Evolution of ice shelf rifts: Implications for formation mechanics and morphological controls

Abstract

Ice shelf rifts are predecessors to iceberg calving events. Observations of their morphology over time and interaction with their surroundings are presented. Newly-available Landsat-derived annual velocity data and laser altimetry from NASA's ICESat, ICESat-2 and Operation IceBridge missions were used to characterize several ice shelf rift systems. Actively propagating ice shelf rifts exhibit uplift on both sides, with an offset in height between the two rift walls, suggesting an asymmetric buoyancy force resulting from the rifting process itself. It is observed that the direction of the asymmetry is the same for rifts within a single ice shelf, but not between ice shelves. This finding suggests a rheological or basal properties influence on rift formation and buoyancy asymmetry. It is shown that this asymmetry can be accounted for by modeling ice shelf rifts as subvertical faults. With time and inactivity, rift walls eventually relax and become rounded off. Measurements of widening suggest that rift infilling is active on many active rifts. Active rifts experience higher spreading rates than do dormant rifts. Lastly, two candidate processes are identified for rift nucleation (subvertical basal crevassing and localized melt). It is found that more than any other ice shelf in this study, rifting in Pine Island Glacier is driven by ocean heat variations and is showing signs of increasing destabilization.