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The Science of Snowflakes

 

There’s nothing more wonderful than that moment in winter when the first flurry of snow falls. Soon, the landscape is transformed and a sense of serenity envelops the countryside. But as fat snowflakes flutter to the ground, we rarely give much thought to what they actually are. Famed for the complexity and uniqueness of their structures, how are snow crystals formed, what shapes do they take and what different types of snow might we experience?

 

A Snowflake is Born

At the heart of every snowflake lies a tiny water droplet, frozen in the high atmosphere to become an ice crystal. This crystal can form purely from water if temperatures fall below −35°C. At temperatures above that, the water drop bonds to a particle of dust or pollen and freezes around it. Either way, a ‘seed’ crystal is created from which a flake can grow.

 

The symmetry of snowflakes is one of nature’s geometrical wonders. Once the seed has formed – and given the right conditions – the crystal starts to grow as additional drops of water attach themselves. This crystallisation is a fixed process, defined by the behaviour of the oxygen and hydrogen atoms that make up the water. As they become solid, they bond together following a predetermined pattern. In the case of snowflakes, that pattern is always hexagonal, having either six sides or six arms.

 

Within the hexagonal framework, as the crystal collects more water it grows into a unique shape. Arms sprout, and from these arms, symmetrical branches might grow. Temperature, humidity and – as the flake grows, becomes heavier and starts to fall – velocity and wind all influence the shape. Each flake’s journey is unique, so its change and growth is distinctive, hence the seemingly infinite variety of crystals. Not all are ornate and lacy, some are plain and unshowy. If the air through which the flakes fall is moist and warmer than freezing, they’ll stick together, becoming big and fluffy. In very cold conditions with little moisture, the crystals stay separate and are harder and smaller as they fall.

 

Theme and Variation – Snowflake Classification

Unsurprisingly, snowflakes have long captured the human imagination. The 17th century was a boom-time for snowflake examination, with natural philosophers and mathematicians including Johannes Kepler and René Descartes trying out their new-fangled microscopes and having a go at drawing and classifying the various forms snowflakes took.

 

Snowflake classification has, however, struggled to reach a definitive consensus about exactly how many basic forms there are. Japanese physicist Ukichiro Nakaya – credited with creating of the first artificial snowflakes – plumped for 41 types, others have gone for anywhere between 7 and 120, depending on their system’s level of sophistication. Basic types include:

 

  • Columns: tiny, plain six-sided cylinders, often with hollow cores. If a variance in temperature occurs during development, the crystal might mutate into a dumbbell-shaped capped column by growing plates on each end.

 

  • Needles: tiny pins of snow, like slim, shaved rods of ice with no lacy embellishments.

 

  • Plates: a starting place for fancier flakes, these are flat, thin discs of ice with closed edges and no branches. If branches form, the flake takes on a star-shape and becomes a stellar plate.

 

  • Stellar dendrites: branching, dendritic (or ‘treelike’) structures give these large crystals their classic star shape with intricate offshoots or facets. They form at around -20°C in conditions where there’s plenty of moisture to cling to the crystal and help it grow elaborately. When the offshoots from the six main branches are numerous and straight, the flakes are known as fernlike stellar dendrites.

 

  • Spatial dendrites: not everything in snowflake world is ordered and precise. When crystals grow in rough conditions or collide and merge as they fall, snowflakes can develop branches sticking out in all directions. If they hit the ground having been smooshed and generally beaten up, they’re called irregulars.

 

Seeing Snowflakes

In your mind’s eye, you know what a snowflake looks like. But how? Your naked eye can’t make out the intricacies of the patterns and even on the biggest, fattest flakes melt away in moments when caught.

 

It’s thanks to Wilson Bentley, a dairy farmer from rural Vermont, that the secret beauty of snowflakes was first immortalised on film. Wilson was born in 1865 and grew up with a fascination for all things miniature. He acquired a microscope and used it to scrutinise the tiny things around him, including Vermont’s abundant snowflakes. With the seemingly miraculous construction of snowflakes revealed by his lens, Wilson developed a new ambition. He wanted to photograph them to capture their ephemeral beauty before they melted away to nothing.

 

Towards the turn of the twentieth century, microscope cameras weren’t a thing, so plucky Wilson devised his own way to photograph individual snowflakes. Working in freezing conditions, he caught some flakes, selected the prettiest, set them on a glass slide and shot the image – all before the crystals sublimated (changed from solid to vapour). No mean feat given that the required exposure time could be anywhere up to 100 seconds. With the image captured, Wilson carefully scraped around the shape of the snowflake on the negative, leaving a stark white silhouette against a black background.

 

Ultimately, Wilson “Snowflake” Bentley amassed images of over 5000 individual snowflakes, concluding along the way that no two were alike. His meticulous work made him the first – and most famous – photomicrographer of snowflakes and his images are now held by the Smithsonian Institute in Washington D.C.

The Uniqueness Myth

The assertion that no two snowflakes are identical is everyone’s favourite snowflake fact. Is it true? Possibly. So far no researcher has found and documented two that are definitively alike. And to assert that no two could be the same, you’d have to check them all. Everywhere. Throughout all of time. Which clearly isn’t going to happen.

 

With more basic crystal forms – plates, needles and columns – it’s extremely likely you could find lots that look much the same. It’s the complex and elaborate stellar forms that differ enormously. With so many variables influencing the growth of a snowflake (including temperature, humidity and wind speed), the probability of two developing in precisely the same manner, with no minor dissimilarities, is remote. Even calculating the potential number of possible formations is mathematically mind-boggling.

 

So as far as anyone’s aware and until it’s proven otherwise, let’s keep believing no two snowflakes are alike.

 

The Many Splendid Forms of Snow

  • Dry / moist / wet / very wet / slush: descriptions of snow depending on the ratio of free water to ice it contains. Snowboarders love it dry (as powder). You’ll need it moist and sticky if you want to build a snowman.

  • Graupel: happens when super-cooled water falls on snow particles, encapsulating them in a shell and creating polystyrene-esque pellets.

  • Snow grains: small balls of ice formed when drizzle hits a sub-zero patch of air.

  • Sleet: when snowflakes fall through a warmer layer of air during their descent, leaving them in a halfway state between snow and rain.

  • Blizzard: strong winds of over 30mph combined with moderate to heavy falling snow. If lying snow is whipped into the air by the wind, it’s called a ground blizzard. Either way, visibility will be reduced to less than 200m.

  • Whiteout: when blizzard conditions get beyond a joke and it’s no longer possible to distinguish the ground from the sky.

  • Flurry: a short burst of snow with little intensity. It rarely lies and is terribly disappointing.

 

The language of snow

Snowy nations like little more than debating who has the most words for the white stuff. The Swedes, Icelanders and Inuits are all in the running with between 25 and 50 words apiece. The Sami – from the far north of Scandinavia and Russia – tally up at over 100. Researchers at Glasgow University gamely had a go at claiming the Scots had over 400 snowy words, but the brief was very loosely interpreted and took into account words that had anything at all to do with snowy weather.

 

But whoever the winner is, there are some corkers out there – from ‘feefle’ (Scots for snow as it swirls around a corner) to ‘kramsnö’ (Swedish for the moist snow needed for snowballs). ‘Krap’ is the wholly appropriate Icelandic word for slush.