Identical Snowflakes? Scientist Ruins Winter For Everyone | Deep Look

By Joshua Cassidy, KQED Science
APRIL 11, 2017
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California’s historic drought is finally over, thanks largely to a relentless parade of powerful storms that have brought the Sierra Nevada snowpack to the highest level in six years, not to mention guaranteed skiing into June. All that snow spurs an age-old question — is every snowflake really unique?

“It’s one of these questions that’s been around forever,” said Ken Libbrecht, a professor of physics at the California Institute of Technology in Pasadena. “I think we all learn it in elementary school, the old saying that no two snowflakes are alike.”
Libbrecht spends most of his time thinking about things like black holes and gravitational waves. But for years the North Dakota native has also delved into the mystery of how snowflakes grow into such a dizzying variety of shapes, all based on the same ingredient — water.

So is it possible to find two snowflakes that are exactly the same?

They can be made in a lab. But when it comes to nature, it’s possible, but you’re not likely to find two that match exactly, Libbrecht said.

“It goes back to how they’re made in the clouds,” he said.

Snow crystals form when humid air is cooled to the point that molecules of water vapor start sticking to each other.

A hexagonal ring forms the base structure of the snow crystal
A hexagonal ring forms the base structure of the snow crystal (Teodros Hailye/KQED)
Water molecules are each made out of one oxygen and two hydrogen atoms. Good ‘ol H2O!

The molecules fit together in the shape of a hexagonal ring with bonds forming between hydrogen of one molecule and the oxygen of another molecule.

As more molecules join the growing crystal, they fit into that repeating shape, which is why you tend to find snowflakes with six arms.

In a refrigerated chamber at his lab, Libbrecht built a device that mimics the conditions found in the clouds.

In the bottom of the chamber, Libbrecht keeps a container of hot water. As the water evaporates, it fills the chamber with water vapor. When the air is as humid as it can get, Libbrecht triggers a puff of condensed air that drops the temperature in the chamber suddenly.

That blast of cold air causes the water molecules to stick to each other, forming tiny ice crystals about the same diameter as a human hair.

In the clouds, crystals usually start forming around a tiny microscopic dust particle. But if the water vapor is cooled quickly enough the crystals can form spontaneously from water molecules alone.

“At this point they they’re just little tiny hexagons,” says Libbrecht. “We call them seed crystals.”

After a few moments of floating around the chamber, the tiny crystals grow big and heavy enough to fall. Libbrecht catches them on a small refrigerated slide.

He adjusts the humidity and temperature and, using a microscope, watches the crystals grow.

Ken Libbrecht uses time-lapse photography to document the snow crystals he grows in his lab.
Ken Libbrecht uses time-lapse photography to document the snow crystals he grows in his lab. (Ken Libbrecht, CalTech)
“After a little practice you can make things that are faceted or branched on demand,” he said. “I can make nice plates or turn the knob and make some branches or make side branches. You can kind of design snow crystals.”

Ice crystals that experience the same conditions grow in similar patterns
Ice crystals that experience the same conditions grow in similar patterns (Ken Libbrecht, CalTech)
Libbrecht found that when he grew multiple crystals on the same plate the crystals experienced the same conditions at the same time. The result: twins!

“I like to call them identical twin snowflakes because, like identical twin people, they’re not absolutely exactly the same but they’re very, very similar,” said Libbrecht.
Twin snow crystals grown under the same controlled conditions
Twin snow crystals grown under the same controlled conditions (Ken Libbrecht/CalTech)
In nature, snowflakes don’t travel together. Instead, each takes its own path through the clouds, experiencing different conditions at different times. Since each crystal takes a different path, they each turn out slightly differently.

And studying how ice crystals grow isn’t just a way to make designer snowflakes. It’s a way to understand and control the way crystals grow.

And that’s important because we use crystals in electric devices ranging from coffee makers to jumbo jets.

“Even with very important things like the semiconductors in computers, we don’t really understand the growth of crystals very well,” said Libbrecht.

“There are recipes to make those silicon wafers that form the backbone of those microchips, but they mostly came about just by trial and error.”

