Generally, the rule of thumb is that when it’s cold, it contracts and when it’s warm, it expands. Not so with frozen pipes, as the ice buildup causes increased pressure inside your pipes, causing it to literally burst out of the pipe.
All that added pressure can sometimes cause the pipes to explode as it cannot contain the ice buildup in your plumbing system.
Often times, the pressure will build and burst right out of the pipe wall or a weak joint in the plumbing system.