Hello,

We noticed you're browsing in private or incognito mode.

To continue reading this article, please exit incognito mode or log in.

Not an Insider? Subscribe now for unlimited access to online articles.

Emerging Technology from the arXiv

A View from Emerging Technology from the arXiv

Solving the Puzzle of Triangular Snowflakes

Snowflakes ought to be hexagonal. So why are triangular ones so often observed?

  • November 27, 2009

The beautiful six-fold symmetry of snowflakes is the result of the hydrogen bonds that water molecules form when they freeze.

But snowflakes can form other shapes too when the growth of the crystal is perturbed on one side. In theory, diamonds, trapezoids and other irregular shapes can all occur. And yet the one most commonly observed (after hexagons) is the triangle. The puzzle for is why? What process causes deformed snowflakes to become triangles rather than say squares or rectangles?

Today, Kenneth Libbrecht at the California Institute of Technology in Pasadena provides an answer. Libbrecht, you may remember, has built an amazing snowflake machine to study the formation of these remarkable tiny crystals.

Their growth and shape, he says, is governed by two processes: the diffusion of water molecules through the air and the molecular dynamics on the surface of the crystal and it is the former that explains triangular crystal formation.

Libbrecht says various phenomena influence the way water molecules get to the surface of a snow crystal but perhaps the most important is aerodynamics. This orients the crystals and ventillates it, determin the rate at which it can grow.

Libbrecht has calculated how small perturbations in the growth rate on one side of a crystal change its shape. He says that whatever the cause of the perturbation, a hexagonal crystal will always continues to change shape in one way or another.

But the curious property of triangular crystals is that they are stable against this kind of change. So when a crystal has become triangular, other perturbations cannot change its shape further.

Triangles are a kind of valley in the energy landscape of snowflake morphology. And this explains why they are so common. Cool!

Keep an eye out for one next time you’re out in the snow.

Ref: arxiv.org/abs/0911.4733: Aerodynamical Effects in Snow Crystal Growth

Tech Obsessive?
Become an Insider to get the story behind the story — and before anyone else.

Subscribe today
Want more award-winning journalism? Subscribe to Insider Plus.
  • Insider Plus {! insider.prices.plus !}*

    {! insider.display.menuOptionsLabel !}

    Everything included in Insider Basic, plus the digital magazine, extensive archive, ad-free web experience, and discounts to partner offerings and MIT Technology Review events.

    See details+

    Print + Digital Magazine (6 bi-monthly issues)

    Unlimited online access including all articles, multimedia, and more

    The Download newsletter with top tech stories delivered daily to your inbox

    Technology Review PDF magazine archive, including articles, images, and covers dating back to 1899

    10% Discount to MIT Technology Review events and MIT Press

    Ad-free website experience

/3
You've read of three free articles this month. for unlimited online access. You've read of three free articles this month. for unlimited online access. This is your last free article this month. for unlimited online access. You've read all your free articles this month. for unlimited online access. You've read of three free articles this month. for more, or for unlimited online access. for two more free articles, or for unlimited online access.