How do snowflakes form?

Snowflakes have captured the human imagination since long before we understood their origins. Even before the invention of the microscope, just holding a snowflake up to your eye could let you see an incredible level of detail — and, it seems, the details were always different. Snowflakes have become a symbol of uniqueness, of the sheer level of variety possible, even within a simple and restrictive framework. People see, or try to see, something about human nature in the birth of such delicate and varied structures.
How could a simple, natural process give rise to that kind of variety? It would seem that a simple process like ice formation would play out fairly predictably, but it turns out that while we may know the basics of how snowflakes form, the random factors that influence their specific pattern are virtually unknowable. From flecks of dust to a passing currents of hot or cold air, there are all sorts of unpredictable factors that give rise to a snowflake’s particular conformation. There are, however, some generalities.

Can you see the repeating pattern?

The first step is always the formation of the initial ice crystal, referred to as a bead. This happens when you have three things: cold air, high humidity, and a nucleation point. The nucleation point is some irregularity, usually a speck of dust, that provides the initial scaffold for those very first ice crystals.
Once ice begins to form in the freezing, humid air, it will quickly grow until it reaches a certain critical point. Past this size, a simple sphere becomes less and less efficient, as heat flows out from the still-forming ice crystals. This heat flow causes fingers of ice to split off radially, almost always six of them. Once these fingers grow out to an equally inefficient length, their tips become the nucleation points for further splits into icy fingers.


The unpredictable part is in the details.

 The initial speck of dust can influence how the snowflake grows, as can a speck added later on in the process, or even just a passing breeze. While it might be technically true to say that no two snowflakes are exactly alike, many are quite similar. This is because they are all derived from identical processes, influenced by only a few variables. With the sheer number of snowflakes that fall around the world every year, it’s a foregone conclusion that quite a few are virtually identical.
A professor at Duke University recently made a video explaining this issue in detail. Take a look at the video, below.


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