Giles Whittell, author of The Secret Life of Snow, is a passionate snow enthusiast. Here he describes how this love of snow was born and how a snowflake is formed.
In 1867 a sister was born to a little girl who lived on a homestead in Wisconsin. They were pioneers: home was a log cabin their father had built in woods on the north bank of the Mississippi. In the summer the woods gave shade. From November to May, like sleeping bears, they surrendered to the snow.
The family moved west as the girls grew up, but life in the snowbound woods held a special place in the younger sister's memory. Her name was Laura Ingalls Wilder and years later she described a winter's day in the cabin:
Ma was busy all day long, cooking good things for Christmas. She baked salt-rising bread and rye'n'Injun bread, and Swedish crackers and a huge pan of baked beans, with salt pork and molasses One morning she boiled molasses and sugar together until they made a thick syrup, and Pa brought in two pans of clean, white snow from outdoors. Laura and Mary each had a pan, and Pa and Ma showed them how to pour the dark syrup in little streams onto the snow.
They made circles and curlicues and squiggledy things, and these hardened at once and were candy. Laura and Mary might eat one piece each, but the rest was saved for Christmas Day.
The description comes from Little House in the Big Woods, which Ingalls Wilder wrote in 1932 and my mother read to me in Africa. I must have been eight at the time and it made an instant, indelible impression. It was air conditioning in book form; a blast of miraculous cold in the heat of a Nigerian summer. It fixed in my mind the idea of snow as a thing of bounty.
Snow irrigates. It gives skiers something to slide on. It covers mountains from Denali to Rakaposhi like thick icing. It is the only thing on Earth that brings peace and quiet to New York City, and it makes curlicues out of molasses.
Snow has a lot in common with religion. It comes from heaven. It changes everything. It creates an alternative reality and brings on irrational behaviour in humans. There is a difference, though. Unlike religion, snow asks searching questions about the mysteries of nature.
What gives a flake its shape? Why are no two alike? How can the same warm wind bring snow to one side of a mountain and dry air to the other? How can rain sweeping up a valley past your window turn to snow in the blink of an eye?
My pleasure in moments like these is not fleeting. It can last for years, to be recalled and savoured like Proust's madeleines, and it's intensified by two things. The first is that moments of pure snow happiness are rare, especially if you live in a low and flat place like England. The second and this, admittedly, is no more than a hunch is that they are even more unlikely in the context of outer space.
The void that Earth hangs in is mainly a sunless, hostile vacuum. Evidence of life is scarce. Evidence of fun is even scarcer. Snow-like precipitation does seem to happen elsewhere in our galaxy, but water-based snow that you can slide down and roll around in requires a very special set of circumstances. Snow needs an atmosphere that can hold water vapour without changing its chemical composition. It needs dramatic upward movements of moist air, either over rising ground or over other, colder air masses. This movement has to lower the temperature of the moisture to freezing or below, and the air has to be naturally seeded with billions of microscopic dust particles around which ice crystals can form.
The odds against all these conditions existing in one place are high, but on Earth it happens all the time. In the thin layer of gas we call the troposphere the ingredients of snow come together routinely, as if in defiance of the cosmos.
How are snowflakes formed?
We now know that snow crystals grow into snowflakes because of three processes acting on them at once. The first two are known as faceting and branching. Imagine the ice crystal building block of any flake as a miniature hexagonal ice hockey puck. Its six sides are prism facets. Its top and bottom are its basal facets. As it falls through cold, moist air, or swirls around in it heedless of gravity, free-floating water molecules from evaporated droplets adhere directly to these facets without passing back through the liquid phase. When they stick to the basal facets the puck thickens. It can quickly become taller than it is wide a column rather than a puck.
When they stick to its prism facets it becomes wider, like a plate, and one of the mysteries of faceting is that both versions can act on one flake but they very rarely do so at the same time. This is there are snowflakes that look like pairs of train wheels on an axle. They grow first through basal faceting to create a column, then through prism faceting to create the wheels, with an abrupt switch from one to the other than no one can quite explain.
For all the oddness of train-wheel shapes, snowflakes generally would be dull if they were shaped only by faceting. They would be small and granular and lie heavy on the ground, like the rough little crystals that pile up next to snow cannons on denuded ski slopes.
What makes snowflakes beautiful is branching. In a crystal's journey through the atmosphere all the parts of its surface are in competition with each other for free-floating water molecules. In this competition, to stick out into the air is to have the edge, so when the prism facets are growing, the corners between them grow faster than the facets themselves. As the corners begin to stick out they catch even more molecules relative to the self-effacing facets, and so they grow faster a positive feedback loop that creates the branches that turn crystals into stars and snow into something light, fluffy and miraculous.
How many flakes are needed for a snowperson?
About 100 million.
How many flakes fall on planet Earth in an average year?
What is the fastest anyone has travelled on skis?
On March 26th 2016, Simone Origone of Italy broke his brother's speed skiing record over a one-kilometre course in Vars, on the edge of the Parc National des crins in France. Between the timing gates at the bottom of the course he clocked 254.958kph or 158.423mph. That is about 70 metres per second.
What makes snow so slippery?
Mainly the very thin layer of water molecules that can remain in fluid form on the surface of a snowpack even in sub-zero temperatures.
Why is snow so quiet?
Unlike raindrops, snowflakes make no sound when they land. As they collect but before they start to weigh on each other and harden they create a soft layer full of air pockets and as sound-absorbent as foam rubber.
What is the snowiest place in Britain?
British snow lasts longest in high Scottish corries where it seldom sees the sun. The slowest to melt is usually on Braeriach in the western Cairngorms, the country's third-highest mountain. In winter the snow that collects in a cleft at the foot of Gharbh Choire Mr, a cliff on Braeriach's north face, can be 75 feet deep. Some of it usually survives the summer snow patch experts believe it has disappeared completely only six times in the last 400 years. Unfortunately that includes 2003, 2006 and 2017, but if average temperatures fell by two degrees this patch could become a glacier.
Edited extract from The Secret Life of Snow by Giles Whittell. Illustrations by Evie Dunne. The Secret Life of Snow is a quest through centuries and continents to reveal the wonders of snow. Along the way Whittell uncovers the mysteries of snow crystals, why avalanches happen and how snow saved a British prime minister's life.