As the water in them freezes, it expands and breaks the vessels.
Why do lead pipes and iron pipes often burst during the winter?
Because the water in them is permitted to freeze, and as there is not room for it to expand, the pipes are burst.
Is ice heavier or lighter than water?
Ice is lighter than the same bulk of water.
How much lighter is ice than water?
Eight gallons of ice weigh no more than seven gallons of water.
Does the ice protect the water beneath it from freezing?
Ice does protect the water from freezing, to a very great extent.
If ice were heavier than water, what would result?