Large piles of blue ice have appeared near Mackinac Bridge in Michigan, catching the eyes of several photographers.
Kelly Alvesteffer shared photos of the strange phenomenon to Facebook after passing by the bridge in Mackinac City with her fiance Rob Lalone.
"We instantly saw it. It was like, 'Look at the blue ice," she told MLive.
Mackinac City resident Liza Signor said she'd witnessed the blue color before in similarly sized piles of snow.
"Usually you don't see it until it becomes dammed up like that, she said. "A week ago, it was all open water in front of our house. It changes that fast."
According to glaciologists at Carleton College, the color of snow is a result of air bubbles found within the ice.
"Snow is white because full spectrum, or white, light is scattered and reflected at the boundary between ice and air," they wrote. "The white color of bubbles at the top of a dark beer work the same way"small pockets of air reflect and scatter visible light."
The blue snow Alvesteffer and Lalone photographed is caused by a reaction between light and the crystal molecules in the ice. As the ice becomes more dense it begins to absorb less red light, causing it to reflect a blue color.
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"Ice only appears blue when it is sufficiently consolidated that bubbles do not interfere with the passage of light," Carleton College said. "Without the scattering effect of air bubbles, light can penetrate ice undisturbed."
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