[fatlazyless]

It seems very unusual.

Maybe the deep freeze temperatures of last week got conducted down the wood piling, freezing the existing moisture inside the wood piling which increased its' buoyancy by 10%, and at the same time the now frozen piling has less surface friction between the piling wood surface and the lake bottom causing the lake bottom to lose its' grip allowing the piling to rise up vertically, held in position by the ice surface.

Probably, some part of the piling is still sticking into the lake bottom, otherwise it would be a leaner or be tipped over, but would not be 90-degree vertical, as it is.