Inverting land uplift near Vatnajökull, Iceland, in terms of lithosphere thickness and viscosity stratification

The episode of climate warming during the 20th century is documented by an ablation of the Vatnajökull ice cap, south-eastern Iceland. Due to the small thickness of the elastic lithosphere and the low viscosity of the asthenosphere below Iceland, the ablation resulted in a retarded land uplift of about 3–8 mm/a in the vicinity of the ice cap. This is confirmed by GPS campaigns carried out south of the ice cap in 1992 and 1996 (Sjöberg et al, 1999). Furthermore, a relative uplift of 12.4 cm along Lake Langisjór south-west of the ice cap was observed between 1959 and 1991 (Sigmundsson & Einarsson, 1992). In the present study, we use a compressible, self-gravitating, spherical earth model with Maxwell viscoelasticity and a load model parabolic in cross section and elliptic in plan view to interpret the observations in terms of viscosity stratification. Our results show that the lithosphere is 10 to 20 km in thickness and the asthenosphere is 7 × 1016 to 3 × 1018 Pas in viscosity.