After causing Hell to freeze over and stopping Niagara Falls in its tracks, the polar vortex gripping the US has led to another incredible natural phenomena - floating ice boulders.

The sub zero temperatures have brought huge, nuclear snowballs to the shores of Lake Michigan.

The incredible basketball sized - and bigger - 'ice balls' have been captured on film at Glen Arbor Township, Michigan, were they cover the entire shoreline.

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Despite appearing as unnatural creations, the boulders are a regular feature of Lake Michigan when temperatures drop below freezing, and are formed by ice clumping together in a similar way to snowballs.

Meteorologist Joe Charlevoix explains: "[When] the water temperature on the Lake Michigan is just a little bit below freezing, so you get a small piece of ice that forms in the water and as waves move back and forth it adds additional water and freezes in layers.

"It gets bigger and bigger, and eventually you get big balls of ice, that are pushed to the shore by the wind."

Some locals have an alternative explanation however: "The creature that dwells within Lake Michigan lays eggs once every 10,000 (or so) years. Evacuate now while you still can!" joked Les Lukacs on the Glen Arbor Facebook page.