Effects of the Last Quaternary Glacial Forebulge on Vertical Land Movement, Sea-Level Change, and Lithospheric Stresses

Abstract

A glacial forebulge is a bending-related upheaval of the lithosphere outside a glaciated area that co-occurs to the depression of the lithosphere below an ice sheet. The forebulge of the last glaciation attracted attention over more than one century, but quantitative descriptions on the geometry of the forebulge are rare. While many studies mention forebulge dynamics as a possible cause for a certain observation, very few studies provide a detailed and systematic exploration of the forebulge's precise dynamics. That way the forebulge became occasionally a rather mysterious structure with many unknowns. We aim to shed light into the forebulge discussion. After reviewing the history of forebulge research, we outline the theory behind the spatio-temporal forebulge development including controlling factors, and present forebulge observations in geological and geodetic records of North America and the northern parts of Central Europe. We use a state-of-the art finite-element model that can fit multiple observations of the last glaciation simultaneously, to illustrate forebulge development in North America and northern Central Europe and address the issue of whether the zero-uplift hinge line is a good indication of the location of the forebulge front. Finally, we discuss effects of the forebulge on the sea-level change pattern and the evolution of lithospheric stresses, which can induce intraplate earthquakes. We also show that the existence of a glacial forebulge outside the ice margin is not consistent with the assumption of isostatic equilibrium at the Last Glacial Maximum, and there is no strain rate-stress paradox.