I would agree with you if the flood was shallower, but it was flood was 15 cubits over the highest mountain. [Gen 7:19-20] Which means that the water table rose more than 30,000 feet over the course of a month and a half, which geologically, is pretty freaking instantaneous. That is at the very least 5 times as much pressure as the pressure-created ice at the bottom of the pacific in the real world here and now.
I would be interested to see the math on this. Whether the thing would break off and apart from shear force caused by buoyancy, or if it would mostly intact.
Of course this totally ignores fact that the volume of and rapidity of the rain would raise the temp of the planet by several hundred degrees Celsius. So there wouldn't be ice or liquid water. But some sort of steam/plasma am9algam.