Most people recognize that water, in its pure form, is colorless. Likewise, snowflakes are clear, but a billion snowflakes in a pile have a distinctive white color.
What Makes Snow White?
To understand the color of snow, we need to know its physical properties. Snow is a form of precipitation composed of tiny ice crystals stuck together. A single ice crystal appears clear, but the snow is different.
During snow formation, hundreds of tiny ice crystals accumulate to form snowflakes. Since lots of air fills the pockets between fluffy snowflakes, layers of snow on the ground are mostly air space.
The reflection of light is why we see snow in the first place. The visible light from the Sun is composed of a series of light wavelengths interpreted by our eyes as different colors. When white light hits an object, our eyes absorb or reflect these wavelengths.
As snow falls through the atmosphere to the ground, light reflects off the surface of ice crystals. The multiple facets or the "faces" of these crystals affect the reflection of light. Some of the light that hits snow gets scattered equally into all spectral colors. Since white light is made up of all colors in the visible spectrum, our eyes perceive the color of snowflakes as white.
No one can see a snowflake at a time, but we usually see millions of snowflakes covering the ground. As light hits the snow layering the bed, there are many spots for light to be reflected; no single wavelength gets absorbed or reflected consistently. Because of this, most of the white light from the Sun that hits the snow will reflect as white light, allowing us to perceive white snow on the ground, too.
It must also be noted that ice is translucent and not transparent. As a result, light cannot pass through ice crystals easily and instead changes directions or reflects off the angles of interior surfaces. Since light bounces back and forth within the crystal, some light is reflected, and some is absorbed.
The millions of ice crystals that bounce, reflect, and absorb light in a snow layer lead to neutral ground. This means there is no preference for one side of the visible spectrum, either red or violet, to be absorbed or reflected. With all the wavelengths of light being reflected, they all bounce together as white.
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Variations of Snow Colors
Snow can also take on other hues, depending on specific conditions. When compacted, snow can appear blue, a common phenomenon in the blue ice of glaciers.
Icebergs, snowpacks, and glaciers can appear blue when light enters them through crevices instead of reflecting off their surfaces. As light travels within the snow and ice, countless crystals scatter it. The farther light travels, the more it gets spread.
Water and ice absorb more red light than blue light, so as the light emerges from the snow layers, the shorter blue wavelength gets reflected toward our eyes. The longer the scattering is repeated, the more noticeable the blue color becomes.
There are also documented cases when snow appears pink or red-tinted in watermelon snow. This distinct color is due to the presence of red freshwater algae that live within the snowpack.
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