The Amazing Life of Snow Flakes

How nature makes these amazing structures

 
By DAVE REESE

You have your stellar dendrites, sectored plates rimed crystals and spatial dendrites.

To us they’re just snowflakes, and we battle them on every front, with shovel, plow and chemicals. We tromp on them with skis and snowshoes. But if you look closer, these frozen water molecules really live a life of their own, and one man has made it his life study to examine just how snowflakes are made.

Physicist Ken Libbrecht has studied “tunable diode lasers” and “interferometer gravitational waves,” but the snowflake is the one thing that still challenges him.
While snowflakes may all be very different, scientists still don’t completely understand why they are completely symmetrical, Libbrecht said. “There are lots of kooky theories out there that involve standing acoustic waves or quantum mechanics,” says Libbrecht, a professor of physics at California Institute of Technology.

While no two snowflakes are the same, scientists have classified 80 different kinds of them, from capped columns to stellar dendrites. Once you learn some of the types of snowflakes, you can go out and study them for yourself. “It’s like bird watching,” Libbrecht said. “When you know the names of the different crystals, you have more fun looking at them.”

The life of snowflake begins when water vapor in a cloud begins to cool. If it’s cold enough within a cloud, the water vapor turns into a solid state — ice. The water molecules, as they turn to ice, begin to “steal” water vapor from nearby molecules.
Then it begins to facet — grow very slowly. As it does this, it attracts other water-vapor molecules. Then the snowflake might get bounced to another part of the cloud where the temperature changes, perhaps losing some of its matter to another snowflake, or losing some of its shape as the ice crystal turns back into vapor.
But since every part of the snowflake experiences the same temperature changes, the snowflake’s “arms” are all identical. The result is usually a hexagonal prism, the most common form of snowflake.

While to the layperson a snowflake simply falls out of the sky, Libbrecht looks at an ice crystal and considers factors like statistical mechanics, surface melting, and “quasi-liquid layers. “That’s where all the action is,” he said.
Not many people study snowflakes at the level that Libbrecht does, and that’s why he decided to write a book about it.          
His book, “The Snowflake – Winter’s Secret Beauty,” is all about snowflakes. The book examines how snowflakes are created, how people study snowflakes, and of course there are plenty of detailed photographs of different kinds of snow crystals.
“The story is terribly interesting,” he said. “We needed a book on this … how is a person supposed to know what he or she is looking at? It’s been pretty successful for that reason.”

Since he lives in southern California, a spot not exactly known as the snowflake capital of the world, Libbrecht creates his own ice crystals in highly controlled environments. In fact he’s making a freezer now that’s only 3 millimeters wide, keeping it tiny so that he can control the temperature down to a tenth of a degree or more.
“You don’t need a cold climate to study snowflakes, just a refrigerator,” he said.
Libbrecht is studying snow crystal growth to gain a better understanding of any kind of growth on the molecular level, from biological organisms to computer-chip technology.
“The same concepts apply to everything that grows,” he says. “Where does a flower gets it’s shape? It’s all about morphogenesis on a molecular scale.”
Snowflake growth is entirely temperature dependent, but the $20,000 question that Libbrecht wants the answer to is why a snowflake that grows at 28 degrees is different from one that grows at 23 degrees, and why the snowflake that grows at five degrees is like the one that grows at 28 degrees.
At around 28 degrees you get plate-like crystals, while five degrees cooler the snowflakes are formed as needle-like, columnar crystals.

“This remains somewhat of a mystery, why the morphology changes,” Libbrecht said. “It has to do with how molecules assemble themselves.”
He recently returned from Fairbanks, Alaska, to study ice-crystal morphology. While he’s gaining ground on how a snowflake actually grows, Libbrecht said there’s still more to learn.
“The funny thing is, this stuff falls out of the sky and there’s still no answers to them,” he said. “They’re fascinating properties.”

While Libbrecht prefers to look at snowflakes at the molecular level, you can enjoy the beautiful properties of a snowflake on your sleeve, or before you make a snowball out of it.

Watch for Yourself

Snowflake watching, like bird watching, requires optics. The best way to begin is with a simple magnifying glass. A smaller, fold-up model works just as well.
The best way to snowflake watch is to just keep a small magnifier in your coat pocket for when the time is right.
As a general rule, warm-weather snowflakes tend to be on the gloppy side, and they often fall in clumps. Cold-weather crystals are more faceted and don't clump up as much. Calm conditions are also better, since the wind tends to break the crystals up before they hit the ground. Often the conditions change with time during a single snowfall, and so does the quality of the snowflakes you can find.
“Occasionally there are some very beautiful things falling out of the sky,” he said. “If you get a magnifying glass it’s a lot of fun.”
 
On the Net: www.snowcrystals.com