The Science of Snowflakes
You don’t have to be a scientist to get a thrill out of these.
We all love snowflakes—more accurately called snow crystals. They are some of nature’s most beautiful designs. Often of astounding intricacy and mind-boggling symmetry, we can hardly believe such perfection exists, or that such variety is even possible. It seems such gorgeous things would be rare. Yet, anyone who lives in a cold climate need only look out a window on a snowy January evening to see hundreds of different snowflakes, each unique, clinging to the outside surface of the window.
Let’s follow the process of snow crystal formation step by step:
Step 1: Somewhere above us in a cold part of the atmosphere, a tiny piece of dust or a very small particle serves as the center or nucleus for a snow crystal. These pieces of dust are extremely small, but studies with an electron microscope have shown every snowflake has a solid nucleus.
Step 2: Water in the atmosphere freezes on the surface of one of these nuclei. As ice forms, water loses the randomness that makes it a liquid state and starts to form a regular lattice that is a hallmark of ice. Notice in this diagram that as liquid water becomes ice, the molecules line up and become more organized—they form a lattice. You can sense the beginning of an organized pattern.
Step 3: As more and more ice molecules are added to the nucleus, the crystal grows outward, often, but not always, in a flat plane. Because of the nature of the angles that H2O molecules bond to one another, every snow crystal has six arms or six sides. Conditions like the saturation of water in the sky, the temperature, and the movement of wind result in various shapes .
Step 4: The environment shapes the crystal. As the ice crystal grows in the atmosphere it does so in an infinite variety of ways. The atmospheric conditions listed in Step 3 are so minutely varied that it is said that no two snowflakes are alike. You can’t PROVE that by the way, but it might be largely true. Scientists have created diagrams like this to show how the different classes of snowflakes result from different environmental conditions.
Notice that those spectacular spikey-like snowflakes occur when the temperature is about 0°F and there is a lot of water vapor in the air. When the air is colder or warmer, snowflakes of the plate type or column type are more likely to result. Needle snowflakes occur when the temperature is quite cold.
Step 4: Snow crystals, when fully formed, will attach themselves to other snow crystals. When thousands of them stick to one another, together they become a snowflake. Their mass is now enough to make them fall as snow, but flakes often break off and land on that cold, January window.
Now that you know the science behind a snowflake, treat yourself by visiting Cal Tech’s magnificent site on the subject. Spend some time and just look at the variety of these icy crystals.
Finally, for those of you interested in the photography of snowflakes, you should know about Wilson Alwyn “Snowflake” Bentley.
Snowflake Bentley took the first picture of a snowflake in 1885. And it wasn’t with his cell phone!
Daniel H. Franck is director of science for K12. He developed the scope and sequence for all science courses for grades 3-12. Dr. Franck has also worked for Holt, Rinehart, Winston, Harcourt, Scholastic, Inc., and Discovery Channel, among others, in developing science textbooks as well as multimedia products for students from kindergarten through high school. He was part of a team of educational specialists that visited the nation of South Africa under the auspices of the U.S. Agency for International Development helping that nation's biology teachers restructure their national science curriculum. Dr. Franck has a Ph.D. in botany from the University of California, Berkeley and has been a professor of botany at the University of Wisconsin.