Getting to know snow

Snow here in the High Country is a thing of beauty, covering the landscape in a peaceful white. It is as valuable now as gold was to the miners in this area and snow is actually a mineral! The definition of a mineral is: “A naturally occurring homogeneous solid, inorganically formed, with a definite chemical composition and an ordered atomic arrangement.”

Snow is beautiful as each snowflake is unique; a slice of a six-sided crystal and every snowflake, like a quartz crystal, is vibrant and vibrating. Snow crystals form in six-sided shapes because water molecules are made of one oxygen and two hydrogen molecules. As water begins to crystallize into ice, its hydrogen molecules hook together in ways that form six-sided crystals.

Snowflakes are agglomerates of many snow crystals. Most snowflakes are less than one-half inch across. Under certain conditions, usually requiring near-freezing temperatures, light winds and unstable, convective atmospheric conditions, much larger and irregular flakes can form. According to the Guinness Book of Records, the largest snowflake ever measured was 15 inches wide and 8 inches thick. This was observed and recorded in 1887 at Fort Keogh, Mont.

So what is snow? It is a form of precipitation within the Earth's atmosphere in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. Since snow is composed of small ice particles, it is a granular material. It has an open and therefore soft structure, unless packed by external pressure.

Snowfall tends to form within regions of upward motion of air around a type of low-pressure system. In mountainous areas, heavy snow is possible where upslope flow is maximized within windward sides of the terrain at elevation if the temperature is low enough.

Why is snow white? Visible sunlight is white and most natural materials absorb some sunlight which gives them their color. Snow, however, reflects most of the sunlight. The complex structure of snow crystals results in countless tiny surfaces from which visible light is efficiently reflected. What little sunlight is absorbed by snow is absorbed uniformly over the wavelengths of visible light, thus giving snow its white appearance.

The fluffiest, lowest density snows typically fall with light winds and temperatures near 15 degrees Fahrenheit. At colder temperatures, the crystal structure and size change. At very cold temperatures near 0 degrees Fahrenheit, crystals tend to be smaller so that they pack more closely together as they accumulate, producing snow that may be denser.

Fresh snow absorbs sound, lowering ambient noise over a landscape because the trapped air between snowflakes absorbs vibration. Walking across snowfall produces a squeaking sound at low temperatures.

A layer of snow is made up of ice grains with air in between the ice grains. Because the snow layer is mostly empty air space, when you step on a layer of snow you compress that layer a little or a lot, depending on how old the snow is. As the snow compresses, the ice grains rub against each other. This creates friction or resistance; the colder the temperature, the greater the friction between the grains of ice. The sudden squishing of the snow at lower temperatures produces the creaking sound. At warmer temperatures closer to melting, this friction is reduced to the point where the sliding of the grains against each other produces little or no noise.

In a snow pack with a significant temperature gradient, large six-sided, cup shaped “depth hoar crystals” form a loosely packed layer at the bottom. Many small non-hibernating mammals depend upon these loose snow crystals for easy construction of tunnels throughout the subnivean environment. This “sugar snow” can often be the weak and unstable layer that causes avalanche hazards.

Snow cover can protect crops from extreme cold. A blanket of snow keeps the ground evenly frozen, preventing frost heaves and protecting the plants from upheaval.

Each snowflake forms around a particle of dust, which is a tiny grain of soil containing a minute amount of minerals. The minerals in snow are absorbed into the soil, and when the ground thaws, they are taken up by the plants. Minerals provide structure and allow communication in cells, plants and animals.

The water content of snow is variable. Ten inches of fresh snow can contain as little as 0.10 inches of water or as much as 5 inches, depending on crystal structure, wind speed and temperature.

One major benefit of a good snow cover is that snow is an excellent insulator of the soil. Without snow, very cold temperatures can freeze the soil deeper and deeper. Generally, temperatures underneath a layer of snow increase about 2 degrees F for each inch of accumulation. Because the soil also gives off some heat, the temperature at the soil surface can be much warmer than the air temperature.

Most skiers are familiar with the many terms referring to snow or snow conditions: boilerplate, breakable crust, powder, champagne powder, corduroy, corn, hard pack, packed powder, moguls, cornice, glacier, flurries and avalanche just to name a few. The most magical moments on the mountain are a sunny morning after a fresh snowfall when sun shining on a few stray flakes in the air look like floating diamonds or stardust against a brilliant blue sky.