"Snow Day" (February 2000)
A poem by Billy Collins. (With an audio recording by the author)
In the language of the Irish, scholars say, there are a dozen words for "peat." In the language of the Arabs, we've been told, there are many words for "sand." I, for my part, grew up speaking a language in which there are perhaps a hundred terms for snow, and I am not a native of Igloolik.
I learned some of those terms from a man named Mark Williams, a former ski-lodge operator who is a geographer at the University of Colorado and a specialist in the properties of snow. "If you're talking about snow crystals in the atmosphere," he told me recently, "well, then, there are scores of terms. There are needles and sheaths and columns. There are pyramids. Cups. Bullets. Plates. Scrolls. Branches. Dendritic crystals. Stellar crystals." And those are just some of the basic forms. Snow crystals also come in combinations. Stellar crystals with plates. Dendritic crystals with branches. Hollow bullets. Bullets with dendrites. Plates with scrolls. Plates with spatial dendrites. Rimed particles. Rimed needle crystals. Lump graupels.
Graupel-like snow with nonrimed extensions. Some of the names of snow crystals (branches, needles, bullets) are appropriately suggestive: in high wind, snow crystals can be as abrasive as sand.
After snow has fallen, the name for it picks up additional qualifiers as it begins to settle or drift, as heat and cold and wind and moisture and the snow's own weight begin to make their influence felt. Freshly fallen snow starts out as what Williams calls an "ice skeleton"—a loose scaffolding of crystals amid an enormous volume of air. To give his students an idea of the ratio of snow to air in a fresh snowfall, Williams has them compress a family-sized loaf of Wonder Bread to its smallest possible size. (It can be reduced to a two-inch cube.)
In fresh snow air can pass with little obstruction from the atmosphere through the snowpack to the ground: given life by differences in the temperature gradient, the snowpack breathes. But time changes that. The snow may metamorphose into what is called equitemperature, or ET, snow. This is snow at its most stable, the delicate crystals having matured into hardy granules in a snowpack of homogeneous temperature. It may turn into melt-freeze snow, more commonly known as corn snow or spring snow. Where the snowpack meets the warmer ground, there may form a weak and porous stratum of what is known as kinetic snow or sugar snow or depth hoar—by whatever name, the mother of avalanches. If the snow survives for more than a year, it may begin hardening into something called firn, which is a step on the way to becoming glacial ice.
I met Mark Williams and a good many of his colleagues at last year's meeting of an organization called the Western Snow Conference, a gathering that occurs every spring when the season's snows are more or less over and the period of snowmelt is well under way. Collectively, the people who attend the Snow Conference meeting—hydrologists,geographers, meteorologists, biologists, chemists, agronomists, utility-company officials, state and federal government officials, representatives of Indian tribes—are known in the gray language of official reports as the "snow-resource community." They are interested in every aspect of the hydrologic cycle of snow, from the formation of the first crystals to the accumulation of snowpack to the onset of snowmelt to the release of the last drops of runoff into the Pacific Ocean or the Gulf of Mexico. They are interested in avalanche theory, in the seeding of clouds with silver iodide to induce snowstorms, in how to add certain bacteria to water so that ski resorts can make snow at higher temperatures. For decades they have been interested above all in the following questions, which turn out to be complicated ones: How much snow has fallen in the western United States in a particular winter? How much water will it turn into? Where will that water go?
Snow is a commodity we usually remember for either the pleasures it offers or the disruptions it causes. We call upon snow, too, for its utility as metaphor: symbol of purity, uniformity, isolation, protection, transience. We tend not to think about snow as the crucial variable upon which urban life and agricultural life in much of the world, particularly the United States—and especially the American West—happen to depend. Indeed, snow is largely missing, as the historian Bernard Mergen observes in a forthcoming study, from recent histories of water policy, in which one would expect it to play a highly visible role. And yet snow, hardened into glaciers, covers 10 percent of the planet's land area. Fresh snow falls each year on nearly one square mile of dry land out of every four; in the Northern Hemisphere the figure is one square mile out of two. Worldwide, at least a third of all the water used for irrigation comes from snow. In the western United States the figure is about 75 percent.
