A White (and Blue?) Winter Wonderland

Occupying about 10 percent of the world’s land and covering about 30,000 square miles of the United States, glaciers are one of nature’s bulldozers – sculpting and carving today’s landscapes with their massive bodies of ice. These giant natural wonders are made up of solid ice, typically a deep, blue color topped with bright, white snow on the surface. While these contrasting colors make for an awe-inspiring photograph, many curious minds wonder, “Why is snow white and glacier ice blue?”

Glaciers begin to form when snow piles up over the years, normally in mountainous, valley, and cold regions such as Alaska or Antarctica. As more snow falls, the snow underneath begins to compress and, over time, air pockets are squeezed out and a thick, dense ice mass known as a glacier is formed. These features – density, object form, and appearance – directly affect how the wavelengths of light interact with an object and the color our eyes will perceive an object to be.

Snow White and the Seven Wavelengths of Light

A color spectrum is composed of light separated into different wavelengths, arranged in the order of red, orange, yellow, green, blue, indigo, and violet (“ROY G. BIV”) is an easy way to remember this order). With the longest wavelength being red and the shortest wavelength being violet, our perception of color is dependent on which of these wavelengths of light an object absorbs or reflects back to our eyes. If all of the wavelengths are reflected to our eyes instead of being absorbed by the object, we perceive whiteness.

This is what happens when we look at snow. Snow is made up of tiny ice crystals and pockets, or bubbles, of air. When sunlight hits snow, the light quickly scatters between ice crystals and air pockets, and then reflects right back to our eyes. None of the seven wavelengths of light are absorbed, explaining why we perceive snow as white. This, however, changes when snow turns into glacial ice.

The Deep Blue, Icy Sea

Most glaciers are quite large, appearing to be a “sea” of ice covering mountains or valleys in cold regions. The thickness and lack of air bubbles within this ice allows sunlight to penetrate it. As the sun beams down, all of the wavelengths of light are absorbed except for blue. This shorter, blue wavelength is reflected to our eyes, causing us to perceive a blue color. If ice appears white, there are still tiny air bubbles in it scattering light and interfering with the absorption of these wavelengths.

As you ski, ice skate, or sled this winter, take a look around. What colors do you see?

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