The 'footloose' mechanism: Iceberg decay from hydrostatic stresses

Tuesday, 16 December 2014
Peter Wadhams, University of Cambridge, Cambridge, United Kingdom, Till J.W. Wagner, University of California San Diego, Scripps Institution of Oceanography, La Jolla, CA, United States, Charles Richard Bates, University of St Andrews, St Andrews, United Kingdom, Pedro Elosegui, CSIC, Barcelona, Spain, Alon A Stern, New York University, New York, NY, United States, Dominic Vella, University of Oxford, Oxford, United Kingdom, Einar Povl Abrahamsen, British Antarctic Survey, Cambridge, United Kingdom, Anna J Crawford, Carleton University, Ottawa, ON, Canada and Keith W Nicholls, NERC British Antarctic Survey, Cambridge, United Kingdom
We study a mechanism of iceberg breakup that may act together with the recognized melt and wave-induced decay processes. Our proposal is based on observations from a recent field experiment on a large ice island in Baffin Bay, East Canada. We observed that successive collapses of the overburden from above an unsupported wavecut at the iceberg waterline created a submerged foot fringing the berg. The buoyancy stresses induced by such a foot may be sufficient to cause moderate-sized bergs to break off from the main berg. A mathematical model is developed to test the feasibility of this mechanism. The results suggest that once the foot reaches a critical length, the induced stresses are sufficient to cause calving. The theoretically predicted maximum stable foot length compares well to the data collected in situ. Further, the model provides analytical expressions for the previously observed ‘rampart-moat’ iceberg surface profiles. Finally, we comment on the implications for the calving of icebergs from shelf fronts, where similar underwater ‘feet’ have been observed.