Ken Libbrecht’s online guide to snowflakes, snow crystals and other ice phenomena: http://snowcrystals.com/

When the road salt seeps, sometimes the manhole covers fly

SETH BORENSTEIN, ASSOCIATED PRESS

WASHINGTON (AP) — Call it another form of March Madness: Not flying basketballs, but flying manhole covers.

Scientific literature traces manhole explosions back nearly a century, but a series of such incidents in Indianapolis, host of the NCAA basketball championships, has authorities looking for a quick solution.

Good luck with that.

A combination of power system design, winter road salt, older electrical cable insulation and basic chemistry have triggered underground explosions in older downtowns, launching 350-pound manhole covers high in the air. One Georgia Tech engineering professor calculated the explosions could have the force of three sticks of dynamite.

“These things have been known to be launched 10 stories; they have found a manhole cover on top of a building in a certain downtown city,” said Daniel O’Neill, who advises several utilities on the problem. “They are dangerous things. There are hundreds of these things happening every year.”

The nonprofit Electric Power Research Institute’s lab in Lenox, Massachusetts, has spent the last 25 years setting off what officials there call “manhole events.” It’s not for fun. Engineers are trying to find a way to keep manhole covers from flying.

“We’re disappointed to say we’ve not yet solved the problem,” said Matt Olearczyk, manager of distribution research for EPRI. He said, his team will keep at the problem “or we’re going to die trying to fix it.”

The EPRI team has come up with partial solutions, such as latching manhole covers to the ground with a hook-and-piston system. When there’s an explosion, those covers lift a few inches to let off some pressure, but not so much as to let in oxygen to stoke the explosion.

Experts do know how and why these explosions happen amid thousands of miles of tightly bundled electrical cables.

It starts with the way electrical power is distributed in older downtowns underground. Cables are linked so that if one fails, others take over, O’Neill said.

Cable insulation can fray or kink due to age, wear and tear, high power loads during the summer and corrosive road salt. That exposes wiring, which can spark and smolder. Especially when the insulation is older and consists of an oily paper, that releases gases, including hydrogen, methane, acetylene, carbon monoxide and ethylene, O’Neill and Olearczyk said.

Then, salty or dirty water gives the electricity a path to the ground and the spark to set off explosions, O’Neill said.

That’s why O’Neill and Olearczyk say they see more blasts events during the winter and in more northerly cities. The salt is a key ingredient. Consolidated Edison once compared manhole explosions to the streets where road salt was used and found a good correlation, O’Neill said.

The expensive process of replacing the cables with plastic insulated modern cables works well, Olearczyk said.

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Online:

EPRI You Tube video of manhole cover explosions: https://www.youtube.com/watch?v=oxTIoWu__-A

So it’s that cold time of year when we should expect a bit of travel disruption and shouldn’t leave the house without hat, gloves and scarves. And as it’s the first time I’ve had to scrape ice off my car in the morning I thought it was about time I turned the snow machine on and let chemstuff.co.uk be a little festive!

It’s also a good excuse to look at the chemistry of snow

Snow is of course formed in clouds where the temperature is less that 0oC (or 273K) this means that the water vapour present will start to crystallise and form a snowflake. Crystals are structures with a very high level of order and we can see this when we look at a snowflake in a lot of detail. Whilst they are not always absolutely symmetrical, snowflakes do follow similar patterns. This is because a snowflake’s shape reflects the internal order of the water molecules. Water molecules in the solid state, such as in ice and snow, form weak bonds (called hydrogen bonds) with one another. These ordered arrangements result in the symmetrical, hexagonal shape of the snowflake. During crystallization, the water molecules align themselves to maximize attractive forces and minimize repulsive forces. Consequently, water molecules arrange themselves in predetermined spaces and in a specific arrangement. Water molecules simply arrange themselves to fit the spaces and maintain symmetry.

As we know water and ice often appear clear and colourless but snow appears to be white, this is because snowflakes have so many surfaces, owing to its crystal structure, that reflect light and scatters most of the rays that hit it.

So whether we have a white christmas this year, or not. If you see a snowflake, why not start to appreciate some of the chemistry behind it!