A fracture mechanics view of iceberg calving from large ice shelves

Iceberg calving, an important mass loss mechanism for marine ice sheets, is an outstanding accounting problem in ice-sheet/ice-shelf models. Various parameterizations have been proposed but there is no consensus regarding relevant physical processes, key parameters and variables, or the applicability the various relationships have to different floating ice geometries. Long rifts at the fronts of Antarctic ice shelves, which become the planes along which icebergs calve, are observed to initiate as fractures along lateral margins of fast-flowing ice or downstream of grounded features. For most of the shelf, inhomogeneities due to structural boundaries limit propagation. Orientations of active fractures are explained by glaciological stresses. In a comparison of fractures observed in small to medium ice shelves around Antarctica, we find that “starter” fractures, derived from upstream, grounded ice, propagate where floating ice advects around a grounded feature or through a narrowing in the ice shelf, as between two grounded features or the embayment walls. This observation follows expectation because it is in such locations that compressive stresses in the transverse direction become relatively large. We use a numerical model of fracture propagation and shelf velocities derived from remote observation to investigate the growth of long fractures in ice shelves. We propose that principal stresses, computed in models of ice shelf flow, can be used to develop a calving parameterization appropriate for embayed marine margins of ice sheets.