Snowflakes: Crystals From The Sky
Durango Herald, Dec 8, 2005
Lisa Branner, Executive Director

A photograph of a snowflake by W.A. Bentley shows off the lacy, intricate pattern formed by the crystal.

W.A. Bentley and I are kindred spirits. We share a common passion for the form of precipitation called snow. While my infatuation typically leads me into the mountains with snowboard in tow, Bentley's fascination required the pioneering use of a photographic microscope. Over the course of his career, he captured more than 5,000 ice crystals on film, revealing both the artistry and complexity of this facet of nature.

With Old Man Winter on the way, it seems fitting to explore some questions about snow.

How does a snowflake form?

There are two ways that snow crystals form in clouds. At warmer temperatures, snow condenses on small dust particles that are suspended in the cloud, forming tiny droplets that freeze. This process is called heterogeneous nucleation. When the air temperature drops below negative-40 Celsius, water vapor converts directly to ice through a process called homogenous nucleation.

What gives a snowflake its intricate form?

The lacy, intricate pattern of a snowflake is determined by the atmospheric conditions experienced by the crystal as it forms. As an ice crystal descends through the atmosphere, it encounters variations in temperature and humidity. Snow crystals tend to form simpler shapes at a lower humidity and more complex shapes when the humidity is high. Colder temperatures produce snowflakes with sharper tips and branched arms or dendrites, while warmer conditions allow snowflakes to grow more slowly, resulting in smoother, less intricate shapes - those sticky, fluffy flakes that are ideal for snowball-making!

Is it true that no two snow crystals are alike?

This is probably one of the most frequently asked questions about snow. The answer depends largely upon how you define the word "alike." The short answer is that it's unlikely that any two snowflakes are absolutely identical. Because each snow crystal experiences a different growth history as it forms, it is improbable that any two snowflakes would be identical.

This article is just the tip of the proverbial iceberg when it comes to information about snow. Visit the Jericho Historical Society's Web site (http://snowflakebentley.com/jhs.htm) to learn more about W.A. Bentley's legacy, or look for the photography collection Snow Crystals by W.A. Bentley and W.J. Humphreys at your local library. It will give you a new appreciation for the white stuff!

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