Mysteries of Snow Revealed
ANDREA SEABROOK, host:
You've shoveled it. You packed it into balls. And if you're in Daytona Beach, Florida, this week, you even got a tiny taste of it. But have you ever look really closely at snow? That's this week's Science Out of the Box.
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SEABROOK: Discover magazine ran a list just a few weeks ago of 20 facts you didn't know about snow. For instance, snow is a mineral like diamonds or salt.
To dig a little deeper into this drift, we called up Dr. Matthew Sturm. He's a senior research scientist and snow expert with the Army's Cold Regions Research Laboratory. That's in Fairbanks, Alaska.
How are you, Dr. Sturm?
Dr. MATTHEW STURM (Snow Expert; Senior Research Scientist, U.S. Army Cold Regions Research Laboratory): I'm fine.
SEABROOK: Good. How cold is it up there today?
Dr. STURM: It's about 10 degrees below zero Fahrenheit.
SEABROOK: Eek. So tell me, Dr. Sturm, how can snow be a mineral?
Dr. STURM: Basically, we're used to water as being a liquid that comes out of the tap. But once the temperature drops below 32 degrees and, of course, water is a solid, and just like any other mineral, it has a molecular structure and properties. If you took a hunk of ice, it feels a lot like a rock, acts a lot like a rock in many ways, has material properties and it is effectively a mineral.
SEABROOK: Now, I also read in this list on Discover magazine that each snowflake has a tiny mote of dust at its center, something it can be volcanic ash, it can space dust.
Dr. STURM: What happens is where there is a cloud in which snowflakes are forming, water doesn't like to freeze. It's very hard for very minute sort of single molecule level amounts of water to freeze and so that the water can actually super cool. And under some conditions, water can stay liquid down to about minus 40 degrees. But if we introduce a piece of dust, a piece of sea salt that's in the atmosphere, that helps the water to freeze. And so what happens is where there are these little moats in the cloud, the water begins to freeze more rapidly. And those become the little hearts or insipient pieces of the snowflakes.
SEABROOK: Is it true that really there are no two snowflakes that are alike if you look at them carefully? Or is it just because there is no two of anything that are just…
Dr. STURM: There are no two of anything that are alike. That would be the basic thing. The second thing is that at least those snowflakes that are fairly ornate, these won't even be visually alike under a microscope. The only hope we find for finding two snowflakes that are absolutely alike at least visually would be the simpler forms, which would be simple hexagonal plates with no arms or branches. If we could search all the snowflakes on Earth in the simpler forms, we might someday find, too, that for all intents and purposes would look close enough to be the same.
SEABROOK: So there's - there are - how many basic patterns of snowflakes are there?
Dr. STURM: There's prisms, low squat prisms. There're plates - always hexagonal, everything is on a hexagonal base. There're dendrites, which what everyone thinks of, they're the Christmas decoration snowflake, kind of a branching thing, capped columns, needles and bullets. When all is said and done, we probably can come up with 30 or 40 general types but probably about six basic forms.
SEABROOK: Dr. Sturm, I understand that you're an expert on what happens to snowflakes once they hit the ground.
Dr. STURM: Yes. Strangely, the world of the cloud where the snowflake forms is a very dynamic world. It's very moist. When they finally fall to the ground, they've been immersed in a new world, totally different temperature and vapor pressure. In other words, how moist it is.
And so they immediately start to change. You can see this actually with a hand lens. If you look the day after a snow fall, you won't see the beautiful pristine snowflakes that fell the day before. They're already breaking up and rounding over. They can change in one of two ways. They can either become very rounded type snow crystals now in the snow pack, or very angular sort of ornate hollow crystals, which is we called kinetic or temperature-gradient forms.
SEABROOK: Any kinds that's best for snowballs?
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Dr. STURM: Typically the rounded ones, and the snow needs to be warm because the thing that makes a good snowball is that the snow sticks together.
SEABROOK: Dr. Matthew Sturm of the Army's Cold Regions Research Lab. Thank you so much for talking to us.
Dr. STURM: Thank you for having me on.
SEABROOK: And Dr. Sturm, we have a little parting gift for playing along with us today. Here's a little story about snow from Stanley McNeal(ph) in Cape Breton, Nova Scotia.
Mr. STANLEY McNEAL: These two old guys, it was in the Gaelic days, I guess. And they were in this old general store over in Scottsville. And these two old fellows were in and they were busy talking Gaelic. And all of a sudden, it started to get rough outside, snowing, blowing, first snow of the year, you know? And one old fellow said in Gaelic, well, I hope to have - we won't get the snow we had last winter. And the other old fellow answered him, there's no way we'll get that. That's melted.
SEABROOK: That's melted.
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Dr. STURM: That's very good.
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