Glacial isostatic adjustment – the spider in the geo-web

Glacial isostatic adjustment (GIA) is the response of the Earth to ice-mass changes associated with glacial loading and unloading. GIA affects the entire Earth system, from the surface down to the core-mantle boundary and from the poles to the equator, spanning timescales from decades to glacial-interglacial periods. It is well known for the ongoing uplift observed in northern Europe and North America, but also for its contribution to past and present sea-level changes. The uplift signal is detected by various geodetic techniques and plays an important role in the interpretation of crustal deformation, vertical land motion, and reference frame stability.

A less well-known effect of GIA is the triggering of earthquakes. These earthquakes are known to have occurred in stable cratons during and after the last glaciation along so-called glacially induced faults. Evidence for such faults has been found across large parts of northern Europe, Greenland and Canada. These earthquakes occur due to stress changes associated with variations in ice-mass loading. GIA-related stresses can persist in regions currently and formerly covered by ice sheets or glaciers, as well as in areas surrounding former ice margins. Even at distances of 200 km or more from the maximum ice margin, GIA-induced stresses can lead to the reactivation of pre-existing faults and the occurrence of glacially triggered earthquakes. These long-lasting stress changes are particularly relevant for the assessment of nuclear waste repositories in regions that are close to, or have previously been covered by, ice sheets, as GIA-related stresses may prevail for several thousands of years after deglaciation.

All these signals, derived from geodesy, tectonics and other disciplines, provide complementary constraints on the GIA process. The interpretation of these observations requires a geodynamic model that simulates the viscoelastic response of the Earth to changing ice loads. These models incorporate lateral and depth-dependent variations in lithospheric thickness and mantle viscosity. By jointly considering multiple observational datasets, these models allow us to assess the sensitivity of GIA signals to Earth structure and to better quantify uncertainties in model estimates.

In this presentation, I will show the current state of GIA research, with an emphasis on the use of geodynamic models for geodetic observations and the analysis of stress changes that improve our understanding of glacially triggered earthquakes. I will present several examples of glacially induced faulting activity and discuss the application of GIA models in the context of nuclear waste repository site selection. Together, these examples highlight the role of GIA in linking geodynamics, geodesy, and tectonics.