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Naturalist NotesSnow Crystalsby Emily Bowman Graf |
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Naturalist NotesSnow Crystalsby Emily Bowman Graf |
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Did you know that there is a difference between snowflakes and snow crystals? Snow crystals are the individual shapes that are formed high in the atmosphere. Sometimes they fall all the way to the earth’s surface as crystals. When you cut "paper snowflakes", you are probably really cutting "paper snow crystals!" If snow crystals clump together, they make a snowflake.
To make a snow crystal, three things need to be present in the air at the same time:
If conditions are just right, water molecules will freeze on the dust, one at a time. Because they join together in a regular pattern, they form a starter "hexagonal plate" crystal. The final crystal shape depends on the temperature and other weather conditions.
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plate crystal |
stellar crystal |
columnar crystal |
needle |
spacial dendrite |
tsuzumi crystal |
irregular flake |
graupel |
ice pellet |
Once a snow crystal reaches the ground, it will probably change, or metamorphose. In fact, if you dig a hole in the snow all the way to the ground, you are likely to see many different kinds of snow along the way. There are several ways metamorphosis can happen.
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Pressure Metamorphism
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This is simply the physical compaction of snow under it’s own weight. As the arms of the snowflake begin to interlock, the thickness of the snowpack is decreased and the density is increased. |
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Melt-Freeze Metamorphism
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If daytime temperatures or solar radiation are enough to melt the top layer of the snowpack, they will likely freeze again at night. The resulting snow is icy and granular (corn snow). If Melt-Freeze and Pressure Metamorphism work together, they can produce a hard, icy snowpack called firn. |
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Equitemperature Metamorphism
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Even if the temperature is consistent throughout the snowpack, individual snow crystals will begin to break down. Because of molecular movement (greater at warmer temps), the fragile points of the snow crystals will break off. |
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Temperature Gradient Metamorphism
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In certain conditions, the temperature at the bottom of the snowpack is greater than that at the top. If this is the case, the snow crystals at the bottom will begin to melt. This water vapor will move upward through the snowpack and refreeze in the top layers. This is called depth hoar, which is extremely weak. In the mountains, this can cause an avalanche. |
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Combination
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Most likely, a combination of snow transformation is taking place, causing constant change and unique snowpack formations. |
Do you want see some beautiful snowflake and crystal photos? Look for a book called "Snow Crystals" by W.A. Bentley and W.J. Humphreys.
Fun Fact: Did you know that the Inuit people recognize and have names for at least 80 different kinds of snow?