MACKINAW CITY, MI - Images of "blue ice" stacking up along the shore near Michigan's iconic Mackinac Bridge are finding lots of fans this week.

Kelly Alvesteffer and her finace, Rob LaLone, were sitting in a restaurant near the Straits of Mackinac over the weekend when they noticed the peculiar hue of the ice out the window.

"We instantly saw it. It was like, 'Look at the blue ice,'" said Alvesteffer, who with LaLone photographs student sports teams for Cedar Springs Public Schools. They are two of a handful of photographers whose blue ice photos are catching people's attention.

Their impromptu trip north netted them dozens of photos for their Facebook pages - and a few images that got a lot of attention after being displayed on a Mackinac Bridge website. More than 1,500 social media shares later, the couple is a bit stunned.

"We were very surprised at how it took off like that," LaLone said Wednesday. "For one thing, we didn't know if (blue ice) was a normal thing or not."

Stunning images of Great Lakes blue ice have cropped up in past winters, adorning ice caves near Lake Superior and tinting snow piles along the shore of Sleeping Bear Dunes.

But what makes it blue? The hue comes from a couple factors, and has to do with the size and shape of molecules in the ice crystals - and how they interact with light, according to the U.S Geological Service.

Liza Signor, who lives in Mackinaw City, said she's seen the blue ice phenomenon before. It's easier to spot when the ice begins to stack up.

"Usually you don't see it until it becomes dammed up like that," she said, referring to the ice piles near the shore and the base of the 5-mile-long bridge. "A week ago, it was all open water in front of our house. It changes that fast."

Signor and her boyfriend, Robert Danielson, were out exploring just before sunset Monday when they captured the images of the ice - and one of a bald eagle whose presence had lured them to the spot in the first place. Her pictures were snapped from the Lake Huron side of the bridge, some 500 feet out onto the ice.

A waitress at the Dam Site Inn in Pellston, Signor said she knows how lucky she is to live at the tip of the Mitten. "Every day I come home on I-75. I crest the hill, I see the bridge. I never get sick of coming into Mackinaw and seeing that bridge.

"I'm always very thankful for it, and for living in such a beautiful area."

For more of Signor's photography, check out her Facebook page.

