in 1992, 1996 and 1999 uplift rates are estimated to be of the order of 5-19 mm yr(-1), and the uplift rate is decreasing by -0.11 +/- 0.01 mm yr(-1) km(-1) with radial distance from the centre of the ice cap. These results deviate from previous Earth rheology models estimated for the region. Our data indicate that the lithosphere thickness might be of the order of 10-20 km and the asthenosphere viscosity may be as low as 5 x 10(17) Pa s, but these parameters need a careful fitting to the estimated uplift rates.