Glacial Erosion in Brittle Wedges: Insights Using Quantified Analog Models

It is becoming increasingly evident that glaciers can play a significant role, when present, in determining the location and intensity of deformation in developing thin-skinned fold-and-thrust belts. It has been suggested that the rapid and highly localized erosion associated with glaciers requires the sudden reorganization of deformation away from the long-term style of faulting associated with the steady-state maintenance of critical taper. We have tested this assertion using scaled frictional analog models in which we test the influence of punctuated erosion on the development of thrust wedges. We have performed a series of analog experiments in which, starting with the same initial convergent geometry and topographic profile, we eroded different parts of the wedge. We then used a variety of analysis tools to quantitatively examine the differences in the wedge’s ongoing structural development, including its topography, surface velocity and strain, and the cross-sectional development of faults. The models demonstrated a distinct difference in internal and surface development depending upon the location of where mass was removed from the wedge. Models with no ‘erosion’ during accretion developed consistent with expectations as predicted by critical wedge theory. Models subjected to ‘glacial erosion’ experienced greater internal deformation and differential uplift. This activity was localized initially near the site where material was removed but quickly caused the reactivation and localization of fault slip on older faults within the wedge. The difference in the location of deformation from model to model was directly correlated to the location and amount of material removed. This suggests that while glacial erosion can be very important on the development of a fold-belt it is highly dependent on the glacier's geometry with respect to the fold-belt and location of the erosion.