Megadunes and Hoar Frost: 6 Facts About Snow

//
This photo of penitentes, ice formations formed in high-altitude regions, was taken in December 2005 along the Chajnantor plain in Chile.
ESO

Winter snowstorms, like the Nor'easter that just slammed New England, transform gray days into winter wonderlands.

So while you're stuck inside, or within snowshoe-walking distance, here are six fun facts about snow, from the idea that no two snowflakes are alike to the bizarre megadunes that blanket Antarctica.

VIDEO: The Weird History Behind Groundhog Day

Unique beauty

According to physicists, it's actually true that no two snowflakes are alike — well, at least when it comes to complex snowflakes.

Snowflakes form when water droplets in the clouds freeze to form a six-sided crystal structure. As the temperature cools, more water vapor freezes and grows in branches from the six sides of the seed crystal. As the crystals form, they are randomly tossed about inside the clouds, which vary in temperature.

The temperature greatly affects how the snowflake forms, so while the simplest hexagonal crystals may look alike, more complicated beauties each have their own unique shapes. (See Stunning Photos of Snowflakes)

PHOTOS: Preparing for Winter Storm Nemo

White triangles

Most snowflakes form dazzling crystal patterns with six sides. But occasionally, a triangular crystal forms, something that has puzzled physicists for years. A 2009 study in the open-access, pre-publish journal arXiv.org revealed that triangular snowflakes form when the six sides of the seed crystals are slightly asymmetric. This makes them wobble randomly as a snowflake falls, allowing the bigger sides to hit the fast-flowing air inside the cloud, and grow at the expense of the smaller sides.

Other snowflakes have even stranger shapes: Some look like hourglasses, others like spools of thread and still others like needles. And while the quintessential snowflake is the six-armed, symmetrical beauty, most versions are hardly so picturesque. In fact, since the arms of a snowflake all grow randomly, asymmetrical snowflakes are more common.

Kenneth Libbrecht, a professor of physics at California Institute of Technology, photographs snowflakes in the field and in his lab. Studio-type lighting, even outdoors, brings out angles, texture and color that are otherwise hard to spot.
Kenneth Libbrecht, Caltech

Snowy shapes

The types of snowflakes that form depend a lot on the temperature and moisture in the clouds, according to a 2005 review in the journal Reports on Progress in Physics. Right around freezing temperatures, hexagonal plates (the cross-section is a two-dimensional hexagon) and the iconic, six-sided snowflake (known as a dendrite) form.

As the temperature cools, snowflakes develop into needles, then hexagonal prisms and even hollow columns. Go colder still, and dendrites form at much larger sizes. And at truly frigid temperatures, the frigid air forms prisms and flat plates.