Calving Behavior of Tidewater Glaciers

Abstract

Tidewater glaciers are important conduits transporting ice from the land to the oceans. The two most important processes that remove mass from tidewater glaciers are iceberg calving and submarine melting. This dissertation seeks to use a novel finite element formulation of the ice dynamics to link iceberg calving to submarine melt. Increased calving and rapid retreat of glaciers can contribute significantly to sea level rise, but the processes controlling glacier retreat remain poorly understood. To improve our understanding of calving, a two-dimensional full Stokes finite element model was developed to calculate the stress field controlling tensile and shear failure. Using idealized rectangular geometries, we find that when rapidly sliding glaciers thin to near buoyancy, full thickness tensile failure occurs, similar to observations motivating height-above-buoyancy calving laws. In contrast, when glaciers are frozen to their beds, basal crevasse penetration is suppressed and calving is minimal. We also find shear stresses are largest when glaciers are thickest. Together, the tensile and shear failure criteria map out a stable envelope in an ice-thickness-water-depth diagram. The upper and lower bounds on cliff height can be incorporated into numerical ice sheet models as boundary conditions, thus bracketing the magnitude of calving rates in marine-terminating glaciers. Moreover, findings indicate that the combination of ice flow and erosion by submarine melt can affect the stress field as well. Our simulations show that for a range of melt rates and melt profiles, submarine melting can both increase and decrease calving rates with the magnitude and sign of the effect determined by the shape of the melt profile and the relative magnitude of average melt rate. Despite the fact that calving is suppressed in some circumstances, the addition of submarine melt almost always increases the total mass loss through the combination of calving and submarine melt. These results suggest that relatively small amounts of submarine melt can significantly increase calving rates and destabilize glaciers, but calving and frontal ablation are increasingly controlled by submarine melting as it continues to increase. Our model not only is able to provide explanations for existing 'calving laws' but is also consistent with observational data. These simulation results also prove that submarine melt can significantly alter the partitioning between calving and melting along with the total frontal ablation, improving our understanding of the interplay between submarine melting and iceberg calving.