Nice Ice

Look: Researchers uncover a link between icicle shape and global warming

by Jennifer Walter

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Snowflakes — wondrous wintry marvels — can take on a variety of unique shapes.

But icicles can also form a range of stunning patterns as well.

Melting ice can create long and impressive — sometimes terrifying — structures.

The size and shape of icicles vary depending on their surroundings. In the Arctic, entire icebergs can be altered by shifts in water temperature and currents.

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Researchers at New York University captured the effects of water temperature on ice shape in a January 28 study in the journal Physical Review Letters.

In a lab, they observed how small changes in temperature — just a few degrees Celsius — completely transformed an icicle’s appearance.

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At 4 degrees Celsius (39.2 degrees Fahrenheit), melting ice created a smooth, spiky icicle, pointed downward.

Courtesy of NYU’s Applied Mathematics Laboratory.

At 4 °C, water reaches its maximum density. The water around the icicle is actually more dense than the ice itself.

That’s why it forms a downward spike: Water flows around it but doesn’t rise up.

Courtesy of NYU’s Applied Mathematics Laboratory.

But at 5.6 °C (42.08 °F), the water around the ice flows both up and down, creating dents. This is similar to how scallop shapes form on icebergs.

Here’s a time-lapse video of the ice growing wavy sides.

Courtesy of NYU’s Applied Mathematics Laboratory.

When the temperature gets even warmer — 8 °C (46.4 °F) — the icicles become spiky and smooth once again, only they point upward instead of downward.

Courtesy of NYU’s Applied Mathematics Laboratory.

Courtesy of NYU’s Applied Mathematics Laboratory.

This time, the icicle has the bulk of its weight toward the bottom of the tank since the warmer water around it rose to the top.

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The study illustrates how temperature changes how water flows, giving ice forms their distinctive shapes. But what does this mean for ice outside the lab, in the real world?

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"Our findings help to explain some characteristic shapes of ice seen in nature, specifically the so-called pinnacle morphology of icebergs that consists of sharp spikes or spires and the so-called scallops that consist of wavy patterns of pits.”

Leif Ristroph, study co-author, in a statement.

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The dramatically different visual appearances could be a helpful indicator for researchers studying melting sea ice.

As the climate crisis continues, looking for certain ice textures could be another way to track warming patterns.

“It's important to better understand the detailed physics and math of melting at smaller scales since these are key components of larger-scale climate models.”

Ristroph, in a statement.

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