From a small seed, tiny bulges form in the six directions preferred by the crystal. |
These grow into needle-shaped arms, the arms in turn develop bulges from which side branches grow, the side branches themselves sprout tiny side branches, and so on. |
The specific branch thickness and spacing are very sensitive to small changes in temperature, humidity, and pressure. |
Since these conditions are almost constant over the size of a snowflake, its six branches grow in a nearly identical fashion. |
The atmosphere in a snow cloud is turbulent over the scale of meters, so each flake takes a different route through the cloud and encounters different sequences of conditions for its growth. |
If we knew how to read it, each snowflake contains a record of the sequence of conditions through which it grew. |
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