Nature is capable of forming ice into some pretty cool shapes over time, and this scene from the Lake Michigan shoreline is a great example, as thousands of giant ice boulders sloshed back and forth in the waves near Glen Arbor, MI earlier this week.
Although it's certainly not something you see every day, and while it is related to the extreme cold that pushed down over North America over the past week, this actually doesn't require any special or unusual conditions to form.
Similar to how giant ice discs can form floating in rivers — like the one seen in North Dakota back in November — all that's required is weather that's cold enough to form ice on moving water. In this case, chunks break off the frozen ice sheets that are floating on top of the lake water, and these chunks are slowly worn into round shapes as they roll back and forth in the waves, knocking against each other and the lake shore. These boulders even accumulate more ice on their surfaces as they slosh about, and can grow to immense size.
There are probably plenty of undocumented cases of this happening in the past, but just last February, a similar scene was captured along the Sleep Bear Dunes National Lakeshore, just to the south of Glen Arbor. Massive ice boulders that washed up along the shoreline and floated in the water were captured on film by local resident Leda Olmsted while she was walking her dog. Apparently, some were as big as beach balls.
It also happened back in January 2010, near South Haven, Michigan, and was reported by the Chicago Tribune.
