Wouter van der Wal

Postglacial sealevels on a spherical, self-gravitating viscoelastic earth: effects of lateral viscosity variations in the upper mantle on the inference of viscosity contrasts in the lower mantle

Abstract Previous studies of lateral viscosity variations on postglacial rebound often neglect the spherical shape of the Earth and the self-gravity of the solid earth and oceans. In this paper, the consistent sealevel equation is solved by the coupled Laplace–finite element method for a spherical, self-gravitating incompressible Maxwell earth. It confirms the importance of self-gravity in the oceans on sealevel computation near the ice margin where the data are most sensitive to the existence of lateral variations in lithospheric thickness and asthenospheric viscosity. The effects of lateral variations in lower mantle viscosity, asthenospheric viscosity and lithospheric thickness are investigated. This paper confirms the finding of earlier investigations. The combined effect of lateral viscosity variations in the lower mantle with reverse viscosity contrasts in the upper mantle is also investigated. For sealevel data near the center of rebound, the effect of lateral viscosity contrast in the lower mantle can be masked by the existence of a reverse lateral viscosity contrasts in the upper mantle. However, this is not the case for sealevel data just outside the ice margin.

Prediction of decadal slope changes in Canada by glacial isostatic adjustment modellingThis article is one of a series of papers published in this Special Issue on the theme GEODESY.

In Canada, glacial isostatic adjustment (GIA) is the dominant process to cause vertical motion of the land surface. A GIA model is presented herein that can be used to predict slope changes at given locations in North America where GIA is the primary cause for vertical motion. Uncertainty in Pleistocene ice cover and viscosity in the Earth’s mantle prevent one from picking a single GIA model from the literature to predict uplift rates in the region. Therefore, in this study, a range of mantle viscosity values as well as two different ice-loading histories are used in a forward model of the GIA process. The combination of viscosities and ice model that gives the best fit to recently available continuous and episodic GPS observations is assumed to provide the best prediction of slope changes in North America. This model can be used to quantify GIA-induced vertical deformation in local geomorphologic studies. We show that the predicted differential uplift rate in the Nelson River with respect to Lake Winnipe...