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We regret that we are no longer accepting new questions for our Alaska Scientist section. Please enjoy the past questions and answers, and thank you to those who have contributed questions or assisted with answers.

Q: Which type of ice is best for building an igloo: sea ice, glacial ice, or another type? Why?
Dave Sheaks, 12x4 Able Seaman, R/V ROGER REVELLE/Jr. High science teacher, St. Paul's Day School, Ventura, CA

Igloos were originally used by Inuits (people of the far north) primarily as an expedient and effective shelter against the wind and cold when traveling or hunting. Some large igloos, or snow domes, were also used as halls for singing, dancing, and other community functions. Both types of igloos were made from snow.

In recent years, with the advent of winter ice festivals, some igloos have been made from ice as decorative displays. They are pretty to look at, but would not have been used as a shelter by the Inuit because of the difficulty of cutting ice blocks and the low insulating ability of ice compared to snow.

Ice conducts heat about 7 to 10 times better than snow of the type that was typically used by the Inuit. This means that a person in an ice igloo would lose heat 7 to 10 times faster than one in a snow igloo. The difference in comfort level between a snow igloo and ice igloo can be experienced by standing in front of a large window on a cold night and then, after a few minutes, moving in front of a section of solid insulated wall. The difference in heat conduction between the window and insulated wall for a typical house is from 6 to 10, in the same range at that for snow and ice igloos. (For me, the window is always much colder and more uncomfortable.)

If one really wants to build an ice igloo, then either glacier ice or ice that has grown in a flooded active gravel pit are the best source materials, as they will be clear and free of bubbles or organic debris. For display purposes, the top layer of ice is usually cut away from the blocks because it contains air bubbles and snow grains, which detract from the appearance of the ice blocks. Ice taken from natural lakes can also be used, but it is more likely to contain air bubbles and organic debris because of decaying organic material at lake bottoms (not usually found in gravel pits).

Sea ice is a poor choice for building ice igloos because it contains small pockets of very salty water called brine. These brine pockets move from the interior of the ice blocks to their surface under the influence of gravity and heat gradients, creating a slimy and very salty surface.

Dr. Jerome B. Johnson, Research Geophysicist, U.S. Army ERDC-Cold Regions Research and Engineering Laboratory

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