Make It Snow!
by Valerie S. Biebuyck
What's your favorite kind of snow? Fluffy, dry, white powder? Or do you like the grayish, wet, slushy kind?
If you are a skier or snowboarder, you want enough snow of just the right type for a perfect run. Winter resorts can manufacture prime snow with machines and snow-making experts. (It's a lot more expensive than the kind Mother Nature makes, costing as much as $4 million per season!)
What are the ingredients for a great batch of snow? Just water and air. But you can't make snow simply by spraying water into cold air. Water freezes when the temperature is 0 degrees C (32 degrees F)—sometimes. If the air contains a lot of moisture (called humidity), such as on a very foggy day, the temperature must be lower than 0 degrees C (32 degrees F) for freezing to occur. Temperature adjusted for humidity is called the “wet bulb” temperature.
A droplet of water needs even more than cold temperatures before it will turn into a snowflake. It also needs a nucleator—a tiny particle, such as a speck of dust or ice, around which to form a crystal.
If the air is very cold and dry, water vapor will crystallize almost instantly. If conditions are less than perfect, more time is required to form a snowflake.
“We call this the flake's hang time,” explains Dave Lacombe, head of snowmaking at the Killington resort in central Vermont.
How do he and his staff actually make snow?
Air is compressed (reduced in volume) in machines at Killington's maintenance facility. The compression process makes the air very hot—about 115 degrees C (240 degrees F). The hot air is sent through other equipment that cools it to about 4 degrees C (40 degrees F) and takes out moisture, because snow is easier to make with dry air.
Meanwhile, water is drawn from a source such as a local reservoir. To cover an acre with a foot of snow requires 180,000 gallons—that's the equivalent of two dozen tractor-trailer trucks full of water.
A network of pipes brings the air and water to hydrants located next to the slopes.
Hoses connect to the hydrants at one end and send the air and water to a snow gun at the other end. The compressed air expands when it is released and breaks down the water. With a roar that sounds like a freight train is barreling up the mountain, the snow gun blows this out as mist, and the mist falls to the ground as snow.
“We used to check the quality of the snow we made on our coat sleeves,” says Lacombe. “We would let it collect there and decide if it was too wet, too dry, or just right.” About 100 people work in Killington's snowmaking department, and each could have a different opinion about the quality of the snow.
All that is changed now, thanks to a computer-filled control room that is staffed 24-hours-a-day, seven-days-a-week, during snowmaking season.
The control room's computers monitor all the factors that must be considered when making snow for a specific area, including temperature, humidity, steepness of each hill, elevation at the snow gun's location, and how many people will ski there. The staffer in the control room looks at the computer screens, determines the correct settings for each snow gun, and radios this information back to the snowmakers on the trails. The information ensures that the right amounts of air and water mix and spray so that perfect snow is made everywhere. “When you can barely make a snowball stick together” is how Lacombe describes the type of snow he wants.
“Some people manufacture automobiles,” he says. “I manufacture snow!”
- What is the chemical formula for the compound that is snow?
[anno: The chemical formula for snow is H2O.]
- What else is needed for this compound to form snow?
[anno: The water needs a nucleator, or a tiny speck of dust or ice.]
- Think of another compound whose state is altered to produce another product. What is the compound? What is its chemical formula? How is the compound used in its different states?
[anno: Answers will vary.]