What Controls Calving? Assessing ‘Calving Law’ Performance for Greenland’s Marine-Terminating Glaciers

The nearly ubiquitous retreat and acceleration of marine-terminating glaciers throughout the Arctic and the Antarctic over the past two decades has been accompanied by widespread glacier acceleration and an increase in iceberg discharge. Thus, in order to accurately predict changes in iceberg discharge in the coming decades, and associated sea level rise, it is imperative that variations in terminus position are accurately simulated by prognostic ice flow models. Most numerical models presently rely on simple ‘calving laws’ to parameterize either the location of the terminus position or the rate of iceberg calving. Although each parameterization has been used to successfully simulate realistic changes in glacier length, the accuracy of terminus change predictions relies on the ability of the calving parameterization to capture the most important process(es) that govern terminus evolution.

Recent observations of crevasse hydrofracture-driven ice shelf collapse in Antarctica and increased surface meltwater impoundment in Greenland support the development and widespread use of a calving law that parameterizes the terminus position as a function of the penetration depth of crevasses. Although damage incurred due to crevassing undoubtedly structurally weakens glacier termini, there presently exists no quantification of this damage, nor are there direct observations of deepening water-filled crevasses. Such fundamental observations are critical to the testing and validation of the crevasse penetration-depth calving law. In this presentation, we use a suite of remotely-sensed observations acquired for Greenland outlet glaciers spanning a wide range of geometries, flow regimes, and climate conditions to estimate dry and water-filled crevasse depths. Crevasse depths are estimated two ways: 1) extracted directly from high-resolution elevation data and 2) calculated from velocity observations under the assumption that longitudinal stretching acts as the primary control on crevasse depth (i.e., using the crevasse penetration-depth calving parameterization). Through these analyses, we assess the validity of the crevasse penetration-depth calving law and compare its performance to simpler, buoyancy-based calving laws for Greenland’s marine-terminating glaciers.