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The Language Of Snow

Didn't know it could talk, did you? Once you learn the lingo, snow speaks volumes about the winter landscape.

By Jamie Bastedo, February 2000

Stellar Crystal

I live way up north in a land of snowy superlatives. Our snow is so dry you can wander through it for hours without getting soaked. It's so fluffy you can dive into a snowbank as easily as falling into a hammock. It's so cold you can build a rock-hard snow shelter in no time. And since the snowpack in these parts lasts a long time- as in any northern or alpine environment-it gets a chance to ripen fully over the winter, creating a fascinating kaleidoscope of layers, shapes, and textures that you can learn to read like a book.

To unlock the secrets of snow, you don't have to live in a Northwest Territories log cabin or an alpine hut near treeline. Whether your snow lasts 6 days or 6 months of the year, you can boost the fun, comfort, traveling ease, and safety of your next winter trek by giving it a closer look.

Signs From Above

So where do we start? How about 10 miles up, where the story begins. Floating around up there in a thickening veil of clouds might be little bits of volcanic ash from the Philippines, or maybe pollen from a California redwood tree, or dust from a Siberian mining road. Cold water vapor gloms onto these little specks, triggering an amazing chain reaction of molecular growth. As a result, snow crystals are born. One by one, other molecules of water vapor are magnetically pulled toward these tiny seed crystals.

At some magic moment, the growing crystals give way to gravity and start free-falling to earth at 2 to 3 miles per hour. Exactly what drops from the sky to your fleece-covered head depends on atmospheric conditions, such as humidity, temperature, and wind.

If it's moderately cold (24 to -14F), classic stellar crystals may fall. Nothing adds that wonderful winter hush to the forest like a fresh dump of stellar crystals. Their complex filigree structures trap sound waves in billions of tiny air pockets, making stellar crystals nature's perfect sound absorbers. They also trap heat better than any other crystal, providing the highest insulation value for cavelike emergency shelters dug into a snowbank.

Milder atmospheric conditions (32 to -9F) often result in platelike hexagonal crystals. Since the slightest turbulence will destroy both stellar crystals and hexagonal plates, when you see either coming down, it's a good sign that winds are relatively calm above your head. Expect stable weather for at least the next few hours.

Cold (below -12F), dry skies may produce pencil-shaped columns, bullets, or needles. As these crystals form in the upper atmosphere, they often create a wide, broken halo of orange and green light around the sun, better known as a sundog. If you see a sundog, expect a snowfall very soon because there's no surer sign. You'll also notice colder temperatures very soon, even if it's relatively mild. In avalanche country, beware of needle-shaped crystals since, when overlain with heavy snow, they offer all the resistance of ball bearings.

Irregular crystals or lumpy grains of ice may fall from mild, wet clouds stirred up by inner turbulence. Some may pass through a wet, sticky cloud and get all gummed up with rime. They may crash into other kinds of crystals and get stuck together in bizarre combinations. Or they may get blown to bits by high winds somewhere along their journey. Although your trail may be calm and dry, all of these kinds of crystals tell you that the upper atmosphere is in turmoil. The crazier the mix of crystals coming down, the more unstable it is overhead. This turmoil could eventually translate into a foot of heavy snow, a horizontal barrage of ice crystals, or a hail storm, or it all could blow over. In any case, expect the unexpected and make a secure camp soon. Then dig in and watch the show.

Down On The Ground

Fresh snow on the ground, in its virgin, undisturbed state, is nothing more than a blanket of air and ice, with most of it being just air (up to 97 percent). Its volume is generally 10 times that of water; 10 buckets of snow to 1 bucket of water. This ratio can vary from 6:1 for wet snow to 30:1 for dry snow. Generally, drier, fluffier snow gives you the best loft for snowshoeing and backcountry skiing. For animal tracking, old, moist snow between 20 and 30F brings out the best in winter's snowy sketch pad.

As it "ripens," snow can undergo a profound metamorphosis in structure, density, and moisture from a variety of causes. High winds can increase the density of surface layers a hundredfold, creating a rock-hard platform you can walk across without sinking. Strong sunlight at temperatures just below freezing can turn surface crystals into spheres and fill some air spaces with water. This makes for lightning-fast skiing if you use the right wax. Pressure from heavy surface snows squeezes air out of the snowpack below, creating dense, slablike middle layers-the raw material for most avalanches.

Down at the very bottom of the snowpack, heat from Earth can literally vaporize old snow. This rising vapor, in turn, recrystallizes as depth hoar or "pukak." In mountainous regions, this layer of loosely spaced crystals is called "avalanche snow" since the sudden collapse of its delicate architecture often detonates an explosion of snow downslope.

With or without the help of wind, heat, or pressure, all snow crystals are energetically unstable and, as if too beautiful to last, they begin to self-destruct soon after they land. Within several weeks, most collapse into undifferentiated blobs of ice that ultimately perish in the warmth of spring.

So, learn to read the secret language of snow while it lasts. Embrace its signs and stories and it will be a good friend to you on the trail.

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