What makes snow important is not only its volume but also its relative dependability. Much of the West is in a state of drought or near-drought, with snowfall having been below normal in seven of the past eight years. In general, though, snow can be far more reliably counted upon to fall in substantial amounts in the mountains during wintertime than rain can be counted upon to fall in the spring and summertime. And snowmelt flows onto the scene at nearly the most useful time of year, having been stored at high altitudes until the weather warms and the demands of agriculture begin to make themselves felt. It is snow that powers the great rivers of the West—the Colorado, the Rio Grande, the Columbia, the Missouri—on their long journeys through sometimes parched or semi-arid terrain, ribbons of brown and silver that at times enverdure entire basins, at times support the merest Nilotic fringe of green. How much water does the West's winter snow turn into? The snowmelt that finds its way into the Columbia River alone in an average year comes to 26 trillion gallons, which is 81 million acre-feet—enough to cover all of Kansas in knee-deep water, or to raise Lake Michigan by almost six feet.
The Western Snow Conference typically holds its meetings someplace in sight of the mountains, where in springtime one can have a ready glimpse of snow. I was invited to attend the sixty-second annual conference, in Santa Fe, New Mexico, by a friend who is a hydrologist in California. I'm not sure why the prospect held such appeal, unless it is simply that snow is my favorite kind of weather. The first article I ever published, on a small printing press given to me on a snowy Christmas when I was six or seven, consisted of what was meant to be a report on snow depth in inches, and was distributed to neighbors. It read, in its entirety: "The snow 15." Snow seems to come into my life in the form of memorable coincidences. The Horatian ode "Diffugere nives . . . ," about the melting of snow in springtime, was the first piece of Latin verse I ever translated completely on my own (it appeared on a test), an achievement that occurred at roughly the same time as my first reading of James Joyce's short story "The Dead," whose most famous words, in the haunting conclusion, are "snow was general all over Ireland." Snow makes me feel as snug as a vole. There were ten major snowstorms in my region of New England last winter, and I contentedly wrote a check to the snowplow man each time.
The focus of the Western Snow Conference's Santa Fe meeting was "Climate Change Effects on Snowmelt Water Supply," a big and important subject, but that was by no means the whole agenda. "Northern Latitude Snow Pillow Installation Procedures." "Snow Accumulation and Ablation Under Fire-altered Lodgepole Pine Forest Canopies." "Snow Chemistry and Physics of the Mogollon Rim in Arizona." There was something here, I realized, for even the most jaded of tastes. At lectures and in associated readings I picked up such arcane pieces of information as that a two-foot square of snow ten inches deep contains about a million snowflakes, and that if the potential precipitation in the earth's atmosphere at any given moment fell all at once, it would cover the entire surface of the planet to a depth of one inch. I was pleased to observe that, as with any professional group that has reached a certain level of maturity, the membership of the Western Snow Conference includes people who display what might be called occupational anthroponymy—that is, whose names resonate with their line of work. I ran into a Phyllis Snow and a Neil Berg, and discovered that a type of diagram used to show inflows and outflows from reservoirs was devised by a man named Rippl.
During my days at the Snow Conference meeting I also grew to admire the pluck and ingenuity of those charged with keeping track of our snow. It has been nearly ninety years since James E. Church fashioned his first snow tubes and began taking wintertime measurements in the mountains of Nevada. Some things haven't changed very much since that time, and some have changed profoundly.
''There is no material of engineering significance that displays the bewildering complexities of snow." I came across that matter-of-fact statement in the Handbook of Snow, an invaluable if glacially paced compendium edited by the eminent Canadian hydrologists D. M. Gray and D. H. Male. The formation of snow begins when water vapor or a supercooled droplet of water forms an ice crystal, almost always hexagonal in shape, around a nucleus consisting of one of the thousands of minute aerosol particles to be found in each cubic centimeter of the lower atmosphere—clay silicate, perhaps, or bits of volcanic ash, or material of extraterrestrial origin. From that moment on, the life of an ice crystal can be played out in various ways. The crystal may fall to the ground in its original form, as it does in the intensely cold regions of the Arctic and Antarctic. Or, more frequently, the ice crystal may grow into a snow crystal, gaining substance by means of sublimation—water vapor turning directly into ice, without passing through a liquid stage. Its shape, or "habit," will be determined mostly by temperature and the amount of water vapor in the air. As snow crystals descend, they may meet up with one another, forming aggregations. We know these as snowflakes. Or a snow crystal may in its descent encounter supercooled water droplets. Riming can then occur, as the droplets freeze immediately upon contact with a solid body. If the riming is substantial, the crystal may become graupel, or snow pellets.
