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During the trip, a number of my shipmates exclaimed over the amazing colors of the ice formations. I asked some of the guides, as well as a few folks who had been there before and studied icebergs, why these icebergs are blue. I got answers but they did not ring true, so I decided to do a little research on our return, to check my facts. Unfortunately, the explanation is not so simple.

Here are some of the ideas that are confusing:

• Photo courtesy of Star Slipock. A small blue iceberg floats near the edge of the glacier.

  Photo courtesy of Star Slipock. Gray fog shrouding the coastline makes the blue color of this iceberg stand out.

  Photo courtesy of Star Slipock. Some icebergs show blue areas and white areas.

  Old icebergs are blue, young ones are not. Age of the ice can be a factor in an iceberg’s color—but not always. The surface of the iceberg also is a factor in its color. If there is a snow covering or a rough surface, an iceberg of older ice will still look whiter.

• Icebergs are blue because of refraction. Refraction of light occurs when light rays enter a medium whose its speed of light transmission differs. Think of what happens when you submerge part of a straight object, such as a pencil, in water. The object appears to bend at the surface. Although there is some refraction in glaciers, but its effect is negligible, and does not cause color in icebergs.
• Glaciers are blue because of light scattering, the same phenomenon that makes the sky blue. The sky looks blue because of an effect called “Rayleigh scattering,” which takes place when the sunlight bounces off the molecules in the atmosphere. Rayleigh scattering occurs primarily through the interaction of light with air molecules.

How Do Icebergs Form?

Icebergs come from glaciers, which are huge, slow-moving fields of ice and snow. They form in areas of high snowfall, where that snow does not fully melt away in warmer weather. The snow accumulates year after year. The weight of each year’s snow compresses the snow underneath, packing it down tightly and causing the older snow to crystallize into denser ice.

The combination of gravity and the weight of the ice causes a glacier to flow, or move. A mountain glacier moves downhill, and if a glacier is near a coastal area, it moves in the direction of the ocean. Where the glacier meets the water, huge chunks of ice continually break off from the face of the glacier in a process known as “calving.” This is how icebergs are born. Once adrift, icebergs are at the mercy of the ocean currents and the wind. Wave action below the surface of the water, and wind erosion above the surface carve the icebergs into interesting shapes.

The Color of Water

First, we need to understand why snow appears white. As water freezes into snow, it crystallizes. A close-up view of a snowflake reveals its many facets, not unlike a cut diamond. These facets, or surfaces, reflect light. As snow accumulates, the snowflakes trap a great deal of air. If you fill a glass to the top with snow and then bring it inside and allow it to melt, you will see that most of what you thought was frozen water was actually air! Because snow contains a lot of trapped air, light hitting it is able to reflect off the many internal surfaces. We see this light as white in color.

Snow looks white, and if you fill a clear glass with water, it looks colorless. So how come when we look at the ocean, the water looks blue? The answer has to do with light wavelengths. Visible light is actually a combination of many different wavelengths of light. Each of these wavelengths has a different amount of energy associated with it. If light is refracted through a prism, all the colors of the spectrum can be seen as a rainbow. The colors always appear in the same order: red, orange, yellow, green, blue, indigo, and violet.

Water is much denser than air. So, as light travels through water, the weaker wavelengths of light—from the red end of the spectrum—quickly filter out, while those from the blue end penetrate the deepest. We see the blue as the color of the ocean.

What Causes Blue Icebergs?

We know that icebergs are made from snow and that snow appears white. In fact, most people think of an iceberg as a huge chunk of white ice, and many icebergs are, in fact, white or gray. So why do we see blue icebergs?

The ice in glaciers has been under enormous pressure for eons. The compression eliminates air and reflective surfaces within the ice. Some glaciers are very old, while some are younger. Icebergs that come from young glaciers have not undergone as much compression. Therefore, there is still a great deal of air and reflective surfaces within the iceberg. The iceberg reflects back much of the light that hits it as white light.

Icebergs from older glaciers have little internal air or reflective surfaces. So when light hits the iceberg, it no longer bounces off. Instead, the light is absorbed. As in water, the longer (red or green) visible wavelengths of light are absorbed, so the light leaving the ice will be blue or blue-green. This is what makes an iceberg “blue.” It is simply capturing the Sun’s emitted light and allowing only the high-energy blue wavelengths to escape. I hope this explanation helps you to understand why there are blue icebergs.