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If a snow crystal formed in an ice cloud passes through a supercooled water cloud, full of antsy droplets, the tiny drops can freeze to the crystal. With a microscope, you can actually see the small beads of the water frozen to the crystal. This process, whereby the snow crystal picks up frozen droplets, is called riming. Riming can partially obscure the original snow crystal -- or it can be so extensive that you can no longer tell the original crystal. When that happens, when the original crystal is obscured, the resulting crystal is called graupel.
It's hard to beat stellars for their sheer beauty, but I'm also something of a graupel connoisseur. Often you can see graupel with the naked eye. It's the winter equivalent to hail, but it's not hail. It looks different. It's smaller than hail and it's soft and very white. At times, it appears very rounded like little beads of styrofoam but, more often, it has a lumpy appearance, which is why some skiers call it popcorn snow.
Periodically during the Gospel Hump trip, the snow falling was primarily graupel. Sometimes it would fall and bounce and bound down slopes like someone was pouring white buckshot over us. During warmer periods of the storm, it would pack together, hardening the surface of the snow so that it could nearly support our weight. On other forays into the backcountry, I've seen plentiful amounts of graupel turn the backcountry into one giant ski area with slopes that appear to have been packed by an army of grooming machines.
Graupel tends to hold its shape for long periods and, as I got the stove going in the kitchen we had fashioned in the snow, I could see a layer of it two or three inches below the surface. I poked it with my Swiss Army knife and the small little ball bearings of snow tumbled out. Its tenacity to hold its shape is almost legendary. One evening when I was in Salt Lake, it snowed one or two inches of graupel. In the morning I brushed it off my truck and started driving south. Some of the snow remained trapped underneath the windshield wipers. In Moab, some 380 miles of highway and Interstate driving to the south, the round little balls of graupel were still there.
Can you imagine that? Snow crystals so tough that they can withstand Interstate driving! Now that's tough. Speaking of tough, super cooled water clouds which create graupel are also responsible for the coating of rime found on trees and rocks at higher elevations. When super cooled water clouds blow across ridges, the water droplets freeze to the side of trees and rocks. You can tell the direction of the prevailing winds by which side of the tree the rime forms on. As the rime forms, it tends to grow into sculpted ribs, called rime feathers, pointing into the wind.
Rime is truly remarkable stuff. Mixed with snow, it can plaster the sides of mountains with deep, massive layers. Most particularly this occurs to the mountains of coastal ranges where the ocean provides a ready source of supercooled water clouds. On the other hand, just the opposite of those tough crystals of graupel, it can form small but delicate formations that crumble with the merest touch.
I came across one of these delicate formations after returning from an overnight trip to the backcountry around my hometown of Pocatello. The night before, fog settled in the valley where I had left my truck. The fog was a low-hanging super cooled water cloud. During the night, there was a slight movement of air from south to north. As the fog moved, small water droplets froze to my car antenna. Upon those droplets, more froze, and more upon those. Each succeeding droplet froze directly on top of the previous droplet, creating small rime spikes extending horizontally, some more than an inch long. I was astonished at its delicacy; just the slightest vibration would knock it apart. It was a magnificent sight - one of the most dramatic demonstrations of supercooled water clouds I've ever seen.
If you were to look carefully at the rime spikes on my car antenna -- or the rime feathers on trees at a high elevation -- you would notice that the color, even in the sun, is not particularly sparkly. In fact, the reflective quality of the crystal can be used to identify rime from precipitated snow. Rime is characteristically dull in color. In sunlight, you'll see minor glitters, but it doesn't have the bright sparkle of freshly fallen snow. That's because the water droplets freeze in a rounded shape and a rounded shape disperses light in all directions. Newly fallen crystals, however, have flat sides, which, like little mirrors, concentrate light in batches, giving it a brilliant, flashing effect.
Speaking of brilliant crystals, there is one crystal that's even more bright and radiant than a stellar: a surface hoar crystal. Admittedly, its name isn't on the glamorous side, but, nonetheless, surface hoar is a crystal blessed with beauty. It forms during cold, clear nights when water vapor in the air sublimates directly on top of the snow surface. Less frequently, it can also form on pine needles and branches of trees and bushes. Surface hoar is, in essence, the ice equivalent to dew.
The sparkle from the surface hoar crystal comes from large flat faces that form during the sublimation process. The flat crystalline faces of surface hoar are often much larger than that of newly fallen snow; so large that you can often see them with the naked eye. With larger, mirror-like faces, surface hoar crystals reflect more light than other crystals. If you see a field of snow glittering and sparkling after a clear night, you'll invariably find that it's caused by surface hoar crystals.
It must have been the surface hoar crystals on my Thanksgiving trip that reminded me of my conversation with Harvey. I had been skiing near a stream. It was a bright morning and the surface of the snow was glittering and sparkling. I knew that the last few days of clear nights had been responsible and there, in a cool depression, I found a magnificent collection of surface hoar crystals. With the nearby open stream providing a ready supply of water vapor, the crystals had grown unimaginably large, reaching across millimeters in size.
I stopped, momentarily stunned. Nothing made by man could match their beauty. It was the same reaction that I had when I found the stellar crystal on my ski pole that splendid morning in the Gospel Hump. I was completely overtaken. Keats must have been gazing at a snow crystal when he said "a thing of beauty is a joy forever." Beauty and joy. The sweepings of heaven's floor are truly the work of a divine force. Yes, I have to admit that Harvey had it right. A skier's passion for his sport is found in something as simple, and divine, as snow.
Ron Watters couldn’t be happier when
it’s cold and snowy. He is the author of eight books including Winter Tales
and Trails and Ski Camping. Working to recognize good outdoor writing by
others, he is the founder and chairman of the national Outdoor Book Awards,
the largest book award program in the outdoor world. He and his wife, and
cross country ski companion, Kathy
live in Pocatello, Idaho. |
