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Abstract. Iceberg A68a calved from Larsen C ice shelf, experienced several major calving when drifting around the South Georgia Island in late 2020. Here, we show for the first time that the decisive factor for its calving was a collision with the surrounding seamount. By treating the iceberg as a deformable body in an established ice-flow model, we show how its collision with the seafloor created huge stresses within the iceberg that led to its disintegration. The drifting and rotating of the iceberg, while grounded, further enhanced its breakup. Moving over a grounded shoal increased the tensile stresses by a factor of almost one hundred more than immobile grounding alone, and rotational motion about the pinning point increased the stresses by another twenty percent. Modeling the fracture and breakup of a large tabular iceberg is an essential step toward better understanding the life cycle of an iceberg. The possible collapse of the marine-based sectors of the great ice sheets in a warming world may lead to a massive increase in the number of icebergs in the surrounding oceans. It will be crucial to be able to understand where such icebergs drift and how they ultimately disintegrate into the ocean.