Snowflake Scientist Reveals Secrets Behind Shapes

Brian Handwerk
for National Geographic News
February 26, 2004
See a snow-crystal photo gallery >>

French philosopher and mathematician René Descartes penned the first detailed account of snow crystal structure in 1637. Three and a half centuries—and countless blizzards—since, scientists still can't fully explain how snowflakes form their unique shapes.

One researcher digging for an answer is Kenneth Libbrecht, a physics professor at the California Institute of Technology in Pasadena.

Pasadena may seem an unlikely base for a snowflake researcher. The city hasn't seen a trace of the white stuff since 1949. But in one corner of the Caltech campus snow is likely to be falling anytime of the year, thanks to experimental cold chambers in a physics lab Libbrecht uses to create "designer" snowflakes.

Libbrecht hopes his experiments can help answer some unsolved mysteries about how snow forms. "It's a matter of degree," Libbrecht said. "We certainly know a lot more than Descartes did, but there are certain aspects that we don't understand."

One puzzle, Libbrecht says, is snow crystals' morphology, or shape. In his lab and in nature, snow formed at different temperatures produces different types of crystals. Some form into plate-like crystals, others are shaped like columns. Libbrecht wants to know why.

Other questions revolve around the role major players, such as humidity, and minor ones, such as wind, play in shaping snow crystals.

As any serious skier knows, snow crystals form just below freezing (32° Fahrenheit/0° Celsius). What he or she may not know is that at those barely subfreezing temperatures, the crystals take the shape of small plates. Drop just a few degrees more, and pencil-like columns of ice appear. Around 5° Fahrenheit (minus 15° Celsius), flakes take the form of large, ornate plates.

"We do not understand why those transitions take place," Libbrecht said. "We can see them in the lab. But this is a pretty basic property that we don't fully understand."

Snow-crystal study is of interest to scientists who form crystals in other materials and to the industries that rely on crystals. Silicon crystals, for example, are crucial to the world of computers.

But Libbrecht says such practical applications don't really motivate him. Rather, he's driven by scientific curiosity.

"We're really not doing this with other applications in mind," he said. "It's just an interesting problem, and we're trying to solve it. I like to say that there are six billion people on the planet, so maybe one of us can be spared to figure this out."

Snow "Field Guide"

Libbrecht has written a new book, The Snowflake: Winter's Secret Beauty, lushly illustrated with snowflake photography by Wisconsin-based photographer Patricia Rasmussen. In the book, Libbrecht addresses one question he hears time and again as one of the world's leading snow experts: Is it really true that no two snowflakes are alike?

Even for scientists, there is a certain inability to answer the question, Libbrecht writes. "It's a funny question, almost like a Zen koan," he writes. "If two identical snowflakes fell, my inquisitive friend, who would know? And how can you say it is so, since you have not checked them all to find out?'

Libbrecht's more scientific answer is an involved examination of just how closely one chooses to look for differences, and how complex a crystal must be for consideration as snowflake. His answer is essentially both yes and no.

While one may never solve the mystery of identical flakes, that shouldn't stop the curious from looking. Libbrecht says all a person needs to study flakes on his or her own is cold, snowy weather (0° to 10° Fahrenheit yields particularly interesting crystals) and a small magnifying glass.

Encouraging amateur snow hounds was a major impetus behind the book, Libbrecht says. "One of the reasons for the book is to create kind of a field guide so that you know what to look for," he said. "It's just good clean fun."

"It doesn't matter where you look. You can see them on a sleeve, or on a car windshield, or on just about anything that catches snowflakes," Libbrecht said. "What you see just depends on what's falling out of the sky."

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