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The Composition of Snow
Wonderful amounts of fluffy snow have been falling from the sky, blessing Lake Tahoe’s resorts and merchants with visitors eager to experience all that Lake Tahoe has to offer in the winter.
As I blaze a trail snowshoeing through the woods, I start to wonder about the science of snow: how do snowflakes form, why are the flakes shaped the way they are and what causes the delightful crunching sound when it’s cold?
Contrary to what many seem to believe, I don’t know much about anything but I wonder about everything. Writing this column keeps my mind alive wondering and my brain fresh researching the answers to all my questions.
Here is what I learned: the science of snow basically comes down to chemistry and the properties of water.
A snowflake begins forming when a tiny dust or pollen particle comes into contact with water vapor high in the earth’s atmosphere.
The water vapor attaches to the particle and freezes into a tiny crystal of ice. This crystal is now heavier than the air so it begins to fall, gathering more water vapor on its journey.
The pattern of bonding forms the crystal into a six-sided figure, due to the water molecule’s composition of two hydrogen atoms and one oxygen atom through a process called hydrogen bonding.
As the water molecules are freezing and compacting, they continue to bond in this six-sided configuration. Right before completing the freezing process, the hydrogen bonds push the molecules to the farther possible distance from each other, causing a 4 degree expansion as the ice crystals set.
This expansion property is the reason why ice floats. Water, unlike most substances, is lighter in solid than liquid form due to this expansion, which is essential to life on Earth. The ice that forms and floats on bodies of water protects the aquatic plant and animal life beneath. Not only that, if ice were to sink, eventually the entire body of water would freeze.
And indeed, over the 4.5 billion years this planet has been in existence, if ice were to sink, the entire planet would have become a giant ice cube and we would not exist.
In this way, hydrogen bonding makes all life on Earth possible.
Snowflakes may incur changes on the way down from high up in the atmosphere. The snow may pass through a warm layer, melting it. A deep cold layer closer to the ground may refreeze it and it will fall as sleet or ice pellets.
In some conditions, snowflakes encounter super-cooled water droplets. When these super-cooled droplets attach to the snowflake, they freeze. If the crystal collects enough of these droplets, it loses its defined shape and falls as a fragile, oblong shape called graupel.
Once on the ground, even if it falls as light and fluffy snow, the flakes will eventually begin the process of thawing under the sun, then refreezing at night, compacting more throughout the days until it becomes snowpack.
If, for some reason, this snowpack were to remain on the ground year-round, as it does in the Polar Regions, it eventually would develop into a mass of ice called a glacier.
For those of us who have had to move it around, shovel it off our decks, drive over it, slip on it and stomp through it, it seems that we have had mounds of snow this season already.
Indeed, depending on where you measure it, the Lake Tahoe area has had between 12 and 25 feet of snow, probably much more on some of the mountain tops.
One of my favorite things about snow, besides snowshoeing through it, is the crunching sound it makes when it’s 10 or 15 degrees or less, as it often is in Minnesota, where I grew up. This is due to the lack of moisture in the snow at low temperatures. The best crunch comes a few hours after the snowfall, when the individual crystals have bonded more snugly together. The crunching sound comes from breaking those bonds as we walk across it.
I’m outside walking every day. When it’s cold, I bundle in many layers, and revel in the crunch.
