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A snow crystal (Kenneth Libbrecht)
A snow crystal (Kenneth Libbrecht)

The science of snowflakes Add to ...

As a northern people, most Canadians spend months each year surrounded by snow. We may curse it as we clear our walkways (tens of millions of flakes per shovelful), or admire it while on skis or riding a snowmobile, but how much attention do we pay to how it got there?

“We are the snowiest country in the world,” Environment Canada senior climatologist David Phillips says. “It’s part of our reputation.”

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During a week when most of the country east of the Rockies is struggling through a cold snap, few would take issue with Canadians not appreciating the beauty of winter. Luckily, there are scientists who make snow their life’s work – and from them we are learning more and more, including an answer to the age-old question: Is every snowflake unique?

Why do snowflakes differ?

All snowflakes begin the same, when a droplet of moisture from a cloud freezes into a tiny bit of ice and begins its descent.

At his popular site, snowcrystals.com, Caltech physics professor and acknowledged snowflake expert Ken Libbrecht notes that all budding flakes form a hexagonal lattice because of the way water molecules fit together. But from that moment, the differing influences on the snowflake multiply.

“They have a complicated path from the sky down to the earth,” University of Regensburg mathematician Harald Garcke, part of a team that helped create a computer model for the growth of snowflakes, explains in an interview from Germany.

“They have different humidity and temperature on the way down. If either changes on the way down, the snowflake will form differently. And each snowflake will have a different path, because the wind blows it.”

The initial crystal will grow as other water condenses onto its surface, turning into a hexagonal prism. Arms will eventually sprout. Dr. Libbrecht, who started examining snow as a cheap and safe way to study crystals, notes that atmospheric conditions are essentially the same across the crystal, meaning that each arm will grow at about the same rate.

Over time, the simple crystal will have grown into a considerably more complicated shape. They can become flat plates, columns or needles. And the arm-like extensions on the more classic shapes can grow their own arms, much the way a tree branches and rebranches.

Is each one unique?

A snowy field can look like a blank canvas, a vista of unremitting uniformity. But examining individual snowflakes reveals astonishing differences from one to the next. Some of these are visible to the naked eye – watch carefully the next time you walk through falling snow – but others require a microscope. Is it true that all snowflakes are unique? While leaders in the field are loath to make a definitive pronouncement, they will say that the odds are stacked against any two being exactly alike.

“It depends on what you mean by alike, and what you mean by snowflake,” says Dr. Libbrecht in an interview from Pasadena, Calif.

Making a point about how hard it is even to winnow down the number of snowflake types, he draws an analogy with bread: The non-connoisseur may think that bread is bread, but to the more discriminating eater, there are infinite varieties of baguette, rye, pumpernickel, sourdough and many others. They share certain fundamental similarities, but each is distinct.

A connoisseur of snowflakes, Dr. Libbrecht has photographed more than 10,000 and still sees ones that surprise him.

Dr. Garcke says the job of attempting to model snowflakes is particularly hard because of the many ways one can develop. “It would be fairly impossible to find two that are identical,” he says.

Why our popular perception is a fraud

The popular perception of what a snowflake looks like stems in large part from a 19th-century American farmer and hobby photographer named Wilson (Snowflake) Bentley. He is believed to have been the first person to photograph snowflakes, using a homemade contraption that married a camera to a microscope, and wearing heavy gloves to prevent his own body heat from destroying the samples. The results were beautiful, star-like images that were seared into the public’s mind.

Their accuracy, however, is questionable. Mr. Bentley photographed the flakes against a backlight and then manipulated the negatives to give the image a black background. In doing so, he is accused of having cleaned up the flakes themselves, allegedly creating an image better than nature had produced.

His process led to a bunfight between Mr. Bentley and German meteorologist Gustav Hellmann, but it did not stop the American’s images from appearing on greeting cards and helping form the popular idea of what a snowflake looks like. As Dr. Libbrecht’s images show, those perfect shapes are not the norm.

“Once you have lots of structure, there’s an infinite, near-infinite, amount of variation,” Dr. Libbrecht says. “A lot of them don’t look like what I call supermodel snowflakes. Small, blocky-type things are far more common than these beautiful, large crystals.”

Where is Canada’s best snow?

Cochrane sits on the Trans-Canada Highway in Ontario, not far from Timmins. It is the start of the Polar Bear Express to Moosonee and invites visitors to expect the “wonderfully unexpected.” For snow-chasers, it has another bonus.

“You actually have snow enthusiasts,” Mayor Peter Politis says from the community. “They frequently come up here to appreciate the snow.”

Dr. Libbrecht is one of them, praising the conditions in Cochrane that allow the creation of great snow. The community is apparently far enough from major bodies of water and, when the temperature is right, the snow falls lightly and slowly.

“Around minus 15 [Celsius], the really nice, large stellar crystals grow,” he says.

“[Northern] Ontario is just kind of ideal. It’s the right temperature and it snows a lot.”

Snowflake shapes

Snowflake expert Ken Libbrecht’s website, snowcrystals.com, shows 35 shapes of snow crystals. Here are four examples:

Needles

They fall under the “column” category of shape – thin, columnar ice crystals that grow when the temperature hits -5C.

Dr. Libbrecht describes them as the kind of snowflakes that look like small bits of white hair on your sleeve.

Capped columns

Dr. Libbrecht says these crystals grow into stubby columns first, then the growth becomes more plate-like when they move into a different region of clouds. They “don’t appear in every snowfall, but you can find them if you look for them,” he says.

Stellar plates

These are common shapes, and form when the temperatures is near -2C or near -15C. The crystals resemble star-shaped plates, Dr. Libbrecht writes, and often have “amazingly elaborate and symmetrical markings.”

Stellar dendrites

These are crystals that are shaped like plates, but have branches. Typically two to four millimetres in diameter, they can be seen with the naked eye, Dr. Libbrecht says.

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Follow on Twitter: @moore_oliver

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