replying to Mark, Doug wrote:
Water is most dense at 39 F (4 C). Therefore, as water approaches 32 F (but
not isothermally), the least dense water (i.e. coldest) floats to the top and
then freezes. In the bucket problem described above, I suspect the frozen ice
was bonded to the sides of the bucket. Then as the rest of the water frozen
under this ice cap it needed to expand upon freezing. Because the water
(under the ice cap) is constrained, the pressure increases. In this case, as
the pressure increase, the pressure needed to expand the walls of the bucket
was lower than the pressure needed to push the ice cap upward. Result:
expanded base of the bucket.

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