Modelling iceberg capsize in the open ocean

At near-grounded glacier termini, calving can lead to the capsize of kilometer-scale (i.e. gigatons) unstable icebergs. The transient contact force applied by the capsizing iceberg on the glacier front generates seismic waves that propagate over teleseismic distances. The inversion of this seismic signal is of great interest to get insight into actual and past capsize dynamics. However, the iceberg size, which is of interest for geophysical and climatic studies, cannot be recovered from the seismic amplitude alone. This is because the capsize is a complex process involving interactions between the iceberg, the glacier and the surrounding water. For this reason, we propose an approach based on the computation of the source force with a mechanical model for various iceberg geometries and the estimation of the iceberg size from a comparison of the computed and seismically inverted time histories of the force. The capsize dynamics is captured by computational fluid dynamic (CFD) simulations for a simple scenario of capsize in the open ocean without glacier front. This approach allows assessing the complexity of the fluid motion around an iceberg. Expressing the results in terms of appropriate dimensionless variables, we show that laboratory scale and field scale capsizes can be directly compared. The capsize dynamics is found to be highly sensitive to the iceberg aspect ratio and to the fluid and ice densities. We present a semi-analytical simplified fluid-structure model (SAFIM) that can be implemented in solid mechanics models dealing with contact dynamics. This model accounts for hydrodynamic forces through calibrated drag and added-mass effects. We show that SAFIM significantly improves the accuracy of the modeled horizontal force and horizontal iceberg velocity compared with existing simplified models. SAFIM has been calibrated against the reference CFD simulations...