Strange natural phenomenon on Lake Michigan has appeared in the wake of the polar vortex in the United States.
The Arctic cyclone, which plunged huge parts of the US and Canada into sub-zero temperatures, has caused balls of ice to wash up by the town of Glen Arbor.
According to meteorologist Joe Charlevoix they were formed from layered ice.
"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,2 he said.
"It gets bigger and bigger, and eventually you get big balls of ice that are pushed to the shore by the wind."
Tom Ulrich, deputy superintendent for the Sleeping Bear Dunes National Lakeshore park, confirmed that the boulders, a regular feature in Lake Michigan winters, were larger than normal this year.