Snow on the ground is not so still By Tony Schumacher  When you're out skiing, snowshoeing or hiking, do
you assume that the snow on the ground all around you is in its final resting place? It just looks so peaceful, frozen and static. After all, you might not really notice it move for four months or so. Oh, but it's actually quite busy in that layer of snow. If you're a curious visitor to the snow covered landscape, maybe you've sensed the snow metamorphosis.
I learned as a kid that snow changes a lot. On our farm, the howling
winds would sweep huge amounts of snow from the fields. I still remember the tiny, nearly invisible crystals stinging my face and covering my clothes with white powder like sand. I was always amazed that the big 4 foot drifts that grew outside our barn could at times be so rock hard that my big dog and I could run over them. Other parts of the drifts would just collapse like marshmallows. Some drifts were like long skinny fingers, others like deep pillows, and yet others were like tall,
curved ocean waves.
As beautiful as snow drifts are, they can be a real nightmare for road crews in open parts of the country. Do you know that scientists have been doing research and computer modeling on snow drift behavior for many years? They run simulations in wind tunnels, really high tech stuff. As it turns out, snow fences and tree windbreaks are still some of the most important tools in controlling where the blowing snow will pile up.
How a Snowpack Changes
Freshly fallen snow starts out as a loose web of ice crystals and enormous volumes of air. Here's a simple yet vivid experiment from Mark Williams of the University of Colorado to help you grasp how much air is really in fresh snow. Imagine a family sized loaf of Wonder Bread as a hunk of fresh snow. Now squeeze it to its smallest size. How small do you think it goes? The answer is about a 2 inch cube. It's rather ironic that something that is mostly air is so hard to walk through,
especially compared to bare pavement.
Air can pass through a fresh snowpack with little resistance to and from the ground. Temperature differences between the ground and air above spur the air movement. So in a sense, the snowpack breathes. Time, however, changes that setup. The snowpack may evolve into what is called equitemperature snow. This is snow at its most stable level. The delicate crystals have matured into hardy granules. This would be more
common toward midwinter. Toward the spring, it turns into melt freeze snow, more commonly known as corn or spring snow. Where the snowpack meets the warmer ground, a weak and porous layer of snow may develop called sugar snow or depth hoar. This is the layer of snowpack that helps trigger avalanches in mountainous areas. It must be monitored religiously. In parts of the world where snow on the ground survives for more than a year, it can begin hardening into something
called firn. It's getting closer at this stage to becoming glacial ice.
Have you ever wondered why the foot of snow that falls in a storm shrinks in depth after a week or so, even if temperatures have been below freezing? The answer is that snow settles, becoming more tightly packed even if it doesn't melt. This is especially true of dry, powdery snow. In general, snow crystals lose their points and become more rounded. Thus they pack closer together. If you have a magnifying glass
at home, look at snow right after it falls, and then each day for a while to see how the crystals change shape. In general, the snowpack doesn't shrink because of losing water content. However, a small amount of the moisture in the snow does sublimate directly into water vapor in the air. This is especially true when it's sunny and cold and a dry wind is blowing over the snow.
Snowrollers
Have you ever seen hundreds of snowballs out in the middle of nowhere
in a field? You think to yourself, who could have possibly made all of those? Well, Mother Nature did. Naturally formed snowballs are called snowrollers and have been observed across North America and most parts of the world with snow. Molded by strong winds, these often hollow, jellyroll shaped snowballs range in size from golf balls to beer barrels. Hopefully these don't pop up on your ski or sled hill the day before you're supposed to hit the trails!
Some very specific conditions must be in place to get these beauties. First, the ground must have an icy, crusty snow, on which new falling snow cannot stick. The next ingredient is about an inch or so of loose, wet, sticky new snow. The optimum air temperature is around 28 to 34 F. Finally, a strong and gusty wind of about 25 mph or higher is needed to build the snowroller. The wind scoops chunks of snow out of the snow field or pushes giant snowflakes downwind. These "seeds" roll,
bounce and tumble like tumbleweeds. Additional snow then clings to the seed and the snowroller grows until it is too heavy for the wind to move. If you come upon some snowrollers be sure to see if they left behind a track. It might be kind of fun to see over how great a distance they developed. Apparently they sometimes have curved and erratic paths as well.
Snow Caves
The elements of gravity, wind, temperature, sunlight and moisture shape
and shear snow, but people do, too. In fact, sculpting a snow cave could save your life some day. Such was the case for famous race car driver Bobby Unser. He and a buddy were stranded in a fierce blizzard in 1996 in Colorado. The temperature at the time was 10 F and the winds were hitting 70 mph. They burrowed into a snowbank and spent several hours there. They gained enough energy and heat in that time to allow them to later walk another 12 hours and find a phone.
Snow is a rather efficient insulator. Experts estimate it can be some 30 to 40 degrees warmer in a well constructed snow cave (with people in it) than out in the open air. Here are some tips on snow cave construction.
1) Don't build a snow cave around a tree well (the depression in the snow that forms at the base of a tree). In fact, in really deep snow, you are better off avoiding tree wells completely. They might be full of powdery snow that can act like quicksand.
2) Look for a location that is out of the wind, preferably up against a steep slope or rock wall, where there is a good bank of compacted snow.
3) Find flat terrain and dig a trench 3 feet deep, 6 to 7 feet long and 2 or 3 feet wide. Cover it with whatever you can such as a canvas, a poncho or tree branches.
4) Don't dig with you hands unless you have no choice. Nearly any tool like a snowshoe, a ski, a cook pot, even a pair of ski goggles will be
more efficient and won't leave you soaked. Also try to avoid working so hard that you break into a heavy sweat.
5) Pack the snow as you dig. Keep the walls sloped and rounded, avoiding corners. A well constructed snow cave should be tubular with little extra space. Be sure it has plenty of ventilation and a tunnel entrance that is slightly lower than the floor. This will prevent cold air from pouring in and warm air from escaping.
6) Don't wait until you are in an emergency to build your first snow cave. Practice before that deep woods winter adventure!
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