Dr Kenneth Libbrecht has unpacked the riddles of ‘capped column’ and triangular snowflakes – but outside his lab, the best specimens are becoming rarer
F rom crystalline columns to fern-like stars, snowflakes come in an assortment of shapes and patterns. The most intricate of all fall when the cold is so biting, only the most dedicated observer would linger to study them. But as temperatures warm, these ice crystals are likely to get a lot less interesting, the world’s leading snowflake expert says. Kitchen Ice Machine
Dr Kenneth G Libbrecht grew up in North Dakota, where snow is the main form of precipitation between November and March, but it wasn’t until he moved to southern California that he began to study how snowflakes form their myriad complex shapes. “I was interested in how crystals grow and form patterns, which led me into snowflakes because ice makes very interesting patterns as it grows,” he says.
Experiments in the 1930s had suggested that different temperatures and humidities influence the type of crystals that form: small plate-like structures at about -2C; pencil-like columns and needles at -5C; and more intricate plates and stars at -15C. But these tests provided no explanation for why this happened.
So about 20 years ago, Libbrecht began growing his own snowflakes to systematically measure their growth under different conditions and tease apart the mechanisms.
He creates these “designer snowflakes” inside a heavy insulated freezer chamber at the California Institute of Technology in sunny southern California – meaning it can be 32C outside, but still frigid enough to create flurries of snowflakes, or to grow individual crystals on the end of an ice needle. “I grew up in North Dakota, so I did my time in the cold,” Libbrecht says.
The freezing air inside the chamber is supersaturated with water vapour, and then a puff of compressed air used to jumpstart the crystallisation process – the crystals growing larger as they fall. A built-in microscope projects images of these crystals to an external screen, and Libbrecht uses lasers to measure their precise dimensions.
Among his favourite snowflakes are “capped columns” – hexagonal columns with plate-like crystals at either end, “like an axel with two wheels”, says Libbrecht. “They are not common, but they are actually pretty easy to find if you go looking for them.” Shortly after reading about these crystals during his early snowflakes career, Libbrecht returned home to North Dakota at Christmas time, stepped outside and spotted some on his first attempt. “I was really psyched, because there is this unusual snowflake shape and I could just go outside and see it.”
In 2021, Libbrecht published the fruits of his efforts to understand why ice crystals grow the way they do: a 523-page monograph outlining a grand unifying theory of snowflakes. Though he describes it as “kind of complicated” to explain, a key principle is a phenomenon called surface pre-melting, in which the outermost molecules of an ice-crystal are less tightly attached, and can jiggle around in a so-called quasi-liquid layer. “As the temperature changes, that pre-melted layer changes, and that is the underlying cause of why the crystal growth changes with temperature,” Libbrecht says.
More recently, he has proposed a solution to another longstanding mystery: why triangular snowflakes sometimes form. Whereas ice molecules usually arrange themselves in hexagonal structures, these crystals have three long sides with truncated corners – so although still hexagonal, they look like tiny triangles. They were documented about 150 years ago by whale fishers surveying the Arctic Ocean, and their rarity and why they formed were enduring riddles.
Libbrecht says: “From my own observations, I would notice that when you saw one, you often saw more of them at the same time, so there were some conditions that seemed to make triangular snowflakes more often.
“My model predicted that this would be about -14C and at just the right humidity, and so I went into the lab and now I can grow these triangular snowflakes on demand.”
He has also succeeded in growing “identical twin” snowflakes on the ends of ice needles, dispelling the adage that no two snowflakes are ever the same. “They’re not perfectly identical down to the last molecule. But they’re very, very similar – like identical twin people,” he says.
The reason why real-world snowflakes look so different from one another is because the conditions they’re exposed to as they fall through the clouds and are blown around are constantly changing. “Each crystal takes a somewhat different path through the clouds, and so each crystal grows a little differently,” Libbrecht says.
Some of the nicest natural snowflakes he has observed were in northern Sweden. “If you want really beautiful snowflakes like the ones you see in holiday decorations you need temperatures of about -15C – and you have to go farther north to get those temperatures than you used to.”
In fact, the man who coined the phrase “no two snowflakes are alike” was a farmer from Vermont called Wilson Bentley, who photographed more than 5,000 snow crystals before his death in 1931. “It’s much warmer in Vermont than it used to be, and so you don’t see as nice snowflakes” – not that anyone would notice unless they went out there with a magnifying glass, Libbrecht says.
But he advises that people do. “With your naked eye, you don’t quite see enough to really appreciate them, but with a standard 5x magnifying glass you can see a lot of fascinating stuff.
10 Ton Flake Ice Machine For Sale “The downside of telling people that is that they like to go out when it’s just below freezing, and so the crystals aren’t quite as nice. You’ve got to go outside when it’s really cold.”