All this activity has a powerful cleansing effect on the atmosphere—"washout" and "snowout," as two of the associated processes are called. A heavy snowstorm gathers particulate matter to itself and drags it to the ground, thereby preserving, until the snow melts, a sample of the atmospheric chemistry prevailing when that particular snowstorm began—a sample that speaks of climatic conditions generally and may speak more specifically of pollution. In the remote interior of Greenland, where the deposits of snowstorms do not disappear, such records go back a long way. A few years ago researchers at the Greenland Icecore Project drilled a hole through the Greenland icecap all the way to bedrock and extracted a core of ice that, if reassembled, would be close to two miles long. The ice at the bottom of the borehole is believed to have been formed from snow that fell some 200,000 years ago.
The symmetry of ice crystals was commented upon by the Chinese in the second century B.C. Europeans had recorded the same observation at least by the Middle Ages. The intellectual pedigree of snow scholarship in the West is distinguished. The Dominican scholastic Albertus Magnus wrote about snow crystals in the thirteenth century. At the beginning of the seventeenth century the same subject beguiled Johannes Kepler. "There must be some definite cause," he wrote in 1609, shortly after making the discovery that the planets travel not in circles but in ellipses, "why, whenever snow begins to fall, its initial formation invariably displays the shape of a six-cornered starlet. For if it happens by chance, why do they not fall just as well with five corners or with seven?" In his pamphlet Kepler drew parallels with honeycombs and the pattern of seeds inside pomegranates, but was unable to explain the flakes' hexagonal form. Somewhat later Rene Descartes discerned that branches sprout off each side of the stems of hexagonal snowflakes at an angle of 60 degrees, with an angle of 120 degrees thus separating the branches themselves. The process is complex, but the hexagonal shape of snowflakes essentially reflects the underlying atomic structure of water. One suspects that even the skeptic Descartes would have offered up a Te Deum had he known that the two hydrogen atoms in a molecule of water branch off the oxygen atom with about 120 degrees of separation.
For all the scientific awareness of the symmetrical character of snow crystals, the ubiquity of their popular image—the one we see in children's paper cutouts and on bags of ice and signs for motels that have air-conditioning—is a relatively recent phenomenon. What snowflakes actually looked like was not widely known until the middle of the nineteenth century, when the book Cloud Crystals, with sketches by "A Lady," was published in the United States. The lady had caught snowflakes on a black surface and then observed them with a magnifying glass. In 1885 Wilson Alwyn ("Snowflake") Bentley, of Jericho, Vermont, began taking photographs of snowflakes through a microscope. Thousands of Bentley's photomicrographs were eventually collected in his book Snow Crystals (1931). The fact that not one of the snowflakes photographed by Bentley was identical to another is probably the basis for the idea that no two snowflakes are ever exactly the same—an idea that is in fact unverifiable.
Into the tubes
Aesthetics did not drive snow science. Even as Wilson Bentley was peering through the camera bellows of his photomicrograph, Americans by the millions were continuing to settle the lands beyond the Mississippi. From 1870 to 1910 the population of California grew by 325 percent. During the same period the population of the eleven western states as a whole grew by 600 percent. The newcomers confronted firsthand a truth about the West presciently stated by the explorer and naturalist John Wesley Powell: "In the whole region, land as mere land is of no value. What is really valuable is the water privilege." Unlike water in the East, water in the West could not be taken for granted; rainfall was in many places nonexistent or seasonal. It was no secret that the snow that fell in wintertime turned into most of the water that appeared in spring—albeit unpredictably in terms of volume and timing. What if some element of predictability was possible? Imagine the consequences for the building and management of reservoirs, the control of flooding, the rational allocation of water among various kinds of users.
Riverine data in some form have been collected by all civilizations, so essential are rivers to commerce and agriculture. Records of the annual high-water level of the Nile, for example, are complete all the way back to A.D. 622, save for one large gap in the early modern period. The U.S. government in the mid-1800s began attempting to gather reliable meteorological information on its rapidly expanding and geographically diverse domains, and by the turn of the century runoff data in the form of hydrographs existed for many of the important western rivers. It occurred to a number of investigators that if, by means of a crude model, one could correlate, year after year, the size of the snowpack at the moment of its greatest extent—the moment of what is now called "ripeness"—with the streamflow, then one would have a powerful forecasting tool. Moreover, if one measured the snowpack not only at the moment of greatest extent, which usually occurs in April, but also in March, February, and January, and kept detailed annual records, one might even be able, eventually, to make a preliminary forecast as early as midwinter, based on past trends. Of course, even if this methodology worked to perfection, it would never reveal how much snow had actually fallen or how much water that snow actually contained. It could, however, reveal that this year's runoff had a certain probability of being, say, roughly 20 percent less than average, or 15 percent more.