Supersized snowflakes: A scientific quest to make enormous snow
How a plan to make the world's largest snowflake was humbled by nature
In London, where I live, you can forget about a white Christmas. The best I can hope for is a pitiful flurry of flakes. So, this year, I am on a mission to create my own snow. And not just any snow: for maximum festive impact, I want to make the world’s largest snowflake.
It will be a challenge. The Guinness world record stands at 38 centimetres across and 20 centimetres thick. This whopper was recorded in Montana in January 1887, when ranch owner Matt Coleman reported seeing snowflakes “larger than milk pans” during a severe storm. Admittedly, some experts are sceptical. “If this was falling from the sky, they would probably need to be wearing crash helmets,” says glaciologist Douglas Mair at the University of Liverpool, UK. Nevertheless, Guinness World Records insists that contemporary sources support the record.
But hold on! There’s an addendum: the largest snow crystal measured 10 millimetres. “A snow crystal is a single crystal of ice,” says Ken Libbrecht, who photographed the record-breaker in Ontario, Canada, in December 2003. The textbook image of a Christmas snowflake is actually a perfect snow crystal, he explains, whereas a snowflake is several crystals joined together. So perhaps I could break a record by making the world’s largest snow crystal instead – how hard can that be? “You’ll be able to grow some ice crystals from water vapour,” says Libbrecht, who makes “designer” snow crystals in his lab at the California Institute of Technology. “But if you want to make it look like a snow crystal – I mean an actual symmetrical snow crystal – that’s a tall order.” Clearly, I will need some help.
My first stop is the Manchester Ice Cloud Chamber at the University of Manchester, UK. This 10-metre-tall, climate-controlled tube was designed to “build” ice clouds like those found high in the atmosphere, to improve the accuracy of weather forecasts.
Atmospheric scientist Paul Connolly, so I am here to find out how that is done.
You start with a supercooled cloud of water vapour, he says. From there, you have two options. If the temperature is above about -38°C (-36°F), an ice crystal will form around a “nucleating particle”, such as pollen or soot. If the temperature is lower than that, “homogeneous nucleation” occurs, with some of the water vapour spontaneously freezing to create the nuclei upon which crystals can form. Either way, under the right conditions, your crystal will begin to grow, drawing in surrounding water molecules from the air. And using the ice cloud chamber has advantages over nature. “We don’t have to wait for the ice crystals to fall kilometres through an atmosphere,” says Connolly. “We can speed up this process and do it within 10 metres.” Unfortunately, however, the largest snow crystals he and his colleagues have created measure just 1 millimetre. Perhaps a bigger chamber would help.
Just down the road is Energy House 2.0, a climate-controlled warehouse run by the University of Salford that is designed to test new construction techniques. “There’s nowhere else like it in the world,” says technical lead Richard Fitton Energy House 2.0 can produce an incredible diversity of temperatures and humidities – including extreme cold – making it the perfect place to try to grow my giant snow crystal.
I have assembled a crack team of experts to help. Alongside Connolly and Fitton, we have Fitton’s colleague Grant Henshaw, Gordon McFiggans, an atmospheric scientist at the University of Manchester, and Mair. Energy House 2.0 has been set to a bone-chilling -18°C (-0.4°F), and there is a snow cannon all ready to go. Stage one, we agree, will be to see if we can encourage the cannon’s ready-made snow crystals to grow bigger. The plan is to fire it twice: low first, and then higher. We are hoping this will provide a lingering cloud of supercooled water vapour for crystals generated at the top of the chamber to fall through. “In the atmosphere, the way we get the largest snowflakes is if small snow crystals can grow in a process known as vapour deposition,” says Connolly. “That means water vapour condenses onto the ice crystals.” This so-called Bergeron-Findeisen process is what we hope to trigger.
The cannon cranks up, jetting out plumes of small, white pellets. In the fog of this snow spray, it is hard to distinguish anything, let alone our hoped-for supercooled cloud. But we manage to swipe a few snow crystals to examine under a microscope. The news isn’t encouraging. Despite our best efforts, the tiny, round crystals aren’t getting any bigger. The problem is the cannon itself, the group agrees. It produces spherical particles, and without rough edges, it is harder for these crystals
So, we are going to have to make ice crystals from scratch. chance is to get the air in the chamber down to -38°C, cold nucleation, because at higher temperatures, only around 1 in a million aerosol particles will act as a nucleus for an ice crystal. But the chamber itself can only be cooled to -20°C (4°F). How can we make the air even colder?
Connolly whips out a plastic drinks bottle and starts pumping air into it with a bicycle pump. “If we let the air out really quickly, then it has to work to push the air molecules outside of the bottle out of the way,” he says. That requires energy – in this case heat – so the escaping gas cools rapidly, lowering the temperature further. We will also need a source of water vapour: a hastily sourced kettle should do the job nicely. And, because the Energy House 2.0 chamber is cavernous, our highly qualified academics rig up a tall, tarpaulin tube in one corner to contain the experiment.
We’ve grown a snowflake
By this point, we have been in the freezing chamber a while, and we are all starting to vibrate with the cold. It is time to put physics to the test. Connolly wriggles into our tube. The kettle is by his feet, boiling furiously, producing plumes of water vapour. We hand him the plastic bottle, and the air pops as the pressure is released. There is a tense, silent wait. Then Connolly exclaims – with more than a hint of relief – that there are a few snowflakes swirling about him. He catches one on a glass slide and posts it out through a gap in the tarpaulin.
The flake is tiny, but size has ceased to matter. We rush to the microscope and inspect our creation. Sure enough, a crystalline structure glimmers into focus, delicate tendrils reaching towards the lens. “It doesn’t look like a single ice crystal,” says McFiggans, peering at it. He thinks we have caught a bundle of ice crystals that have joined together in their fall through the chamber. “We’ve grown a snowflake,” he says. A round of applause clatters through the chamber.
Our snowflake is less than 2 millimetres in size, not even close to rivalling Libbrecht‘s snow crystal, let alone Coleman’s milk- pan-sized flakes. But I’m not counting this as a failure. Discovering just how complex it is to form a single snow crystal has left me with a newfound appreciation for the magic of those dancing white flecks. I will never look at a snowflake the same way again.
Giant snowflakes Watch Madeleine Cuff attempt to make the largest snowflake