It’s usually cold and rainy in Leeds, but imagine, just for a second, that you’re somewhere snowy; the cold bites at your cheeks and the snow is floating down. You hold out your hands and a snowflake lands on the end of your finger. Looking closely at this snowflake, you see a myriad of complexity and clarity.

Gradually, the snowflake melts into water. But no fear, as the next one that lands on your finger will be as unique as the last and all those that follow.

Such beauty is a mainstay on our Christmas trees, lights and in our minds when we think about Christmas. An innumerable amount of snowflakes fall every year, and you’d be very hard pressed to ever find a clone. How does nature create such small and intricate objects?

The key is in the chemical forces, determining the angles of each molecular bond and the environment in which the snowflake is formed. Snowflake growth is very sensitive to temperature and humidity and influences how one forms and grows.

Snowflakes are self-assembled when water vapour in the air condenses directly into solid ice, around ten kilometres above us. As more vapour condenses on this snow crystal, the nucleus grows by deposition on the surface. Between -2.8°C and 0°C, the crystals form six-sided plates (six-sided due to the way hydrogen atoms bond to an oxygen atom to create water). Below this range, needles form. Even cooler temperatures yield hollow columns, and even cooler temperatures than that produce plates and columns again. Already, we can see the reasons for this intricate object. As a snowflake falls, it experiences various micro-environments and even the smallest change in temperature and humidity can affect its growth, with each “arm” growing independently. Drier air usually encourages the growth of flat surfaces and a higher humidity encourages growth at the tips, edges and corners, with a higher amount of water vapour leading to a faster-growing and more intricate crystal.

It was once assumed that no two snowflakes are identical, but the main question prevails: who would know? There are claims of discovery but given the relatively miniscule amount of snowflakes studied, it would take rather a long time and rather a lot of snowflakes to disprove the assumption. The number of ways you can possibly create a snowflake is vast and the various parameter ranges are just as vast but never say never.

In this day and age, there are still question marks regarding precisely how these factors affect snowflake growth, but this hasn’t stopped snowflakes being a symbol of a White Christmas for most of Europe and North America. As well as this, we use the snowflake to represent cold and wintery conditions, snow tyres are labelled with a snowflake and the symbol for the 2002 Winter Olympics in Salt Lake City was a snowflake.

So there you have it. Next time you find yourself in the middle of snowfall take a second to take out your finger, catch a snowflake, and gaze at its complexity; the product of a complex process, a symbol of Christmas and a triumph of nature.


Sandy Kelly


[Image:Alexey Kljatov, image hosted on Flickr]




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