Last Saturday, Andre Poineau had a feeling there would be a good, hard freeze at his cottage along the shores of Lake Charlevoix near Boyne City, Michigan. But when he went down to the house to have a look the morning after a zero-degree night, he found the lake’s surface perfectly frozen, and eerily clear.
So clear, in fact, that he took a shovel with him to probe the ice as he went, since it lacked bubbles, sediment, cracks or any other clues to indicate where it might be thinner from one place to the next. He chopped a hole in the ice to see how thick it was: about 2 inches. So unnerved was he by walking out onto it that he didn’t dare go in past the point where he knew that if he fell in, the water would only reach his armpits.
“Plus, if I did go through, the shovel would give me a wide surface to be able to pull myself up on,” Poineau chuckles. (See the bull moose frozen in mortal combat.)
Though he rarely posts on his Facebook page, Poineau put a handful of snaps of himself and a companion treading with care on the glass-clear ice, making it appear as if they were pulling a biblical stunt. No, they’re not faked, he says; they’re just ordinary cell phone pictures taken with an iPhone 6. The pictures have since been reposted tens of thousands of times on sites around the Internet.
Poineau is amused by the attention the photos have received, but to him, it’s not an unusual phenomenon. He says the lake freezes just like this from time to time. He’s lived on Lake Charlevoix for all of his 63 years and has seen it similarly crystalline at least half a dozen times. As a young man, he and friends would have fun startling the unsuspecting trout, pike and smallmouth bass that dwell in deeper waters by skating above their heads.
“I don’t think there’s any great mystery to why it happens,” Poineau says. “When the wind is dead calm and the water is at or below freezing, it goes perfectly like that.”
By his recollection, the overnight temperature on January was right at 0 degrees Fahrenheit, with not a breath of wind, and no snow or other precipitation. And because of the presence of invasive zebra mussels, he says the lake water is always extremely clear.
George Leshkevich, a physical scientist who has studied ice formation on the Great Lakes with the National Oceanic and Atmospheric Administration for 44 years, says that when air temperatures are so low that water loses much of its residual heat, large, perfectly formed ice crystals can grow down into the water column without obstruction by sediments, bubbles, or movement by the water.
On the Great Lakes, wave action from wind prevents this “plate glass ice” from staying flat for very long, though it can grow to be quite thick. He’s seen it 30 inches thick, he says.
“I’ve seen clear ice pile up near the Straits of Mackinaw, where it looks like giant mounds of broken plate glass,” Leshkevich says.
Researchers sometimes also call this “black ice,” since lakes covered with it are completely opaque to satellites; light passes through so perfectly that none is reflected back into space.
“The key is to freeze water very slowly so that impurities and air bubble have a chance to rise to the surface and, in the case of air, escape.,” explains Tamela Maciel in a blog post from 2014 on a similar phenomenon that occurred on a lake in Slovakia. She is an astrophysicist with the National Space Center in Leicester, U.K. “A slow freezing also allows bigger ice crystals to form, which have few surfaces to scatter light.”
Maybe people are so surprised it happens because they don’t go out to look around when it’s so cold, Poineau says. “It was a beautiful, sunny day, and there wasn’t a soul around,” he adds. “Nobody goes down to check it out.”