Ask Ellen: Why is there blue ice at the Straits of Mackinac?

Ask Ellen

GRAND RAPIDS, Mich. (WOOD) — Tourists have been flocking to the Straits of Mackinac, where tons of blue ice chunks have been stacking up along the shoreline.

This is a phenomenon that doesn’t happen every year but isn’t completely new to the Straits.

The ice isn’t actually blue, but according to various scientists, there are three main reasons the ice appears blue to the human eye.

BIG CRYSTALS

According to Ted Scambos, a research scientist at the National Snow and Ice Data Center interviewed by Mashable, weather conditions are key to blue-appearing ice formations. If ice is allowed to freeze slowly and evenly, the ice tends to have larger ice crystals. This means stretches of cold weather with very little wind can often lead to blue ice.

Blue ice over the Straits of Mackinac in February 2021. (Courtesy 9&10 News)

Larger ice crystals scatter light differently than smaller ice crystals. Larger ice crystals allow light to penetrate deeper into the structure. Tiny ice crystals, like snow, usually reflect light quickly back into the atmosphere. This fast reflection makes snow appear white.

When light is allowed to penetrate deeper into an ice structure, it allows for more of the “red” spectrum of the light to be absorbed out. The deeper the white light is allowed to travel through the ice, the more blue it appears. According to Carleton College fellow Benjamin Drummond, absorption of light at the red end of the spectrum is six times greater than at the blue end of the spectrum. That means the more red light that is absorbed, the more we see blue.

NO BUBBLES

The farther light is allowed to travel into an ice structure, the more blue it looks (see above section as to why). Bubbles can drastically limit how far light can penetrate the ice.

Bubbles often create an opaque look to the ice. They also tend to have a reflection effect similar to snow, reflecting light back to the eye before it has had time to push deep into the ice.

Ice that is sufficiently consolidated is most likely to appear blue.

Blue ice over the Straits of Mackinac in February 2021. (Courtesy 9&10 News)

PURE WATER

This is a huge kudos to Michigan’s Great Lakes. Blue ice can only form where the water is very clean and pure. Contaminants in water will affect how light travels through the ice. Sediment, pollution, algae or murk will all reduce the brilliant blue affect.

Glaciers in the Arctic and Antarctic often take on a blue appearance, also due to the fact the water is generally very clean.

Locals at the Straits of Mackinac say blue ice doesn’t form every year, but when it does, it is a huge economic boost.

Blue ice over the Straits of Mackinac in February 2021. (Courtesy 9&10 News)

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