Curious Nature: Snowflake science
Vail, CO, Colorado
While we await belated snow to cover the Vail Valley, thinking about snow may be the next best thing to having it. That could have been the case in Ft. Keogh, Mont., in 1887, when folks discovered a snowflake, reputedly a record-breaker, that was 15 inches wide and 8 inches thick!
That gargantuan snowflake could have been a single snow crystal of ice or, more likely, a few snow crystals stuck together that form puffier balls, or snowflakes. Snowflake is a general term that refers to a single crystal or a few stuck together.
If you know a student in the valley who has participated in the Walking Mountains Science Center’s third-grade snow science field program, ask that student to refresh what you remember about snow crystal formation. You will be reminded that it all begins with water vapor. Evaporation from oceans, lakes, rivers, from plant transpiration and even from our exhaling puts water vapor into the air. When parcels of air cool down, the water vapor they hold condenses. When this happens near the ground, the water may condense as dew on the ground. High above ground, water vapor condenses onto dust particles in the air and forms tiny droplets containing at least one dust particle. A cloud is a huge collection of these water droplets suspended in the air.
Ingredients that need to be present to form snow crystals are a nucleating particle (dust or dirt), water vapor (water molecules in the air), and freezing temperatures. Just as with raindrops, snow crystals begin as droplets of water that condense on specks of dust. The droplets freeze and more droplets condense and freeze on them (remember how ice will stick to your tongue?). If the cloud temperature stays below freezing, enough droplets will freeze and collect to form snow crystals (snowflakes). When the snowflakes get heavy enough, they descend to earth.
There are six main types of snow crystals: needles, columns, stars, plates, columns capped with plates and dendrites. Slender and columnar needles tend to look like white hair and form a dense snowpack that can produce an avalanche under the right conditions. Columns are produced when the air is drier. They are generally smaller and have a higher density than star crystals. Star crystals are formed at temperatures near negative 15 degrees Celsius and are among the most common type of snowflakes. Plates are star crystals that are essentially moisture-starved. They form when there isn’t enough water vapor available to form the delicate arms of a classic star. Capped columns form when the crystals pass through different temperature and moisture zones on the journey to the ground. The columns form first, usually at higher and drier regions of a cloud, and combine with star crystals as they fall through lower and wetter cloud elevations. Dendrites are three-dimensional star crystals with arms growing on more than a single plane and connect randomly to a central structure.
Because of the way water molecules fit together, most snowflakes are six-sided, though some can have as few as three and as many as 12 sides. Higher moisture density and barometric pressure can produce snow crystals with more sides. Six-sided hexagonal crystals are shaped in high clouds. Needles or flat six-sided crystals are shaped in middle-height clouds and a wide variety of six-sided shapes are formed in low clouds. In very cold conditions, we experience fine and powdery snow, which is comprised of snow crystals of simple design, usually needle or rod shaped. In warmer conditions, snow crystals become much larger and more complex in design such as a star. This is why snow crystals in Fairbanks may look different that those in warmer climates.
Although all snow crystals may not be the same on all sides (uneven temperatures and presence of dirt may cause lop-sidedness), most are symmetrical and intricate. Water molecules simply arrange themselves to fit the spaces and maintain symmetry, resulting in symmetrical shape.
Although we know snow is on its way, for those of you who may doubt, or just want to do a fun, easy experiment with youngsters near you, try preserving Vail Valley snowflakes:
What you will need: Piece of glass, hairspray (aerosol, not pump), snow.
Freeze a piece of glass and the hairspray before the next snowfall. (Both may be stored in the freezer until you need them.) When you’re ready to collect snowflakes, spray your chilled glass with the chilled hairspray and go outside and let some snowflakes settle on the glass. When you have enough flakes bring the glass indoors and allow it to thaw at room temperature for about 15 minutes. If you have a magnifying glass, examine your find more closely and see if you can distinguish shape and size of your Colorado snowflakes.
Natalia Hanks is senior development officer at Walking Mountains Science Center and enjoys spending time exploring the winter woods on snowshoes.