“They say that every snowflake is different. If that were true, how could the world go on? How could we ever get up off our knees? How could we ever recover from the wonder of it?” -Jeanette Winterson
Here in Portland, it’s just cold for now. But much of the world has been blanketed in those familiar white flakes, and recently. Snow is one of those simple things that nature just does, but it’s still as wonderful for most of us as it was when we were little kids.
Rather than liquid freezing, snow comes from water vapor — the gaseous form of water — changing directly into the solid, ice phase, a process known as deposition. The water molecules link together in a beautiful hexagonal crystal, like so.
At least, that’s how they do it in a lab. In real life, the formation of the first snow crystals happen the same way any phase transition does: you need an imperfection to start it. The most common culprit, up in the clouds? A microscopic speck of dust.
The water vapor clings to the dust, freezes in this hexagonal shape, and then begins to grow into a snowflake as more ice forms around the initial crystal. How do the snowflakes form? Well, we can go to the Electron Microscopy Unit’s Snow Page, and see a variety of snowflakes under an electron microscope.
Some of them look very hexagonal, to be sure.
But others appear to be much “pointier”, or dendritic.
Some of them look like the traditional “snowflake” shape you learned about as a child.
Well, those hexagons often grow into much longer crystals and more intricate shapes than you’ve probably ever imagined.
What determines the shape of a crystal, you ask?
Temperature, the amount of water (in all its phases) in the environment, and the random luck of where you happen to be with respect to the last bit of crystal you formed.
That is why, to a good degree of certainty, we can state that no two snowflakes are identical!
And of course, no article about snow would be complete without showing you how to make your own snow if the temperature is below about -30 Fahrenheit (or -35 Celsius).