Snowflake science: Why so thin and flat?

Snow crystals appear in an endless variety of beautiful shapes. When this crystal was forming in the clouds, the edges of its plate-like branches were only about one micrometer (0.00004 inches) thick, making the edges about as sharp as a razor blade.

Few people pay close attention to the form that snow crystals—a.k.a. snowflakes—take as they fall from the sky. But in the late 1990s, Libbrecht’s interest in the tiny white doilies was piqued.

The Caltech physics professor, who until then had worked to better understand the sun and to detect cosmic gravitational waves, happened across an article describing one of many common snowflake structures, a capped column, which looks something like an icy thread bobbin under the microscope.

Such a snowflake starts out, as all do, as a hexagonal crystal of ice. As it grows, accumulating water molecules from the air, it forms a tiny column. Then it encounters conditions elsewhere in the cloud that promote the growth of platelike structures, so it ends up with platelike caps at both ends of the column.

“I read about capped columns, and I just thought, ‘I grew up in snow country. How come I’ve never seen one of these?’” Libbrecht says. The next time he went home to North Dakota, he grabbed a magnifying glass and headed outside. “I saw capped columns. I saw all these different snowflakes,” he says. “It’s very easy. It’s just that I had never looked.”

Since then, he has published seven books of snowflake photographs, including a field guide for other eager snowflake watchers. And his library of snowflake images boasts more than 10,000 photographs.

But Libbrecht is a physicist, so beyond capturing stunning pictures, he wanted to understand the molecular dynamics that dictate how ice crystals grow. For that, he’s developed methods for growing and analyzing snowflakes in the lab.

Now Libbrecht believes he’s on his way to explaining one of the major outstanding questions of snowflake science, a question at the heart of his original interest in capped columns all those years ago.

www.futurity.org